[libvirt] [PATCH v3 4/4] logical: Display thin lv's found in a libvirt managed volume group

Ján Tomko jtomko at redhat.com
Wed Feb 3 08:23:12 UTC 2016

On Tue, Feb 02, 2016 at 11:14:01AM -0500, John Ferlan wrote:
> On 02/02/2016 08:30 AM, Pavel Hrdina wrote:
> > On Tue, Feb 02, 2016 at 09:11:51AM +0100, Ján Tomko wrote:
> >> On Mon, Feb 01, 2016 at 03:29:53PM -0500, John Ferlan wrote:
> >>> Modify the regex for the 'devices' (a/k/a 'extents') from "(\\S+)"
> >>> (e.g., 1 or more) to "(\\S*)" (e.g., zero or more).
> >>>
> >>> Then for any "thin" lv's found, mark the volume as a sparse volume so
> >>> that the volume wipe algorithm doesn't work.
> >>>
> >>> Since a "thin" segtype has no devices, this will result in any "thin"
> >>> lv part of some thin-pool within a volume group used as a libvirt pool
> >>> to be displayed as a possible volume to use.
> >>>
> >>
> >> A thin pool is another layer on top of some of the LVs in the VG.
> >> I think it deserves a separate pool type.
> > 
> > I must agree with Jan, and also already wrote the same for v2 patch.  The thin
> > pool and thin LV shouldn't be mixed with normal logical pool even they share the
> > same VG.
> > 
> If LVM allows it, then who are we to say it cannot or shouldn't work or
> how it should be configured?

Even if they are mixed in the same VG, we could show the "thick" LVs
in the type='logical' pool and the thin ones in type='thin'.

> Thin pools were introduced in LVM2
> (2.02.89) according to what I've found. That's a few releases behind the
> 2.02.132 I have on my f23 laptop. Nothing in the description creating a
> thin-pool requires it's own volume group although sure some "best
> practices" indicate creating vg's as the container for a thin-pool.
> I can certainly understand and agree in principle to creating a "strong
> preference" to have a thin-pool be a libvirt pool because it simplifies
> things such as allocated/capacity management and physical device source
> listing.

This is my reasoning - with all the thick and thin volumes grouped
together, having free space in one does not mean there is free space for

> So should I assume then the desire from the review viewpoint is to not
> support thin lv's at this point in time?

But I cannot speak for the silent majority.

> And that would be because we
> want them to be configured a specific way?  FWIW: if someone did that -
> we still won't be able to support it without this patch.

How so? This patch displays the thin ('V') volumes in type='logical'
pools. With a new pool type, the 'logical' pool could keep ignoring
the thin pools and volumes, just like we skip directories in 'fs' pools.

> Any thoughts on the VIR_STORAGE_VOL_LOGICAL*_REGEX's? (depending on the
> answer to the prior question with the obvious change of using S+ instead
> of S* for devices)?

They do look more readable to me.

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