Date: Fri, 24 Nov 2023 21:07:45 -0800 From: Rick Macklem <rick.macklem@gmail.com> To: Mike Karels <mike@karels.net> Cc: Konstantin Belousov <kostikbel@gmail.com>, Alexander Leidinger <Alexander@leidinger.net>, Rick Macklem <rmacklem@freebsd.org>, src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: f5f277728ade - main - nfsd: Fix NFS access to .zfs/snapshot snapshots Message-ID: <CAM5tNy6r6hvP0basw5SMGE%2B5yBe=JUw7312e%2B_6V2vFXojUSfw@mail.gmail.com> In-Reply-To: <CAM5tNy6bG%2Bii3HVW2PVj__AdZ8GGbH0L6H7h456kpt4pYn54Lw@mail.gmail.com> References: <202311231525.3ANFPBo6039293@gitrepo.freebsd.org> <987d4593d50b9cbffb9b6443d3825499@Leidinger.net> <ZWCe8k_lxWSpDA1L@kib.kiev.ua> <F4EB20B7-5AB8-4448-84BB-462BC7C37398@karels.net> <CAM5tNy5zLnDwxWuJ_u87k-c6WPwwp=MNjvDVto0=A9mwpyWc=g@mail.gmail.com> <CAM5tNy47MLeWdPEhV9LgVH84KB7Gmwpqmzxb62OET52Pn7pWJA@mail.gmail.com> <CAM5tNy5%2BKgsHo4Q7Eth1pU5M1SJzWcnRK%2BRGvHipyf_rHHQJGA@mail.gmail.com> <CAM5tNy6huM-LQmqhX1%2B=LFrwGy1cq37YqtwZVyc8jL88P0i3QQ@mail.gmail.com> <CAM5tNy6bG%2Bii3HVW2PVj__AdZ8GGbH0L6H7h456kpt4pYn54Lw@mail.gmail.com>
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Just to summarize... Mike Karels has done a simple test that works, so I don't know why my tests have misbehaved. I will do some more tests in a few weeks. If you encounter problems accessing snapshots under .zfs/snapshot over NFS when you have added the patch in PR#275200, please post. rick On Fri, Nov 24, 2023 at 6:52=E2=80=AFPM Rick Macklem <rick.macklem@gmail.co= m> wrote: > > On Fri, Nov 24, 2023 at 4:15=E2=80=AFPM Rick Macklem <rick.macklem@gmail.= com> wrote: > > > > On Fri, Nov 24, 2023 at 3:35=E2=80=AFPM Rick Macklem <rick.macklem@gmai= l.com> wrote: > > > > > > On Fri, Nov 24, 2023 at 8:16=E2=80=AFAM Rick Macklem <rick.macklem@gm= ail.com> wrote: > > > > > > > > On Fri, Nov 24, 2023 at 7:58=E2=80=AFAM Rick Macklem <rick.macklem@= gmail.com> wrote: > > > > > > > > > > On Fri, Nov 24, 2023 at 5:18=E2=80=AFAM Mike Karels <mike@karels.= net> wrote: > > > > > > > > > > > > CAUTION: This email originated from outside of the University o= f Guelph. Do not click links or open attachments unless you recognize the s= ender and know the content is safe. If in doubt, forward suspicious emails = to IThelp@uoguelph.ca. > > > > > > > > > > > > > > > > > > On 24 Nov 2023, at 7:02, Konstantin Belousov wrote: > > > > > > > > > > > > > On Fri, Nov 24, 2023 at 08:50:22AM +0100, Alexander Leidinger= wrote: > > > > > > >> Am 2023-11-23 16:25, schrieb Rick Macklem: > > > > > > >>> The branch main has been updated by rmacklem: > > > > > > >>> > > > > > > >>> URL: https://cgit.FreeBSD.org/src/commit/?id=3Df5f277728ade= c4c5b3e840a1fb16bd16f8cc956d > > > > > > >>> > > > > > > >>> commit f5f277728adec4c5b3e840a1fb16bd16f8cc956d > > > > > > >>> Author: Rick Macklem <rmacklem@FreeBSD.org> > > > > > > >>> AuthorDate: 2023-11-23 15:23:33 +0000 > > > > > > >>> Commit: Rick Macklem <rmacklem@FreeBSD.org> > > > > > > >>> CommitDate: 2023-11-23 15:23:33 +0000 > > > > > > >>> > > > > > > >>> nfsd: Fix NFS access to .zfs/snapshot snapshots > > > > > > >>> > > > > > > >>> When a process attempts to access a snapshot under > > > > > > >>> /<dataset>/.zfs/snapshot, the snapshot is automounted. > > > > > > >>> However, without this patch, the automount does not > > > > > > >>> set mnt_exjail, which results in the snapshot not being > > > > > > >>> accessible over NFS. > > > > > > >>> > > > > > > >>> This patch defines a new function called vfs_exjail_clo= ne() > > > > > > >>> which sets mnt_exjail from another mount point and > > > > > > >>> then uses that function to set mnt_exjail in the snapsh= ot > > > > > > >>> automount. A separate patch that is currently a pull r= equest > > > > > > >>> for OpenZFS, calls this function to fix the problem. > > > > > > >> > > > > > > >> May the same/similar fix like for ZFS be needed / useful for= nullfs mounted > > > > > > >> stuff? > > > > > > >> > > > > > > >> I have a ZFS dataset which is mounted via nullfs into a jail= . This > > > > > > >> nullfs-mount is then exported via samba. In samba I have the= shadow-copy > > > > > > >> stuff enabled, but it doesn't work, as