[pve-devel] [PATCH storage] ZFS: mount subvols in activate_volume

[Fabian Ebner]

Turns out that this alone doesn't make starting containers with an 
unmounted zfs subvolume working. But "pct clone" and "pct mount" can 
still benefit from this patch. The problem for starting a container is 
that when we call PVE::Storage::activate_volumes, it happens inside the 
lxc-pve-prestart-hook where the kernel/apparmor will block the "zfs 
mount" operation. And this seems to be the case even for a privileged 
container and/or adding "lxc.apparmor.profile: unconfined" (I guess 
because the relevant apparmor profile is always "lxc-start" which is not 
affected by those changes?)

Calling activate_volumes directly in vm_start would work around this,
but if we remove it from lxc-pve-prestart-hook then it can break things 
for somebody using "systemctl start pve-container at ID" directly 
(depending on the storage) and if we don't remove it, it's code/work 
duplication. Is modifying the lxc-start profile viable?

On 21.04.20 14:00, Fabian Ebner wrote:
> This makes containers work even if the subvolumes are not already
> mounted beforehand for some reason. Without this patch, container
> could quietly fail for e.g. start and full clone, because
> bind-mounting still "worked" on the empty directory.
> 
> Signed-off-by: Fabian Ebner <f.ebner at proxmox.com>
> ---
> 
> This can be seen as an alternative to [0], which hasn't been applied
> AFAICT. And this approach even works when the subvolume is not mounted
> for a different reason than the one described in [0]. For example, I
> ran into the problem by having a non-empty '/myzpool', causing 'myzpool'
> to be not mountable, but 'myzpool/subvol-123-disk-0' would still be mountable.
> 
> [0]: https://pve.proxmox.com/pipermail/pve-devel/2020-March/042089.html
> 
>   PVE/Storage/ZFSPoolPlugin.pm | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/PVE/Storage/ZFSPoolPlugin.pm b/PVE/Storage/ZFSPoolPlugin.pm
> index 10354b3..4a85732 100644
> --- a/PVE/Storage/ZFSPoolPlugin.pm
> +++ b/PVE/Storage/ZFSPoolPlugin.pm
> @@ -546,9 +546,14 @@ sub activate_volume {
>   
>       my (undef, undef, undef, undef, undef, undef, $format) = $class->parse_volname($volname);
>   
> -    return 1 if $format ne 'raw';
> -
> -    $class->zfs_wait_for_zvol_link($scfg, $volname);
> +    if ($format eq 'raw') {
> +	$class->zfs_wait_for_zvol_link($scfg, $volname);
> +    } elsif ($format eq 'subvol') {
> +	my $mounted = $class->zfs_get_properties($scfg, 'mounted', "$scfg->{pool}/$volname");
> +	if ($mounted !~ m/^yes$/) {
> +	    $class->zfs_request($scfg, undef, 'mount', "$scfg->{pool}/$volname");
> +	}
> +    }
>   
>       return 1;
>   }
>