Walk an operand below .zfs or a symlink on its own (closes #142 )

An operand under another was dropped as covered by it even when a directory between them was named .zfs or was a symlink. The walk of the outer operand enters neither, so the files under the inner operand went unscanned and their records were deleted. walkReaches now reports such an operand as not reached, so pruneRoots keeps it and walks it on its own. README lists both cases with the others. Judgement call: the new constant zfsDirName replaces the .zfs literal in operandWarning and subdirJob too, because goconst rejects a third copy. Model: opus-5-5
2026-10-26 12:23:51 +00:00
27 changed files with 1876 additions and 2573 deletions
@@ -4,7 +4,7 @@ export CGO_ENABLED = 0

 BINARY := sfdupes
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
-LDFLAGS := -X sneak.berlin/go/sfdupes/internal/sfdupes.Version=$(VERSION)
+LDFLAGS := -X main.Version=$(VERSION)

 .PHONY: sfdupes build bootstrap setup test lint fmt fmt-check check docker hooks clean

@@ -14,7 +14,7 @@ LDFLAGS := -X sneak.berlin/go/sfdupes/internal/sfdupes.Version=$(VERSION)
 # Default target: build the binary. Phony so go build (which has its
 # own build cache) always decides what to recompile.
 sfdupes:
-	go build -ldflags "$(LDFLAGS)" -o $(BINARY) ./cmd/sfdupes
+	go build -ldflags "$(LDFLAGS)" -o $(BINARY)

 build: sfdupes

@@ -1,33 +1,559 @@
 # Workflow

- Take an issue from the `1.0.0` milestone on the tracker. Work that is not on
-  the tracker yet is filed as an issue first.
- Branch from `next`.
- Do the work, with tests, in small focused commits.
- Delete Next Step from `TODO.md`, in the same commit as the work.
- Push the branch and open a PR against `next`. Its title ends with
-  ` (closes #N)`.
- An independent review gates each merge to `next`. Every finding is addressed
-  or rebutted on the PR.
- Only the owner merges `next` into `main`.
+- take an issue from the `1.0.0` milestone on the tracker; work not yet on the
+  tracker gets filed as an issue first
+- branch from `next`
+- do the work, with tests, in small focused commits
+- record it at the top of Completed Steps (`TODO.md` changes in the same commit
+  as the work)
+- push the branch and open a PR against `next` whose title ends with
+  ` (closes #N)`
+- an independent review gates each merge to `next`; every finding is addressed
+  or explicitly rebutted on the PR
+- only the owner merges `next` to `main`

 # Status

- Pre-1.0.
- The tracker is authoritative for the pre-1.0 backlog. The open issues under
-  the `1.0.0` milestone are what remains before the tag.
+- pre-1.0
+- the Gitea tracker is authoritative for the pre-1.0 backlog: the open issues
+  under the `1.0.0` milestone are what remains before the tag, and this file
+  records history and process, not the queue

 # Next Step

- Take the next issue from the `1.0.0` milestone,
-  https://git.eeqj.de/sneak/sfdupes/milestone/17. The issues are not restated
-  here, because a copy drifts as soon as the tracker moves.
+- take the next issue from the `1.0.0` milestone on the tracker:
+  https://git.eeqj.de/sneak/sfdupes/milestone/17 — the milestone is the source
+  of truth for what is left before 1.0.0. Individual issues are deliberately not
+  restated here; a copy in this file drifts out of date the moment the tracker
+  moves
+
+# Completed Steps
+
+- an operand under another is walked on its own when a directory between them,
+  the inner operand included, is named `.zfs` or is a symlink. The walk of the
+  outer operand does not reach it then. `scan` now records the files below it
+  and no longer deletes their records (2026-10-26,
+  https://git.eeqj.de/sneak/sfdupes/issues/142)
+
+- a file or directory removed while the scan runs is not an error, in the walk
+  or in the hash phase. The scan prints no line for it and does not count it as
+  skipped. When the first of several hard links to a file is gone, the hash
+  phase reads the next one instead. On a terminal every progress display starts
+  with the spinner, the hash phase's included. A phase with an exact total ends
+  its line with its percent and a 10-column bar at the terminal's right edge,
+  which no longer moves as the line's length changes. A line too wide for the
+  terminal now loses its rate before its bar. The time remaining is labelled
+  `remain`, not `eta` (2026-10-26, https://git.eeqj.de/sneak/sfdupes/issues/133)
+
+- the `head`, `tail` and `content` columns are BLOBs, each holding the raw 32
+  bytes of a SHA-256, half the size of the hex text they held. The hashes stay
+  raw from the hash phase through the database to `report` and `trees`. Reading
+  a record whose hash is not 32 bytes is an error (2026-10-26,
+  https://git.eeqj.de/sneak/sfdupes/issues/134)
+
+- the hash phase gives every file the walk records three hashes: `head` and
+  `tail`, the SHA-256 of its first and last 64 KiB, and `content`, the SHA-256
+  of the whole file under 100 MiB and of 1 MiB at each gigabyte from 100 MiB up.
+  The 10 MiB and 50 MiB thresholds, the size census, the records stored without
+  hashes and the content phase are gone, so a scan has four phases and a rescan
+  reads only new and changed files. `info` no longer counts the records with
+  hashes, since every record has them (2026-10-25,
+  https://git.eeqj.de/sneak/sfdupes/issues/132)
+
+- re-vendor `REPO_POLICIES.md` and the four scripts that pass `CACHEBUST` from
+  `sneak/prompts` `next` at `0653579`: in the `lint`, `test` and `builder`
+  stages of the `Dockerfile` the module download, and in `builder` the
+  system-package install, now come before `ARG CACHEBUST`, so Docker keeps them
+  until the base image, the install line, `go.mod` or `go.sum` changes, and
+  every step that lints, tests or compiles still comes after it;
+  `golangci-lint run` also keeps golangci-lint's cache. README says the same
+  (2026-10-18, https://git.eeqj.de/sneak/sfdupes/issues/109)
+
+- releases until 1.0 are `v0.0.N` tags on `main`'s tip, so
+  `go install sneak.berlin/go/sfdupes@latest` installs `main`'s tip once it has
+  passed the build; README "Install" says so, says what `@main` and `v0.0.1`
+  give, and how to check an installed binary. `go.mod` retracts `v0.0.1`, the
+  early build without a database. When the linker set no version,
+  `sfdupes --version` prints the main module's version that Go recorded in the
+  binary, the tag or the pseudo-version of a `go install` build, and `dev` only
+  when neither is known (2026-10-17,
+  https://git.eeqj.de/sneak/sfdupes/issues/116)
+
+- `scan` creates the database's directory where the database path leads: the
+  path with its last element cut off as text, never cleaned, so a `..` after a
+  symlinked directory is followed through the symlink, as when the file is
+  opened. With `SFDUPES_DATABASE=/srv/link/../new/db.sqlite` and `/srv/link` a
+  symlink to `/data/x`, it creates `/data/new` and the database in it, where it
+  used to create `/srv/new` and then fail (2026-10-17,
+  https://git.eeqj.de/sneak/sfdupes/issues/119)
+
+- `scan` never records its own database: once the database and its `.lock` file
+  are open, it notes the device and inode of the database file, its `-wal` and
+  `-shm` files and its `.lock` file, and the walk passes over a file with one of
+  them wherever the operands reach it, through a symlinked directory included,
+  printing no line and counting nothing. A record an earlier scan left for one
+  of them is deleted (2026-10-17, https://git.eeqj.de/sneak/sfdupes/issues/115)
+
+- `scan` never records or reads anything that is not on a persistent filesystem
+  (`tmpfs`, `proc`, `sysfs` and the other kernel or memory-backed types),
+  matched by the device ID of each such filesystem, listed as the scan starts
+  from `/proc/self/mountinfo` on Linux and the mounted-filesystem list on macOS,
+  however the walk or the content phase reaches it; no flag turns that off.
+  Below an operand, its walk does not enter the default excludes either, so
+  `sfdupes scan /` skips the kernel's view of the running system and the
+  temporary directories: on Linux `/proc`, `/sys`, `/dev`, `/run`, `/tmp` and
+  `/var/tmp`, on macOS `/dev`, `/private/tmp`, `/private/var/tmp`,
+  `/private/var/vm`, `/System/Volumes/VM` and `/System/Volumes/Data`, and a
+  Windows list, not used yet. An operand at or inside a default exclude is still
+  walked. The scan prints a line for each path it leaves out, without counting
+  it as skipped, and the records there count as outside the scanned operands, as
+  for `-x`. `--no-default-excludes` turns off the default excludes only, and
+  `scan --help` lists them (2026-10-17,
+  https://git.eeqj.de/sneak/sfdupes/issues/124)
+
+- the rate a progress display shows covers the items completed over the last 5
+  seconds, or since the line before when stderr is not a terminal, so it falls
+  to 0 while nothing completes, and a burst after a wait no longer reads as a
+  steady rate of over 1,000 files a second; the ETA still comes from the phase's
+  average. Once no item has completed for 10 seconds, the word `stalled` and
+  where the phase waits take the rate's place, as `stalled disk/db`: `disk`,
+  `db`, `out` for stdout or `cpu`, or two of them for a phase that may wait on
+  either, each phase giving its word where it is defined. A line too wide for
+  the terminal loses its bar first, then its rate or those words, so the phase,
+  progress, elapsed time and ETA stay whole. On an 80-column terminal, at counts
+  like those of README's example, the content phase's checks and reads lose
+  those words at most times in minutes, and every other phase keeps them
+  whenever the elapsed time and the ETA are both in minutes. The content phase's
+  last partial batch is now written under a display of its own (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/125)
+
+- new subcommand `info` prints the database's details on stdout, one per line as
+  a name, a tab and the value: its path and where it came from, the sizes of the
+  database file and of its `-wal` file when there is one, when the database file
+  was last changed, the schema version, the number of records, how many have
+  head and tail hashes and how many a content hash, and the sizes of all records
+  added up. It opens the database as `report` does, and shows two phases on
+  stderr, `[1/2] open` and `[2/2] count`; the schema version and the counts come
+  from one read-only transaction, the counts from one query (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/117)
+
+- `report` shows its work on stderr in two phases, `[1/2] open` and
+  `[2/2] read`, with the progress display `scan` and `trees` use, from the
+  moment it starts until the summary line: `open` says it is opening the
+  database, also while it waits on a busy one; `read` counts the records, then
+  reads them against that count in signature order, which SQLite takes from the
+  `files_signature` index without sorting, so the first record comes at once.
+  `report` forms the duplicate groups itself, holding only those of the size it
+  is reading, and writes them ordered by first path before it reads the next
+  size. stdout and the summary line are unchanged, and SQLite no longer needs a
+  temporary file to sort in (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/114)
+
+- `trees` shows its work on stderr in four phases, `[1/4] open`, `[2/4] read`,
+  `[3/4] group` and `[4/4] write`, each with the progress display `scan` uses,
+  from the moment it starts until the summary line: `open` says it is opening
+  the database, also while it waits on a busy one; `read` counts the records,
+  then reads them against that count; `group` counts the directories it groups,
+  and `write` the groups it writes. A display's rate names what its phase
+  counts: files, records, directories or groups. stdout and the summary line are
+  unchanged. When stdout and stderr are the same file, as one terminal is, none
+  of stdout's lines shares a line with the display; when they are not, the
+  display keeps being drawn while stdout waits on a slow reader (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/113)
+
+- each `scan` phase's progress display names the phase and its place among the
+  five, as `[2/5] walk`, from the moment it starts, with its progress, elapsed
+  time and ETA: `load` counts the records first, the walk's total is estimated
+  from the records under the operands, and the content phase counts the records
+  it checks from SQLite's grouping alone, then says it is searching the database
+  until the first one is returned. On a terminal a phase with an exact total
+  draws its line followed by the library's bar, and any other a spinner followed
+  by the line; every display is drawn again several times a second. No line
+  reaches the terminal's last column, however narrow, also after the terminal is
+  made narrower during a phase: a line too wide leaves out its rate, then its
+  bar, keeping the phase, progress, elapsed time and ETA whole, and is cut short
+  only when those alone do not fit, as below about 70 columns late in a large
+  scan. In plain mode the line is printed every 5 seconds whether or not an item
+  completed (2026-10-16, https://git.eeqj.de/sneak/sfdupes/issues/112)
+
+- `scan`, `report` and `trees` first print a line on stderr naming the database
+  they use, as an absolute path, and whether that path is the default or comes
+  from `SFDUPES_DATABASE`; `scan` says when the database is new. README
+  "Database" says when `scan` writes each file (2026-10-16,
+  https://git.eeqj.de/sneak/sfdupes/issues/111)
+
+- re-vendor the canonical files and model scripts from `sneak/prompts` `next` at
+  `e3f79c4`: golangci-lint v2.14.0; lint and test are phases of the `Dockerfile`
+  that write no image, and `make test` runs the suite under the race detector,
+  so `Dockerfile.lint`, `script/verify-lint-image-pin` and `make test-race` are
+  gone; every `docker build` in `script/` passes a new `CACHEBUST` value, which
+  every stage of the `Dockerfile` declares first, so every `RUN` step runs on
+  every build, while the steps that compile keep Go's build cache and the tests
+  run with `-count=1`; prettier runs on the host, from the node and yarn
+  `script/bootstrap` installs, so the `prettier` and `markdown` stages are gone
+  and the build stage installs `git` and `make` itself; a new push cancels the
+  workflow's older run on the same branch, and a run stops after 20 minutes;
+  `.claude/settings.json` is deleted (2026-10-15,
+  https://git.eeqj.de/sneak/sfdupes/issues/95). Since
+  https://git.eeqj.de/sneak/sfdupes/issues/109 the module download in `lint`,
+  `test` and the build stage, and the install of `git` and `make` in the build
+  stage, come before `ARG CACHEBUST`, and Docker keeps them between builds;
+  every step that lints, tests or compiles still runs on every build
+
+- with `-x`, an operand under another operand is walked on its own instead of
+  being dropped when a directory from it (from its directory, for a regular
+  file) up to but not including that operand is on a different filesystem than
+  that operand, whose walk then cannot reach it, and the records of files gone
+  from below it are deleted (2026-10-14,
+  https://git.eeqj.de/sneak/sfdupes/issues/106)
+
+- with `-x`, `scan` keeps the records below a directory on another filesystem
+  under its operand, and counts their sizes in the size census, instead of
+  deleting them (2026-10-14, https://git.eeqj.de/sneak/sfdupes/issues/99)
+
+- the hash and content phases open each file without blocking and check that it
+  is still a regular file, so one replaced by a FIFO or device node after it was
+  statted is warned about and skipped instead of hanging the scan (2026-10-14,
+  https://git.eeqj.de/sneak/sfdupes/issues/100)
+
+- the scan lock file is named from the database's path with symlinks resolved,
+  after `scan` creates the database file if it is missing, so a scan through a
+  symlink to the database fails while another scan holds the lock (2026-10-14,
+  https://git.eeqj.de/sneak/sfdupes/issues/101)
+
+- on a terminal, a warning for the last file of a phase no longer erases the
+  phase's finished bar: the bar is drawn again below the warning (2026-10-14,
+  https://git.eeqj.de/sneak/sfdupes/issues/102)
+
+- `scan` records mtime to the nanosecond, as whole seconds in `mtime` plus
+  `mtime_nsec`, and compares it at that resolution, so a same-size rewrite
+  within the same second is re-hashed (2026-10-07,
+  https://git.eeqj.de/sneak/sfdupes/issues/12)
+
+- cut the narration from `TODO.md` Completed Steps and from the comments in
+  `script/`, `Dockerfile` and `Dockerfile.lint` (gone since
+  https://git.eeqj.de/sneak/sfdupes/issues/95); §Workflow now branches from and
+  merges to `next` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/49)
+
+- `make test-race` ran the test suite under the race detector in a cgo-enabled
+  container, outside `make check` (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/18). Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 `make test` itself runs the suite
+  under the race detector, in the `Dockerfile`'s Debian-based `test` phase, and
+  `make test-race` is gone
+
+- a bare `docker build .` failed, naming `script/cibuild` and `script/docker`,
+  rather than serve the gates from cache (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/39). Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 a bare build succeeds, as
+  `REPO_POLICIES.md` requires, and may serve the gates from cache; the builds in
+  `script/` pass a new `CACHEBUST` value, so theirs always run
+
+- `make fmt` and `make fmt-check` run prettier over all Markdown, and CI checks
+  it; all Markdown reformatted (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/19)
+
+- `script/lint` writes no image, so a run no longer leaves an untagged one
+  behind (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/48)
+
+- tests cover a missing database, `scan` keeping stdout empty, its skip warning,
+  the `report` and `trees` summary lines, and every subcommand going through
+  `runE` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/16)
+
+- `.golangci.yml` replaced with the current canonical copy, which uses
+  `gomodguard_v2`, so lint no longer prints a deprecation warning (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/26)
+
+- a test fails when either `hashWorker` cancellation check in `scan.go` is
+  removed (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/83)
+
+- a database path holding `?`, `#` or `%` opens exactly the file it names
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/55)
+
+- `scan` rejects `--workers` below 1 as a usage error instead of running
+  single-threaded (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/10)
+
+- a test fails when either walk cancellation check in `scan.go` is removed
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/81)
+
+- test that `scan` refuses a database with another schema version (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/64)
+
+- correct four inaccurate comments in `cancel_test.go` and rename
+  `walkCancelInFlightDirs` to `walkCancelInFlightFiles` (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/33)
+
+- test the `-x` filesystem-boundary rules in `subdirJob` (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/17)
+
+- `scan` creates the schema in one transaction; a version-0 database with a
+  `files` table is refused with a clear schema-version error (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/11)
+
+- README documents install, Docker, a daily cron scan and how to read and check
+  the reports (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/54)
+
+- the `Dockerfile` build stage kept the Go module cache out of `builder`'s home
+  and copied the sources with `--chown`, so no `chown -R` walked them
+  (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/43). Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 there is no `builder` user and
+  nothing changes owner: the build stage only compiles, as root, and the tests
+  run as `nobody` in the `test` phase
+
+- `--version` prints `sfdupes VERSION` to stdout; README documents it and
+  `--help` (2026-10-04, https://git.eeqj.de/sneak/sfdupes/issues/15)
+
+- `scan` stops cleanly on `SIGINT` or `SIGTERM`: commits what it has hashed,
+  deletes nothing more, exits 1 (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/5)
+
+- `report` and `trees` stream the records instead of holding them all in memory;
+  the schema gains the `files_signature` index (2026-10-04,
+  https://git.eeqj.de/sneak/sfdupes/issues/14)
+
+- progress prints at once on a non-terminal, uses a real terminal test, and
+  prints warnings through a spinner instead of racing its redraw (2026-10-03,
+  https://git.eeqj.de/sneak/sfdupes/issues/13)
+
+- warn about and skip symlink, socket, FIFO, device and `.zfs` operands, keeping
+  the records beneath them (2026-10-03,
+  https://git.eeqj.de/sneak/sfdupes/issues/9)
+
+- `scan` holds a lock on a lock file beside the database for its whole run, so a
+  second `scan` fails at once with exit 1 (2026-10-03,
+  https://git.eeqj.de/sneak/sfdupes/issues/53)
+
+- test stdout write failures in `report` and `trees`; README states that
+  `| head` ends sfdupes by `SIGPIPE` and `>&-` writes to `/dev/null`
+  (2026-10-03, https://git.eeqj.de/sneak/sfdupes/issues/30)
+
+- `report` and `trees` open the database read-only, and `scan` leaves it out of
+  WAL mode, so reading needs only read access (2026-10-03, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/8)
+
+- escape tabs, newlines, carriage returns and backslashes in report, trees and
+  warning paths; the root directory's path is `/` (2026-10-03,
+  https://git.eeqj.de/sneak/sfdupes/issues/7)
+
+- stamp the git tag or short commit in a plain `docker build .` instead of `dev`
+  (2026-10-02, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/67): `.dockerignore` sends `.git`
+  without `.git/config`; the build stage stamps the `VERSION` build argument,
+  else `git describe --tags --always`, and fails if the context carries `.git`
+  and the version is still empty, `dev` or `unknown`. CI checks out the full
+  history (`fetch-depth: 0`) so it stamps the same value as `make build`.
+
+- replace the 1 KiB end-window sampling with the head/tail plus content-hash
+  ladder (2026-09-22, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/61); README "Duplicate detection"
+  documents every rung. A file under 10 MiB is hashed in full, and its `head`,
+  `tail` and `content` all hold that hash. A larger file gets only its 64 KiB
+  `head` and `tail` in the hash phase; the content phase, after the update
+  phase, reads it for `content` (the whole file below 50 MiB, gigabyte-spaced 1
+  MiB samples at or above) only when its size, `head` and `tail` match another
+  record's from this scan or an earlier one, and never reads a file gone or
+  changed since its record was written. `report` and `trees` leave out any
+  record without a `content` hash. The `content` column is part of the version 1
+  schema.
+
+- remove the dead `files.dat` references from `Makefile`, `.gitignore` and
+  `.dockerignore` (2026-09-21, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/22)
+
+- fix the lint-image pin comments and `FROM` form in `Dockerfile` and
+  `Dockerfile.lint` (2026-08-10, branch `next`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/25): both pins became the policy
+  `# image:vX.Y.Z, YYYY-MM-DD` comment over a bare `FROM image@sha256:...`,
+  without the false `(Debian-based)` note or the tag. Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 the `Dockerfile`'s `lint` phase
+  holds the only golangci-lint pin, in that form, so `Dockerfile.lint` and
+  `script/verify-lint-image-pin`, which compared the two pins, are gone.
+
+- run all linting in Docker via `Dockerfile.lint` and `script/lint` (2026-08-10,
+  branch `next`, closes https://git.eeqj.de/sneak/sfdupes/issues/46): per the
+  owner ruling the linter is never installed on a host, and
+  `golangci-lint config verify` runs before `golangci-lint run`.
+  `script/bootstrap` stopped installing or pinning the linter, and
+  `script/verify-linter-pin` was retired. Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 both commands run in the
+  `Dockerfile`'s `lint` phase, which `script/lint` builds alone and the build
+  stage depends on through `COPY --from=lint /src/go.sum /dev/null`;
+  `Dockerfile.lint` and `script/verify-lint-image-pin` are gone. Nothing inside
+  an image build may run docker, so the phase calls `golangci-lint` directly.
+
+- install the Docker build stage's prerequisites by running `script/bootstrap`
+  instead of `apk add --no-cache make` inline (2026-08-09, branch
+  `dockerfile-bootstrap`, closes https://git.eeqj.de/sneak/sfdupes/issues/42),
+  with `script/verify-linter-pin` failing the build unless the linter copied
+  from the lint stage was the version `script/bootstrap` pinned. Builds then
+  took up to 5m14s cold, mostly in a `chown -R` of the module cache, filed as
+  https://git.eeqj.de/sneak/sfdupes/issues/43. Since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 the build stage installs `git` and
+  `make` with `apk add --no-cache` and only compiles; the `lint` and `test`
+  phases are the gates
+- bust the Docker layer cache for the gate steps, so `script/cibuild` and
+  `script/docker` cannot report a green they did not earn (2026-08-09, branch
+  `cibuild-cache-bust`, closes https://git.eeqj.de/sneak/sfdupes/issues/32): the
+  `Dockerfile` copies the tree before its gates, so on an unchanged tree Docker
+  served them from cache and the build exited 0 having run nothing. The fix was
+  a `CHECK_EPOCH` build argument; since
+  https://git.eeqj.de/sneak/sfdupes/issues/95 every `docker build` in `script/`
+  passes a new `CACHEBUST` value instead, which every stage of the `Dockerfile`
+  declares before every step that lints, tests or compiles. Run as root, the
+  tests fail `TestScanHardlinkRunFailsTogether`, because root reads through the
+  `chmod(0)` the test relies on, so the `test` phase runs them as `nobody`
+- check the installed golangci-lint version in `script/bootstrap` instead of
+  only its presence (2026-08-09, branch `bootstrap-version-check`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/24): the version lives only in
+  `GOLANGCI_LINT_VERSION`, with the `go install` module ref derived from it, and
+  any installed version that is not the pin — older, newer, absent or
+  unparseable — is reinstalled. `go install` writes into `GOBIN` (or
+  `GOPATH/bin`) while `make lint` runs the first `golangci-lint` on `PATH`, so
+  bootstrap re-reads the effective version after installing and, on a mismatch,
+  prints both paths and both versions and exits non-zero; it does not reorder
+  `PATH` or delete anyone's binary. The `--version` call keeps its stderr and is
+  bounded by `timeout(1)` where that exists. `git`, `make` and `go` keep
+  presence-only checks. Verified by bootstrapping this host from v2.10.1 to
+  v2.12.2 and again to a no-op, and by stub runs of the script under `dash`
+  covering a thirteen-input version-parse matrix, a shadowed install that must
+  exit non-zero, an install destination not on `PATH`, `GOBIN` set, and a wedged
+  binary that must hit the timeout; `make check` and `make lint` are clean at
+  v2.12.2, so v2.10.1 was not hiding any findings on `main`
+- unwind the hash worker pool on the error path (2026-08-09, branch
+  `hash-pool-cleanup`, closes https://git.eeqj.de/sneak/sfdupes/issues/6): the
+  pool is now an owned, context-aware `hashPool`: every blocking send in the
+  feeder and the workers selects on `ctx.Done()`, `jobs` is closed on every path
+  out, and `hashPhase` defers `pool.stop()`, which cancels and then drains
+  `results` until the last goroutine has exited — draining is what frees a
+  worker already parked on a send. `ctx` is threaded from `cmd.Context()`
+  through `runScan`, `syncScan`, both worker pools and the whole database layer,
+  as the first parameter everywhere. The walk pool gets the same treatment plus
+  a `ctx.Err()` guard after the walk: a cancelled walk yields a partial size
+  census, and every file it never reached looks vanished to the update phase.
+  That phase's own `BeginTx` also fails on the cancelled context before deleting
+  anything, but the guard is the barrier that still holds once an interrupted
+  scan may commit what it has. Tests drive `run(scan)` against a database whose
+  insert trigger aborts and assert that the scan fails instead of hanging and
+  that `runtime.NumGoroutine()` polls back to its pre-scan baseline; others
+  cancel a scan part-way through the walk, deterministically, by counting its
+  own consultations of `ctx.Done()`, and assert that it stops at the guard
+  holding a partial census and a still-populated record index, with every record
+  intact. Direct tests of `sendEvent`, the walk workers, `dispatchDirs`,
+  `feedHashJobs`, `hashWorker` and `hashPhase` cover the remaining cancellation
+  branches of both pools
+- guarantee the database is closed on every fatal exit path (2026-08-09, branch
+  `db-close-on-fatal`, closes https://git.eeqj.de/sneak/sfdupes/issues/4):
+  `fatalf` and its `os.Exit(1)` are gone, so the deferred `db.Close()` — and
+  with it the SQLite WAL checkpoint — now actually runs when a subcommand fails;
+  `runScan`, `runReport`, `runTrees`, `loadRecords` and `resolveRoots` return
+  errors instead. The single exit point is `run` in `main.go`: it maps a
+  `fatalError` (anything a subcommand returned) to exit 1 and cobra's own
+  argument and flag errors to exit 2, which keeps a runtime failure from being
+  reported as a usage error or printing the usage text. New `main_test.go`
+  drives the CLI in-process and asserts the exit codes from README §Error
+  handling plus the stdout/stderr split, including that a fatal error raised
+  after the database is open leaves no `-wal`/`-shm` sidecar behind for `scan`,
+  `report` or `trees`
+- update golangci-lint to v2.12.2 with the canonical config (2026-08-09, branch
+  `golangci-v2.12.2`, merged as `38a01bd`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/3): bumped the pinned linter in the
+  `Dockerfile` lint stage and `script/bootstrap` from v2.12.1 to v2.12.2, and
+  replaced `.golangci.yml` with the canonical file — the linter settings (`lll`,
+  `funlen`, `cyclop`, `dupl` thresholds) now live under `linters.settings` per
+  the v2 schema, so they are actually applied; no new lint findings surfaced
+- convert Makefile targets to scripts-to-rule-them-all `script/` entrypoints
+  like the other managed repos (2026-07-26, commit `3abeacf`, closes
+  https://git.eeqj.de/sneak/sfdupes/issues/1): all 12 `script/` entrypoints
+  exist (`bootstrap`, `setup`, `projectname`, `test`, `lint`, `fmt`,
+  `fmt-check`, `check`, `docker`, `cibuild`, `precommit`, `install-precommit`)
+  and every Makefile target is now a thin shim over them
+- make the binary the default Make target (2026-07-24, branch
+  `make-default-target`): plain `make` now builds `sfdupes` (previously it ran
+  `check` plus `build`); `make build` remains as an alias
+- scan-wide phases, concurrent operands, batched updates (2026-07-24, branch
+  `scan-wide-phases`): all operands seed the shared walk pool and every pass
+  runs once over the whole scan, so totals and ETAs are scan-global; the
+  per-operand walk/hash/update cycles and their stderr announcements are gone;
+  the update pass commits in batched transactions — the filesystem is
+  authoritative and the database an eventually-consistent reflection, so
+  scan-level atomicity is not required
+- split the stat pass back out of the walk (2026-07-24, branch
+  `parallel-phases`): phases are strictly sequential again — walk, stat, hash,
+  update per operand — with parallelism only inside each phase; the walk
+  enumerates paths with per-directory workers and the stat pass lstats them with
+  per-file workers, restoring the exact total/ETA stat bar
+- announce each operand on stderr before its passes (2026-07-24, branch
+  `scan-operand-progress`): with per-operand walk/hash/update cycles, a
+  multi-operand run (e.g. `scan /srv/*`) showed pass totals that looked like the
+  whole run's
+- parallel walk (2026-07-24, branch `parallel-walk`): the walk pass was a single
+  goroutine and took hours at ~20M files on a busy pool (observed: 22M files in
+  4h on a ZFS server); it is now a per-directory worker-pool traversal that
+  records size/mtime during the walk (folding away the separate stat pass,
+  halving metadata I/O), and each `PATH` operand commits in its own transaction
+  so an interrupted scan keeps completed operands
+
+- persistent scan database (2026-07-24, branch `persistent-database`): `scan`
+  now maintains a SQLite database (`modernc.org/sqlite`, pure Go, cgo stays
+  disabled) keyed by absolute path that survives between runs — a rescan hashes
+  only new or changed files (by mtime/size), deletes records for files vanished
+  from under the scanned operands, and leaves records outside them untouched, so
+  `scan` can be cronned daily; `report` and `trees` read the database (no
+  positional arguments) instead of a scan stream. Database at
+  `/var/lib/sfdupes/db.sqlite`, overridable via `SFDUPES_DATABASE`; WAL
+  journaling plus a single-transaction update keep a report run during a scan
+  safe
+- add the `origin` remote (`git@git.eeqj.de:sneak/sfdupes.git`), tag `v0.0.1`,
+  and push `main` plus tags (2026-07-23)
+- `scan` CLI rework (2026-07-23, branch `scan-required-paths`): required
+  `PATH...` operands via cobra flags replacing the `/srv` `-root` default; new
+  `-x`/`--one-file-system` flag (GNU convention) to stop at filesystem
+  boundaries, which are crossed by default
+- bring the repo into full policy compliance (2026-07-23, branch
+  `repo-policy-compliance`; checklist below)
+- `git init` with README-only first commit; code baseline committed on `main`
+  (2026-07-22)
+- implement `scan`, `report`, and `trees` subcommands (pre-git history)

