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Cygwin: fchmodat: add limited support for AT_SYMLINK_NOFOLLOW 

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.
This commit is contained in:
Ken Brown 2021-01-26 15:54:05 -05:00
parent 253352e796
commit 883abd9d7d
1 changed files with 15 additions and 5 deletions
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20
winsup/cygwin/syscalls.cc
View File

@ -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 & AT_SYMLINK_NOFOLLOW)
{
/* 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) {}