[LTP] [PATCH] NFS: add atomic_open for NFSv3 to handle O_TRUNC correctly.

[NeilBrown]

On Tue, 11 Jun 2024, Amir Goldstein wrote:
> On Tue, Jun 11, 2024 at 5:30 AM NeilBrown <neilb@suse.de> wrote:
> >
> > On Fri, 07 Jun 2024, James Clark wrote:
> > >
> > > Hi Neil,
> > >
> > > Now that your fix is in linux-next the statvfs01 test is passing again.
> > > However inotify02 is still failing.
> > >
> > > This is because the test expects the IN_CREATE and IN_OPEN events to
> > > come in that order after calling creat(), but now they are reversed. To
> > > me it seems like it could be a test issue and the test should handle
> > > them in either order? Or maybe there should be a single inotify event
> > > with both flags set for the atomic open?
> >
> > Interesting....  I don't see how any filesystem that uses ->atomic_open
> > would get these in the "right" order - and I do think IN_CREATE should
> > come before IN_OPEN.
> 
> Correct.
> 
> >
> > Does NFSv4 pass this test?
> 
> Probably not.
> 
> >
> > IN_OPEN is generated (by fsnotify_open()) when finish_open() is called,
> > which must be (and is) called by all atomic_open functions.
> > IN_CREATE is generated (by fsnotify_create()) when open_last_lookups()
> > detects that FMODE_CREATE was set and that happens *after* lookup_open()
> > is called, which calls atomic_open().
> >
> > For filesystems that don't use atomic_open, the IN_OPEN is generated by
> > the call to do_open() which happens *after* open_last_lookups(), not
> > inside it.
> 
> Correct.
> 
> >
> > So the ltp test must already fail for NFSv4, 9p ceph fuse gfs2 ntfs3
> > overlayfs smb.
> >
> 
> inotify02 does not run on all_filesystems, only on the main test fs,
> which is not very often one of the above.
> 
> This is how I averted the problem in fanotify16 (which does run on
> all_filesystems):
> 
> commit 9062824a70b8da74aa5b1db08710d0018b48072e
> Author: Amir Goldstein <amir73il@gmail.com>
> Date:   Tue Nov 21 12:52:47 2023 +0200
> 
>     fanotify16: Fix test failure on FUSE
> 
>     Split SAFE_CREAT() into explicit SAFE_MKNOD() and SAFE_OPEN(),
>     because with atomic open (e.g. fuse), SAFE_CREAT() generates FAN_OPEN
>     before FAN_CREATE (tested with ntfs-3g), which is inconsistent with
>     the order of events expected from other filesystems.
> 
> inotify02 should be fixed similarly.

Alternately - maybe the kernel should be fixed to always get the order
right.
I have a patch.  I'll post it separately.

Thanks for your confirmation that my understanding is correct!

NeilBrown


> 
> I did not find any other inotify test that watches IN_CREATE.
> I did not find any other fanotify test that watches both FAN_CREATE
> and FAN_OPEN.
> 
> Thanks,
> Amir.
>