Consider the scenario where systems A and B share a filesystem mounted on /mnt. A: cd /mnt/a/b B: mv /mnt/a/b /mnt/a/c/d A: ls /mnt/a/c/d So in third step the lookup returns a cached inode, to which a cached dentry with positive refcount already refers. I can basically think of two possibilities: 1) instantiate new dentry 'd' with the inode 2) move the old dentry 'b' to the new dentry 'd' With 1, there's a problem of directory aliasing, which means the VFS doesn't ensure any more that directory loops can't happen. NFS looks like it does this, and relies on the server to avoid loops. 2 suffers from locking problems, since lookup already holds a i_mutex on /mnt/a/c so it can't acquire either the rename_mutex or i_mutex on /mnt/a which would be needed to safely move the dentry. Now if a new object is created at /mnt/a/b B: touch /mnt/a/b A: ls /mnt/a/b In case of 1 the old dentry will have to be unhashed and replaced with the new object. This means that some things will no longer work for processes using the old dentry as CWD. In NFS we'd get a nice ESTALE error. Does somebody have any thoughts on this? Could this be done in a better way? Thanks, Miklos - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
