Bug 958510

This bug was not selected to be addressed in Red Hat Enterprise Linux 6. We will look at it again within the Red Hat Enterprise Linux 7 product.

Upstream patches:
https://www.redhat.com/archives/libvir-list/2015-February/msg00697.html

Fixed upstream as of
commit 155ca616eb231181f6978efc9e3a1eb0eb60af8a
Author:     Ján Tomko <jtomko>
CommitDate: 2015-03-02 08:07:11 +0100

    Allow creating volumes with a backing store but no capacity
    
    The tool creating the image can get the capacity from the backing
    storage. Just refresh the volume afterwards.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=958510

git describe: v1.2.13-17-g155ca61

Verified on libvirt-1.2.15-2.el7.x86_64

Steps
1. test vol-create
# cat BZ958510 
<volume>
  <name>demo</name>
  <source>
  </source>
  <target>
    <format type='qcow2'/>
  </target>
  <backingStore>
    <path>/var/lib/libvirt/images/vm1.raw</path>
  </backingStore>
</volume>

# virsh vol-create default BZ958510 
Vol demo created from BZ958510

# virsh vol-info demo default
Name:           demo
Type:           file
Capacity:       5.00 GiB
Allocation:     196.00 KiB

# virsh vol-dumpxml demo default
<volume type='file'>
  <name>demo</name>
  <key>/var/lib/libvirt/images/demo</key>
  <source>
  </source>
  <capacity unit='bytes'>5368709120</capacity>
  <allocation unit='bytes'>200704</allocation>
  <target>
    <path>/var/lib/libvirt/images/demo</path>
    <format type='qcow2'/>
    <permissions>
      <mode>0600</mode>
      <owner>0</owner>
      <group>0</group>
      <label>system_u:object_r:virt_image_t:s0</label>
    </permissions>
    <timestamps>
      <atime>1432804118.667607029</atime>
      <mtime>1432804118.616607010</mtime>
      <ctime>1432804118.666607029</ctime>
    </timestamps>
  </target>
  <backingStore>
    <path>/var/lib/libvirt/images/vm1.raw</path>
    <format type='raw'/>
    <permissions>
      <mode>0644</mode>
      <owner>107</owner>
      <group>107</group>
      <label>system_u:object_r:svirt_image_t:s0:c469,c778</label>
    </permissions>
    <timestamps>
      <atime>1432804118.667607029</atime>
      <mtime>1432520901.532815217</mtime>
      <ctime>1432520901.532815217</ctime>
    </timestamps>
  </backingStore>
</volume>

start a vm with demo, it works well
 <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/demo'/>
      <backingStore type='file' index='1'>
        <format type='raw'/>
        <source file='/var/lib/libvirt/images/vm1.raw'/>
        <backingStore/>
      </backingStore>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </disk>

# virsh vol-delete demo default
Vol demo deleted

2. test vol-create-from
# cat BZ958510 
<volume>
  <name>demo</name>
  <source>
  </source>
  <target>
    <format type='qcow2'/>
  </target>
</volume>

# qemu-img info /var/lib/libvirt/images/vm1.raw 
image: /var/lib/libvirt/images/vm1.raw
file format: raw
virtual size: 5.0G (5368709120 bytes)
disk size: 1.3G

# virsh vol-create-from default BZ958510 --inputpool default vm1.raw
Vol demo created from input vol vm1.raw

# virsh vol-info demo default
Name:           demo
Type:           file
Capacity:       5.00 GiB
Allocation:     2.00 GiB

# qemu-img info /var/lib/libvirt/images/demo 
image: /var/lib/libvirt/images/demo
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 2.0G
cluster_size: 65536
Format specific information:
    compat: 0.10

start a vm with demo, it works well
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/demo'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </disk>

3. negative test: dir type vol with backing file
# cat BZ958510 
<volume type='dir'>
  <name>demo</name>
  <source>
  </source>
  <target>
    <format type='dir'/>
  </target>
<backingStore>
    <path>/var/lib/libvirt/images/vm1.raw</path>
  </backingStore>
</volume>

# virsh vol-create default BZ958510 
error: Failed to create vol from BZ958510
error: this function is not supported by the connection driver: backing storage not supported for directories volumes

4. negative test: raw type vol with backing file
# cat BZ958510 
<volume type='file'>
  <name>demo</name>
  <source>
  </source>
  <target>
    <format type='raw'/>
  </target>
<backingStore>
    <path>/var/lib/libvirt/images/vm1.raw</path>
  </backingStore>
</volume>

# virsh vol-create default BZ958510 
error: Failed to create vol from BZ958510
error: this function is not supported by the connection driver: backing storage not supported for raw volumes

5. negative test: lack of capacity in rbd pool
# cat BZ958510-RBD 
<volume type='network'>
  <name>demo</name>
  <source>
  </source>
</volume>

# virsh vol-create rbd BZ958510-RBD 
error: Failed to create vol from BZ958510-RBD
error: XML error: missing capacity element

6. negative test: vol with backing file in rbd pool. The issue is tracked in bz1223177

# cat BZ958510-RBD 
<volume type='network'>
  <name>demo</name>
  <source>
  </source>
<backingStore>
    <path>/var/lib/libvirt/images/vm1.raw</path>
  </backingStore>
</volume>

# virsh vol-create rbd BZ958510-RBD 
error: Failed to create vol from BZ958510-RBD
error: failed to remove volume 'libvirt-pool/demo': No such file or directory

# virsh vol-list rbd | grep demo
 demo                 libvirt-pool/demo 

# virsh vol-delete demo rbd
error: Failed to delete vol demo
error: failed to remove volume 'libvirt-pool/demo': No such file or directory

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2202.html