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

[Sergio de Almeida Lenzi <nervoso%k1.com.br@localhost>]

Em sex, 2023-06-16 às 07:55 +0000, J. Hannken-Illjes escreveu:

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

I was just thinking in zfs make the same behavior as in FreeBSD... that it does not show the mountpoints on snapshots,

but I do now now if FreeBSD keep them mounted, just do not show.

besides... if I leave the snapshot directory... and come back later... it remounts the snapshot again...

We have lots NetBSD system running on ZFS that does not reboots for months in crytical mission as fileservers

exporting smb on top of zfs. for 32 tb on 4 16TB drives.. the users sometimes "misses" files and they have a "smbshare" named "backup", that

walks over the snapshot tree... when they do that, after some time, there are a great number of mount points...

I was just wondering if the open files, would exsauted and the server would lock or reboot...

we also use the zfs sync=disabled.. and always with a 2 mirror drives on every zpool...