Re: [Virtio-fs] [PATCH 3/4] fuse: Call vfs_get_tree() for submounts

Greg Kurz
2021-06-03T07:34:30Z

On Thu, 27 May 2021 15:24:40 +0200
Max Reitz <mreitz@redhat.com> wrote:

> On 25.05.21 17:02, Greg Kurz wrote:
> > We recently fixed an infinite loop by setting the SB_BORN flag on
> > submounts along with the write barrier needed by super_cache_count().
> > This is the job of vfs_get_tree() and FUSE shouldn't have to care
> > about the barrier at all.
> >
> > Split out some code from fuse_dentry_automount() to a new dedicated
> > fuse_get_tree_submount() handler for submounts and call vfs_get_tree().
> >
> > The fs_private field of the filesystem context isn't used with
> > submounts : hijack it to pass the FUSE inode of the mount point
> > down to fuse_get_tree_submount().
>
> What exactly do you mean by “isn’t used”? virtio_fs_init_fs_context()
> still sets it (it is non-NULL in fuse_dentry_automount() after
> fs_context_for_submount()). It does appear like it is never read, but
> one thing that definitely would need to be done is for it to be freed
> before putting mp_fi there.
>

Oops... yes it should. Thanks for the catch !

> So I think it may technically be fine to use this field, but then
> virtio_fs_init_fs_context() shouldn’t set it for submounts (should be
> discernible with fsc->purpose), and perhaps that should be a separate patch.
>

Yes, I'll do just that.

> (Apart from that, this patch looks good to me, though.)
>
> Max
>
> > Finally, adapt virtiofs to use this.
> >
> > Signed-off-by: Greg Kurz <groug@kaod.org>
> > ---
> > fs/fuse/dir.c | 58 +++++++--------------------------------------
> > fs/fuse/fuse_i.h | 6 +++++
> > fs/fuse/inode.c | 44 ++++++++++++++++++++++++++++++++++
> > fs/fuse/virtio_fs.c | 3 +++
> > 4 files changed, 62 insertions(+), 49 deletions(-)
>