* Rich Felker: > On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote: >> * Rich Felker: >> >> > coreutils should be opting to use the system-provided lchmod, which is >> > safe, and correctly handling error returns (silently treating >> > EOPNOTSUPP as success) rather than as hard errors. >> >> glibc's lchmod always returns ENOSYS (except on Hurd). I don't know how >> lchmod is used in coreutils, but I suspect it is not particularly >> useful. > > When preserving permissions (cp -p, archive extraction, etc.), you > want lchmod to work correctly just for the purpose of *not* following > the link and thereby unwantedly changing the permissions of the link > target. But, fchmodat with AT_SYMLINK_NOFOLLOW works just as well and > is standard, and that's really what coreutils should be using.
I think you misread what I wrote: lchmod *always* returns ENOSYS. Even if the file is not a symbolic link. Likewise, fchmodat with AT_SYMLINK_NOFOLLOW *always* returns ENOTSUP. The reason for this is that the kernel does not provide a suitable system call to implement this, even though some file systems allow a mode change for symbolic links. I think we can do better, although I should note that each time we implement such emulation in userspace, it comes back to bite us eventually. Thanks, Florian
