du: dedupe reflink bytes

[aaron-ang]

Close #3906.

Dedupe reflink bytes only when --apparent-size or --bytes flag is set, based on GNU du page.

Implementation

• Keep track of shared extents while walking extent mapping using fiemap ioctl: https://www.kernel.org/doc/Documentation/filesystems/fiemap.txt.
• Only increment bytes if extent has not been seen.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/shuf/shuf-reservoir. tests/shuf/shuf-reservoir is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/sort/sort-stale-thread-mem. tests/sort/sort-stale-thread-mem is passing on 'main'. Maybe you have to rebase?
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will degrade performance by 7.84%

⚡ 2 improved benchmarks
❌ 1 regressed benchmark
✅ 247 untouched benchmarks
⏩ 70 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Memory	sort_numeric[500000]	48.7 MB	47.3 MB	+3.06%
⚡	Memory	sort_key_field[500000]	32.8 MB	31.4 MB	+4.63%
❌	Memory	cp_large_file[16]	110.3 KB	119.7 KB	-7.84%

---

_{Comparing aaron-ang:du-reflink-count (26a4b12) with main (98d3dba)}

Footnotes

1. 70 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/retry. tests/tail/retry is passing on 'main'. Maybe you have to rebase?

[ChrisDryden]

Somehow this is the first time I've seen this notation, this is really nice and would be nice to cleanup our other cfg code

[ChrisDryden]

Just to clarify that my understanding matches yours. This would be extending past GNU's capabilities instead of matching GNU's capabilities right? Given that its a big change I imagine it would be something that would be reviewed after the issues with GNU compatibility are sorted out

[ChrisDryden]

I think this is a pre-existing bug, theres another open PR about moving that seen_inodes out of this loop so that when you pass multiple file names it can deduplicate. Ideally this would be moved outside of the loop too

[aaron-ang]

I've updated it.

[aaron-ang]

Just to clarify that my understanding matches yours. This would be extending past GNU's capabilities instead of matching GNU's capabilities right? Given that its a big change I imagine it would be something that would be reviewed after the issues with GNU compatibility are sorted out

yea that's right.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/follow-name (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/dd/stderr is no longer failing!
Congrats! The gnu test tests/tac/tac-2-nonseekable is no longer failing!
Congrats! The gnu test tests/tail/follow-stdin is no longer failing!