Re: kern/53616: dom0 crashes when dumping domU images with vnd+fss

[Frédéric Fauberteau <triaxx%NetBSD.org@localhost>]

The following reply was made to PR kern/53616; it has been noted by GNATS.

From: =?UTF-8?Q?Fr=C3=A9d=C3=A9ric_Fauberteau?= <triaxx%NetBSD.org@localhost>
To: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
Cc: gnats-bugs%netbsd.org@localhost, kern-bug-people%netbsd.org@localhost,
 gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost, netbsd-bugs-owner%netbsd.org@localhost
Subject: Re: kern/53616: dom0 crashes when dumping domU images with vnd+fss
Date: Wed, 19 Sep 2018 07:03:28 +0200

 Le 2018-09-18 17:19, Manuel Bouyer a écrit :
 > On Tue, Sep 18, 2018 at 02:35:01PM +0000, triaxx%NetBSD.org@localhost wrote:
 >> >Description:
 >> I weekly backup my 3 VMs by snapshoting the associated image file:
 >> 1) vndconfig over the vm.img
 >> 2) mount the vnd device
 >> 3) fssconfig over the mountpoint
 >> 4) dd the fss device over the network
 > 
 > Are the VMs still running while you do this ?
 > If so it's no surprise that the dom0 panic: one of its mounted
 > filesystem got modified in its back ... you can't have the same 
 > filesystem
 > in use by 2 different OS instances at the same time.
 > 
 > You would need to snapshot and do the backup from the VM itself.
 
 Yes they run. But my idea was to not modify the mounted fs and to dump a 
 snapshot.
 I did that with lvm on Linux in a previous life.
 It's true my current script did not mount the vnd device with '-o ro' 
 option.
 I will test again by explicitly mounting my fs in read-only mode.
 
 Maybe I misunderstand and one of the commands I used does syscalls that 
 modify fs.