Bug 1119784

Upstream patch proposed.
https://www.redhat.com/archives/libvir-list/2014-October/msg00124.html

Test with the following build, this bug is verified.

libvirt-1.2.8-7.el7.x86_64
qemu-kvm-rhev-2.1.2-10.el7.x86_64
kernel-3.10.0-205.el7.x86_64

Scenario 1: report reason of BLOCK_IO_ERROR while unplug the device
1. start a guest with usb disk.
# virsh dumpxml rhel7|grep disk  -A5
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/sdc'/>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
    </disk>
# virsh start rhel7
Domain rhel7 started

2. do the following dd operation inside guest.
# dd if=/dev/urandom of=/dev/vdb bs=1M
3. unplug usb stick from host.

4. there is ""reason": "Input/output error"" following BLOCK_IO_ERROR in libvirtd.log:
2014-11-20 12:28:24.613+0000: 2245: debug : qemuMonitorIOProcess:399 : QEMU_MONITOR_IO_PROCESS: mon=0x7fc168001570 buf={"timestamp": {"seconds": 1416486504, "microseconds": 612675}, "event": "BLOCK_IO_ERROR", "data": {"device": "drive-virtio-disk1", "com.redhat_debug_info": {"message": "Input/output error", "errno": 5}, "nospace": false, "com.redhat_reason": "eio", "reason": "Input/output error", "operation": "write", "action": "report"}}^M
{"timestamp": {"seconds": 1416486504, "microseconds": 612796}, "event": "BLOCK_IO_ERROR", "data": {"device": "drive-virtio-disk1", "com.redhat_debug_info": {"message": "Input/output error", "errno": 5}, "nospace": false, "com.redhat_reason": "eio", "reason": "Input/output error", "operation": "write", "action": "report"}}^M
{"timestamp": {"seconds": 1416486504, "microseconds": 612889}, "event": "BLOCK_IO_ERROR", "data": {"device": "drive-virtio-disk1", "com.redhat_debug_info": {"message": "Input/output error", "errno": 5}, "nospace": false, "com.redhat_reason": "eio", "reason": "Input/output error", "operation": "write", "action": "report"}}^M
{"timestamp": {"seconds": 1416486504 len=1023


Scenario 2: report reason of BLOCK_IO_ERROR while no space
1. create one lvm which is 500M.
  LV Path                /dev/vg_flang/lv_flang
  LV Name                lv_flang
  VG Name                vg_flang
  LV UUID                NhJ6o5-B49l-tqjj-3Hsa-XaNj-jA8T-dhijel
  LV Write Access        read/write
  LV Creation host, time localhost.localdomain, 2014-11-21 15:59:51 +0800
  LV Status              available
  # open                 0
  LV Size                500.00 MiB
  Current LE             125
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     8192
  Block device           253:3

2. new one guest with this lvm, please choose the disk type as qcow2, the disk dumpxml should be like following one:

<disk type='block' device='disk'>
      <driver name='qemu' type='qcow2' cache='none' io='native'/>
      <source dev='/dev/vg_flang/lv_flang'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
    </disk>

3. guest will be paused, error ""reason": "No space left on device"" will be get in libvirtd.log as expected.
2014-11-21 08:37:19.263+0000: 7613: debug : qemuMonitorIOProcess:399 : QEMU_MONITOR_IO_PROCESS: mon=0x7f4af00095b0 buf={"timestamp": {"seconds": 1416559039, "microseconds": 262858}, "event": "BLOCK_IO_ERROR", "data": {"device": "drive-virtio-disk0", "__com.redhat_debug_info": {"message": "No space left on device", "errno": 28}, "nospace": true, "__com.redhat_reason": "enospc", "reason": "No space left on device", "operation": "write", "action": "stop"}}

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/RHSA-2015-0323.html