Description of problem:
This issue originally is reported by users, for example, there are 3 pool XML files({A,B,C}.xml) and 2 pools(A.xml, B.xml) source path specify the same target, then there are different target for rest of 1 pool(C.xml). when I define pool A.xml and B.xml, as expected, libvirt raises "Storage source conflict with pool: 'xx'", however, B.xml can be successfully defined after I defined C.xml. 
    

Version-Release number of selected component (if applicable):
# rpm -q libvirt
libvirt-0.9.10-14.el6.x86_64

How reproducible:
always

Steps to Reproduce:

# virsh pool-define A.xml 
Pool A defined from A.xml

# virsh pool-define B.xml 
error: Failed to define pool from B.xml
error: operation failed: Storage source conflict with pool: 'B'

# virsh pool-define C.xml 
Pool C defined from C.xml

# virsh pool-define B.xml 
Pool B defined from B.xml


# virsh pool-dumpxml A.xml
<pool type='iscsi'>
  <name>A</name>
  <uuid>ba58183c-9cff-022a-4204-b161cd67a750</uuid>
  <capacity unit='bytes'>0</capacity>
  <allocation unit='bytes'>0</allocation>
  <available unit='bytes'>0</available>
  <source>
    <host name='192.168.58.160'/>
    <device path='iqn.2011-01.com.usi:storage.iscsi1'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
    <permissions>
      <mode>0700</mode>
      <owner>-1</owner>
      <group>-1</group>
    </permissions>
  </target>
</pool>

# virsh pool-dumpxml B.xml
<pool type='iscsi'>
  <name>B</name>
  <uuid>d2cd5eb1-32bc-833f-c93a-f56b0b85853c</uuid>
  <capacity unit='bytes'>0</capacity>
  <allocation unit='bytes'>0</allocation>
  <available unit='bytes'>0</available>
  <source>
    <host name='192.168.58.160'/>
    <device path='iqn.2011-01.com.usi:storage.iscsi1'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
    <permissions>
      <mode>0700</mode>
      <owner>-1</owner>
      <group>-1</group>
    </permissions>
  </target>
</pool>

# virsh pool-dumpxml C.xml
<pool type='iscsi'>
  <name>C</name>
  <uuid>f145fcaa-d53d-a4f1-67bb-3a28831250b5</uuid>
  <capacity unit='bytes'>0</capacity>
  <allocation unit='bytes'>0</allocation>
  <available unit='bytes'>0</available>
  <source>
    <host name='192.168.58.160'/>
    <device path='iqn.2011-01.com.usi:storage.iscsi2'/>
  </source>
  <target>
    <path>/dev/disk/by-path</path>
    <permissions>
      <mode>0700</mode>
      <owner>-1</owner>
      <group>-1</group>
    </permissions>
  </target>
</pool>


Actual results:
There are the same target for Pool A and B, but I can successfully define B if I define a other Pool C(different target) between A and B.

Expected results:
Don't allow define a pool with the same target.

Additional info:
In addition, I can successfully define a domain with the same source file now, it probably is a common issues.