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

From: Max Reitz
Date: Thu May 27 2021 - 09:25:01 EST

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.

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.

(Apart from that, this patch looks good to me, though.)


Finally, adapt virtiofs to use this.

Signed-off-by: Greg Kurz <groug@xxxxxxxx>
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(-)