On Jan 27 13:53, Ken Brown via Cygwin-patches wrote:
> Allow fchmodat with the AT_SYMLINK_NOFOLLOW flag to succeed on
> non-symlinks. Previously it always failed, as it does on Linux. But
> POSIX permits it to succeed on non-symlinks even if it fails on
> symlinks.
>
> The reason for following POSIX rather than Linux is to make gnulib
> report that fchmodat works on Cygwin. This improves the efficiency of
> packages like GNU tar that use gnulib's fchmodat module. Previously
> such packages would use a gnulib replacement for fchmodat on Cygwin.
> ---
> winsup/cygwin/syscalls.cc | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/winsup/cygwin/syscalls.cc b/winsup/cygwin/syscalls.cc
> index 4cc8d07f5..5da05b18a 100644
> --- a/winsup/cygwin/syscalls.cc
> +++ b/winsup/cygwin/syscalls.cc
> @@ -4787,17 +4787,27 @@ fchmodat (int dirfd, const char *pathname, mode_t
> mode, int flags)
> tmp_pathbuf tp;
> __try
> {
> - if (flags)
> + if (flags & ~AT_SYMLINK_NOFOLLOW)
> {
> - /* BSD has lchmod, but Linux does not. POSIX says
> - AT_SYMLINK_NOFOLLOW is allowed to fail on symlinks; but Linux
> - blindly fails even for non-symlinks. */
> - set_errno ((flags & ~AT_SYMLINK_NOFOLLOW) ? EINVAL : EOPNOTSUPP);
> + set_errno (EINVAL);
> __leave;
> }
> char *path = tp.c_get ();
> if (gen_full_path_at (path, dirfd, pathname))
> __leave;
> + if (flags)
For clarity, and on the off-chance that new flags are added to fchmodat,
it might be better to check for (flags & AT_SYMLINK_NOFOLLOW) here
explicitely. Your choice.
> + {
> + /* BSD has lchmod, but Linux does not. POSIX says
> + AT_SYMLINK_NOFOLLOW is allowed to fail on symlinks.
> + Linux blindly fails even for non-symlinks, but we allow
> + it to succeed. */
> + path_conv pc (path, PC_SYM_NOFOLLOW, stat_suffixes);
> + if (pc.issymlink ())
> + {
> + set_errno (EOPNOTSUPP);
> + __leave;
> + }
> + }
> return chmod (path, mode);
> }
> __except (EFAULT) {}
> --
> 2.30.0
Looks good.
Thanks,
Corinna
