Re: [musl] [PATCH v2 8/8] use new SYS_fchmodat2 syscall to implement fchmodat with flags

[Rich Felker <dalias@libc.org>]

On Sun, Feb 18, 2024 at 03:26:50AM +0100, Gaël PORTAY wrote:
> commit 0dc4824479e357a3e23a02d35527e23fca920343 worked around for lack
> of flags argument in syscall for fchmodat.
> 
> linux 6.6 introduced a new syscall, SYS_fchmodat2, fixing this
> deficiency. use it if any flags are passed, and fallback to the old
> strategy on ENOSYS. continue using the old syscall when there are no
> flags. this is the exact same strategy used when SYS_faccessat2 was used
> to implement faccessat with flags.
> ---
>  src/stat/fchmodat.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/src/stat/fchmodat.c b/src/stat/fchmodat.c
> index 41db0c46..a3f407e3 100644
> --- a/src/stat/fchmodat.c
> +++ b/src/stat/fchmodat.c
> @@ -5,6 +5,11 @@
>  
>  int fchmodat(int fd, const char *path, mode_t mode, int flag)
>  {
> +	if (flag) {
> +		int ret = __syscall(SYS_fchmodat2, fd, path, mode, flag);
> +		if (ret != -ENOSYS) return __syscall_ret(ret);
> +	}
> +
>  	if (!flag) return syscall(SYS_fchmodat, fd, path, mode);
>  
>  	if (flag != AT_SYMLINK_NOFOLLOW)
> -- 
> 2.43.2

I've reordered this to avoid confusing repeating conditionals, so it's
now:

	if (!flag) return syscall(SYS_fchmodat, fd, path, mode);

+       int ret = __syscall(SYS_fchmodat2, fd, path, mode, flag);
+       if (ret != -ENOSYS) return __syscall_ret(ret);

...

(with the later declaration of ret removed).

Thanks for getting these patches in to make it into the release!

Rich