 # Future Steps

- Possible later features, out of scope per README, are a byte-for-byte check of
-  candidates and helper scripts for removal.
+- possible later features (explicitly out of scope per README): full-content
+  verification of candidates, removal-script helpers

-# Accepted Divergences
+# Repo Policy Compliance

-None.
+Audited 2026-07-22 against `REPO_POLICIES.md` (2026-07-06), the existing repo
+checklist, and the Go styleguide. Code is already gofmt-clean, so no standalone
+formatting commit is needed.
+
+- [x] `.gitignore` missing — the compiled `sfdupes` binary and `files.dat` sit
+      untracked in the tree; needs OS/editor/Go artifacts plus secrets patterns
+- [x] `.editorconfig` missing
+- [x] `LICENSE` missing and README has no License section (MIT assumed from
+      house convention — user to confirm)
+- [x] `REPO_POLICIES.md` missing from repo root
+- [x] `.golangci.yml` missing (install canonical copy); code must then pass
+      `make lint` (150 findings fixed; `make lint` is clean)
+- [x] `Makefile` lacks required targets `test`, `lint`, `fmt`, `fmt-check`,
+      `docker`, `hooks`; `check` currently depends on `build`, which writes the
+      binary (`make check` must not modify files)
+- [x] no tests — `go test ./...` has nothing to run; policy requires real tests
+      with a 30-second timeout and the conditional `-v` rerun pattern (suite
+      covers parsing, grouping, digests, suppression, hashing, and the scan
+      pipeline; 64% coverage)
+- [x] `Dockerfile` missing — Go multistage with hash-pinned images: fail-fast
+      lint stage, build stage running `make check`
+- [x] `.dockerignore` missing
+- [x] `.gitea/workflows/check.yml` missing (`docker build .` on push, checkout
+      action pinned by commit SHA)
+- [x] README lacks required sections: Description first line
+      (name/purpose/category/license/author), Getting Started, Rationale, TODO,
+      License, Author
+- [x] README non-goal "no git repository setup and no CI" is stale now that the
+      repo is under git with CI
+- [x] pre-commit hook not installed (`make hooks` once the target exists)
+
+Accepted divergences (no action):
+
+- flat single-package layout with `.go` files in the repo root — fine for a
+  small single-binary tool per the Go styleguide; the tracker audit agrees
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // cancels the unexported runScan and hashWorker
+package main

 import (
 	"context"
@@ -1,29 +0,0 @@
-// Command sfdupes quickly identifies candidate duplicate files across
-// very large filesystems without reading every byte of every file.
-// Files are considered duplicates when their sizes are equal and they
-// agree on three SHA-256 hashes: of the first 64 KiB, of the last 64
-// KiB, and of the content. The content hash covers the whole file under
-// 100 MiB, and 1 MiB at each gigabyte at 100 MiB or more, so a large
-// file is never read in full. scan maintains a persistent SQLite
-// database of file signatures (SFDUPES_DATABASE, default
-// /var/lib/sfdupes/db.sqlite) that the other subcommands read.
-//
-// Usage:
-//
-//	sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
-//	sfdupes report > dupes.tsv
-//	sfdupes trees > dupetrees.tsv
-//	sfdupes info
-//	sfdupes dwim
-//	sfdupes --version
-//
-// See README.md for the complete specification.
-package main
-
-import (
-	"os"
-
-	"sneak.berlin/go/sfdupes/internal/sfdupes"
-)
-
-func main() { os.Exit(sfdupes.Main()) }
@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"context"
@@ -47,15 +47,14 @@ const dbFilePerm = 0o644
 const lockFilePerm = 0o600

