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

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

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.