stty: support any baud on Linux, replace nix with rustix

[oech3]

• Closes stty: support arbitrary baudrate (at least on linux) as GNU coreutils 9.8 #8719 . rustix manages baud rate by u32 on all platforms. But OS itself should support any baud to actually use any baud. This PR adds support for any baud on Linux kernel (since bsd was already supported at nix crate).
• Closes stty: support B460800 and B921600 baud rates #14989 too since rustix has u32 -> enum decoder.

[codspeed]

Merging this PR will regress 1 benchmark

⚠️ 118 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

• sort_unique_utf8_locale
• sort_numeric_utf8_locale
• cksum_default
• dd_copy_64k_blocks
• dd_copy_partial
• cksum_multiple_files
• cksum_crc32b
• du_deep_tree[(100, 3)]
• du_all_wide_tree[(5000, 500)]
• sort_long_common_prefix_utf8_locale
• …and 108 more

ℹ️ 1 benchmark has no flame graph

The flamegraph could not be generated because too much time was spent in runtime internals, making the visualization not useful for performance analysis.

• sort_dictionary_order[500000]

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

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	factor_five_38_bit_primes	1.6 s	1.7 s	-5.48%
⚡	Simulation	factor_three_39_bit_primes	567 ms	357.1 ms	+58.78%

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 oech3:stty-unsafe (0ad3f39) with main (7654e67)}

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:

Note: The gnu test tests/stty/bad-speed is now being skipped but was previously passing.

[xtqqczze]

Would it be possible to separate the refactor replacing nix with rustix from the fix for #8719 into separate PRs?

[oech3]

It is very difficult since rustix automatically supports any baud and nix and rustix cannot be mixed.

[xtqqczze]

Closes #14989

@oech3 Could you please clarify in the PR description whether these changes support arbitrary baud rates across all platforms, or only on Linux?

[xtqqczze]

@oech3 #14989 is not for Linux, is the issue fully resolved by this PR?

[oech3]

I don't think that we need to support all labeled targets, but yes. https://github.com/bytecodealliance/rustix/blob/287214b889865d8e1406a0ee71cc409b6f6191c8/src/termios/types.rs#L740 .

Missing macOS and bsd are not problem since they use any baud (as same as nix).

[xtqqczze]

By switching from nix to rustix we can support more platforms, e.g. AIX.