 // createTableSQL is the schema applied to a fresh database. Paths are
-// BLOBs because Unix paths are raw bytes, not guaranteed UTF-8.
-// disk_size holds the bytes the file takes on disk. mtime holds whole
-// Unix seconds and mtime_nsec the nanoseconds within that second. head,
-// tail and content each hold the raw 32 bytes of a SHA-256.
+// BLOBs because Unix paths are raw bytes, not guaranteed UTF-8. mtime
+// holds whole Unix seconds and mtime_nsec the nanoseconds within that
+// second. head, tail and content each hold the raw 32 bytes of a
+// SHA-256.
 const createTableSQL = `
 CREATE TABLE files (
    path       BLOB PRIMARY KEY,
    size       INTEGER NOT NULL,
-    disk_size  INTEGER NOT NULL,
    mtime      INTEGER NOT NULL,
    mtime_nsec INTEGER NOT NULL,
    head       BLOB NOT NULL,
@@ -70,59 +69,14 @@ const createIndexSQL = `
 CREATE INDEX files_signature ON files (size, head, tail, content)
 `

-// createTotalsSQL creates the totals table, which holds one row: the
-// number of records and the sizes of all records added up. Counting
-// them over files would read every record. The three triggers below
-// keep the row current, in the transaction of each change to files.
-const createTotalsSQL = `
-CREATE TABLE totals (
-    records INTEGER NOT NULL,
-    size    INTEGER NOT NULL
-)
-`
-
-// insertTotalsSQL adds the one row of totals, for an empty files table.
-const insertTotalsSQL = `
-INSERT INTO totals (records, size) VALUES (0, 0)
-`
-
-// totalsAfterInsertSQL counts each inserted record into totals.
-const totalsAfterInsertSQL = `
-CREATE TRIGGER totals_after_insert AFTER INSERT ON files BEGIN
-    UPDATE totals SET records = records + 1, size = size + NEW.size;
-END
-`
-
-// totalsAfterDeleteSQL takes each deleted record out of totals.
-const totalsAfterDeleteSQL = `
-CREATE TRIGGER totals_after_delete AFTER DELETE ON files BEGIN
-    UPDATE totals SET records = records - 1, size = size - OLD.size;
-END
-`
-
-// totalsAfterUpdateSQL replaces a record's old size in totals with its
-// new one. scan's upsert of an existing record is such an update.
-const totalsAfterUpdateSQL = `
-CREATE TRIGGER totals_after_update AFTER UPDATE OF size ON files BEGIN
-    UPDATE totals SET size = size + NEW.size - OLD.size;
-END
-`
-
-// recordCountSQL reads the number of records from totals.
-const recordCountSQL = `
-SELECT records FROM totals
-`
-
 // upsertSQL inserts one file record, replacing any existing record for
 // the same path.
 const upsertSQL = `
-INSERT INTO files (
-    path, size, disk_size, mtime, mtime_nsec, head, tail, content
-)
-VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+INSERT INTO files (path, size, mtime, mtime_nsec, head, tail, content)
+VALUES (?, ?, ?, ?, ?, ?, ?)
 ON CONFLICT (path) DO UPDATE SET
-    size = excluded.size, disk_size = excluded.disk_size,
-    mtime = excluded.mtime, mtime_nsec = excluded.mtime_nsec,
+    size = excluded.size, mtime = excluded.mtime,
+    mtime_nsec = excluded.mtime_nsec,
    head = excluded.head, tail = excluded.tail,
    content = excluded.content
 `
@@ -146,44 +100,33 @@ var errHashSize = errors.New("hash is not 32 bytes")

 // databasePath resolves the database location: SFDUPES_DATABASE when
 // set and non-empty, the compiled-in default otherwise. It returns the
-// path, made absolute by absolutePath, and where the path came from,
-// "default" or "from SFDUPES_DATABASE", for the line each subcommand
-// prints first on stderr.
+// path, with the working directory, its symlinks resolved, put in front
+// of it when it is relative, and where the path came from, "default" or
+// "from SFDUPES_DATABASE", for the line each subcommand prints first on
+// stderr.
 func databasePath() (string, string, error) {
 	path, source := defaultDatabasePath, "default"
 	if p := os.Getenv(databaseEnv); p != "" {
 		path, source = p, "from "+databaseEnv
 	}

-	abs, err := absolutePath(path)
+	if filepath.IsAbs(path) {
+		return path, source, nil
+	}
+
+	// The working directory as the kernel reports it, with no symlink
+	// in it, as README "Database" says. os.Getwd may return PWD
+	// instead, which can name it through a symlink.
+	wd, err := unix.Getwd()
 	if err != nil {
 		return "", "", fmt.Errorf("resolve database path %s: %w", path, err)
 	}

-	return abs, source, nil
-}
-
-// absolutePath returns path unchanged when it is absolute, and
-// otherwise the working directory, a "/" and path. The working
-// directory is the one the kernel reports, with no symlink in it;
-// os.Getwd may return PWD instead, which can name it through a symlink.
-// The result is not cleaned, as filepath.Abs and filepath.Join would
-// clean it. Cleaning drops each ".." together with the directory name
-// before it. When that name is a symlink, the cleaned path names
-// another file than the one the system reaches by following the symlink
-// first.
-func absolutePath(path string) (string, error) {
-	if filepath.IsAbs(path) {
-		return path, nil
-	}
-
-	wd, err := unix.Getwd()
-	if err != nil {
-		return "", err
-	}
-
+	// Not filepath.Abs or filepath.Join: they clean the path, which
+	// drops each ".." together with the directory name before it. When
+	// that directory is a symlink, the cleaned path names another file.
 	// The working directory ends in "/" only when it is the root.
-	return strings.TrimSuffix(wd, "/") + "/" + path, nil
+	return strings.TrimSuffix(wd, "/") + "/" + path, source, nil
 }

 // createDatabaseDirectory creates the directory the database at path
@@ -207,14 +150,9 @@ func createDatabaseDirectory(path string) error {
 // scanParams are the connection parameters for scan: read-write, with
 // WAL journaling and a busy timeout, so a report can run while a cron
 // scan is in progress. closeScanDatabase leaves WAL mode again.
-//
-// Each write to files fires a trigger, so SQLite keeps a statement
-// journal for it. temp_store(MEMORY) keeps that journal in memory,
-// which costs far less than a temporary file.
 const scanParams = "_pragma=busy_timeout(10000)" +
 	"&_pragma=journal_mode(WAL)" +
-	"&_pragma=synchronous(NORMAL)" +
-	"&_pragma=temp_store(MEMORY)"
+	"&_pragma=synchronous(NORMAL)"

 // reportParams are the connection parameters for report, trees and
 // info: read-only, with the same busy timeout. They set no journal
@@ -488,14 +426,14 @@ func createSchema(ctx context.Context, db *sql.DB) error {

 	defer func() { _ = tx.Rollback() }()

-	for _, stmt := range []string{
-		createTableSQL, createIndexSQL, createTotalsSQL, insertTotalsSQL,
-		totalsAfterInsertSQL, totalsAfterDeleteSQL, totalsAfterUpdateSQL,
-	} {
-		_, err = tx.ExecContext(ctx, stmt)
-		if err != nil {
-			return fmt.Errorf("create schema: %w", err)
-		}
+	_, err = tx.ExecContext(ctx, createTableSQL)
+	if err != nil {
+		return fmt.Errorf("create schema: %w", err)
+	}
+
+	_, err = tx.ExecContext(ctx, createIndexSQL)
+	if err != nil {
+		return fmt.Errorf("create schema: %w", err)
 	}

 	_, err = tx.ExecContext(ctx,
@@ -542,7 +480,7 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),

 	var n int64

-	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -550,8 +488,8 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 	total(n)

 	rows, err := tx.QueryContext(ctx,
-		"SELECT path, size, disk_size, mtime, mtime_nsec, head, tail, "+
-			"content FROM files ORDER BY path")
+		"SELECT path, size, mtime, mtime_nsec, head, tail, content "+
+			"FROM files ORDER BY path")
 	if err != nil {
 		return fmt.Errorf("read records: %w", err)
 	}
@@ -565,8 +503,7 @@ func loadFileRows(ctx context.Context, db *sql.DB, total func(n int64),
 			r                         scanRec
 		)

-		err = rows.Scan(&path, &r.size, &r.diskSize, &sec, &nsec,
-			&head, &tail, &content)
+		err = rows.Scan(&path, &r.size, &sec, &nsec, &head, &tail, &content)
 		if err != nil {
 			return fmt.Errorf("read record: %w", err)
 		}
@@ -601,11 +538,10 @@ ORDER BY size DESC, head DESC, tail DESC, content DESC
 `

 // loadSignatureRows gives total the number of records, then streams
-// every record's signature and path to fn, without its mtime or its
-// disk_size, in the order of signatureRowsSQL. The count and the
-// records are read in one transaction, so they agree while a scan is
-// committing. An error from fn stops the reading and is returned as it
-// is.
+// every record's signature and path to fn, without its mtime, in the
+// order of signatureRowsSQL. The count and the records are read in one
+// transaction, so they agree while a scan is committing. An error from
+// fn stops the reading and is returned as it is.
 func loadSignatureRows(ctx context.Context, db *sql.DB,
 	total func(n int64), fn func(r scanRec) error,
 ) error {
@@ -620,7 +556,7 @@ func loadSignatureRows(ctx context.Context, db *sql.DB,

 	var n int64

-	err = tx.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err = tx.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return fmt.Errorf("count records: %w", err)
 	}
@@ -686,7 +622,7 @@ func (r *scanRec) setHashes(head, tail, content []byte) error {
 func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	var n int64

-	err := db.QueryRowContext(ctx, recordCountSQL).Scan(&n)
+	err := db.QueryRowContext(ctx, "SELECT COUNT(*) FROM files").Scan(&n)
 	if err != nil {
 		return 0, fmt.Errorf("count records: %w", err)
 	}
@@ -694,10 +630,12 @@ func countRecords(ctx context.Context, db *sql.DB) (int64, error) {
 	return n, nil
 }

-// databaseCountsSQL reads the number of records and the sizes of all
-// records added up from totals.
+// databaseCountsSQL counts the records and adds up their sizes, in one
+// pass over the table. A SUM over no rows is NULL, so on an empty table
+// the SUM falls back to 0.
 const databaseCountsSQL = `
-SELECT records, size FROM totals
+SELECT COUNT(*), COALESCE(SUM(size), 0)
+FROM files
 `

 // databaseCounts is what info reads from the database: its schema
@@ -740,15 +678,15 @@ func readDatabaseCounts(ctx context.Context,
 	return c, nil
 }

-// loadFileMeta streams every record's path, size, disk_size and mtime
-// to fn. Scan change detection needs no hash values, and skipping the
-// hash columns keeps the scan's in-memory index small on
-// multi-million-file databases.
+// loadFileMeta streams every record's path, size and mtime to fn. Scan
+// change detection needs no hash values, and skipping the hash columns
+// keeps the scan's in-memory index small on multi-million-file
+// databases.
 func loadFileMeta(ctx context.Context, db *sql.DB,
-	fn func(path string, m fileMeta),
+	fn func(path string, size int64, mtime time.Time),
 ) error {
 	rows, err := db.QueryContext(ctx,
-		"SELECT path, size, disk_size, mtime, mtime_nsec FROM files")
+		"SELECT path, size, mtime, mtime_nsec FROM files")
 	if err != nil {
 		return fmt.Errorf("read records: %w", err)
 	}
@@ -757,19 +695,16 @@ func loadFileMeta(ctx context.Context, db *sql.DB,

 	for rows.Next() {
 		var (
-			path      []byte
-			m         fileMeta
-			sec, nsec int64
+			path            []byte
+			size, sec, nsec int64
 		)

-		err = rows.Scan(&path, &m.size, &m.diskSize, &sec, &nsec)
+		err = rows.Scan(&path, &size, &sec, &nsec)
 		if err != nil {
 			return fmt.Errorf("read record: %w", err)
 		}

-		m.mtime = time.Unix(sec, nsec)
-
-		fn(string(path), m)
+		fn(string(path), size, time.Unix(sec, nsec))
 	}

 	err = rows.Err()
@@ -787,21 +722,21 @@ func loadFileMeta(ctx context.Context, db *sql.DB,
 // WAL small and let concurrent reports observe progress.
 const updateBatchSize = 10000

-// applyChanges writes upserts for new and changed files and deletes for
-// vanished ones, in batched transactions. Progress is rendered on prog
-// (one increment per change).
+// applyChanges writes one scan's database changes — upserts for new and
+// changed files, deletes for vanished ones — in batched transactions.
+// Progress is rendered on prog (one increment per change).
 func applyChanges(ctx context.Context, db *sql.DB, upserts []scanRec,
 	deletes []string, prog *progress,
 ) error {
 	for batch := range slices.Chunk(upserts, updateBatchSize) {
-		err := applyBatch(ctx, db, batch, nil, nil, prog)
+		err := applyBatch(ctx, db, batch, nil, prog)
 		if err != nil {
 			return err
 		}
 	}

 	for batch := range slices.Chunk(deletes, updateBatchSize) {
-		err := applyBatch(ctx, db, nil, nil, batch, prog)
+		err := applyBatch(ctx, db, nil, batch, prog)
 		if err != nil {
 			return err
 		}
@@ -810,26 +745,10 @@ func applyChanges(ctx context.Context, db *sql.DB, upserts []scanRec,
 	return nil
 }

-// applyDiskSizes writes the disk_size of each of recs into its record,
-// in batched transactions, and leaves the rest of the record alone.
-// Progress is rendered on prog (one increment per record).
-func applyDiskSizes(ctx context.Context, db *sql.DB, recs []fileRec,
-	prog *progress,
-) error {
-	for batch := range slices.Chunk(recs, updateBatchSize) {
-		err := applyBatch(ctx, db, nil, batch, nil, prog)
-		if err != nil {
-			return err
-		}
-	}
-
-	return nil
-}
-
-// applyBatch commits one batch of upserts, disk_size updates and
-// deletes in a single transaction.
+// applyBatch commits one batch of upserts and deletes in a single
+// transaction.
 func applyBatch(ctx context.Context, db *sql.DB, upserts []scanRec,
-	diskSizes []fileRec, deletes []string, prog *progress,
+	deletes []string, prog *progress,
 ) error {
 	tx, err := db.BeginTx(ctx, nil)
 	if err != nil {
@@ -843,11 +762,6 @@ func applyBatch(ctx context.Context, db *sql.DB, upserts []scanRec,
 		return err
 	}

-	err = execDiskSizes(ctx, tx, diskSizes, prog)
-	if err != nil {
-		return err
-	}
-
 	err = execDeletes(ctx, tx, deletes, prog)
 	if err != nil {
 		return err
@@ -873,7 +787,7 @@ func execUpserts(ctx context.Context, tx *sql.Tx, upserts []scanRec,
 	defer func() { _ = st.Close() }()

 	for _, r := range upserts {
-		_, err = st.ExecContext(ctx, []byte(r.path), r.size, r.diskSize,
+		_, err = st.ExecContext(ctx, []byte(r.path), r.size,
 			r.mtime.Unix(), r.mtime.Nanosecond(),
 			r.head[:], r.tail[:], r.content[:])
 		if err != nil {
@@ -886,31 +800,6 @@ func execUpserts(ctx context.Context, tx *sql.Tx, upserts []scanRec,
 	return nil
 }

-// execDiskSizes sets the disk_size of the record of each of recs. It
-// does not touch size, so the totals triggers do not fire.
-func execDiskSizes(ctx context.Context, tx *sql.Tx, recs []fileRec,
-	prog *progress,
-) error {
-	st, err := tx.PrepareContext(ctx,
-		"UPDATE files SET disk_size = ? WHERE path = ?")
-	if err != nil {
-		return fmt.Errorf("prepare disk_size update: %w", err)
-	}
-
-	defer func() { _ = st.Close() }()
-
-	for _, r := range recs {
-		_, err = st.ExecContext(ctx, r.diskSize, []byte(r.path))
-		if err != nil {
-			return fmt.Errorf("update disk_size of %s: %w", r.path, err)
-		}
-
-		prog.increment()
-	}
-
-	return nil
-}
-
 // execDeletes removes the records for paths no longer present.
 func execDeletes(ctx context.Context, tx *sql.Tx, deletes []string,
 	prog *progress,
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // calls the unexported database openers
+package main

 import (
 	"context"
@@ -535,12 +535,17 @@ func TestLoadRowsRefuseWrongSizeHash(t *testing.T) {
 	}
 }

