Date: Fri, 24 Nov 2023 16:15:06 -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: <CAM5tNy6huM-LQmqhX1%2B=LFrwGy1cq37YqtwZVyc8jL88P0i3QQ@mail.gmail.com> In-Reply-To: <CAM5tNy5%2BKgsHo4Q7Eth1pU5M1SJzWcnRK%2BRGvHipyf_rHHQJGA@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>
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On Fri, Nov 24, 2023 at 3:35=E2=80=AFPM Rick Macklem <rick.macklem@gmail.co= m> wrote: > > On Fri, Nov 24, 2023 at 8:16=E2=80=AFAM Rick Macklem <rick.macklem@gmail.= com> wrote: > > > > On Fri, Nov 24, 2023 at 7:58=E2=80=AFAM Rick Macklem <rick.macklem@gmai= l.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 of Gu= elph. Do not click links or open attachments unless you recognize the sende= r and know the content is safe. If in doubt, forward suspicious emails to I= Thelp@uoguelph.ca. > > > > > > > > > > > > On 24 Nov 2023, at 7:02, Konstantin Belousov wrote: > > > > > > > > > On Fri, Nov 24, 2023 at 08:50:22AM +0100, Alexander Leidinger wro= te: > > > > >> 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=3Df5f277728adec4c5= b3e840a1fb16bd16f8cc956d > > > > >>> > > > > >>> 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_clone() > > > > >>> which sets mnt_exjail from another mount point and > > > > >>> then uses that function to set mnt_exjail in the snapshot > > > > >>> automount. A separate patch that is currently a pull reque= st > > > > >>> for OpenZFS, calls this function to fix the problem. > > > > >> > > > > >> May the same/similar fix like for ZFS be needed / useful for nul= lfs mounted > > > > >> stuff? > > > > >> > > > > >> I have a ZFS dataset which is mounted via nullfs into a jail. Th= is > > > > >> nullfs-mount is then exported via samba. In samba I have the sha= dow-copy > > > > >> stuff enabled, but it doesn't work, as the jails can't access th= e snapshot. > > > > > > > > > > Jails cannot access snapshots because, as I understand, snapshots > > > > > are mounts. Nullfs does not provide an option to recursively bypa= ss > > > > > into mounts. The patch you responded to does not automatically mo= unts > > > > > 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 patch= . > > > > I don't know the mechanics, but it doesn't use nullfs, and the snap= shot > > > > does not show up as a separate filesystem with the mount command. > > > Yes. ZFS essentially does an automount of the snapshots under .zfs/sn= apshot. > > > (As I understand it, there are non-default ZFS options that allow the= se 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 snapshots. > > Once you "cd <some-snapshot>", the vnodes are associated with the ZFS > > mount (dataset) and not this weird snapshot fs. (That is why it doesn'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 will > > post if I do so. > Yes, it is broken in a similar way. With a nullfs mount on top of a ZFS m= ount > 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 automou= nt. 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. rick > > Again, sorry for the breakage, rick > > > > > rick > > > > > > > > Now, as for what happens when nullfs is on top of ZFS, I do not know. > > > What Kostik says about nullfs recursing into mounts suggests it will = not work. > > > I will look at it, but since I am headed to Florida for a few weeks, = it may > > > not happen until the end of the year. > > > > > > If someone can test this case and determine if there is no NFS client= 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 appreciated. > > > > > > rick > > > > > > > > > > > Mike > > > > > > > > > You might try to set up something with autofs, no idea if it coul= d be made > > > > > to work usefully. > > > >
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