[libvirt] [PATCH] Drop virStorageBackendLogicalMatchPoolSource

[John Ferlan]

On 06/16/2016 06:03 AM, Ján Tomko wrote:
> On Wed, Jun 15, 2016 at 06:45:59PM -0400, John Ferlan wrote:
>>
>>
>> On 06/15/2016 01:19 PM, Ján Tomko wrote:
>>> Regression introduced by commit 71b803a for [1] that prevents
>>> starting up
>>> a logical pool created with <source><device path=''></source>
>>> after it has been moved to a different physical volume.
>>
>> Is there a bug for this?  XML examples?
>>
>> Is an empty source device path string a valid value?  Reading
>> http://libvirt.org/formatstorage.html doesn't give me that impression.
> 
> I meant any pool with a <device> specified, not an empty path.

But the patch is specifically targeted at removing the _logical pool
check.  So the question is, is it "legal" for a logical pool to "start"
with an empty string as a source device path? Secondarily I'm curious
what's the use case of that?

> 
> The whole point of LVM is abstraction from the lower layers so we
> shouldn't ever be checking this.
> 

So it's OK to activate/start a pool where the source device path is
incorrect?

>>
>> "device
>>    Provides the source for pools backed by physical devices (pool types
>> fs, logical, disk, iscsi, zfs). May be repeated multiple times depending
>> on backend driver. Contains a required attribute path which is either
>> the fully qualified path to the block device node or for iscsi the iSCSI
>> Qualified Name (IQN). Since 0.4.1"
>>
>>
>>>
>>> For logical pools <source><name> contains the name of the volume group
>>> and uniquely identifies the VG on the host.
>>>
>>> This also speeds up startup for pools that do not have any <device>s
>>> specified.
>>>
>>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1025230
>>> ---
>>>  src/storage/storage_backend_logical.c | 104
>>> +---------------------------------
>>>  1 file changed, 2 insertions(+), 102 deletions(-)
>>>
>>
>> This essentially reverts a patch that was used to resolve a bz without a
>> patch to resolve the issue in the bug.  What's the proposal/patch to
>> resolve the issue from the bug?
>>
> 
> The issue in the bug is just cosmetic and should not block fixing this
> regresion.
> 

How is it just cosmetic?  Let's say we allow starting a pool with an
incorrect or invalid source device path. Any attempt to "use" or "list"
a volume in the pool would fail.

I will agree that it would seem unlikely in a "real world" situation
that an admin would create/configure a logical pool using a vgname that
is not associated with the provided source device path; however, to me
it seems just as unlikely that the source device path is either not
provided or is set to ''.

Curious what others think. If the patch gets reverted, then so be it. We
should then at least document that libvirt does not check or care if the
source device path for a logical pool is valid or not (and update the
bug thusly).

John

John