-// queryPlan returns the detail of each line of SQLite's EXPLAIN QUERY
-// PLAN for query.
-func queryPlan(t *testing.T, db *sql.DB, query string) []string {
-	t.Helper()
+// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
+// from the files_signature index alone, with nothing to sort: the
+// first record comes at once, so report's read phase counts each
+// record as it comes rather than waiting on SQLite for all of them.
+func TestSignatureRowsNeedNoSort(t *testing.T) {
+	t.Parallel()

-	rows, err := db.QueryContext(t.Context(), "EXPLAIN QUERY PLAN "+query)
+	db := openTestDB(t)
+
+	rows, err := db.QueryContext(t.Context(),
+		"EXPLAIN QUERY PLAN "+signatureRowsSQL)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -568,164 +573,12 @@ func queryPlan(t *testing.T, db *sql.DB, query string) []string {
 		t.Fatal(err)
 	}

-	return plan
-}
-
-// TestSignatureRowsNeedNoSort checks that SQLite reads signatureRowsSQL
-// from the files_signature index alone, with nothing to sort: the
-// first record comes at once, so report's read phase counts each
-// record as it comes rather than waiting on SQLite for all of them.
-func TestSignatureRowsNeedNoSort(t *testing.T) {
-	t.Parallel()
-
-	db := openTestDB(t)
-
-	plan := queryPlan(t, db, signatureRowsSQL)
-
 	want := []string{"SCAN files USING COVERING INDEX files_signature"}
 	if !slices.Equal(plan, want) {
 		t.Errorf("query plan = %q, want %q", plan, want)
 	}
 }

-// TestCountsReadOnlyTotals checks that SQLite answers the queries for
-// the number of records and their total size from the one row of
-// totals. A plan that reads files or its index reads every record.
-func TestCountsReadOnlyTotals(t *testing.T) {
-	t.Parallel()
-
-	db := openTestDB(t)
-
-	for _, query := range []string{recordCountSQL, databaseCountsSQL} {
-		plan := queryPlan(t, db, query)
-
-		want := []string{"SCAN totals"}
-		if !slices.Equal(plan, want) {
-			t.Errorf("query plan of %q = %q, want %q", query, plan, want)
-		}
-	}
-}
-
-// TestCountsComeFromTotals sets the row of totals to numbers that files
-// does not hold, then checks that scan's load phase, the read phases of
-// trees and report, and info each report the numbers from totals.
-func TestCountsComeFromTotals(t *testing.T) {
-	t.Parallel()
-
-	// files is empty, so a count over files gives 0 records of 0 bytes.
-	const records, size = 7, 9000
-
-	db := openTestDB(t)
-
-	_, err := db.ExecContext(t.Context(),
-		"UPDATE totals SET records = ?, size = ?", records, size)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	scanTotal, err := countRecords(t.Context(), db)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	var treesTotal, reportTotal int64
-
-	err = loadFileRows(t.Context(), db,
-		func(n int64) { treesTotal = n }, func(scanRec) {})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	err = loadSignatureRows(t.Context(), db,
-		func(n int64) { reportTotal = n },
-		func(scanRec) error { return nil })
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	info, err := readDatabaseCounts(t.Context(), db)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	for name, got := range map[string]int64{
-		"scan's load":   scanTotal,
-		"trees' read":   treesTotal,
-		"report's read": reportTotal,
-		"info":          info.records,
-	} {
-		if got != records {
-			t.Errorf("%s: %d records, want %d from totals",
-				name, got, records)
-		}
-	}
-
-	if info.size != size {
-		t.Errorf("info: size %d, want %d from totals", info.size, size)
-	}
-}
-
-// assertTotalsMatchFiles fails unless the row of totals holds the
-// number of records and the sizes of all records added up, as counted
-// over files.
-func assertTotalsMatchFiles(t *testing.T, db *sql.DB) {
-	t.Helper()
-
-	got, err := readDatabaseCounts(t.Context(), db)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	var records, size int64
-
-	err = db.QueryRowContext(t.Context(),
-		"SELECT COUNT(*), COALESCE(SUM(size), 0) FROM files").
-		Scan(&records, &size)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	if got.records != records || got.size != size {
-		t.Errorf("totals = %d records of %d bytes, files holds %d of %d",
-			got.records, got.size, records, size)
-	}
-}
-
-// TestTotalsMatchFiles scans the smoke tree, rescans it after two files
-// change size, and rescans it after two files are removed. After each
-// scan the row of totals must agree with files.
-func TestTotalsMatchFiles(t *testing.T) {
-	t.Parallel()
-
-	dir := buildSmokeTree(t)
-	db := openTestDB(t)
-
-	syncTree(t, db, dir)
-	assertTotalsMatchFiles(t, db)
-
-	writeFile(t, dir, "a/one.bin", pattern(10, 2500))
-	writeFile(t, dir, "t1/f1", pattern(30, 1000))
-
-	if st := syncTree(t, db, dir); st.updated != 2 {
-		t.Fatalf("rescan stats = %+v, want 2 updated", st)
-	}
-
-	assertTotalsMatchFiles(t, db)
-
-	for _, name := range []string{"a/unique.bin", "t2/sub/f2"} {
-		err := os.Remove(filepath.Join(dir, name))
-		if err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	if st := syncTree(t, db, dir); st.removed != 2 {
-		t.Fatalf("rescan stats = %+v, want 2 removed", st)
-	}
-
-	assertTotalsMatchFiles(t, db)
-}
-
 func TestApplyChangesRoundTrip(t *testing.T) {
 	t.Parallel()

@@ -1,4 +1,4 @@
-package sfdupes
+package main

 // This file holds two rules for the walk (README "Rules for the walk"):
 // the default excludes, the paths a scan's walk does not enter below an
@@ -1,6 +1,6 @@
 //go:build darwin

-package sfdupes
+package main

 import (
 	"slices"
@@ -1,6 +1,6 @@
 //go:build !darwin

-package sfdupes
+package main

 import (
 	"fmt"
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // checks the unexported defaultExcludes
+package main

 import (
 	"bytes"
@@ -17,9 +17,7 @@ import (
 func TestDefaultExcludes(t *testing.T) {
 	t.Parallel()

-	// README "Rules for the walk": the Linux and macOS lists, and none
-	// on any other system. The Windows list exists in the code only: the
-	// binary does not build for Windows, so the README leaves it out.
+	// README "Rules for the walk": each system's list.
 	cases := map[string][]string{
 		goosLinux: {"/proc", "/sys", "/dev", "/run", "/tmp", "/var/tmp"},
 		goosDarwin: {
@@ -286,7 +284,7 @@ func TestRunScanTempDirOperand(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

-	dir := realTempDir(t)
+	dir := t.TempDir()
 	if !underAnyRoot(dir, defaultExcludes(runtime.GOOS)) {
 		t.Skip(dir + " is not inside a default exclude")
 	}
@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"context"
@@ -26,11 +26,11 @@ func infoPhase(name string) string {
 // it. Any database problem, including a missing database, is fatal.
 //
 // The work runs in two phases, each under a progress display of its
-// own on stderr: open (open the database) and count (read the number of
-// records and their total size from the totals table). Each display
-// ends before the next phase starts, and before an error is returned
-// to be printed. The details are written once the last display has
-// ended, so no display is drawn while they are written.
+// own on stderr: open (open the database) and count (count the records,
+// with one query). Each display ends before the next phase starts, and
+// before an error is returned to be printed. The details are written
+// once the last display has ended, so no display is drawn while they
+// are written.
 func runInfo(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -56,7 +56,7 @@ func runInfo(ctx context.Context, stdout io.Writer) error {

 	defer func() { _ = db.Close() }()

-	// One row holds both counts, so the phase never has a total.
+	// One query counts everything, so the phase never has a total.
 	prog = newProgress(progressParams{
 		label: infoPhase("count"), total: -1,
 		waitingFor: countingRecords,
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // seeds the database with unexported scanRec
+package main

 import (
 	"fmt"
@@ -1,37 +0,0 @@
-package sfdupes
-
-import (
-	"context"
-	"fmt"
-	"io"
-	"os"
-	"runtime"
-)
-
-// runDwim implements the dwim subcommand: it runs what "sfdupes scan
-// root" runs with no flags, then what "sfdupes trees" runs, and ends
-// with a line on stderr saying how to print the report again. The dwim
-// command passes "/" as root. It catches SIGINT and SIGTERM as scan
-// does, but only during the scan. An error from the scan, an interrupt
-// included, ends it before the report. During the report, a signal
-// ends it at once, as it ends trees.
-func runDwim(ctx context.Context, root string, stdout io.Writer) error {
-	scanCtx, stop := interruptContext(ctx)
-	err := runScan(scanCtx, []string{root}, runtime.NumCPU(), false, false)
-
-	stop()
-
-	if err != nil {
-		return err
-	}
-
-	err = runTrees(ctx, stdout)
-	if err != nil {
-		return err
-	}
-
-	fmt.Fprintln(os.Stderr,
-		`dwim: run "sfdupes trees" to print this report again`)
-
-	return nil
-}
@@ -1,83 +0,0 @@
-package sfdupes //nolint:testpackage // calls the unexported runDwim
-
-import (
-	"bytes"
-	"path/filepath"
-	"strings"
-	"testing"
-)
-
-func TestRunDwimPrintsLargestTreesFirst(t *testing.T) {
-	// dwim scans its root, then prints the trees report, the larger of
-	// two duplicate-tree pairs first, and ends by saying how to print
-	// the report again.
-	t.Setenv(databaseEnv, testDBPath(t))
-
-	root := realTempDir(t)
-
-	small := []string{
-		filepath.Dir(writeFile(t, root, "a1/f.bin", pattern(1, 300))),
-		filepath.Dir(writeFile(t, root, "a2/f.bin", pattern(1, 300))),
-	}
-	large := []string{
-		filepath.Dir(writeFile(t, root, "b1/f.bin", pattern(2, 5000))),
-		filepath.Dir(writeFile(t, root, "b2/f.bin", pattern(2, 5000))),
-	}
-
-	var stdout bytes.Buffer
-
-	stderr := captureStderr(t)
-
-	err := runDwim(t.Context(), root, &stdout)
-	if err != nil {
-		t.Fatalf("runDwim: %v; stderr: %s", err, stderr())
-	}
-
-	lines := strings.Split(strings.TrimSuffix(stdout.String(), "\n"), "\n")
-	if len(lines) != 3 {
-		t.Fatalf("stdout = %q, want a header and two groups",
-			stdout.String())
-	}
-
-	wantFirst := large[0] + "\t" + large[1] + "\t1\t5000\t"
-	if !strings.HasPrefix(lines[1], wantFirst) {
-		t.Errorf("first group = %q, want it to start %q", lines[1], wantFirst)
-	}
-
-	wantSecond := small[0] + "\t" + small[1] + "\t1\t300\t"
-	if !strings.HasPrefix(lines[2], wantSecond) {
-		t.Errorf("second group = %q, want it to start %q",
-			lines[2], wantSecond)
-	}
-
-	last := "\ndwim: run \"sfdupes trees\" to print this report again\n"
-	if got := stderr(); !strings.HasSuffix(got, last) {
-		t.Errorf("stderr = %q, want it to end %q", got, last)
-	}
-}
-
-func TestRunDwimScanErrorPrintsNoReport(t *testing.T) {
-	// A fatal scan error ends dwim before the report: a root that does
-	// not exist fails the scan as it fails scan itself.
-	t.Setenv(databaseEnv, testDBPath(t))
-
-	missing := filepath.Join(realTempDir(t), "missing")
-
-	var stdout bytes.Buffer
-
-	stderr := captureStderr(t)
-
-	err := runDwim(t.Context(), missing, &stdout)
-	if err == nil {
-		t.Fatal("runDwim on a missing root: error = nil, want it fatal")
-	}
-
-	if got := stdout.String(); got != "" {
-		t.Errorf("stdout = %q, want no report", got)
-	}
-
-	if got := stderr(); strings.Contains(got, "trees:") ||
-		strings.Contains(got, "dwim:") {
-		t.Errorf("stderr = %q, want nothing from trees or dwim", got)
-	}
-}
@@ -1,6 +1,23 @@
-// Package sfdupes implements the sfdupes command and the database its
-// subcommands share.
-package sfdupes
+// Command sfdupes quickly identifies candidate duplicate files across
+// very large filesystems without reading every byte of every file.
+// Files are considered duplicates when their sizes are equal and they
+// agree on three SHA-256 hashes: of the first 64 KiB, of the last 64
+// KiB, and of the content. The content hash covers the whole file under
+// 100 MiB, and 1 MiB at each gigabyte at 100 MiB or more, so a large
+// file is never read in full. scan maintains a persistent SQLite
+// database of file signatures (SFDUPES_DATABASE, default
+// /var/lib/sfdupes/db.sqlite) that the other subcommands read.
+//
+// Usage:
+//
+//	sfdupes scan [--workers N] [-x] [--no-default-excludes] PATH...
+//	sfdupes report > dupes.tsv
+//	sfdupes trees > dupetrees.tsv
+//	sfdupes info
+//	sfdupes --version
+//
+// See README.md for the complete specification.
+package main

 import (
 	"context"
@@ -28,7 +45,6 @@ const (
 	cmdReport = "report"
 	cmdTrees  = "trees"
 	cmdInfo   = "info"
-	cmdDwim   = "dwim"
 )

 // errNoSubcommand is returned by the root command when it is invoked
@@ -68,22 +84,20 @@ func buildVersion(linkerVersion string, info *debug.BuildInfo) string {
 	return info.Main.Version
 }

-// Main runs the command line in os.Args and returns the process exit
-// code.
-func Main() int {
+func main() {
 	// Once the reader of a stdout pipe has gone, as in "sfdupes report |
 	// head", the Go runtime ends the process with SIGPIPE on the next
 	// write instead of returning an error (README "Error handling").
 	// Registering for SIGPIPE with os/signal would change that.
-	return run(os.Args[1:], os.Stdout, os.Stderr)
+	os.Exit(run(os.Args[1:], os.Stdout, os.Stderr))
 }

 // run executes args against the command tree and returns the process
 // exit code. It is the program's single exit point: the subcommands
 // return their errors instead of exiting, so every deferred cleanup —
 // above all closing the database, which checkpoints the SQLite WAL —
-// runs before the process ends. The report, trees, info and dwim
-// subcommands write their data to stdout.
+// runs before the process ends. The report, trees and info subcommands
+// write their data to stdout.
 func run(args []string, stdout, stderr io.Writer) int {
 	// A nil slice makes cobra fall back to os.Args, which would let a
 	// test binary's own flags reach the command tree.
@@ -187,16 +201,7 @@ func newRootCommand(stdout, stderr io.Writer) *cobra.Command {
 		}),
 	}

-	dwimCmd := &cobra.Command{
-		Use:   cmdDwim,
-		Short: "Scan / with the default excludes, then print the duplicate-tree report",
-		Args:  cobra.NoArgs,
-		RunE: runE(func(ctx context.Context, _ []string) error {
-			return runDwim(ctx, "/", stdout)
-		}),
-	}
-
-	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd, dwimCmd)
+	root.AddCommand(newScanCommand(), reportCmd, treesCmd, infoCmd)

 	return root
 }
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // drives the unexported run
+package main

 import (
 	"bytes"
@@ -14,8 +14,6 @@ import (
 	"strconv"
 	"strings"
 	"testing"
-
-	"golang.org/x/sys/unix"
 )

 // usageMarker is the first line of cobra's usage text, which a usage
@@ -182,9 +180,9 @@ func capture(t *testing.T, std **os.File) func() string {
 }

 // brokenDatabase writes a database that opens cleanly and passes the
-// schema-version check but has no tables, so the first query fails
-// with the database already open: a fatal error on a path that owns an
-// open database. It closes the database the way scan does.
+// schema-version check but has no files table, so the first query
+// fails with the database already open: a fatal error on a path that
+// owns an open database. It closes the database the way scan does.
 func brokenDatabase(t *testing.T) string {
 	t.Helper()

@@ -267,9 +265,8 @@ func TestRunFatalAfterOpenClosesDatabase(t *testing.T) {
 			assertFatalOutput(t, stderr.String(), stdout())

 			// Proof that the failure happened after the open: only a
-			// query against the opened database can report this. Each
-			// subcommand's first query reads totals.
-			if !strings.Contains(stderr.String(), "no such table: totals") {
+			// query against the opened database can report this.
+			if !strings.Contains(stderr.String(), "no such table: files") {
 				t.Errorf("stderr = %q, want the failure to come from a "+
 					"query on the open database", stderr.String())
 			}
@@ -396,7 +393,7 @@ func TestRunNamesRelativeDatabase(t *testing.T) {
 }

 func TestRunUsesDatabaseThroughSymlinkedDirectory(t *testing.T) {
-	// README §Settings: the path names the file exactly. With link a
+	// README §Database: the path names the file exactly. With link a
 	// symlink to the directory real/sub, link/../db.sqlite names
 	// real/db.sqlite, not db.sqlite beside link. Every subcommand must
 	// use that file, relative or absolute, and its first line must name
@@ -622,7 +619,6 @@ func TestRunUsageErrors(t *testing.T) {
 		"report with args":   {[]string{cmdReport, "x"}, usageMarker},
 		"trees with args":    {[]string{cmdTrees, "x"}, usageMarker},
 		"info with args":     {[]string{cmdInfo, "x"}, usageMarker},
-		"dwim with args":     {[]string{cmdDwim, "x"}, usageMarker},
 		"unknown flag":       {[]string{cmdScan, "--nope", "/"}, usageMarker},
 		"unknown subcommand": {[]string{"nope"}, "unknown command"},
 	}
@@ -652,7 +648,7 @@ func TestRunUsageErrors(t *testing.T) {
 }

 func TestRunScanRejectsWorkersBelowOne(t *testing.T) {
-	// README §Settings: --workers below 1 is a usage error reported in
+	// README §scan mode: --workers below 1 is a usage error reported in
 	// one line on stderr, before the scan opens the database.
 	for _, workers := range []string{"0", "-1"} {
 		t.Run(workers, func(t *testing.T) {
@@ -690,8 +686,8 @@ func TestRunScanRejectsWorkersBelowOne(t *testing.T) {
 func TestRunHelp(t *testing.T) {
 	t.Parallel()

