[libvirt] [PATCH 4/4] logical: Adjust regex for devices

[John Ferlan]

...
>>
>> However, after some more "investigation" of the environment - I think
>> perhaps there's still a couple of loose ends. Keeping the 'segtype'
>> field may be necessary/useful... Details follow if interested ;-)
> 
> Yes, you're right and I did a bad job during review.  The segtype is required
> and we should always consider it, there is like 20 segtypes right now and some
> of them could also use 'stripes'.
> 

The 'segtype' is currently only required because commit id '82c1740a'
added 'segtype' and 'stripes' to resolve a bz (or more than one
depending on how far you chase) by using 'segtype' to determine whether
more than one existed. It also did quite a few things in one step which
by today's review standards is a bad thing ;-).

However, that only worked for "striped" lv's. If there was a "mirror"
lv, then while the mirror could be found, the vol-dumpxml output is
wrong because it only parsed 1 extent (incorrectly at that):

  <source>
    <device path='lv_test_mirror_rimage_0(0),lv_test_mirror_rimage_1'>
      <extent start='0' end='33554432'/>
    </device>
  </source>

instead of something like (if using 'stripes' to get nsegments):

  <source>
    <device path='lv_test_mirror_rimage_0'>
      <extent start='0' end='33554432'/>
    </device>
    <device path='lv_test_mirror_rimage_1'>
      <extent start='0' end='33554432'/>
    </device>
  </source>

Linking 'nsegments' to 'striped' lv's is a "limitation".

Anyway, dropping 'segtype' wasn't necessarily bad unless you needed
"more information", such as perhaps the lv thin pool source when
nsegments == 0. This becomes obvious once the change to use "(\\S*)"
instead of "(\\S+)" hits. Now we can "see" thin lv's in a volume group.
Not sure what else becomes visible, though.  The problem is you then get:

 <source>
 </source>

But that's fixable... The interesting part about <source> is that it's
an output only (virStorageVolDefParseXML doesn't read it). So, by adding
a new parse field 'pool_lv', we can then check 'segtype' to be "thin"
and if so, store the new field in a new vol->source.thin_pool field.

Still cannot create a thin lv pool/volume without using the lvcreate
command. Nor can one create a mirror or stripe lv using libvirt's
vol-create command. One just cannot "find" a thin lv right now...

John