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>

3 files changed, 93 insertions, 4 deletions

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 2aaf3eaaf13d..5f3368ab0fa9 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1378,7 +1378,59 @@ static int fuse_notify_inval_entry(struct fuse_conn *fc, unsigned int size,
         down_read(&fc->killsb);
         err = -ENOENT;
         if (fc->sb)
-                err = fuse_reverse_inval_entry(fc->sb, outarg.parent, &name);
+                err = fuse_reverse_inval_entry(fc->sb, outarg.parent, 0, &name);
+        up_read(&fc->killsb);
+        kfree(buf);
+        return err;
+
+err:
+        kfree(buf);
+        fuse_copy_finish(cs);
+        return err;
+}
+
+static int fuse_notify_delete(struct fuse_conn *fc, unsigned int size,
+                              struct fuse_copy_state *cs)
+{
+        struct fuse_notify_delete_out outarg;
+        int err = -ENOMEM;
+        char *buf;
+        struct qstr name;
+
+        buf = kzalloc(FUSE_NAME_MAX + 1, GFP_KERNEL);
+        if (!buf)
+                goto err;
+
+        err = -EINVAL;
+        if (size < sizeof(outarg))
+                goto err;
+
+        err = fuse_copy_one(cs, &outarg, sizeof(outarg));
+        if (err)
+                goto err;
+
+        err = -ENAMETOOLONG;
+        if (outarg.namelen > FUSE_NAME_MAX)
+                goto err;
+
+        err = -EINVAL;
+        if (size != sizeof(outarg) + outarg.namelen + 1)
+                goto err;
+
+        name.name = buf;
+        name.len = outarg.namelen;
+        err = fuse_copy_one(cs, buf, outarg.namelen + 1);
+        if (err)
+                goto err;
+        fuse_copy_finish(cs);
+        buf[outarg.namelen] = 0;
+        name.hash = full_name_hash(name.name, name.len);
+
+        down_read(&fc->killsb);
+        err = -ENOENT;
+        if (fc->sb)
+                err = fuse_reverse_inval_entry(fc->sb, outarg.parent,
+                                               outarg.child, &name);
         up_read(&fc->killsb);
         kfree(buf);
         return err;
@@ -1597,6 +1649,9 @@ static int fuse_notify(struct fuse_conn *fc, enum fuse_notify_code code,
         case FUSE_NOTIFY_RETRIEVE:
                 return fuse_notify_retrieve(fc, size, cs);
 
+        case FUSE_NOTIFY_DELETE:
+                return fuse_notify_delete(fc, size, cs);
+
         default:
                 fuse_copy_finish(cs);
                 return -EINVAL;
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);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 09337bcc2554..a571584a091a 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -755,9 +755,15 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
 /**
  * File-system tells the kernel to invalidate parent attributes and
  * the dentry matching parent/name.
+ *
+ * If the child_nodeid is non-zero and:
+ *    - matches the inode number for the dentry matching parent/name,
+ *    - is not a mount point
+ *    - is a file or oan empty directory
+ * then the dentry is unhashed (d_delete()).
  */
 int fuse_reverse_inval_entry(struct super_block *sb, u64 parent_nodeid,
-                             struct qstr *name);
+                             u64 child_nodeid, struct qstr *name);
 
 int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
                  bool isdir);