Created attachment 1139883 [details]
libvirt log and virtlogd log

Description of problem:
There is no enough disk space for qemu log, guest starts failed:
# virsh start rhel7.2
error: Failed to start domain rhel7.2
error: internal error: Process exited prior to exec: 

Version-Release number of selected component (if applicable):
libvirt-1.3.2-1.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.Mount a disk with little space left on /var/log/libvirt/qemu
# df
/dev/sdb3                                                        12972     12952        20 100% /var/log/libvirt/qemu

2.Guest rhel7.2 has a log file existing in the directory:
# ls /var/log/libvirt/qemu/
rhel7.2.log  rhel7.2.log.0  test.out

3.
# virsh start rhel7.2
error: Failed to start domain rhel7.2
error: internal error: Process exited prior to exec:

4.Check guest log file, the last line is incomplete:
# tail -1 /var/log/libvirt/qemu
2016-03-24 10:15:31.579+0000: starting up libvirt version: 1.3.2, package: 1.el

5.If no qemu log file exits before guest starts, guest start with clear error message:
# ls /var/log/libvirt/qemu/

# virsh start rhel7.2
error: Failed to start domain rhel7.2
error: Unable to open file: /var/log/libvirt/qemu/rhel7.2.log: No space left on device


Actual results:
Guest start failed with error "Process exited prior to exec:"

Expected results:
Guest start failed with more clear error message.

Additional info: