On Tue, 2020-05-19 at 07:00 +0300, Amir Goldstein wrote: > On Tue, May 19, 2020 at 1:30 AM Gregory Farnum <gfarnum@xxxxxxxxxx> wrote: > > Maybe we resolved this conversation; I can't quite tell... > > I think v2 patch wraps it up... > > [...] > Agreed. > > > > Questions: > > > > 1. Does sync() result in fully purging inodes on MDS? > > > > > > I don't think so, but again, that code is not trivial to follow. I do > > > know that the MDS keeps around a "strays directory" which contains > > > unlinked inodes that are lazily cleaned up. My suspicion is that it's > > > satisfying lookups out of this cache as well. > > > > > > Which may be fine...the MDS is not required to be POSIX compliant after > > > all. Only the fs drivers are. > > > > I don't think this is quite that simple. Yes, the MDS is certainly > > giving back stray inodes in response to a lookup-by-ino request. But > > that's for a specific purpose: we need to be able to give back caps on > > unlinked-but-open files. For NFS specifically, I don't know what the > > rules are on NFS file handles and unlinked files, but the Ceph MDS > > won't know when files are closed everywhere, and it translates from > > NFS fh to Ceph inode using that lookup-by-ino functionality. > > > > There is no protocol rule that NFS server MUST return ESTALE > for file handle of a deleted file, but there is a rule that it MAY return > ESTALE for deleted file. For example, on server restart and traditional > block filesystem, there is not much choice. > > So returning ESTALE when file is deleted but opened on another ceph > client is definitely allowed by the protocol standard, the question is > whether changing the behavior will break any existing workloads... > Right -- that was sort of the point of my original question about the xfstest. The fact that ceph wasn't returning ESTALE in this situation didn't seem to be technically _wrong_ to me, but the xfstest treated that as a failure. It's probably best to return ESTALE since that's the conventional behavior, but I don't think it's necessarily required for correct operation in general. FWIW, if we ever implement O_TMPFILE in ceph, then we may need to revisit this code. With that, you can do a 0->1 transition on i_nlink, which blows some of the assumptions we're making here out of the water. > > > > 2. Is i_nlink synchronized among nodes on deferred delete? > > > > IWO, can inode come back from the dead on client if another node > > > > has linked it before i_nlink 0 was observed? > > > > > > No, that shouldn't happen. The caps mechanism should ensure that it > > > can't be observed by other clients until after the change. > > > > > > That said, Luis' current patch doesn't ensure we have the correct caps > > > to check the i_nlink. We may need to add that in before we can roll with > > > this. > > > > > > > 3. Can an NFS client be "migrated" from one ceph node to another > > > > with an open but unlinked file? > > > > > > > > > > No. Open files in ceph are generally per-client. You can't pass around a > > > fd (or equivalent). > > > > But the NFS file handles I think do work across clients, right? > > > > Maybe they can, but that would be like NFS server restart, so > all bets are off w.r.t open but deleted files. > They do work across clients, but a file handle is just an identifier for an inode. That's completely orthogonal to whether the file is open. -- Jeff Layton <jlayton@xxxxxxxxxx>
