FUSE: Notifying the kernel of deletion.

Allows a FUSE file-system to tell the kernel when a file or directory is
deleted. If the specified dentry has the specified inode number, the kernel will
unhash it.

The current 'fuse_notify_inval_entry' does not cause the kernel to clean up
directories that are in use properly, and as a result the users of those
directories see incorrect semantics from the file-system. The error condition
seen when 'fuse_notify_inval_entry' is used to notify of a deleted directory is
avoided when 'fuse_notify_delete' is used instead.

The following scenario demonstrates the difference:
1. User A chdirs into 'testdir' and starts reading 'testfile'.
2. User B rm -rf 'testdir'.
3. User B creates 'testdir'.
4. User C chdirs into 'testdir'.

If you run the above within the same machine on any file-system (including fuse
file-systems), there is no problem: user C is able to chdir into the new
testdir. The old testdir is removed from the dentry tree, but still open by user
A.

If operations 2 and 3 are performed via the network such that the fuse
file-system uses one of the notify functions to tell the kernel that the nodes
are gone, then the following error occurs for user C while user A holds the
original directory open:

muirj@empacher:~> ls /test/testdir
ls: cannot access /test/testdir: No such file or directory

The issue here is that the kernel still has a dentry for testdir, and so it is
requesting the attributes for the old directory, while the file-system is
responding that the directory no longer exists.

If on the other hand, if the file-system can notify the kernel that the
directory is deleted using the new 'fuse_notify_delete' function, then the above
ls will find the new directory as expected.

Signed-off-by: John Muir <john@jmuir.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

1 files changed, 30 insertions, 2 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 344577933f62..bef8c3011d31 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -868,7 +868,7 @@ int fuse_update_attributes(struct inode *inode, struct kstat *stat,
 }
 
 int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,
-			     struct qstr *name)
+			     u64 child_nodeid, struct qstr *name)
 {
 	int err = -ENOTDIR;
 	struct inode *parent;
@@ -895,8 +895,36 @@ int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,
 
 	fuse_invalidate_attr(parent);
 	fuse_invalidate_entry(entry);
+
+	if (child_nodeid != 0 && entry->d_inode) {
+		mutex_lock(&entry->d_inode->i_mutex);
+		if (get_node_id(entry->d_inode) != child_nodeid) {
+			err = -ENOENT;
+			goto badentry;
+		}
+		if (d_mountpoint(entry)) {
+			err = -EBUSY;
+			goto badentry;
+		}
+		if (S_ISDIR(entry->d_inode->i_mode)) {
+			shrink_dcache_parent(entry);
+			if (!simple_empty(entry)) {
+				err = -ENOTEMPTY;
+				goto badentry;
+			}
+			entry->d_inode->i_flags |= S_DEAD;
+		}
+		dont_mount(entry);
+		clear_nlink(entry->d_inode);
+		err = 0;
+ badentry:
+		mutex_unlock(&entry->d_inode->i_mutex);
+		if (!err)
+			d_delete(entry);
+	} else {
+		err = 0;
+	}
 	dput(entry);
-	err = 0;
 
  unlock:
 	mutex_unlock(&parent->i_mutex);