> On Dec 14, 2022, at 12:37 AM, Ian Kent <raven@xxxxxxxxxx> 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. > > >> >> 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. > > Yep, saw that, ;) I'm not sure if there is consensus on this patch. It's been pushed to nfsd's for-rc branch for wider testing, but if there's a strong objection I can pull it out before the next -rc PR. -- Chuck Lever
