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Date:   Thu, 6 Jul 2023 21:02:36 +0000
From:   Seth Arnold <seth.arnold@canonical.com>
To:     Jeff Layton <jlayton@kernel.org>
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Subject: Re: [apparmor] [PATCH v2 08/92] fs: new helper:
 simple_rename_timestamp
Message-ID: <20230706210236.GB3244704@millbarge>
References: <20230705185812.579118-1-jlayton@kernel.org>
 <20230705185812.579118-3-jlayton@kernel.org>
 <3b403ef1-22e6-0220-6c9c-435e3444b4d3@kernel.org>
 <7c783969641b67d6ffdfb10e509f382d083c5291.camel@kernel.org>
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On Wed, Jul 05, 2023 at 08:04:41PM -0400, Jeff Layton wrote:
>=20
> I don't believe it's an issue. I've seen nothing in the POSIX spec that
> mandates that timestamp updates to different inodes involved in an
> operation be set to the _same_ value. It just says they must be updated.
>=20
> It's also hard to believe that any software would depend on this either,
> given that it's very inconsistent across filesystems today. AFAICT, this
> was mostly done in the past just as a matter of convenience.

I've seen this assumption in several programs:

mutt buffy.c
https://sources.debian.org/src/mutt/2.2.9-1/buffy.c/?hl=3D625#L625

  if (mailbox->newly_created &&
      (sb->st_ctime !=3D sb->st_mtime || sb->st_ctime !=3D sb->st_atime))
    mailbox->newly_created =3D 0;


neomutt mbox/mbox.c
https://sources.debian.org/src/neomutt/20220429+dfsg1-4.1/mbox/mbox.c/?hl=
=3D1820#L1820

  if (m->newly_created && ((st.st_ctime !=3D st.st_mtime) || (st.st_ctime !=
=3D st.st_atime)))
    m->newly_created =3D false;


screen logfile.c
https://sources.debian.org/src/screen/4.9.0-4/logfile.c/?hl=3D130#L130

  if ((!s->st_dev && !s->st_ino) ||             /* stat failed, that's new!=
 */
      !s->st_nlink ||                           /* red alert: file unlinked=
 */
      (s->st_size < o.st_size) ||               /*           file truncated=
 */
      (s->st_mtime !=3D o.st_mtime) ||            /*            file modifi=
ed */
      ((s->st_ctime !=3D o.st_ctime) &&           /*     file changed (move=
d) */
       !(s->st_mtime =3D=3D s->st_ctime &&          /*  and it was not a ch=
ange */
         o.st_ctime < s->st_ctime)))            /* due to delayed nfs write=
 */
  {

nemo libnemo-private/nemo-vfs-file.c
https://sources.debian.org/src/nemo/5.6.5-1/libnemo-private/nemo-vfs-file.c=
/?hl=3D344#L344

		/* mtime is when the contents changed; ctime is when the
		 * contents or the permissions (inc. owner/group) changed.
		 * So we can only know when the permissions changed if mtime
		 * and ctime are different.
		 */
		if (file->details->mtime =3D=3D file->details->ctime) {
			return FALSE;
		}


While looking for more examples, I found a perl test that seems to suggest
that at least Solaris, AFS, AmigaOS, DragonFly BSD do as you suggest:
https://sources.debian.org/src/perl/5.36.0-7/t/op/stat.t/?hl=3D158#L140


Thanks

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