Description of problem:
1. virt-xml-validate the "unknown" type logical volume pool xml, will meet error, but the pool can be created successfully, whether via pool-create or pool-create-as command.

2. virt-xml-validate the ＂auto＂ type logical volume pool xml, the xml is validated, but the pool can NOT be created successfully, whether via pool-create or pool-create-as command.

Version-Release number of selected component (if applicable):
libvirt-1.1.1-29.el7_0.1.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Validate the 'unknown' type logical volume pool xml
# cat pool-logical.xml 
 <pool type='logical'>
       <name>HostVG</name>
       <source>
         <name>HostVG</name>
         <format type='unknown'/>
         <device path='/dev/sda6'/>
       </source>
       <target>
         <path>/dev/HostVG</path>
       </target>
     </pool>

# virt-xml-validate pool-logical.xml 
pool-logical.xml:4: element name: Relax-NG validity error : Element source has extra content: name
pool-logical.xml:1: element pool: Relax-NG validity error : Element pool failed to validate content
pool-logical.xml fails to validate

2. Create pool with above xml

# virsh pool-create pool-logical.xml 
Pool HostVG created from pool-logical.xml

[root@yangyangtest yy]# virsh pool-list --all
Name                 State      Autostart 
-----------------------------------------
default              active     yes       
HostVG               active     no      
  
[root@yangyangtest yy]# virsh pool-destroy HostVG
Pool HostVG destroyed

[root@yangyangtest yy]# virsh pool-create-as HostVG logical --target /dev/HostVG --source-format unknown
Pool HostVG created

[root@yangyangtest yy]# virsh pool-list --all
Name                 State      Autostart 
-----------------------------------------
default              active     yes       
HostVG               active     no 

3. Validate the 'auto' type logical volume pool xml
# cat pool-logical.xml 
 <pool type='logical'>
       <name>HostVG</name>
       <source>
         <name>HostVG</name>
         <format type='auto'/>
         <device path='/dev/sda6'/>
       </source>
       <target>
         <path>/dev/HostVG</path>
       </target>
     </pool>
# virt-xml-validate pool-logical.xml 
pool-logical.xml validates

4. Create pool with above xml
# virsh pool-create pool-logical.xml 
error: Failed to create pool from pool-logical.xml
error: XML error: unknown pool format type auto

# virsh pool-create-as HostVG logical --target /dev/HostVG --source-format auto
error: Failed to create pool HostVG
error: XML error: unknown pool format type auto

Actual results:
While the source format of pool is "unknown", virt-xml-validate failed, but the pool can be created succussfully.
While the source format of pool is "auto", virt-xml-validate pass, but the pool failed to be created.


Expected results:
1.The result of virt-xml-validate should be keeping consistent with the creating result.
It means, if the virt-xml-validate command pass, then creating pool successfully;
if virt-xml-validate command fail, then creating pool fail.

2.In the following doc link, 
http://www.libvirt.org/storage.html#StorageBackendLogical
we can find that 
 The logical volume pool supports the following formats:

    auto - automatically determine format
    lvm2 

If pool type "unknown" is supported instead of "auto", the doc should be updated. If not, libvirt should support to create a logical pool with auto type instead of "unknown".

Additional info:

I also hit the issue in RHEL6. Will it be fixed in RHEL6, OR is it necessary to clone it in RHEL6?