Re: [PATCH] Cygwin: chown: make sure ctime gets updated when necessary

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Jan 25 14:16, Ken Brown via Cygwin-patches wrote:
> On 1/25/2021 1:57 PM, Corinna Vinschen via Cygwin-patches wrote:
> > On Jan 25 12:24, Ken Brown via Cygwin-patches wrote:
> > > Following POSIX, ensure that ctime is updated if chown succeeds,
> > > unless the new owner is specified as (uid_t)-1 and the new group is
> > > specified as (gid_t)-1.  Previously, ctime was unchanged whenever the
> > > owner and group were both unchanged.
> > > 
> > > Aside from POSIX compliance, this fix makes gnulib report that chown
> > > works on Cygwin.  This improves the efficiency of packages like GNU
> > > tar that use gnulib's chown module.  Previously such packages would
> > > use a gnulib replacement for chown on Cygwin.
> > > ---
> > >   winsup/cygwin/fhandler_disk_file.cc | 10 +++++++++-
> > >   1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/winsup/cygwin/fhandler_disk_file.cc b/winsup/cygwin/fhandler_disk_file.cc
> > > index 07f9c513a..72d259579 100644
> > > --- a/winsup/cygwin/fhandler_disk_file.cc
> > > +++ b/winsup/cygwin/fhandler_disk_file.cc
> > > @@ -863,6 +863,7 @@ fhandler_disk_file::fchown (uid_t uid, gid_t gid)
> > >     tmp_pathbuf tp;
> > >     aclent_t *aclp;
> > >     int nentries;
> > > +  bool noop = true;
> > >     if (!pc.has_acls ())
> > >       {
> > > @@ -887,11 +888,18 @@ fhandler_disk_file::fchown (uid_t uid, gid_t gid)
> > >   				    aclp, MAX_ACL_ENTRIES)) < 0)
> > >       goto out;
> > > +  /* According to POSIX, chown can be a no-op if uid is (uid_t)-1 and
> > > +     gid is (gid_t)-1.  Otherwise, even if uid and gid are unchanged,
> > > +     we must ensure that ctime is updated. */
> > >     if (uid == ILLEGAL_UID)
> > >       uid = old_uid;
> > > +  else
> > > +    noop = false;
> > >     if (gid == ILLEGAL_GID)
> > >       gid = old_gid;
> > > -  if (uid == old_uid && gid == old_gid)
> > 
> > Basically ok, but why not just
> > 
> >       if (uid == ILLEGAL_UID && gid == ILLEGAL_GID)
> > 
> > instead of the noop var?
> 
> I went back and forth on that.  Following your suggestion, the code looks like this:
> 
>   if (uid == ILLEGAL_UID && gid == ILLEGAL_GID)
>     {
>       ret = 0;
>       goto out;
>     }
>   if (uid == ILLEGAL_UID)
>     uid = old_uid;
>   if (gid == ILLEGAL_GID)
>     gid = old_gid;
> 
> I was trying to avoid checking uid == ILLEGAL_UID and gid == ILLEGAL_GID
> twice.  But on second thought, it's probably silly to worry about that.  The
> code is cleaner without the noop variable.

Both is ok with me, whatever you think more spiffy here.


Thanks,
Corinna