[Libguestfs] [PATCH INCOMPLETE] daemon: Reimplement LVM filters using lvmdevices command

[Nir Soffer]

On Tue, Jun 1, 2021 at 4:38 PM Richard W.M. Jones <rjones at redhat.com> wrote:
>
> LVM2 managed to break device filters.  This patch attempts a fix.
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1965941
>
> However it is not working, because the new "lvmdevices" command which
> is supposed to be used to set the new filters does not work for
> partitioned whole devices.  As far as I can tell there is no way to
> emulate the old behaviour of filtering such a device.  (Adding filters
> for each partition in the device is one possible workaround, but the
> filters will be out of date as soon as a new partition is created on
> the device.)

The best way to use lvm filter is to use a filter that includes only
the devices you want lvm to use, and reject everything else:

    "a|^/dev/sda1$|", "r|.*|"

With this there are never any surprises when someone adds a new
device or partition. You need to add the new device to the filter to
use it.

This is how ovirt configures lvm filter on hosts so they use only the
devices needed by the host and cannot access the devices used by
guests, managed by ovirt.

ovirt lvm commands override the host filter using:

    --config "device { filter = ["a|^/dev/sdb$|", "r|.*|"] }"

So it can manage vgs used by ovirt to provide guest disks.

With --config you don't need to modify the guest when you make changes.

Using the new devices file should be much simpler since it keeps the
same semantics without the need to manage a filter.

Nir