Shuveb Hussain wrote:
Hi, I observed this while using the python bindings and accessing a remote host with libvirt:import libvirt c = libvirt.open('xen://veetee/') c.getInfo()['i686', 2021, 2, 1864, 1, 1, 2, 1]c.getInfo()['i686', 2021, 2, 1864, 1, 1, 2, 1] # remove network cable from remote machine nowc.getInfo()# blocks forever.... What is the problem here and is there a solution to this? I am running FC7 and here is the version info from virsh: virsh # version Compiled against library: libvir 0.3.2 Using library: libvir 0.3.2 Using API: Xen 3.0.1 Running hypervisor: Xen 3.1.0 I observed this for more than 10 mins, it was still hung.
This is simply a TCP issue, and nothing to do with libvirt or the remote protocol.
I repeated your experiment using a virsh shell and the nodeinfo command, which essentially does the same thing. After yanking the network cable I observed that the sendto(2) syscall succeeded and the recvfrom(2) syscall failed:
sendto(4, "\27\3\1\1\20\246\325\207<\320\0230E<\352\4x\310E\1O*g\204!\254\n\234O
N\23\310"..., 277, 0, NULL, 0) = 277 recvfrom(4, [... strace hangs here ...]On the wire I could see using tcpdump that TCP was repeatedly trying to send the request packet and getting no response:
19:25:17.108067 IP oirase.55065 > amd.16514: P 1474:1623(149) ack 1082 win 107 <nop,nop,timestamp 703462318 117574265> 19:25:17.108360 IP oirase.55065 > amd.16514: P 1623:1900(277) ack 1082 win 107 <nop,nop,timestamp 703462319 117574265> 19:25:17.308306 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703462519 117574265> 19:25:17.710212 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703462921 117574265> 19:25:18.514030 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703463725 117574265> 19:25:20.121667 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703465333 117574265> 19:25:23.336940 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703468549 117574265> 19:25:29.766483 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703474981 117574265> 19:25:42.625568 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703487845 117574265> 19:26:08.344739 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703513573 117574265> 19:32:42.572441 IP oirase.55065 > amd.16514: P 1474:1900(426) ack 1082 win 107 <nop,nop,timestamp 703907941 117574265>
[etc]On the broader issue, libvirt calls are synchronous -- this is done to reduce the complexity of the interface and implementation. If you need them to be asychronous, use a separate thread (or process) to make the calls.
Rich. -- Emerging Technologies, Red Hat - http://et.redhat.com/~rjones/ Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 03798903
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