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

[Amir Goldstein]

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.

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.