uucore: share replace_link's atomic replace

[abendrothj]

replace_link creates a temporary link and renames it over the target. The temporary-name and renameat part moves into replace_entry_at, which creates the entry through a callback relative to an open directory, so mv can replace special files and directory entries the same way.

The parent is now opened with DirFd::open_anchor, so ln -sf and cp -sf replacing an entry in a directory with write and search but no read permission work, as with GNU 9.12, instead of failing with EACCES. Running out of temporary names reports a translated error.

Closes #15112

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[codspeed]

Merging this PR will degrade performance by 2.92%

⚠️ 79 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• hostname_ip_lookup[100000]
• cksum_crc
• cksum_default
• dd_copy_partial
• cksum_raw_output
• factor_multiple_u64s[2]
• du_wide_tree[(5000, 500)]
• timer_expiry_latency[0.02]
• timeout_enforced
• dd_copy_4k_blocks
• …and 69 more

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 3 improved benchmarks
❌ 2 regressed benchmarks
✅ 144 untouched benchmarks
⏩ 306 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
❌	three_39_bit_primes	583.2 ms	719.2 ms	-18.9%
❌ ⚠️	hostname_ip_lookup[100000]	169.5 µs	177.3 µs	-4.38%
⚡	five_38_bit_primes	1.6 s	1.5 s	+4.42%
⚡ ⚠️	cksum_crc	33.6 ms	32.6 ms	+3.25%
⚡ ⚠️	cksum_default	33.9 ms	32.8 ms	+3.13%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing abendrothj:uucore-replace-entry-at (f5b87ae) with main (6292c03)}

Footnotes

1. 306 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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