[libvirt] [PATCH 5/5] storage: Add helper to compare logical pool def against pvs output

[Ján Tomko]

On Wed, Dec 16, 2015 at 07:46:18AM -0500, John Ferlan wrote:
> 
> 
> On 12/16/2015 07:02 AM, Ján Tomko wrote:
> > On Mon, Dec 07, 2015 at 03:47:58PM -0500, John Ferlan wrote:
> >> https://bugzilla.redhat.com/show_bug.cgi?id=1025230
> >>
> >> Add a new helper virStorageBackendLogicalMatchPoolSource to compare the
> >> pool's source name against the output from a 'pvs' command to list all
> >> volume group physical volume data on the host.  In addition, compare the
> >> pool's source device list against the particular volume group's device
> >> list to ensure the source device(s) listed for the pool match what the
> >> was listed for the volume group.
> >>
> >> Then for pool startup or check API's we need to call this new API in
> >> order to ensure that the pool we're about to start or declare active
> >> during checkPool has a valid definition vs. the running host.
> >>
> > 
> > This patch breaks starting of logical pools with no source devices.
> > 
> > Jan
> > 
> 
> Not enough information for me to go on... Can you provide sample XML
> that works prior to the change? From just your description I assume you
> mean:
> 
> <source>
>     <name>xxx</name>
>     <format type='lvm2'/>
> </source>
> 

In my case it's:
  <source>
    <name>vg</name>
    <format type='unknown'/>
  </source>
  <target>
    <path>/dev/vg</path>
    ...
  </target>

(Also, if the vg_name matches the pool name, the whole <source> element
can be omitted)

> instead of having a
> 
>     <device path='/dev/sde'/>
> 
> As the source device
> 
> Without a source device how would pool-build work (vgcreate)? 

It would not, and pool-build is the only time when the list of physical
volumes is required.

Libvirt also uses the list for pool-delete, but this is IMO a bug,
considering that we do not keep this list up to date and it could end up
calling pvremove on PVs that are no longer a part of that VG.


Thinking about it some more, the point of LVM is to abstract from the
physical volumes, so I do not think we should burden the user with the
task of updating the pool's XML every time the underlying PVs change
(i.e. the USB hard drives were plugged in in a different order).


Instead of logging a warning / rejecting the pool, could we update the
source devices list on pool refresh?

Jan
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: Digital signature
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20151216/ba7426a5/attachment-0001.sig>