[PATCH v8] linux: Add openat2 (BZ 31664)

[Florian Weimer]

* Adhemerval Zanella:

> The openat2 syscall was added on Linux 5.6, as an extension of openat.
> Unlike other open-like functions, the kernel only provides the LFS
> variant (so files larger than 4GB always succeed, unlike other
> functions with an offset larger than off_t).  Also, similar to other
> open functions, the new symbol is a cancellable entrypoint.
>
> The test case added only stress tests for some of the syscalls' provided
> functionality, and it is based on an existing kernel self-test.
>
> A fortify wrapper is added to verify the argument size if not larger
> than the current support open_how struct.
>
> Gnulib added an openat2 module, which uses read-only for the open_how
> argument [1].  There is no clear indication whether the kernel will
> indeed use the argument as in-out, how it would do so, or for which
> kind of functionality [2]. Also, adding a potentially different prototype
> than gnulib only would add extra unnecessary friction and extra
> wrappers to handle it.
>
> Checked on x86_64-linux-gnu and aarch64-linux-gnu.
>
> [1] https://gitweb.git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commit;h=0b97ffdf32bdab909d02449043447237273df75e
> [2] https://sourceware.org/pipermail/libc-alpha/2025-September/169740.html
>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Adhemerval, Carlos, is this patch accepted, or does it need further
review?

Thanks,
Florian