the jails can't acces= s the snapshot. > > > > > > > > > > > > > > Jails cannot access snapshots because, as I understand, snaps= hots > > > > > > > are mounts. Nullfs does not provide an option to recursively = bypass > > > > > > > into mounts. The patch you responded to does not automaticall= y mounts > > > > > > > snapshots on clients, it only allows them to mount if wanted. > > > > > > > > > > > > It works for me, with main and this change, or 13.2 without a p= atch. > > > > > > I don't know the mechanics, but it doesn't use nullfs, and the = snapshot > > > > > > does not show up as a separate filesystem with the mount comman= d. > > > > > Yes. ZFS essentially does an automount of the snapshots under .zf= s/snapshot. > > > > > (As I understand it, there are non-default ZFS options that allow= these to be > > > > > mounted manually instead.) > > > > > I can now see that these automounts are 'real mounts" in the > > > > > mountlist. The only reason > > > > > they are not visible is that they have MNT_IGNORE set on them. > > > > Oh and I forgot to mention that this automount is for some weird in > > > > memory file system that does just enough so you can see the snapsho= ts. > > > > Once you "cd <some-snapshot>", the vnodes are associated with the Z= FS > > > > mount (dataset) and not this weird snapshot fs. (That is why it doe= sn't need to > > > > be exported, but did need mnt_exjail to be set properly.) > > > > > > > > I might be able to test a nullfs over ZFS case later to-day and wil= l > > > > post if I do so. > > > Yes, it is broken in a similar way. With a nullfs mount on top of a Z= FS mount > > > that is exported to an NFS client, you can access the snapshots under > > > .zfs/snapshot > > > if the mnt_exjail checks are commented out. > > > However, if the checks are done, they fail. > > > > > > So, yes, something similar to what ZFS will do is needed for nullfs. > > > Now I have to figure out how/when it can be done. I will play with it= to-day, > > > but it probably won't get fixed until late Dec. > > Oops. Now my test is not working, even when the mnt_exjail check is > > commented out. > > (When I NFS mount the ZFS <dataset>, I can see the snapshots under > > .zfs/snapshot, > > but when I NFS mount the nullfs mount that is on top of the ZFS > > <dataset> I do not see it. > > > > So, I think Kostik is correct and it does not see the .zfs/snapshot aut= omount. > > > > I don't know how I screwed up on the first test after I disabled the > > mnt_exjail check, but > > it does not appear to have broken this case after all. > More info. Thanks to some off-list info from Mike Karels I tried it again= . > It turns out that the nullfs on top of ZFS export (the nullfs mount must = be > exported) sorta works. When you cd .zfs/snapshot/<snapshot-name>, it > works. > > What doesn't work is: > cd .zfs/snapshot > ls > --> which does not show the snapshot names > The snapshot names are shown for a mount of the ZFS file system. > > So, it seems that the Readdir has issues for a nullfs on top of ZFS > export for the .zfs/snapshot directory. I will poke at it some more > in late Dec., but it does not seem to be a problem related to mnt_exjail. > > rick > > > > > rick > > > > > > > > Again, sorry for the breakage, rick > > > > > > > > > > > rick > > > > > > > > > > > > > > Now, as for what happens when nullfs is on top of ZFS, I do not k= now. > > > > > What Kostik says about nullfs recursing into mounts suggests it w= ill not work. > > > > > I will look at it, but since I am headed to Florida for a few wee= ks, it may > > > > > not happen until the end of the year. > > > > > > > > > > If someone can test this case and determine if there is no NFS cl= ient access > > > > > for snapshots under .zfs after applying the patch that is an > > > > > attachment in PR#275200 > > > > > when nullfs is over the ZFS file system, that would be appreciate= d. > > > > > > > > > > rick > > > > > > > > > > > > > > > > > Mike > > > > > > > > > > > > > You might try to set up something with autofs, no idea if it = could be made > > > > > > > to work usefully. > > > > > >
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