Re: [PATCH 4/4] fuse: drop dentry on failed revalidate

From: Anand Avati
Date: Wed Aug 07 2013 - 12:31:23 EST

On 8/7/13 8:44 AM, Miklos Szeredi wrote:
On Tue, Aug 6, 2013 at 10:06 PM, Anand Avati <avati@xxxxxxxxxx> wrote:
On 8/6/13 7:30 AM, Miklos Szeredi wrote:

From: Anand Avati <avati@xxxxxxxxxx>

Drop a subtree when we find that it has moved or been delated. This can
done as long as there are no submounts under this location.

If the directory was moved and we come across the same directory in a
future lookup it will be reconnected by d_materialise_unique().

Signed-off-by: Anand Avati <avati@xxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
fs/fuse/dir.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 131d14b..4ba5893 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -226,8 +226,13 @@ static int fuse_dentry_revalidate(struct dentry
*entry, unsigned int flags)
if (!err) {
struct fuse_inode *fi = get_fuse_inode(inode);
if (outarg.nodeid != get_node_id(inode)) {
+ int ret = 0;
+ if (check_submounts_and_drop(entry) != 0)
+ ret = 1;
fuse_queue_forget(fc, forget,
outarg.nodeid, 1);
- return 0;
+ return ret;

If outarg.nodeid != get_node_id(inode), then we have to return 0 no matter
what (whether we successfully dropped the entry or not), no?

If we return 0 in that case (we failed to invalidate the dentry), then
the VFS will call d_invalidate() which will fail. The result is the

Or are you
trying to forcefully keep the path to reach the submount alive? If so, we
still fail in inode_permission() .. -> getattr() of the dir inode, no?

Yes. But the path to the mountpoint should still be reachable (for
the purpose of unmounting for example). I'm including an interesting
discussion between Al and Linus about this (mailing lists weren't
CC-d, but I don't think they'd mind).

Thanks for attaching the thread. Was very educative! I still do not quite understand - will umount() still work when inode_permission()[->getattr()] on the ancestors fail (with ESTALE etc.)? Wouldn't path resolution itself abort and fail and therefore do_umount() never called? I understand that the path to the mountpoint being reachable through the dentry chain is a necessity for umounting, but is just that really sufficient?

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