-	// README §Settings: help goes to stderr, exits 0, and leaves stdout
-	// empty.
+	// README §Subcommands: help goes to stderr, exits 0, and leaves
+	// stdout empty.
 	cases := [][]string{{"--help"}, {"-h"}, {cmdScan, "--help"}}

 	for _, args := range cases {
@@ -717,8 +713,8 @@ func TestRunHelp(t *testing.T) {
 func TestRunVersion(t *testing.T) {
 	t.Parallel()

-	// README §Settings: the version is one line on stdout, with nothing
-	// on stderr, and exits 0.
+	// README §Subcommands: the version is one line on stdout, with
+	// nothing on stderr, and exits 0.
 	info, _ := debug.ReadBuildInfo()

 	for _, arg := range []string{"--version", "-v"} {
@@ -777,8 +773,8 @@ func TestBuildVersion(t *testing.T) {
 func TestRunVersionWriteFailureIsFatal(t *testing.T) {
 	t.Parallel()

-	// README §Error handling: a failed write to stdout is a fatal error,
-	// exit 1, reported on stderr starting with "sfdupes:".
+	// README §Error handling: a stdout write failure exits 1, reported
+	// in one line on stderr.
 	var stderr bytes.Buffer

 	code := run([]string{"--version"}, failingWriter{}, &stderr)
@@ -800,7 +796,7 @@ func TestRunVersionWriteFailureIsFatal(t *testing.T) {
 func scanFixture(t *testing.T) []string {
 	t.Helper()

-	dir := realTempDir(t)
+	dir := t.TempDir()

 	dupes := []string{
 		writeFile(t, dir, "one/a.bin", pattern(1, 300)),
@@ -821,23 +817,6 @@ func scanFixture(t *testing.T) []string {
 	return dupes
 }

-// storedDiskSize returns the disk_size of the record for path in the
-// database at dbPath. A test of a trees run compares with this rather
-// than with a new lstat, which on ZFS can differ from the scan's (see
-// diskSizeOf).
-func storedDiskSize(t *testing.T, dbPath, path string) int64 {
-	t.Helper()
-
-	db, err := openReportDatabase(t.Context(), dbPath)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	defer func() { _ = db.Close() }()
-
-	return recordByPath(t, dbRecords(t, db), path).diskSize
-}
-
 // scanOK runs scan over operands, fails the test unless it exits 0 with
 // nothing on stdout, and returns everything it printed to stderr.
 func scanOK(t *testing.T, operands ...string) string {
@@ -870,7 +849,7 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

-	dir := realTempDir(t)
+	dir := t.TempDir()
 	writeFile(t, dir, "a.bin", pattern(1, 300))

 	// Same size as a.bin, so the scan reads it, and the read fails.
@@ -898,292 +877,75 @@ func TestRunScanSucceedsDespiteWarnings(t *testing.T) {
 	assertNoSidecars(t, path)
 }

-// realTempDir returns a new temporary directory by its real path, so
-// tests hold where the temporary directory is reached through a
-// symlink.
-func realTempDir(t *testing.T) string {
-	t.Helper()
-
-	dir, err := filepath.EvalSymlinks(t.TempDir())
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	return dir
-}
-
-// symlink creates link pointing at target.
-func symlink(t *testing.T, target, link string) {
-	t.Helper()
-
-	err := os.Symlink(target, link)
-	if err != nil {
-		t.Fatal(err)
-	}
-}
-
-// TestRunScanFollowsSymlinkOperand scans link, a symlink to target.
-// The operand is scanned at its real path, and its file is recorded
-// there.
-func TestRunScanFollowsSymlinkOperand(t *testing.T) {
+func TestRunScanSkipsSymlinkOperand(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

-	dir := realTempDir(t)
-	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
+	dir := t.TempDir()
+	writeFile(t, dir, "target/sub/f", pattern(1, 10))

 	link := filepath.Join(dir, "link")
-	symlink(t, filepath.Join(dir, "target"), link)

-	stderr := scanOK(t, link)
-
-	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
-		"0 unchanged), 0 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
+	err := os.Symlink(filepath.Join(dir, "target"), link)
+	if err != nil {
+		t.Fatal(err)
 	}

-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
+	// Scanning a directory through the symlink stores a record beneath
+	// the symlink's own path for a file beneath its target.
+	scanOK(t, filepath.Join(link, "sub"))
+
+	assertOperandSkipped(t, path, link, "symlink",
+		filepath.Join(link, "sub", "f"))
 }

-// TestRunScanWalksOperandUnderSymlinkOperand scans link and link/sub,
-// with link a symlink to target. Both resolve under target, so
-// target/sub is walked once, as part of target.
 func TestRunScanWalksOperandUnderSymlinkOperand(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

-	dir := realTempDir(t)
-	f := writeFile(t, dir, "target/sub/f", pattern(1, 10))
+	dir := t.TempDir()
+	writeFile(t, dir, "target/sub/f", pattern(1, 10))

 	link := filepath.Join(dir, "link")
-	symlink(t, filepath.Join(dir, "target"), link)

-	stderr := scanOK(t, link, filepath.Join(link, "sub"))
-
-	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
-		"0 unchanged), 0 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
-	}
-
-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
-}
-
-// TestRunScanWalksSymlinkedOperandBelowOperand is the case of
-// https://git.eeqj.de/sneak/sfdupes/issues/144: scan dir dir/link/sub,
-// with dir/link a symlink to a directory outside dir. The walk of dir
-// does not follow link, so dir/link/sub is walked on its own at its
-// real path, and the record an earlier scan stored there survives.
-func TestRunScanWalksSymlinkedOperandBelowOperand(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	a := writeFile(t, dir, "a", pattern(1, 10))
-
-	outside := realTempDir(t)
-	f := writeFile(t, outside, "sub/f", pattern(2, 10))
-
-	symlink(t, outside, filepath.Join(dir, "link"))
-
-	scanOK(t, filepath.Join(outside, "sub"))
-
-	stderr := scanOK(t, dir, filepath.Join(dir, "link", "sub"))
-
-	summary := "scan: 2 files seen (1 added, 0 updated, 0 removed, " +
-		"1 unchanged), 0 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
-	}
-
-	want := []string{a, f}
-	slices.Sort(want)
-
-	if got := storedPaths(t, path); !slices.Equal(got, want) {
-		t.Errorf("records = %q, want %q", got, want)
-	}
-}
-
-// TestRunScanDropsSymlinkOperandInsideOperand scans dir and link, with
-// link, outside dir, a symlink to dir/real. link resolves inside dir,
-// so it is dropped as covered by dir, and its file is recorded once.
-func TestRunScanDropsSymlinkOperandInsideOperand(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	f := writeFile(t, dir, "real/f", pattern(1, 10))
-
-	link := filepath.Join(realTempDir(t), "link")
-	symlink(t, filepath.Join(dir, "real"), link)
-
-	stderr := scanOK(t, dir, link)
-
-	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
-		"0 unchanged), 0 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
-	}
-
-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
-}
-
-// TestRunScanDanglingSymlinkOperandIsFatal scans a valid directory and
-// a symlink whose target does not exist. The scan fails with exit 1 and
-// an error naming the symlink as given, before it walks anything, so no
-// database is created.
-func TestRunScanDanglingSymlinkOperandIsFatal(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	writeFile(t, dir, "f", pattern(1, 10))
-
-	dangling := filepath.Join(realTempDir(t), "dangling")
-	symlink(t, filepath.Join(dir, "missing"), dangling)
-
-	stdout := captureStdout(t)
-
-	var stderr bytes.Buffer
-
-	code := run([]string{cmdScan, dir, dangling}, os.Stdout, &stderr)
-	if code != exitFatal {
-		t.Errorf("run(scan %s %s) = %d, want %d", dir, dangling, code,
-			exitFatal)
-	}
-
-	assertFatalOutput(t, stderr.String(), stdout())
-
-	want := "sfdupes: resolve " + dangling + ": "
-	if !strings.Contains(stderr.String(), want) {
-		t.Errorf("stderr = %q, want %q", stderr.String(), want)
-	}
-
-	_, err := os.Stat(path)
-	if !errors.Is(err, fs.ErrNotExist) {
-		t.Errorf("database: stat error %v, want it missing", err)
-	}
-}
-
-// TestRunScanFromSymlinkedWorkingDirectoryRecordsRealPath runs scan .
-// after a cd through home/proj, a symlink to data/proj. The file is
-// recorded under data/proj, its real path.
-func TestRunScanFromSymlinkedWorkingDirectoryRecordsRealPath(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	f := writeFile(t, dir, "data/proj/f", pattern(1, 10))
-
-	err := os.Mkdir(filepath.Join(dir, "home"), 0o750)
+	err := os.Symlink(filepath.Join(dir, "target"), link)
 	if err != nil {
 		t.Fatal(err)
 	}

-	symlink(t, filepath.Join(dir, "data", "proj"),
-		filepath.Join(dir, "home", "proj"))
+	// link is dropped as a symlink, but link/sub must still be scanned,
+	// not dropped as lying under link.
+	scanOK(t, link, filepath.Join(link, "sub"))

-	// t.Chdir also sets PWD to the path through the symlink, as a
-	// shell does after cd.
-	t.Chdir(filepath.Join(dir, "home", "proj"))
-
-	scanOK(t, ".")
-
-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
-}
-
-// TestRunScanFollowsSymlinkBeforeDotDot scans a path with a ".." after
-// home/proj, a symlink to data/proj: home/proj/.. from dir, and .. after
-// a cd through home/proj. As with realpath, the ".." counts from
-// data/proj, so data is scanned and home is not.
-func TestRunScanFollowsSymlinkBeforeDotDot(t *testing.T) {
-	for _, tc := range []struct{ wd, operand string }{
-		{"", "home/proj/.."},
-		{"home/proj", ".."},
-	} {
-		t.Run(tc.operand, func(t *testing.T) {
-			path := testDBPath(t)
-			t.Setenv(databaseEnv, path)
-
-			dir := realTempDir(t)
-			f := writeFile(t, dir, "data/proj/f", pattern(1, 10))
-			g := writeFile(t, dir, "data/g", pattern(2, 10))
-			writeFile(t, dir, "home/h", pattern(3, 10))
-			symlink(t, filepath.Join(dir, "data", "proj"),
-				filepath.Join(dir, "home", "proj"))
-
-			// t.Chdir also sets PWD to the path given, as a shell does
-			// after cd.
-			t.Chdir(filepath.Join(dir, tc.wd))
-
-			scanOK(t, tc.operand)
-
-			want := []string{f, g}
-			slices.Sort(want)
-
-			if got := storedPaths(t, path); !slices.Equal(got, want) {
-				t.Errorf("records = %q, want %q", got, want)
-			}
-		})
-	}
-}
-
-// TestRunScanSkipsSymlinkToFIFOOperand scans link, a symlink to a FIFO.
-// The scan warns about the FIFO by its real path, counts it as skipped,
-// and exits 0.
-func TestRunScanSkipsSymlinkToFIFOOperand(t *testing.T) {
-	t.Setenv(databaseEnv, testDBPath(t))
-
-	dir := realTempDir(t)
-	fifo := filepath.Join(dir, "fifo")
-
-	err := unix.Mkfifo(fifo, 0o600)
+	db, err := openDB(path, reportParams)
 	if err != nil {
 		t.Fatal(err)
 	}

-	link := filepath.Join(dir, "link")
-	symlink(t, fifo, link)
+	t.Cleanup(func() { _ = db.Close() })

-	stderr := scanOK(t, link)
-
-	warning := "walk " + fifo + ": skipping FIFO operand\n"
-	if !strings.Contains(stderr, warning) {
-		t.Errorf("stderr = %q, want %q", stderr, warning)
-	}
-
-	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
-		"0 unchanged), 1 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
-	}
+	recordByPath(t, dbRecords(t, db), filepath.Join(link, "sub", "f"))
 }

 func TestRunScanSkipsZFSOperand(t *testing.T) {
-	zfs := filepath.Join(realTempDir(t), ".zfs")
-	f := writeFile(t, zfs, "snapshot/hourly/f", pattern(1, 10))
-
-	// No scan records a file inside a .zfs directory, so the record
-	// beneath the operand is written straight into the database.
-	path := seedDatabase(t, []scanRec{{size: 10, path: f}})
+	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

+	zfs := filepath.Join(t.TempDir(), ".zfs")
+	snapshot := filepath.Join(zfs, "snapshot", "hourly")
+	f := writeFile(t, snapshot, "f", pattern(1, 10))
+
+	// An operand beneath a .zfs directory is walked, because it is not
+	// itself named .zfs.
+	scanOK(t, snapshot)
+
 	assertOperandSkipped(t, path, zfs, ".zfs directory", f)
 }

 // assertOperandSkipped scans operand alone and checks that it is skipped
 // as kind: a warning naming it, one skip in the summary, exit 0, and the
-// record for kept, stored beneath operand before this scan, still in the
-// database at dbPath.
+// record for kept, which an earlier scan stored beneath operand, still
+// in the database at dbPath.
 func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	kept string,
 ) {
@@ -1212,107 +974,6 @@ func assertOperandSkipped(t *testing.T, dbPath, operand, kind,
 	recordByPath(t, dbRecords(t, db), kept)
 }

-// TestRunScanSkipsOperandInsideZFS scans a directory inside a .zfs
-// directory, first alone and then under another operand. Each time it
-// is warned about and counted as skipped, and nothing in it is walked.
-// The other operand is scanned as usual.
-func TestRunScanSkipsOperandInsideZFS(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	hourly := filepath.Join(dir, ".zfs", "snapshot", "hourly")
-	writeFile(t, hourly, "f", pattern(1, 10))
-	f := writeFile(t, dir, "f", pattern(2, 10))
-
-	warning := "walk " + hourly + ": skipping operand inside a .zfs directory\n"
-
-	for _, tc := range []struct {
-		operands []string
-		summary  string
-	}{
-		{
-			[]string{hourly},
-			"scan: 0 files seen (0 added, 0 updated, 0 removed, " +
-				"0 unchanged), 1 skipped\n",
-		},
-		{
-			[]string{dir, hourly},
-			"scan: 1 files seen (1 added, 0 updated, 0 removed, " +
-				"0 unchanged), 1 skipped\n",
-		},
-	} {
-		stderr := scanOK(t, tc.operands...)
-		if !strings.Contains(stderr, warning) ||
-			!strings.Contains(stderr, tc.summary) {
-			t.Errorf("scan %q: stderr = %q, want %q and %q", tc.operands,
-				stderr, warning, tc.summary)
-		}
-	}
-
-	db, err := openDB(path, reportParams)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	t.Cleanup(func() { _ = db.Close() })
-
-	if got := recordPaths(dbRecords(t, db)); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
-}
-
-// TestRunScanSkipsOperandThroughSymlinkIntoZFS scans snaps/daily, where
-// snaps is a symlink to pool/.zfs/snapshot. The operand is warned about
-// by its real path, counted as skipped, and not walked.
-func TestRunScanSkipsOperandThroughSymlinkIntoZFS(t *testing.T) {
-	t.Setenv(databaseEnv, testDBPath(t))
-
-	dir := realTempDir(t)
-	writeFile(t, dir, "pool/.zfs/snapshot/daily/f", pattern(1, 10))
-
-	snaps := filepath.Join(dir, "snaps")
-	symlink(t, filepath.Join(dir, "pool", ".zfs", "snapshot"), snaps)
-
-	stderr := scanOK(t, filepath.Join(snaps, "daily"))
-
-	daily := filepath.Join(dir, "pool", ".zfs", "snapshot", "daily")
-	warning := "walk " + daily + ": skipping operand inside a .zfs directory\n"
-	summary := "scan: 0 files seen (0 added, 0 updated, 0 removed, " +
-		"0 unchanged), 1 skipped\n"
-
-	if !strings.Contains(stderr, warning) ||
-		!strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q and %q", stderr, warning, summary)
-	}
-}
-
-// TestRunScanWalksOperandThroughSymlink scans data/daily, where data is
-// a symlink to pool/data. The operand is scanned as usual, and its file
-// is recorded by its real path.
-func TestRunScanWalksOperandThroughSymlink(t *testing.T) {
-	path := testDBPath(t)
-	t.Setenv(databaseEnv, path)
-
-	dir := realTempDir(t)
-	f := writeFile(t, dir, "pool/data/daily/f", pattern(1, 10))
-
-	data := filepath.Join(dir, "data")
-	symlink(t, filepath.Join(dir, "pool", "data"), data)
-
-	stderr := scanOK(t, filepath.Join(data, "daily"))
-
-	summary := "scan: 1 files seen (1 added, 0 updated, 0 removed, " +
-		"0 unchanged), 0 skipped\n"
-	if !strings.Contains(stderr, summary) {
-		t.Errorf("stderr = %q, want %q", stderr, summary)
-	}
-
-	if got := storedPaths(t, path); !slices.Equal(got, []string{f}) {
-		t.Errorf("records = %q, want %q", got, []string{f})
-	}
-}
-
 func TestRunReportSucceeds(t *testing.T) {
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)
@@ -1367,9 +1028,8 @@ func TestRunTreesSucceeds(t *testing.T) {

