Bug 1371758

Added upstream:

commit 3de7da9448a5edb8440eeeb32b98f282880229e1
Author: Peter Krempa <pkrempa>
Date:   Mon Sep 5 15:15:22 2016 +0200

    util: storage: Add json pseudo protocol support for legacy RBD strings
    
    RBD in qemu still uses only the legacy 'filename' syntax.

It works well with upstream libvirt:
# qemu-img create -f qcow2 -b 'json:{"file.driver":"rbd","file.filename":"rbd:rbd/hhan:mon_host=10.73.75.52"}' /var/lib/libvirt/images/rbd.img
Formatting '/var/lib/libvirt/images/rbd.img', fmt=qcow2 size=104857600 backing_file=json:{"file.driver":"rbd",,"file.filename":"rbd:rbd/hhan:mon_host=10.73.75.52"} encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16

# virsh attach-disk V  /var/lib/libvirt/images/nbd.img vdb --subdriver qcow2  
Disk attached successfully

Read/Write on the image works well.
# virsh dumpxml V|awk '/<disk/,/<\/disk/'                                     
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/V.qcow2'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/nbd.img'/>
      <backingStore type='network' index='1'>
        <format type='raw'/>
        <source protocol='nbd'>
          <host name='10.66.6.236' port='8888'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0e' function='0x0'/>
    </disk>
# virsh detach-disk V vdb                
Disk detached successfully

verify the bug

version:
libvirt-3.2.0-2.el7.x86_64
qemu-kvm-rhev-2.8.0-6.el7.x86_64

steps:

[root@lmen1 ~]# qemu-img create -f qcow2 -b 'json:{"file.driver":"rbd","file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"}' /var/lib/libvirt/images/test1.qcow2
Formatting '/var/lib/libvirt/images/test1.qcow2', fmt=qcow2 size=104857600 backing_file=json:{"file.driver":"rbd",,"file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"} encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16


[root@lmen1 ~]# qemu-img info /var/lib/libvirt/images/test1.qcow2
image: /var/lib/libvirt/images/test1.qcow2
file format: qcow2
virtual size: 100M (104857600 bytes)
disk size: 196K
cluster_size: 65536
backing file: json:{"file.driver":"rbd","file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"}
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false


[root@lmen1 ~]# virsh attach-disk test /var/lib/libvirt/images/test1.qcow2 sda --subdriver qcow2  
Disk attached successfully

[root@lmen1 ~]# virsh domblklist test
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/test.qcow2
sda        /var/lib/libvirt/images/test1.qcow2


[root@lmen1 ~]# virsh dumpxml test
...
 <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/test1.qcow2'/>
      <backingStore type='network' index='1'>
        <format type='raw'/>
        <source protocol='rbd' name='lmen/test.img'>
          <host name='10.73.75.52'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sda' bus='scsi'/>
      <alias name='scsi0-0-0-0'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>

...

the disk can be read/wrote in the guest

[root@lmen1 ~]# virsh detach-disk test sda
Disk detached successfully

Blocked by BZ1457088 in RHEL7.4.

verify the bug 

version：
libvirt-3.2.0-11.el7.x86_64
qemu-kvm-rhev-2.9.0-12.el7.x86_64

steps:

1)create the img

[root@lmen1 ~]# qemu-img create -f qcow2 -b 'json:{"file.driver":"rbd","file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"}' /var/lib/libvirt/images/test1.qcow2
qemu-img: Warning: 'filename' option specified. This is an unsupported option, and may be deprecated in the future
Formatting '/var/lib/libvirt/images/test1.qcow2', fmt=qcow2 size=104857600 backing_file=json:{"file.driver":"rbd",,"file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"} encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16


[root@lmen1 ~]# qemu-img info /var/lib/libvirt/images/test1.qcow2
image: /var/lib/libvirt/images/test1.qcow2
file format: qcow2
virtual size: 100M (104857600 bytes)
disk size: 196K
cluster_size: 65536
backing file: json:{"file.driver":"rbd","file.filename":"rbd:lmen/test.img:mon_host=10.73.75.52"}
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

2)hotplug

[root@lmen1 ~]# virsh attach-disk test /var/lib/libvirt/images/test1.qcow2 sdb --subdriver qcow2  
Disk attached successfully

[root@lmen1 ~]# virsh domblklist test
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/RHEL-7.4-x86_64-latest.qcow2
sda        rhel7.3.iso
sdb        /var/lib/libvirt/images/test1.qcow2

[root@lmen1 ~]# virsh dumpxml test
...
 <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/test1.qcow2'/>
      <backingStore type='network' index='1'>
        <format type='raw'/>
        <source protocol='rbd' name='lmen/test.img'>
          <host name='10.73.75.52'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sdb' bus='scsi'/>
      <alias name='scsi0-0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
...

the disk can be read/wrote in the guest

[root@lmen1 ~]# virsh detach-disk test sdb
Disk detached successfully

[root@lmen1 ~]# virsh domblklist test
Target     Source
------------------------------------------------
hda        /var/lib/libvirt/images/RHEL-7.4-x86_64-latest.qcow2
sda        rhel7.3.iso

there is not the disk in the guest

3）coldplug

start a guest with xml:
  <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/test1.qcow2'/>
      <target dev='sdb' bus='scsi'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>

[root@lmen1 ~]# virsh start test
Domain test started

[root@lmen1 ~]# virsh dumpxml test
...
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/test1.qcow2'/>
      <backingStore type='network' index='1'>
        <format type='raw'/>
        <source protocol='rbd' name='lmen/test.img'>
          <host name='10.73.75.52'/>
        </source>
        <backingStore/>
      </backingStore>
      <target dev='sdb' bus='scsi'/>
      <alias name='scsi0-0-0-1'/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
...

the disk can be read/wrote in the guest

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://access.redhat.com/errata/RHEA-2017:1846

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://access.redhat.com/errata/RHEA-2017:1846

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://access.redhat.com/errata/RHEA-2017:1846