[abendrothj]

Closes #15329

When the destination was missing, or cp had removed or renamed it (--remove-destination, -f, --backup), cp created the new file without O_EXCL. Whatever appeared at that name in between was opened, and a symlink was followed.

cp now creates the file exclusively in those cases and fails if anything is there, with GNU's messages. A destination that is overwritten in place is opened as before. The flag lives in uucore's create_dest_restrictive, where exclusive replaces nofollow. Its only nofollow caller, mv's cross-device fallback, now creates exclusively too, as GNU mv does. mv can't be paused between its removal and the create, so that path has no test of its own; the uucore unit tests cover the exclusive create. --attributes-only creates exclusively on Windows too; the Windows data copy still uses fs::copy. util/check-safe-traversal.sh accepts O_EXCL as well as O_NOFOLLOW for mv's create.

Checked against GNU coreutils 9.12 for --remove-destination with a symlink, a dangling symlink and a regular file created after the removal: messages and exit status match. Added test_cp_does_not_open_dest_recreated_after_removal, which fails without the change on macOS and Linux.

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[codspeed]

Merging this PR will improve performance by 13.13%

1 warning, 1 note

⚠️ 118 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

⚡ 2 improved benchmarks
✅ 399 untouched benchmarks
⏩ 70 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	CPU Simulation	true_consecutive_calls	350.2 ns	294.7 ns	+18.85%
⚡	Memory	du_deep_tree[(100, 3)]	82.4 KB	76.5 KB	+7.68%

Tip

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_{Comparing abendrothj:cp-recreate-dest-exclusive (9d7881e) with main (29550e9)²}

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. ↩

2. No successful run was found on main (744e299) during the generation of this report, so 29550e9 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

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