On Thu, Dec 29, 2016 at 04:49:54PM +0100, Richard Weinberger wrote: > Bruce, > > On 29.12.2016 16:34, J. Bruce Fields wrote: > >> That way UBIFS can provide a 64bit readdir() cookie which is required for NFS3. > > > > Sounds good. And if a matching entry isn't found (as in the case of a > > concurrent unlink), what happens? The answer must be the same as for > > ext4, but I've forgotten the details.... I guess it must find the next > > highest cookie (thinking of the cookie as a 64-bit integer of some kind) > > that exists in the directory. And that must be the same order that > > readdir normally returns entries in. > > If a 64bit cookie is not found, the lookup function returns -ENOENT. > In UBIFS we cannot just select a higher or lower key (cookie in this case), > since it is the B-tree key and would point to a completely different > entry. > > So, in case of a concurrent unlink() one would succeed and one fail with > -ENOENT. Unless I miss something that seems okay to me. Unlink takes (parent directory, name), not a directory cookie. The problem is concurrent unlink and nfs readdir. So: NFS server returns readdir result with cookie X Somebody unlinks the entry at X. NFS server gets readdir request with cookie X. Then the NFS client will get a spurious -ENOENT. I'm not sure how best to reproduce that.... Maybe: Create a directory on an nfs-exported filesystem with lots of entries. Start a loop (or loops?) renaming directory entries within the directory as fast as possible (or deleting and creating entries; I assume it's the same thing for our purposes). read the directory from an nfs client. I'm not sure how many entries is "lots".... Ideally you want a single read of the directory to require the client to make lots of READDIR requests to the server. You could help by running: echo 1024 >/proc/fs/nfsd/max_block_size before starting knfsd. That should force it to return no more than 1K of data in each READDIR reply. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
