On Fri, 2024-04-05 at 15:47 +0100, Daire Byrne wrote: > Apologies for dragging up an old thread, but I've had to tackle > wayward negative lookup storms again and I have obviously half > forgotten what I learned in this thread last time (even after > re-reading it!). > > Can I just ask if I understand correctly and that there was an > intention a long time ago to be able to serve negative dentries from > a > "complete" READDIRPLUS result? > > https://www.cs.helsinki.fi/linux/linux-kernel/2002-30/0108.html > > So if we did a readdirplus on a directory then immediately fired > random non existent lookups at the directory, it could be served from > the readdirplus result? i.e. not in readdir result, then return > ENOENT > without needing to ask server? > > But that is not the case today because you can't track the > "completeness" of a READDIRPLUS result for a directory over time (in > page cache)? Or is it all due to needing to deal with case > insensitive > filesystems (which I would think effects positive lookups too)? > > I did try to decipher the v6.6 fs/nfs/dir.c READDIR bits but I > quickly > got lost... > > Cheers, > > Daire If the question is whether the client trusts that a READDIR call to the server returns all the names that can be successfully looked up, then the answer is "no". It's not even a question of case sensitivity. There are plenty of servers out there that will allow you to look up names that won't ever appear in the results of a READDIR (or READDIRPLUS) call. Having a hidden ".snapshot" directory is, for instance, a popular way to present snapshots. So no, we're not ever going to implement any negative dentry cache scheme that relies on READDIR/READDIRPLUS. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
