work around linux not honoring write_at for O_APPEND files

[the8472]

the workaround only applies on kernels >= 6.9

fixes #140867

[rustbot]

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[the8472]

Weird, the kernel should be new enough.

[rust-log-analyzer]

The job mingw-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

  CACHE_DOMAIN: ci-caches.rust-lang.org
  PR_CI_JOB: 1
  IMAGE: mingw-check-2
##[endgroup]
Linux fv-az1618-111 6.11.0-1015-azure #15~24.04.1-Ubuntu SMP Thu May  1 02:52:08 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
##[group]Run src/ci/scripts/collect-cpu-stats.sh
src/ci/scripts/collect-cpu-stats.sh
shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
---
DirectMap4k:      143296 kB
DirectMap2M:     7196672 kB
DirectMap1G:    11534336 kB
##[endgroup]
Executing ldd --version &&         python3 ../x.py test --stage 1 std -- write
+ ldd --version
ldd (Ubuntu GLIBC 2.35-0ubuntu3.10) 2.35
Copyright (C) 2022 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Written by Roland McGrath and Ulrich Drepper.
+ python3 ../x.py test --stage 1 std -- write
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.05s
##[endgroup]
downloading https://static.rust-lang.org/dist/2025-05-27/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz
extracting /checkout/obj/build/cache/2025-05-27/rustfmt-nightly-x86_64-unknown-linux-gnu.tar.xz to /checkout/obj/build/x86_64-unknown-linux-gnu/rustfmt
---
failures:

---- fs::tests::file_test_append_write_at stdout ----

thread 'fs::tests::file_test_append_write_at' panicked at library/std/src/fs/tests.rs:507:5:
assertion `left == right` failed
  left: [105, 116, 39, 115, 32, 110, 111, 116, 32, 119, 111, 114, 107, 105, 110, 103, 33, 32, 32, 32]
 right: [105, 116, 39, 115, 32, 32, 32, 32, 32, 119, 111, 114, 107, 105, 110, 103, 33]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- os::unix::fs::tests::write_vectored_at stdout ----

thread 'os::unix::fs::tests::write_vectored_at' panicked at library/std/src/os/unix/fs/tests.rs:57:5:
assertion `left == right` failed
  left: [112, 119, 114, 105, 116, 101, 118, 32, 105, 115, 32, 110, 111, 116, 32, 119, 111, 114, 107, 105, 110, 103, 33, 32, 32, 32, 32, 103, 114, 101, 97, 116, 32, 32]
 right: [112, 119, 114, 105, 116, 101, 118, 32, 105, 115, 32, 32, 32, 32, 32, 103, 114, 101, 97, 116, 32, 32, 33]