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GeezerVison is showing github.com — cmp: don't reopen /dev/null on Linux by oech3 · Pull Request #267 · uutils/diffutils

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@oech3

@oech3 oech3 commented Aug 5, 2026

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Don't reopen 2nd /dev/null at fn is_stdout_dev_null on Linux.

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@github-actions

github-actions Bot commented Aug 5, 2026

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GNU diffutils testsuite comparison:

Test results comparison:
  Current:   TOTAL: 33 / PASSED: 0 / FAILED: 33 / SKIPPED: 0
  Reference: TOTAL: 33 / PASSED: 8 / FAILED: 21 / SKIPPED: 4

Changes from main branch:
  TOTAL: +0
  PASSED: -8
  FAILED: +12

New test failures (12):
  - basic
  - bignum
  - brief-vs-stat-zero-kernel-lies
  - bug-64316
  - cmp
  - diff3
  - help-version
  - large-subopt
  - strcoll-0-names
  - strip-trailing-cr
  - timezone
  - y2038-vs-32bit
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sylvestre
sylvestre reviewed Oct 18, 2026
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Comment thread Cargo.toml Outdated
diff = "0.1.13"
itoa = "1.0.11"
regex = "1.10.4"
rustix = { version = "1.1.4", features = ["fs"] }

@sylvestre sylvestre Oct 18, 2026

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do we really need a new dependency to save one stat() call?
please justify it, or use std (as_fd().try_clone_to_owned() + MetadataExt::rdev())

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@oech3 oech3 Oct 18, 2026

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try_clone needs additional fcntl call.

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sylvestre
sylvestre reviewed Oct 18, 2026
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Comment thread Cargo.toml Resolved

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sylvestre
sylvestre reviewed Oct 18, 2026
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Comment thread src/cmp.rs Resolved

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sylvestre
sylvestre reviewed Oct 18, 2026
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Comment thread src/cmp.rs Resolved

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@oech3
cmp: don't reopen /dev/null on Linux
3ce9076
@oech3
oech3 force-pushed the linux-dev-null branch from 6e6618c to 3ce9076 Compare October 18, 2026 09:09
sylvestre
sylvestre reviewed Oct 18, 2026
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Comment thread src/cmp.rs

#[cfg(any(target_os = "linux", target_os = "android"))]
fn is_stdout_dev_null() -> bool {
// as_fd().try_clone_to_owned() needs additional overhead of fcntl

@sylvestre sylvestre Oct 18, 2026

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the unix version below doesn't need fcntl either (from_raw_fd + forget)
could you please do the same with MetadataExt::rdev() + FileTypeExt::is_char_device() and drop rustix?

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@oech3 oech3 Oct 18, 2026

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Is needs unsafe. Is it OK? clap-rs already pulls rustix.

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@oech3 oech3 Oct 18, 2026

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I think std does not have a feature to check major/minor.

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@sylvestre

sylvestre commented Oct 23, 2026

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The only thing left is whether rustix is needed at all. std can do the same without fcntl, the way the existing unix path already does.
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@oech3

oech3 commented Oct 23, 2026 •
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Other unix has 2nd open call at Ok(dev_null) = fs::metadata("/dev/null"). But Linux does not. I'll reconsider how to do same things with std.
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@oech3

oech3 commented Oct 23, 2026

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It seems possible, but some magic numbers and bit shift is needed to avoid libc-like crates.
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@oech3 @sylvestre
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