[abendrothj]

--from was checked on a stat of the name and the change was then made by name, so a rename landing in between changed a file that never had the required owner.

On Linux, a non-directory operand and every -R entry are now held open with O_PATH when --from is given, checked to be the file that was stat'd and to still pass --from, and changed through that descriptor with fchownat(AT_EMPTY_PATH). A file found replaced is left alone and counts as a failure, which only -v reports, as GNU 9.12 does for operands and under -L/-H. Under -R -P, GNU 9.12 changes the replacement by name; this leaves it alone too, so here it exits 1 where GNU exits 0. Without --from nothing changes.

Unreadable directory operands, -R -H symlink targets, -R -v failure lines, -h with -H/-L, the descriptor walk on other platforms and holding the file without O_PATH are in follow-ups: #15124, #15125, #15126, #15127, #15128, #15129.

Part of #15027

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[codspeed]

Merging this PR will not alter performance

1 warning, 1 note

⚠️ 121 benchmarks are dominated by system calls

System calls cannot be simulated consistently and are left out of the measure. The reported value understates the real cost. Switch to the Walltime instrument to measure them.

Learn more about system calls

See affected benchmarks

ℹ️ 1 benchmark has no flamegraph

The flamegraph wasn't generated: most of the time was spent in runtime internals, which would leave nothing useful to analyze.

See affected benchmarks

✅ 401 untouched benchmarks
⏩ 70 skipped benchmarks¹

---

_{Comparing abendrothj:chown-from-by-fd (63b9cf2) with main (18bc31f)}

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. ↩

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[sylvestre]

this is too large, can we make it smaller?

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[abendrothj]

Split it up. This PR now only has the core change, three files, +247/-32: on Linux, with --from, the operand and each -R entry are held open with O_PATH, checked to be the file that was stat'd and to still pass --from, and changed through that descriptor with fchownat(AT_EMPTY_PATH). The rest is in follow-ups, each based on the one before: unreadable directory operands (#15124), --from on symlink targets under -R -H (#15125), -v failure lines for -R entries (#15126), -h with -H/-L (#15127), the descriptor walk on the other platforms (#15128), and holding the file without O_PATH (#15129). Until the earlier ones merge, each diff also shows the commits it's based on.

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[abendrothj]

@sylvestre since I split this up on Oct 6, it's only the --from fix: three files, +247/-32, most of it in perms.rs. It still merges cleanly with main. The follow-ups (#15124–#15129) can wait until this one is in. Could you take another look when you have time?

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[github-actions]

Binary size comparison:

Individual binary size comparison VS main (threshold: >=5% AND >=4 KB).

Total size of compared binaries: 155.07 MB (-280 KB, -0.18%)

Significant per-binary changes:
  date     2.61 MB ->    2.30 MB  (-316 KB, -11.81%)