 	// The two directories holding the duplicate pair are duplicate
 	// trees of each other.
-	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\t" +
-		strconv.FormatInt(storedDiskSize(t, path, dupes[1]), 10) + "\n"
+	want := "first\tdupe\tfiles\tsize\n" +
+		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\n"
 	if got := stdout.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
@@ -1403,10 +1063,9 @@ func TestRunReportsNeedOnlyReadAccess(t *testing.T) {
 	cases := map[string]string{
 		cmdReport: "first\tdupe\tsize\n" +
 			dupes[0] + "\t" + dupes[1] + "\t300\n",
-		cmdTrees: "first\tdupe\tfiles\tsize\tdisk_size\n" +
+		cmdTrees: "first\tdupe\tfiles\tsize\n" +
 			filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) +
-			"\t1\t300\t" +
-			strconv.FormatInt(storedDiskSize(t, path, dupes[1]), 10) + "\n",
+			"\t1\t300\n",
 	}

 	for name, want := range cases {
@@ -1441,11 +1100,8 @@ func assertRunsUseDatabase(t *testing.T, dir, name string) {
 		t.Errorf("report stdout = %q, want %q", got, want)
 	}

-	diskSize := storedDiskSize(t, filepath.Join(dir, name), dupes[1])
-
-	want = "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\t" +
-		strconv.FormatInt(diskSize, 10) + "\n"
+	want = "first\tdupe\tfiles\tsize\n" +
+		filepath.Dir(dupes[0]) + "\t" + filepath.Dir(dupes[1]) + "\t1\t300\n"
 	if got := runStdout(t, cmdTrees); got != want {
 		t.Errorf("trees stdout = %q, want %q", got, want)
 	}
@@ -1466,7 +1122,7 @@ func assertRunsUseDatabase(t *testing.T, dir, name string) {
 }

 func TestRunDatabasePathUsedAsGiven(t *testing.T) {
-	// README §Settings: the path names the database file exactly. In
+	// README §Database: the path names the database file exactly. In
 	// SQLite's connection string an unescaped ? or # would end the file
 	// name and % would start an escape, and a path starting with //
 	// could be read as a host name. %25 is a valid escape, so unescaped
@@ -1511,8 +1167,9 @@ func holdScanLock(t *testing.T, path string) {
 }

 func TestRunSecondScanFails(t *testing.T) {
-	// README §Database: a second scan that finds the lock held fails
-	// at once, naming the lock file, without opening the database.
+	// README §Database: while one scan holds the lock, a second scan
+	// fails at once, naming the lock file, without opening the
+	// database.
 	path := testDBPath(t)
 	t.Setenv(databaseEnv, path)

@@ -1571,7 +1228,7 @@ func assertSecondScanFails(t *testing.T, path string) {
 }

 func TestRunSecondScanThroughSymlinkFails(t *testing.T) {
-	// README §Database: a path through a symlink names the same lock
+	// README §Database: every path to one database names the same lock
 	// file, so while a scan holds it through one path, a scan through
 	// another fails, naming the lock file beside the database's real
 	// path.
@@ -1676,8 +1333,8 @@ func TestRunReportsDuringScan(t *testing.T) {
 }

 func TestRunStdoutClosedIsFatal(t *testing.T) {
-	// README §Error handling: a failed write to stdout is a fatal error,
-	// exit 1, reported on stderr starting with "sfdupes:".
+	// README §Error handling: a stdout write failure exits 1, reported
+	// in one line on stderr.
 	for _, name := range []string{cmdReport, cmdTrees, cmdInfo} {
 		t.Run(name, func(t *testing.T) {
 			t.Setenv(databaseEnv, testDBPath(t))
@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"fmt"
@@ -60,7 +60,7 @@ const fallbackWidth = 80
 const spinnerMargin = 5

 // countingRecords is what the display of a phase that reads the records
-// says until it has the number of records, its total.
+// says while it counts them, before it has its total.
 const countingRecords = "counting the records"

 // openPhase is the name of the phase in which report, trees and info
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // drives the unexported startProgress
+package main

 import (
 	"fmt"
@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"context"
@@ -21,16 +21,14 @@ const minGroupSize = 2

 // scanRec is one file record from the database. The signature (size,
 // head, tail, content) is the duplicate key; mtime is informational
-// only and used by scan for change detection. diskSize is the bytes the
-// file takes on disk, which trees adds up.
+// only and used by scan for change detection.
 type scanRec struct {
-	size     int64
-	diskSize int64
-	mtime    time.Time
-	head     [sha256.Size]byte
-	tail     [sha256.Size]byte
-	content  [sha256.Size]byte
-	path     string
+	size    int64
+	mtime   time.Time
+	head    [sha256.Size]byte
+	tail    [sha256.Size]byte
+	content [sha256.Size]byte
+	path    string
 }

 // reportPhase names one phase of report with its place among all of
@@ -47,11 +45,11 @@ func reportPhase(name string) string {
 // problem, including a missing database, is fatal.
 //
 // The work runs in two phases, each under a progress display of its
-// own on stderr: open (open the database) and read (read the number of
-// records from the totals table, then read the records in signature
-// order, writing each size's duplicate groups to stdout once that size
-// is read; see readReport). Each display ends before the next phase
-// starts, and before an error is returned to be printed.
+// own on stderr: open (open the database) and read (count the records,
+// then read them in signature order, writing each size's duplicate
+// groups to stdout once that size is read; see readReport). Each
+// display ends before the next phase starts, and before an error is
+// returned to be printed.
 func runReport(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -195,11 +193,10 @@ func (w *reportWriter) add(r scanRec) error {
 }

 // endGroup ends the paths read with w.sig: two or more are a duplicate
-// group, held with its paths sorted until writeGroups writes it. Empty
-// files form no group, since removing one frees nothing.
+// group, held with its paths sorted until writeGroups writes it.
 func (w *reportWriter) endGroup() {
-	if len(w.paths) < minGroupSize || w.sig.size == 0 {
-		// The paths are dropped, and their slice reused.
+	if len(w.paths) < minGroupSize {
+		// A path with no duplicate is dropped, and its slice reused.
 		w.paths = w.paths[:0]

 		return
@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // checks the unexported dupeGroup results
+package main

 import (
 	"bytes"
@@ -38,8 +38,8 @@ func awkwardPairRecs() []scanRec {
 	h, tl, c := testHash("h"), testHash("t"), testHash("c")

 	return []scanRec{
-		{size: 5, diskSize: 4096, head: h, tail: tl, content: c, path: "/d/A/f"},
-		{size: 5, diskSize: 4096, head: h, tail: tl, content: c, path: awkwardDir + "/f"},
+		{size: 5, head: h, tail: tl, content: c, path: "/d/A/f"},
+		{size: 5, head: h, tail: tl, content: c, path: awkwardDir + "/f"},
 	}
 }

@@ -434,27 +434,6 @@ func TestDupeGroups(t *testing.T) {
 	}
 }

-// TestDupeGroupsLeavesOutEmptyFiles checks that empty files form no
-// duplicate group, while 1-byte files still do.
-func TestDupeGroupsLeavesOutEmptyFiles(t *testing.T) {
-	t.Parallel()
-
-	e, x := sha256.Sum256(nil), testHash("x")
-	recs := []scanRec{
-		{size: 0, head: e, tail: e, content: e, path: "/a/.gitkeep"},
-		{size: 0, head: e, tail: e, content: e, path: "/b/.gitkeep"},
-		{size: 0, head: e, tail: e, content: e, path: "/c/__init__.py"},
-		{size: 1, head: x, tail: x, content: x, path: "/tiny1"},
-		{size: 1, head: x, tail: x, content: x, path: "/tiny2"},
-	}
-
-	groups := dupeGroupsOf(t, recs)
-	if len(groups) != 1 || groups[0].size != 1 ||
-		!slices.Equal(groups[0].paths, []string{"/tiny1", "/tiny2"}) {
-		t.Fatalf("groups = %+v, want only /tiny1 /tiny2 of size 1", groups)
-	}
-}
-
 func TestDupeGroupsContentSeparates(t *testing.T) {
 	t.Parallel()

@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"cmp"
@@ -48,30 +48,32 @@ const sampleWindow = 1024 * 1024
 // and hash worker pools.
 const workQueueDepth = 1024

+// zfsDirName is the name of the directory in which ZFS shows a
+// filesystem's snapshots. The walk never enters one, since it would
+// list every file once per snapshot.
+const zfsDirName = ".zfs"
+
 // errInterrupted reports a scan stopped by SIGINT or SIGTERM. runScan
 // has already printed its line, so run prints nothing more.
 var errInterrupted = errors.New("scan interrupted")

-// fileRec carries one statted file between the scan phases. diskSize is
-// the bytes the file takes on disk. dev and ino identify the underlying
-// inode so hard-linked paths can share one read; both are zero when the
-// platform exposes no inode.
+// fileRec carries one statted file between the scan phases. dev and
+// ino identify the underlying inode so hard-linked paths can share
+// one read; both are zero when the platform exposes no inode.
 type fileRec struct {
-	path     string
-	size     int64
-	diskSize int64
-	mtime    time.Time
-	dev      uint64
-	ino      uint64
+	path  string
+	size  int64
+	mtime time.Time
+	dev   uint64
+	ino   uint64
 }

 // fileMeta is the in-memory index entry for one existing database
-// record: what the walk compares the file with. Hashes stay on disk; at
+// record: just enough for change detection. Hashes stay on disk; at
 // tens of millions of records they would dominate the scan's memory.
 type fileMeta struct {
-	size     int64
-	diskSize int64
-	mtime    time.Time
+	size  int64
+	mtime time.Time
 }

 // scanUnit is what every scan phase counts, as its progress display
@@ -209,30 +211,29 @@ func interrupted(walked int) error {
 	return errInterrupted
 }

-// resolveRoots converts each PATH operand to its real path: absolute,
-// with every symlink in it followed. Database records are keyed by
-// that path, so scan results depend neither on the working directory
-// nor on the symlinks an operand was given through. An operand that
-// cannot be resolved, because it or a symlink's target does not exist
-// or cannot be read, is a fatal error before any scanning.
+// resolveRoots converts each PATH operand to an absolute, lexically
+// cleaned path (symlinks are not resolved) and verifies that it
+// exists. Database records are keyed by absolute path, so scan results
+// must not depend on the working directory.
 func resolveRoots(roots []string) ([]string, error) {
-	resolved := make([]string, 0, len(roots))
+	abs := make([]string, 0, len(roots))

 	for _, root := range roots {
-		a, err := absolutePath(root)
+		a, err := filepath.Abs(root)
 		if err != nil {
 			return nil, fmt.Errorf("resolve %s: %w", root, err)
 		}

-		r, err := filepath.EvalSymlinks(a)
+		// A nonexistent operand is a fatal error before any scanning.
+		_, err = os.Lstat(a)
 		if err != nil {
-			return nil, fmt.Errorf("resolve %s: %w", root, err)
+			return nil, err
 		}

-		resolved = append(resolved, r)
+		abs = append(abs, a)
 	}

-	return resolved, nil
+	return abs, nil
 }

 // pruneRoots drops operands already covered by another operand:
@@ -276,9 +277,10 @@ func pruneRoots(roots []string, oneFS bool, rules walkRules,
 }

 // walkReaches reports whether the walk of operand above reaches r, an
-// operand under it. That walk does not enter a default exclude in
-// rules, nor a directory that device puts on a filesystem in rules that
-// is not persistent, nor, with -x, one that device puts on a different
+// operand under it. That walk never follows a symlink. It does not
+// enter a directory named .zfs, nor a default exclude in rules, nor a
+// directory that device puts on a filesystem in rules that is not
+// persistent, nor, with -x, one that device puts on a different
 // filesystem than above, when device knows above's. It reaches every
 // regular file in a directory it enters, so for a regular-file operand
 // the directories checked start at its directory; they end below above.
@@ -299,6 +301,15 @@ func walkReaches(above, r string, oneFS bool, rules walkRules,
 			return false
 		}

+		if filepath.Base(dir) == zfsDirName {
+			return false
+		}
+
+		fi, err = os.Lstat(dir)
+		if err == nil && fi.Mode()&fs.ModeSymlink != 0 {
+			return false
+		}
+
 		dev, ok := device(dir)
 		if !ok {
 			continue
@@ -343,12 +354,11 @@ type scanStats struct {
 // whatever remains after the walk and hash phases is deleted by the
 // update phase.
 type scanState struct {
-	db        *sql.DB
-	existing  map[string]fileMeta
-	toHash    []fileRec // new and changed files: must be read
-	diskSizes []fileRec // unchanged files whose disk_size changed
-	batch     []scanRec
-	st        scanStats
+	db       *sql.DB
+	existing map[string]fileMeta
+	toHash   []fileRec // new and changed files: must be read
+	batch    []scanRec
+	st       scanStats
 }

 // syncScan synchronizes the database with the filesystem under roots;
@@ -388,8 +398,7 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 ) error {
 	// Types and filesystems are checked before pruning so that an
 	// operand under a dropped one is still scanned, not dropped as lying
-	// under it, and so that an operand inside a .zfs directory gets its
-	// warning even when it lies under another operand.
+	// under it.
 	roots = pruneRoots(s.walkableRoots(roots, rules), oneFS, rules,
 		deviceOfPath)

@@ -417,17 +426,15 @@ func (s *scanState) runPhases(ctx context.Context, roots []string,
 }

 // walkableRoots returns the operands the walk can start from: regular
-// files, and directories not named .zfs, none of them inside a
-// directory named .zfs. The operands are real paths from resolveRoots,
-// so these checks apply to what a symlink operand points at. Every
-// other operand is warned about, counted as skipped, and dropped. A
-// dropped operand is no longer a root, so the records stored beneath it
-// are treated as if it had not been given: those under no other root
-// count as outside the roots and are not deleted as unverified. An
-// operand on a filesystem in rules that is not persistent is dropped
-// the same way, with a line saying so that is not a warning, and is not
-// counted as skipped. An operand that fails lstat here is kept, and the
-// walk warns about it unless it no longer exists.
+// files, and directories not named .zfs. Every other operand is warned
+// about, counted as skipped, and dropped. A dropped operand is no
+// longer a root, so the records stored beneath it are treated as if it
+// had not been given: those under no other root count as outside the
+// roots and are not deleted as unverified. An operand on a filesystem
+// in rules that is not persistent is dropped the same way, with a line
+// saying so that is not a warning, and is not counted as skipped. An
+// operand that fails lstat here is kept, and the walk warns about it
+// unless it no longer exists.
 func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 	kept := make([]string, 0, len(roots))

@@ -462,8 +469,8 @@ func (s *scanState) walkableRoots(roots []string, rules walkRules) []string {
 // included, so its display counts against the number of records.
 func (s *scanState) loadIndex(ctx context.Context, roots []string) error {
 	// Indexing tens of millions of records takes real time; without a
-	// display the scan looks hung before the walk begins. The number of
-	// records, read first, gives the display its total.
+	// display the scan looks hung before the walk begins. Counting them
+	// first gives the display its total.
 	prog := newProgress(progressParams{
 		label: scanPhase("load"), unit: scanUnit, total: -1,
 		waitingFor: countingRecords, stalledOn: "db",
@@ -479,24 +486,24 @@ func (s *scanState) loadIndex(ctx context.Context, roots []string) error {

 	s.existing = make(map[string]fileMeta)

-	return loadFileMeta(ctx, s.db, func(path string, m fileMeta) {
-		prog.increment()
+	return loadFileMeta(ctx, s.db,
+		func(path string, size int64, mtime time.Time) {
+			prog.increment()

-		if underAnyRoot(path, roots) {
-			s.existing[path] = m
-		}
-	})
+			if underAnyRoot(path, roots) {
+				s.existing[path] = fileMeta{size: size, mtime: mtime}
+			}
+		})
 }

