unix: add preadv2 and pwritev2 to android by Elie-Kh · Pull Request #5157 · rust-lang/libc

Elie-Kh · 2026-06-08T16:16:35Z

Add preadv2 and pwrite2 to linux and Android, making majority of linux_like based systems have support, to allow using the new flags introduced in #4452. Move definitions to linux_like/mod.rs instead of each separate system alone.

Relevant tests in libc-test/semver have been updated - no tests to modify
No placeholder or unstable values like *LAST or *MAX are
included (see #3131)
[~] Tested locally (cd libc-test && cargo test --target mytarget);
especially relevant for platforms that may not be checked in CI

Getting error while testing locally due to different linux version and mismatch of SW_MAX and MS_NOUSER. Modifying those to match local system (0x11 and 0x80000000) shows passing tests using cargo test.

Unable to test other systems, need to run CI

Android source for preadv2 and pwritev2 support: https://android.googlesource.com/platform/bionic/+/cf59e19e22fc7c4795fd955eeecd1f457d79eba0/libc/include/sys/uio.h#117

rustbot · 2026-06-08T16:16:38Z

Some changes occurred in an Android module

cc @maurer

JohnTitor · 2026-06-08T21:12:11Z

Seems you messed up the commits in the branch, could you fix it to have exact one commit?

Elie-Kh · 2026-06-08T21:31:37Z

Sure thing, it's been a minute since I've worked with github, let me fix that

Elie-Kh · 2026-06-08T21:43:05Z

And that should have it fixed!

JohnTitor · 2026-06-14T00:20:30Z

Seems you need some more ignores: https://github.com/rust-lang/libc/actions/runs/27483200559/job/81234642626?pr=5157

tgross35

Can you please link the Android sources you are referencing so we don't need to dig them up? (This is requested in the PR template)

View changes since this review

tgross35 · 2026-06-21T08:56:52Z

+    #[cfg_attr(gnu_file_offset_bits64, link_name = "preadv64v2")]
+    pub fn preadv2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
+    #[cfg_attr(gnu_file_offset_bits64, link_name = "pwritev64v2")]
+    pub fn pwritev2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;


I think these aren't available in uclibc so should be left as is (link a source please if this isn't accurate)

Can the linux_like/ilnux module be restored to the way it was before? I don't think there is any reason for this part of the change.

You are correct for uclibc, I added a cfg to skip. I explained in another comment that the change is being introduced in crosvm, we benefit from having Linux support.

It was already supported on Linux prior to this PR? You're moving the definitions from the gnu and musl modules to linux then disabling uclibc, which is no net change.

rustbot · 2026-06-21T08:58:34Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

tgross35 · 2026-06-24T03:35:02Z

+    #[cfg_attr(gnu_file_offset_bits64, link_name = "preadv64v2")]
+    pub fn preadv2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
+    #[cfg_attr(gnu_file_offset_bits64, link_name = "pwritev64v2")]
+    pub fn pwritev2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;


Can the linux_like/ilnux module be restored to the way it was before? I don't think there is any reason for this part of the change.

tgross35 · 2026-07-20T18:11:17Z

+    #[cfg_attr(gnu_file_offset_bits64, link_name = "preadv64v2")]
+    pub fn preadv2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
+    #[cfg_attr(gnu_file_offset_bits64, link_name = "pwritev64v2")]
+    pub fn pwritev2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;


It was already supported on Linux prior to this PR? You're moving the definitions from the gnu and musl modules to linux then disabling uclibc, which is no net change.

Add preadv2 and pwrite2 to Android, to allow using the new flags introduced in rust-lang#4452. Add flags to Android too Skip test on Android due to the definitions being introduced in API 33

rustbot · 2026-07-20T18:32:33Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

tgross35

Thanks!

View changes since this review

Add preadv2 and pwrite2 to Android, to allow using the new flags introduced in rust-lang#4452. Add flags to Android too Skip test on Android due to the definitions being introduced in API 33 (backport <rust-lang#5157>) (cherry picked from commit 63fde92)

rustbot added the S-waiting-on-review label Jun 8, 2026

Elie-Kh force-pushed the linux-preadwritev2 branch from ec99a98 to fe75a48 Compare June 8, 2026 16:47

rustbot added the A-CI Area: CI-related items label Jun 8, 2026