On Wed, 2022-12-14 at 13:37 +0800, Ian Kent wrote: > On 14/12/22 08:39, Jeff Layton wrote: > > On Wed, 2022-12-14 at 07:14 +0800, Ian Kent wrote: > > > On 14/12/22 04:02, Jeff Layton wrote: > > > > On Tue, 2022-12-13 at 19:00 +0000, Chuck Lever III wrote: > > > > > > On Dec 13, 2022, at 1:08 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > > > > > > > > > > > If v4 READDIR operation hits a mountpoint and gets back an error, > > > > > > then it will include that entry in the reply and set RDATTR_ERROR for it > > > > > > to the error. > > > > > > > > > > > > That's fine for "normal" exported filesystems, but on the v4root, we > > > > > > need to be more careful to only expose the existence of dentries that > > > > > > lead to exports. > > > > > > > > > > > > If the mountd upcall times out while checking to see whether a > > > > > > mountpoint on the v4root is exported, then we have no recourse other > > > > > > than to fail the whole operation. > > > > > Thank you for chasing this down! > > > > > > > > > > Failing the whole READDIR when mountd times out might be a bad idea. > > > > > If the mountd upcall times out every time, the client can't make > > > > > any progress and will continue to emit the failing READDIR request. > > > > > > > > > > Would it be better to skip the unresolvable entry instead and let > > > > > the READDIR succeed without that entry? > > > > > > > > > Mounting doesn't usually require working READDIR. In that situation, a > > > > readdir() might hang (until the client kills), but a lookup of other > > > > dentries that aren't perpetually stalled should be ok in this situation. > > > > > > > > If mountd is that hosed then I think it's unlikely that any progress > > > > will be possible anyway. > > > The READDIR shouldn't trigger a mount yes, but if it's a valid automount > > > > > > point (basically a valid dentry in this case I think) it should be listed. > > > > > > It certainly shouldn't hold up the READDIR, passing into it is when a > > > > > > mount should occur. > > > > > > > > > That's usually the behavior we want for automounts, we don't want mount > > > > > > storms on directories full of automount points. > > > > > > > We only want to display it if it's a valid _exported_ mountpoint. > > > > The idea here is to only reveal the parts of the namespace that are > > exported in the nfsv4 pseudoroot. The "normal" contents are not shown -- > > only exported mountpoints and ancestor directories of those mountpoints. > > > > We don't want mountd triggering automounts, in general. If the > > underlying filesystem was exported, then it should also already be > > mounted, since nfsd doesn't currently trigger automounts in > > follow_down(). > > Umm ... must they already be mounted? > > > Can't it be a valid mount point either not yet mounted or timed out > > and umounted. In that case shouldn't it be listed, I know that's > > not the that good an outcome because its stat info will change when > > it gets walked into but it's usually the only sane choice. > Yes, it does need to already be mounted. The proposed kernel patches from Richard only trigger an automount if the parent mount is exported with -o crossmnt. I think this is necessary to avoid nfs client activity triggering automounts of filesystems that are not exported. > > > > > There is also a separate patchset by Richard Weinberger to allow nfsd to > > trigger automounts if the parent filesystem is exported with -o > > crossmnt. That should be ok with this patch, since the automount will be > > triggered before the upcall to mountd. That should ensure that it's > > already mounted by the time we get to upcalling for its export. > -- Jeff Layton <jlayton@xxxxxxxxxx>
