Re: kern/57467: zfs cannot umount snapshots once access it via /usr/.zfs/shapshots/ ....

["J. Hannken-Illjes" <hannken%mailbox.org@localhost>]

The following reply was made to PR kern/57467; it has been noted by GNATS.

From: "J. Hannken-Illjes" <hannken%mailbox.org@localhost>
To: NetBSD GNATS <gnats-bugs%netbsd.org@localhost>
Cc: 
Subject: Re: kern/57467: zfs cannot umount snapshots once access it via
 /usr/.zfs/shapshots/ ....
Date: Fri, 16 Jun 2023 09:53:53 +0200

 > On 16. Jun 2023, at 05:55, David Holland <dholland-bugs%netbsd.org@localhost> wrote:
 > 
 > The following reply was made to PR kern/57467; it has been noted by GNATS.
 > 
 > From: David Holland <dholland-bugs%netbsd.org@localhost>
 > To: gnats-bugs%netbsd.org@localhost
 > Cc: 
 > Subject: Re: kern/57467: zfs cannot umount snapshots once access it via
 > /usr/.zfs/shapshots/ ....
 > Date: Fri, 16 Jun 2023 03:53:04 +0000
 > 
 > On Wed, Jun 14, 2023 at 03:15:02PM +0000, Michael van Elst wrote:
 >>> If I patch zfsmount to set the VV_ROOT  will it work?
 >> 
 >> vnodes are part of the kernel. I don't know if that will work or if this
 >> wreaks havoc...
 > 
 > Could go either way.
 > 
 > Without VV_ROOT, what happens with getcwd and/or looking up .. from
 > the top? Seems likely to be bust.
 
 ZFS tries to hide this mount as much as possible.  When NFS exporting
 a ZFS file system the control directory AND the snapshots here are
 on the same export.
 
 See zfs_vnops.c, lines 2071 and 3105 for ".." and getcwd support.
 
 What is the benefit of unmounting snapshots from the snapshot control
 directory?  They will remount on the next lookup anyway.
 
 --
 J. Hannken-Illjes - hannken%mailbox.org@localhost