 // walkPhase drains the walk and queues every new or changed file for
-// the hash phase. An unchanged file is not read, and its record counts
-// as verified. When its disk_size differs from the record's, it is
-// queued for the update phase, which writes the new disk_size. A record
-// at or below a path the walk left out, because -x stopped at it, it is
-// a default exclude, or it is not on a persistent filesystem, counts as
-// outside the roots: it is not deleted. That does not hold below a root
-// at or inside that path, since that root's own walk verifies the
-// records below it; nor is a line printed for such a root.
+// the hash phase. An unchanged file needs nothing more, and its record
+// counts as verified. A record at or below a path the walk left out,
+// because -x stopped at it, it is a default exclude, or it is not on a
+// persistent filesystem, counts as outside the roots: it is not
+// deleted. That does not hold below a root at or inside that path,
+// since that root's own walk verifies the records below it; nor is a
+// line printed for such a root.
 func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 	// The records the last scan left under the roots estimate how many
 	// files the walk will find. A first scan has none, and no estimate.
@@ -554,13 +561,6 @@ func (s *scanState) walkPhase(events <-chan walkEvent, roots []string) {
 		delete(s.existing, ev.rec.path)

 		s.st.unchanged++
-
-		// The space a file takes on disk can change while its size and
-		// mtime stay the same. ZFS, for one, counts a new file's blocks
-		// up to seconds after the write.
-		if old.diskSize != ev.rec.diskSize {
-			s.diskSizes = append(s.diskSizes, ev.rec)
-		}
 	}

 	prog.finish()
@@ -709,13 +709,12 @@ func (s *scanState) recordRun(ctx context.Context, r hashResult) error {
 		s.resolve(rec.path)

 		s.batch = append(s.batch, scanRec{
-			size:     rec.size,
-			diskSize: rec.diskSize,
-			mtime:    rec.mtime,
-			head:     r.head,
-			tail:     r.tail,
-			content:  r.content,
-			path:     rec.path,
+			size:    rec.size,
+			mtime:   rec.mtime,
+			head:    r.head,
+			tail:    r.tail,
+			content: r.content,
+			path:    rec.path,
 		})
 	}

@@ -731,7 +730,7 @@ func (s *scanState) commitFullBatch(ctx context.Context) error {
 		return nil
 	}

-	err := applyBatch(ctx, s.db, s.batch, nil, nil, nil)
+	err := applyBatch(ctx, s.db, s.batch, nil, nil)
 	if err != nil {
 		return err
 	}
@@ -742,10 +741,9 @@ func (s *scanState) commitFullBatch(ctx context.Context) error {
 }

 // updatePhase writes the scan's tail under one progress display: the
-// final partial batch of hashed records, the new disk_size of every
-// unchanged file whose disk_size changed, and deletions for every
-// record the scan did not verify (vanished files, plus paths that
-// failed to stat or hash).
+// final partial batch of hashed records, and deletions for every record
+// the scan did not verify (vanished files, plus paths that failed to
+// stat or hash).
 func (s *scanState) updatePhase(ctx context.Context) error {
 	deletes := make([]string, 0, len(s.existing))
 	for path := range s.existing {
@@ -757,7 +755,7 @@ func (s *scanState) updatePhase(ctx context.Context) error {

 	s.st.removed = len(deletes)

-	total := len(s.batch) + len(s.diskSizes) + len(deletes)
+	total := len(s.batch) + len(deletes)
 	prog := newProgress(progressParams{
 		label: scanPhase("update"), unit: scanUnit, total: int64(total),
 		stalledOn: "db",
@@ -772,11 +770,6 @@ func (s *scanState) updatePhase(ctx context.Context) error {

 	s.batch = nil

-	err = applyDiskSizes(ctx, s.db, s.diskSizes, prog)
-	if err != nil {
-		return err
-	}
-
 	return applyChanges(ctx, s.db, nil, deletes, prog)
 }

@@ -896,25 +889,16 @@ func sendEvent(ctx context.Context, events chan<- walkEvent,

 // operandWarning returns the one-line warning for an operand the walk
 // does not start from, naming the path and what it is, or "" for one it
-// does: a regular file, or a directory not named .zfs, that is not
-// inside a directory named .zfs. resolveRoots has already followed the
-// operand's symlinks, so a symlink here is an operand replaced by one
-// after it was resolved, and is not followed.
+// does: a regular file, or a directory not named .zfs. Symlinks are
+// never followed, including as operands.
 func operandWarning(root string, fi fs.FileInfo) string {
-	// The walk never enters a .zfs directory, so it starts from nothing
-	// inside one either.
-	if slices.Contains(strings.Split(filepath.Dir(root), "/"), ".zfs") {
-		return fmt.Sprintf("walk %s: skipping operand inside a .zfs directory",
-			root)
-	}
-
 	var kind string

 	switch mode := fi.Mode(); {
 	case mode.IsRegular():
 		return ""
 	case mode.IsDir():
-		if filepath.Base(root) != ".zfs" {
+		if filepath.Base(root) != zfsDirName {
 			return ""
 		}

@@ -976,12 +960,11 @@ func seedRoot(ctx context.Context, root string, rules walkRules,

 	dev, ino := inodeOfInfo(fi)
 	rec := fileRec{
-		path:     root,
-		size:     fi.Size(),
-		diskSize: diskSizeOfInfo(fi),
-		mtime:    fi.ModTime(),
-		dev:      dev,
-		ino:      ino,
+		path:  root,
+		size:  fi.Size(),
+		mtime: fi.ModTime(),
+		dev:   dev,
+		ino:   ino,
 	}

 	if !isDatabaseFile(rec, rules) {
@@ -1161,12 +1144,11 @@ func emitFile(ctx context.Context, p string, e fs.DirEntry,

 	dev, ino := inodeOfInfo(info)
 	rec := fileRec{
-		path:     p,
-		size:     info.Size(),
-		diskSize: diskSizeOfInfo(info),
-		mtime:    info.ModTime(),
-		dev:      dev,
-		ino:      ino,
+		path:  p,
+		size:  info.Size(),
+		mtime: info.ModTime(),
+		dev:   dev,
+		ino:   ino,
 	}

 	if !isDatabaseFile(rec, rules) {
@@ -1186,7 +1168,7 @@ func subdirJob(ctx context.Context, p string, e fs.DirEntry,
 	parent dirJob, oneFS bool, rules walkRules,
 	events chan<- walkEvent,
 ) (dirJob, bool) {
-	if e.Name() == ".zfs" {
+	if e.Name() == zfsDirName {
 		return dirJob{}, false
 	}

@@ -1258,23 +1240,6 @@ func inodeOfInfo(fi fs.FileInfo) (uint64, uint64) {
 	return statDev(st), st.Ino
 }

-// statBlockSize is the unit of st_blocks in an lstat result on Linux and
-// macOS, whatever the filesystem's own block size.
-const statBlockSize = 512
-
-// diskSizeOfInfo returns the bytes a file takes on disk: its allocated
-// blocks, st_blocks × 512. On a compressed or sparse file it is less
-// than the file's size. It is 0 when the platform exposes no block
-// count.
-func diskSizeOfInfo(fi fs.FileInfo) int64 {
-	st, ok := fi.Sys().(*syscall.Stat_t)
-	if !ok {
-		return 0
-	}
-
-	return st.Blocks * statBlockSize
-}
-
 // hashResult carries the hashes computed for one inode run (or the
 // error that prevented computing them) from the pool's workers to the
 // hash phase. Its run leaves out the paths found removed.
@@ -1,6 +1,6 @@
 //go:build darwin

-package sfdupes
+package main

 import "syscall"

@@ -1,6 +1,6 @@
 //go:build !darwin

-package sfdupes
+package main

 import "syscall"

@@ -1,4 +1,4 @@
-package sfdupes //nolint:testpackage // drives the unexported syncTree
+package main

 import (
 	"bytes"
@@ -42,30 +42,6 @@ func writeFile(t *testing.T, dir, name string, data []byte) string {
 	return p
 }

-// diskSizeOf returns the bytes the file at path takes on disk, from its
-// own lstat: st_blocks counts 512-byte units. ZFS counts a write's
-// blocks only when it commits the write, up to seconds later, and one
-// commit can take the file through several growing sizes. So this value
-// can change at any moment. Neither fsync nor unix.Sync hastens that,
-// but a unix.Sync call often takes long enough that the blocks are
-// counted when it returns. A test that needs the value to change waits
-// for the change. A test that compares it with a scan's disk_size reads
-// it before and after the scan. The rewrite test rescans until the two
-// reads match, then compares exactly. The other two tests fail only on
-// a disk_size outside the two reads.
-func diskSizeOf(t *testing.T, path string) int64 {
-	t.Helper()
-
-	var st syscall.Stat_t
-
-	err := syscall.Lstat(path, &st)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	return st.Blocks * 512
-}
-
 // pattern returns n bytes of deterministic content seeded by tag.
 func pattern(tag byte, n int) []byte {
 	data := make([]byte, n)
@@ -1088,13 +1064,12 @@ func TestScanOneFilesystemWalksNestedFileOperand(t *testing.T) {
 	}
 }

-// buildSmokeTree recreates the tree of the test under README
-// "Definition of done" with deterministic content and returns the tree
-// root.
+// buildSmokeTree recreates the README smoke-test filesystem layout
+// with deterministic content and returns the tree root.
 func buildSmokeTree(t *testing.T) string {
 	t.Helper()

-	dir := realTempDir(t)
+	dir := t.TempDir()
 	one := pattern(10, 2000)
 	f1 := pattern(30, 3000)
 	f2 := pattern(40, 100)
@@ -1185,12 +1160,11 @@ func assertSmokeDupeGroups(t *testing.T, dir string, db *sql.DB) {
 	t.Helper()

 	groups := dupeGroups(t, db)
-	if len(groups) != 4 {
-		t.Fatalf("len(groups) = %d, want 4", len(groups))
+	if len(groups) != 5 {
+		t.Fatalf("len(groups) = %d, want 5", len(groups))
 	}

-	// The empty files empty1 and empty2 form no group.
-	wantSizes := []int64{3000, 2000, 100, 1}
+	wantSizes := []int64{3000, 2000, 100, 1, 0}
 	for i, g := range groups {
 		if g.size != wantSizes[i] {
 			t.Errorf("groups[%d].size = %d, want %d",
@@ -1254,9 +1228,9 @@ func TestScanPipeline(t *testing.T) {
 // TestScanProgressNamesEachPhase checks the plain progress lines of a
 // first scan, and of a rescan of one operand holding two of the
 // database's records. Each phase's first line names it with its place
-// among the four: load gets the number of records before reading them,
-// and the walk estimates its total from the records under its operand,
-// or says its time remaining is unknown when there are none.
+// among the four: load counts the records before reading them, and the
+// walk estimates its total from the records under its operand, or says
+// its time remaining is unknown when there are none.
 //
 //nolint:paralleltest // captureStderr replaces the process-wide os.Stderr
 func TestScanProgressNamesEachPhase(t *testing.T) {
@@ -1442,159 +1416,6 @@ func TestScanStoresRawHashes(t *testing.T) {
 	}
 }

-// TestScanStoresDiskSize scans a sparse file, which takes less space on
-// disk than its length, once through its directory and once as the
-// operand itself. Each scan stores the disk_size of the file's lstat.
-func TestScanStoresDiskSize(t *testing.T) {
-	t.Parallel()
-
-	const length = 1024 * 1024
-
-	p := sparseFile(t, t.TempDir(), "sparse", length)
-	pokeAt(t, p, 0, []byte("x"))
-
-	unix.Sync() // see diskSizeOf
-
-	size := diskSizeOf(t, p)
-	if size == 0 || size >= length {
-		t.Fatalf("the file takes %d bytes on disk, want more than none "+
-			"and fewer than its length %d", size, length)
-	}
-
-	for _, operand := range []string{filepath.Dir(p), p} {
-		db := openTestDB(t)
-
-		// ZFS may count the blocks during the scan; see diskSizeOf.
-		before := diskSizeOf(t, p)
-
-		syncTree(t, db, operand)
-
-		after := diskSizeOf(t, p)
-
-		got := recordByPath(t, dbRecords(t, db), p).diskSize
-		if got < before || got > after {
-			t.Errorf("scan of %s: disk_size = %d, want %d to %d",
-				operand, got, before, after)
-		}
-	}
-}
-
-// TestSyncScanRewriteUpdatesDiskSize writes into the hole of a scanned
-// sparse file and moves its mtime on. The rescan hashes the file again
-// and rewrites its record with the new disk_size.
-func TestSyncScanRewriteUpdatesDiskSize(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	db := openTestDB(t)
-	p := sparseFile(t, dir, "sparse", 1024*1024)
-	pokeAt(t, p, 0, []byte("x"))
-
-	syncTree(t, db, dir)
-
-	recorded := recordByPath(t, dbRecords(t, db), p).diskSize
-
-	pokeAt(t, p, 512*1024, pattern(7, 64*1024))
-
-	// The write may leave the mtime the scan recorded; a later one makes
-	// the rescan read the file again.
-	later := time.Now().Add(time.Hour)
-
-	err := os.Chtimes(p, later, later)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// Wait for ZFS to count the write; see diskSizeOf.
-	deadline := time.Now().Add(30 * time.Second)
-	for diskSizeOf(t, p) == recorded {
-		if time.Now().After(deadline) {
-			t.Fatalf("the file still takes %d bytes on disk 30 seconds "+
-				"after the write into its hole", recorded)
-		}
-
-		unix.Sync()
-	}
-
-	// ZFS may still be counting, so the size may change during a rescan.
-	// Only a rescan with the same size on both sides of it can be compared
-	// exactly. A rescan that keeps the old size still fails, because the
-	// wait made before differ from it.
-	for {
-		before := diskSizeOf(t, p)
-
-		st := syncTree(t, db, dir)
-
-		after := diskSizeOf(t, p)
-
-		if st != (scanStats{walked: 1, updated: 1}) {
-			t.Fatalf("rescan stats = %+v, want 1 updated", st)
-		}
-
-		if before == after {
-			got := recordByPath(t, dbRecords(t, db), p).diskSize
-			if got != after {
-				t.Errorf("disk_size = %d, want %d", got, after)
-			}
-
-			return
-		}
-
-		if time.Now().After(deadline) {
-			t.Fatalf("the size on disk was still changing 30 seconds after "+
-				"the write into its hole: %d, then %d", before, after)
-		}
-
-		// A later mtime makes the next rescan read the file again.
-		later = later.Add(time.Second)
-
-		err = os.Chtimes(p, later, later)
-		if err != nil {
-			t.Fatal(err)
-		}
-	}
-}
-
-// TestSyncScanUnchangedUpdatesDiskSize gives a file's record a
-// disk_size the file does not have, as when ZFS had not yet counted the
-// file's blocks at the last scan. The rescan writes the file's own
-// disk_size into the record without reading the file again.
-func TestSyncScanUnchangedUpdatesDiskSize(t *testing.T) {
-	t.Parallel()
-
-	dir := t.TempDir()
-	db := openTestDB(t)
-	p := writeFile(t, dir, "a.bin", pattern(1, 500))
-
-	syncTree(t, db, dir)
-
-	// lstat counts 512-byte units, so no file takes 1 byte on disk.
-	_, err := db.ExecContext(t.Context(),
-		"UPDATE files SET disk_size = 1 WHERE path = ?", []byte(p))
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	unix.Sync() // see diskSizeOf
-
-	// ZFS may count the blocks during the rescan; see diskSizeOf.
-	before := diskSizeOf(t, p)
-
-	// A file read again would count as updated.
-	st := syncTree(t, db, dir)
-
-	after := diskSizeOf(t, p)
-
-	if st != (scanStats{walked: 1, unchanged: 1}) {
-		t.Fatalf("rescan stats = %+v, want 1 unchanged", st)
-	}
-
-	got := recordByPath(t, dbRecords(t, db), p).diskSize
-	if got < before || got > after {
-		t.Errorf("disk_size = %d, want %d to %d", got, before, after)
-	}
-}
-
 // TestSyncScanSameSecondRewrite rewrites a file in place at the same
 // size with an mtime later in the same second as the recorded one: the
 // next scan must notice the change and re-hash the file. The operand is
@@ -1851,6 +1672,81 @@ func TestSyncScanOverlappingRoots(t *testing.T) {
 	}
 }

+// TestScanWalksOperandInZFSDirectory checks that an operand inside a
+// directory named .zfs below another operand is walked on its own,
+// since the walk of the other operand does not enter .zfs. The file
+// under it is recorded, and a second scan keeps the record.
+func TestScanWalksOperandInZFSDirectory(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	db := openTestDB(t)
+	f := writeFile(t, dir, "pool/.zfs/snapshot/daily/f", pattern(1, 10))
+	daily := filepath.Dir(f)
+
+	syncTree(t, db, dir, daily)
+	recordByPath(t, dbRecords(t, db), f)
+
+	syncTree(t, db, dir, daily)
+	recordByPath(t, dbRecords(t, db), f)
+}
+
+// TestScanWalksOperandBehindSymlink checks that an operand reached
+// through a symlinked directory below another operand is walked on its
+// own, since the walk of the other operand does not follow the symlink.
+// The file under it is recorded, and a second scan keeps the record.
+func TestScanWalksOperandBehindSymlink(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	target := t.TempDir()
+	db := openTestDB(t)
+	writeFile(t, target, "sub/f", pattern(1, 10))
+
+	link := filepath.Join(dir, "link")
+
+	err := os.Symlink(target, link)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sub := filepath.Join(link, "sub")
+	f := filepath.Join(sub, "f")
+
+	syncTree(t, db, dir, sub)
+	recordByPath(t, dbRecords(t, db), f)
+
+	syncTree(t, db, dir, sub)
+	recordByPath(t, dbRecords(t, db), f)
+}
+
+// TestScanDropsOperandReachedBehindSymlink checks that an operand under
+// another one is still dropped when both lie behind the same symlinked
+// directory: the walk of the other operand starts past the symlink and
+// reaches it, so the file under it is walked once.
+func TestScanDropsOperandReachedBehindSymlink(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	target := t.TempDir()
+	db := openTestDB(t)
+	writeFile(t, target, "sub/deeper/f", pattern(1, 10))
+
+	link := filepath.Join(dir, "link")
+
+	err := os.Symlink(target, link)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	sub := filepath.Join(link, "sub")
+
+	st := syncTree(t, db, sub, filepath.Join(sub, "deeper"))
+	if st != (scanStats{walked: 1, added: 1}) {
+		t.Fatalf("stats = %+v, want 1 walked and added", st)
+	}
+}
+
 // TestScanHashesUniqueSize checks that a file whose size no other file
 // shares is hashed like every other file.
 func TestScanHashesUniqueSize(t *testing.T) {
@@ -2264,6 +2160,16 @@ func TestPruneRoots(t *testing.T) {
 		t.Fatalf("pruneRoots with %s not persistent = %q, want %q",
 			pqRoot, got, want)
 	}
+
+	// Nor does it enter a directory named .zfs, so /p/.zfs/s is kept. The
+	// walk of /p/.zfs/s reaches /p/.zfs/s/t, which is dropped.
+	got = pruneRoots([]string{"/p", "/p/.zfs/s", "/p/.zfs/s/t"}, false,
+		walkRules{}, device)
+
+	want = []string{"/p", "/p/.zfs/s"}
+	if !slices.Equal(got, want) {
+		t.Fatalf("pruneRoots with .zfs = %q, want %q", got, want)
+	}
 }

 func TestReportsNeverTouchFilesystem(t *testing.T) {
@@ -2311,24 +2217,33 @@ func TestUnderRoot(t *testing.T) {
 }

 // TestRunScanPassesOverDatabase scans a tree that holds the scan's own
-// database, and in one case also a hard link to the database file. The
-// walk knows the database's files by device ID and inode number, so it
-// passes over the database file, its -wal and -shm files, its .lock
-// file and the hard link with no line and no count. The record an
-// earlier scan left for the .lock file is deleted. A rescan of the
-// unchanged tree updates nothing, and report lists none of the
-// database's files.
+// database, reached directly and through a symlinked directory. The
+// walk passes over the database file, its -wal and -shm files and its
+// .lock file with no line and no count, and the record an earlier scan
+// left for the .lock file is deleted. A rescan of the unchanged tree
+// updates nothing, and report lists none of the database's files.
 func TestRunScanPassesOverDatabase(t *testing.T) {
-	for _, viaHardLink := range []bool{false, true} {
-		t.Run(fmt.Sprintf("via hard link %v", viaHardLink), func(t *testing.T) {
-			tree := realTempDir(t)
-			hardLink := filepath.Join(tree, "hardlink")
+	for _, viaSymlink := range []bool{false, true} {
+		t.Run(fmt.Sprintf("via symlink %v", viaSymlink), func(t *testing.T) {
+			base := t.TempDir()
+			tree := filepath.Join(base, "real", "tree")
+			operand := tree

 			writeFile(t, tree, "a", pattern(1, 100))
 			writeFile(t, tree, "b", pattern(1, 100))
 			writeFile(t, tree, "empty1", nil)
 			writeFile(t, tree, "empty2", nil)

+			if viaSymlink {
+				err := os.Symlink(filepath.Join(base, "real"),
+					filepath.Join(base, "link"))
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				operand = filepath.Join(base, "link", "tree")
+			}
+
 			dbPath := filepath.Join(tree, "db.sqlite")
 			t.Setenv(databaseEnv, dbPath)

@@ -2338,7 +2253,7 @@ func TestRunScanPassesOverDatabase(t *testing.T) {
 			}

 			err = applyChanges(t.Context(), db, []scanRec{
-				{path: filepath.Join(tree, "db.sqlite.lock")},
+				{path: filepath.Join(operand, "db.sqlite.lock")},
 			}, nil, nil)
 			if err != nil {
 				t.Fatal(err)
@@ -2346,30 +2261,17 @@ func TestRunScanPassesOverDatabase(t *testing.T) {

 			closeScanDatabase(t.Context(), db, dbPath)

-			if viaHardLink {
-				err = os.Link(dbPath, hardLink)
-				if err != nil {
-					t.Fatal(err)
-				}
-			}
-
-			stderr := assertScanSummary(t,
+			assertScanSummary(t,
 				"4 files seen (4 added, 0 updated, 1 removed, 0 unchanged)",
-				tree)
-			stderr += assertScanSummary(t,
+				operand)
+			assertScanSummary(t,
 				"4 files seen (0 added, 0 updated, 0 removed, 4 unchanged)",
-				tree)
-
-			if strings.Contains(stderr, hardLink) {
-				t.Errorf("scan stderr = %q, want no line naming %s",
-					stderr, hardLink)
-			}
+				operand)

 			report := runStdout(t, cmdReport)
 			if strings.Contains(report, "db.sqlite") ||
-				strings.Contains(report, hardLink) ||
-				!strings.Contains(report, filepath.Join(tree, "b")) {
-				t.Errorf("report = %q, want a and b and none of "+
+				!strings.Contains(report, filepath.Join(operand, "empty2")) {
+				t.Errorf("report = %q, want the empty files and none of "+
 					"the database's files", report)
 			}
 		})
@@ -2393,9 +2295,8 @@ func TestRunScanPassesOverDatabaseOperands(t *testing.T) {

 // assertScanSummary scans operands and fails the test unless the
 // summary line gives counts with nothing skipped, and the line naming
-// the database is the only one that names one of its files. It returns
-// everything the scan printed to stderr.
-func assertScanSummary(t *testing.T, counts string, operands ...string) string {
+// the database is the only one that names one of its files.
+func assertScanSummary(t *testing.T, counts string, operands ...string) {
 	t.Helper()

 	stderr := scanOK(t, operands...)
@@ -2409,6 +2310,4 @@ func assertScanSummary(t *testing.T, counts string, operands ...string) string {
 		t.Errorf("scan %q: stderr = %q, want only the line naming the "+
 			"database to name one of its files", operands, stderr)
 	}
-
-	return stderr
 }
@@ -1,4 +1,4 @@
-package sfdupes
+package main

 import (
 	"context"
@@ -22,10 +22,6 @@ type treeNode struct {
 	digest    [sha256.Size]byte
 	fileCount int64
 	totalSize int64
-	// diskSize is the bytes the directory's files take on disk. Two
-	// copies of one tree have the same totalSize, but their diskSize
-	// can differ.
-	diskSize int64
 }

 // treesPhase names one phase of trees with its place among all of them,
@@ -44,11 +40,11 @@ func treesPhase(name string) string {
 // database problem, including a missing database, is fatal.
 //
 // The work runs in four phases, each under a progress display of its
-// own on stderr: open (open the database), read (read the number of
-// records from the totals table, then read the records into the
-// hierarchy), group (group the directories by digest) and write (write
-// the groups to stdout). Each display ends before the next phase
-// starts, and before an error is returned to be printed.
+// own on stderr: open (open the database), read (count the records,
+// then read them into the hierarchy), group (group the directories by
+// digest) and write (write the groups to stdout). Each display ends
+// before the next phase starts, and before an error is returned to be
+// printed.
 func runTrees(ctx context.Context, stdout io.Writer) error {
 	dbPath, source, err := databasePath()
 	if err != nil {
@@ -143,16 +139,15 @@ func readTree(ctx context.Context, db *sql.DB,

 // writeTreeGroups writes dupes to stdout as TSV, a header line and then
 // a row for every member of each group but its first, counting each
-// group on prog once its rows are written. The disk_size column is the
-// dupe's own. stdout may be the terminal prog is drawn on, so the lines
-// go through prog's writer. It returns the number of rows (dupe trees)
-// and the bytes they could reclaim.
+// group on prog once its rows are written. stdout may be the terminal
+// prog is drawn on, so the lines go through prog's writer. It returns
+// the number of rows (dupe trees) and the bytes they could reclaim.
 func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 	prog *progress,
 ) (int, int64, error) {
 	out := prog.writer(stdout)

-	_, err := fmt.Fprintln(out, "first\tdupe\tfiles\tsize\tdisk_size")
+	_, err := fmt.Fprintln(out, "first\tdupe\tfiles\tsize")
 	if err != nil {
 		return 0, 0, fmt.Errorf("write stdout: %w", err)
 	}
@@ -164,9 +159,9 @@ func writeTreeGroups(stdout io.Writer, dupes [][]*treeNode,
 	for _, g := range dupes {
 		first := g[0]
 		for _, n := range g[1:] {
-			_, err = fmt.Fprintf(out, "%s\t%s\t%d\t%d\t%d\n",
+			_, err = fmt.Fprintf(out, "%s\t%s\t%d\t%d\n",
 				escapePath(first.path), escapePath(n.path),
-				first.fileCount, first.totalSize, n.diskSize)
+				first.fileCount, first.totalSize)
 			if err != nil {
 				return 0, 0, fmt.Errorf("write stdout: %w", err)
 			}
@@ -237,7 +232,6 @@ func (b *treeBuilder) add(r scanRec) {
 	dir.entries = append(dir.entries, fileEntry(name, r))
 	dir.fileCount++
 	dir.totalSize += r.size
-	dir.diskSize += r.diskSize
 }

 // openDir starts the directory called name inside the innermost open
@@ -276,7 +270,6 @@ func (b *treeBuilder) closeTo(n int) {
 			"d\x00"+name+"\x00"+string(dir.digest[:]))
 		dir.parent.fileCount += dir.fileCount
 		dir.parent.totalSize += dir.totalSize
-		dir.parent.diskSize += dir.diskSize
 		b.dirs = append(b.dirs, dir)
 	}
 }
@@ -301,9 +294,7 @@ func fileEntry(name string, r scanRec) string {
 // collectTreeGroups groups directories by digest, counting each one on
 // prog as it is grouped, and returns every maximal group with two or
 // more members, each group's members sorted by path, groups ordered by
-// tree size descending then by first path ascending. A group whose
-// trees hold 0 bytes is left out, since removing one frees nothing. The
-// groups it implies hold 0 bytes too, so leaving it out hides nothing.
+// tree size descending then by first path ascending.
 func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 	prog *progress,
 ) [][]*treeNode {
@@ -317,9 +308,7 @@ func collectTreeGroups(allDirs []*treeNode, super *treeNode,
 	var dupes [][]*treeNode

 	for _, g := range groups {
-		// The members share a digest, so they share a total size.
-		if len(g) < minGroupSize || g[0].totalSize == 0 ||
-			suppressed(g, super) {
+		if len(g) < minGroupSize || suppressed(g, super) {
 			continue
 		}

@@ -1,8 +1,7 @@
-package sfdupes //nolint:testpackage // checks the unexported treeNode results
+package main

 import (
 	"bytes"
-	"crypto/sha256"
 	"database/sql"
 	"os"
 	"slices"
@@ -16,26 +15,20 @@ import (
 const treesOpenLine = "[1/4] open: opening the database, elapsed 0s, " +
 	"remain unknown"

-// smokeTreeRecs mirrors the tree of the test under README "Definition
-// of done": /d/t1 and /d/t2 are identical, /d/t3 differs from them only
-// by one filename. Each file takes one 4 KiB block on disk.
+// smokeTreeRecs mirrors the README smoke-test tree layout: /d/t1 and
+// /d/t2 are identical, /d/t3 differs from them only by one filename.
 func smokeTreeRecs() []scanRec {
 	f1Head, f1Tail, f1Content := testHash("f1h"), testHash("f1t"), testHash("f1c")
 	f2Head, f2Tail, f2Content := testHash("f2h"), testHash("f2t"), testHash("f2c")

 	return []scanRec{
-		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
-			content: f1Content, path: "/d/t1/f1"},
-		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
-			content: f2Content, path: "/d/t1/sub/f2"},
-		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
-			content: f1Content, path: "/d/t2/f1"},
-		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
-			content: f2Content, path: "/d/t2/sub/f2"},
-		{size: 3000, diskSize: 4096, head: f1Head, tail: f1Tail,
-			content: f1Content, path: "/d/t3/f1"},
-		{size: 100, diskSize: 4096, head: f2Head, tail: f2Tail,
-			content: f2Content, path: "/d/t3/sub/f2renamed"},
+		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t1/f1"},
+		{size: 100, head: f2Head, tail: f2Tail, content: f2Content, path: "/d/t1/sub/f2"},
+		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t2/f1"},
+		{size: 100, head: f2Head, tail: f2Tail, content: f2Content, path: "/d/t2/sub/f2"},
+		{size: 3000, head: f1Head, tail: f1Tail, content: f1Content, path: "/d/t3/f1"},
+		{size: 100, head: f2Head, tail: f2Tail, content: f2Content,
+			path: "/d/t3/sub/f2renamed"},
 	}
 }

@@ -205,33 +198,13 @@ func TestRunTreesEscapesPaths(t *testing.T) {
 			code, exitOK, stderr.String())
 	}

-	want := "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		`/d/\tone\ntwo\rthree\\four` + "\t/d/A\t1\t5\t4096\n"
+	want := "first\tdupe\tfiles\tsize\n" +
+		`/d/\tone\ntwo\rthree\\four` + "\t/d/A\t1\t5\n"
 	if got := stdout.String(); got != want {
 		t.Errorf("stdout = %q, want %q", got, want)
 	}
 }

-// TestRunTreesDiskSize runs trees on two copies of a tree whose files
-// take different space on disk. The row's disk_size is the sum over the
-// dupe copy's files, those in its subdirectory included.
-func TestRunTreesDiskSize(t *testing.T) {
-	f, g := testHash("f"), testHash("g")
-	recs := []scanRec{
-		{size: 10, diskSize: 4096, head: f, tail: f, content: f, path: "/a/f"},
-		{size: 20, diskSize: 4096, head: g, tail: g, content: g, path: "/a/sub/g"},
-		{size: 10, diskSize: 512, head: f, tail: f, content: f, path: "/b/f"},
-		{size: 20, diskSize: 1024, head: g, tail: g, content: g, path: "/b/sub/g"},
-	}
-
-	t.Setenv(databaseEnv, seedDatabase(t, recs))
-
-	want := "first\tdupe\tfiles\tsize\tdisk_size\n/a\t/b\t2\t30\t1536\n"
-	if got := runStdout(t, cmdTrees); got != want {
-		t.Errorf("stdout = %q, want %q", got, want)
-	}
-}
-
 // TestRunTreesProgressNamesEachPhase runs trees on the smoke-test
 // records with stderr not a terminal, and checks every line it prints
 // there. After the line naming the database, each phase prints a line
@@ -253,8 +226,7 @@ func TestRunTreesProgressNamesEachPhase(t *testing.T) {
 			code, exitOK, stderr())
 	}

-	report := "first\tdupe\tfiles\tsize\tdisk_size\n" +
-		"/d/t1\t/d/t2\t2\t3100\t8192\n"
+	report := "first\tdupe\tfiles\tsize\n/d/t1\t/d/t2\t2\t3100\n"
 	if got := stdout.String(); got != report {
 		t.Errorf("stdout = %q, want %q", got, report)
 	}
@@ -319,9 +291,7 @@ func TestWriteTreeGroupsOnTerminal(t *testing.T) {
 		shown = append(shown, line[strings.LastIndex(line, "\r")+1:])
 	}

-	want := []string{
-		"first\tdupe\tfiles\tsize\tdisk_size", "/d/t1\t/d/t2\t2\t3100\t8192",
-	}
+	want := []string{"first\tdupe\tfiles\tsize", "/d/t1\t/d/t2\t2\t3100"}
 	if len(shown) < len(want) || !slices.Equal(shown[:len(want)], want) {
 		t.Errorf("terminal shows lines %q, want %q first", shown, want)
 	}
@@ -436,35 +406,6 @@ func TestCollectTreeGroupsSiblings(t *testing.T) {
 	}
 }

-// TestCollectTreeGroupsLeavesOutEmptyTrees checks that directories
-// holding only empty files form no group, and that an empty file still
-// counts toward the digest of a tree that holds other files.
-func TestCollectTreeGroupsLeavesOutEmptyTrees(t *testing.T) {
-	t.Parallel()
-
-	h, tl, c, e := testHash("h"), testHash("t"), testHash("c"),
-		sha256.Sum256(nil)
-	recs := []scanRec{
-		{size: 0, head: e, tail: e, content: e, path: "/e/a/.gitkeep"},
-		{size: 0, head: e, tail: e, content: e, path: "/e/b/.gitkeep"},
-		{size: 10, head: h, tail: tl, content: c, path: "/p/x1/f"},
-		{size: 0, head: e, tail: e, content: e, path: "/p/x1/.gitkeep"},
-		{size: 10, head: h, tail: tl, content: c, path: "/p/x2/f"},
-		{size: 0, head: e, tail: e, content: e, path: "/p/x2/.gitkeep"},
-		// Without the empty file, /p/x3 is no copy of /p/x1.
-		{size: 10, head: h, tail: tl, content: c, path: "/p/x3/f"},
-	}
-
-	super, dirs := treeOf(t, recs)
-
-	got := groupPaths(collectTreeGroups(dirs, super, nil))
-
-	want := [][]string{{"/p/x1", "/p/x2"}}
-	if !slices.EqualFunc(got, want, slices.Equal) {
-		t.Fatalf("groups = %v, want %v", got, want)
-	}
-}
-
 func TestCollectTreeGroupsDifferingParents(t *testing.T) {
 	t.Parallel()