[libvirt] virDomainAttachDevice error during disk hotplug

[Deepak C Shetty]

On 08/19/2013 03:13 PM, Daniel P. Berrange wrote:
> On Fri, Aug 16, 2013 at 03:48:25PM -0500, Doug Goldstein wrote:
>> On Fri, Aug 16, 2013 at 8:30 AM, Daniel P. Berrange <berrange at redhat.com>wrote:
>>
>>> On Fri, Aug 16, 2013 at 06:51:21PM +0530, Deepak C Shetty wrote:
>>>> On 08/10/2013 06:20 PM, Deepak C Shetty wrote:
>>>>> 2013-08-10 11:19:41.772+0000: 1091: debug :
>>>>> qemuMonitorIOProcess:345 : QEMU_MONITOR_IO_PROCESS:
>>>>> mon=0x7f92f0007830 buf={"return": "could not open disk image
>>>>> /var/run/vdsm/3333017d-1278-4bfb-8129-62bded257399: Invalid
>>>>> argument\r\n", "id": "libvirt-67"}^M
>>>> Any suggestions from anyone on why "Invalid Argument" is being returned ?
>>> QEMU's error reporting for disk configs is known to be worse than
>>> useless.  You can't infer anything useful from "Invalid Argument"
>>> I'm afraid.
>>>
>>>
>> I'm going to go out on a limb here and say its an O_DIRECT error. Reason
>> I'm guessing this is that O_DIRECT is not supported on tmpfs and when you
>> attempt to open() a file with O_DIRECT and its not supported you'll get
>> back -EINVAL from the kernel. Newer systems have /run as tmpfs and /var/run
>> symlinked to /run.
> Oh, yes, good one.
>
> I really wish QEMU would provide a better error message for this case,
> since people hit it all the time

And (thanks to my colleague bharata) removing "cache=none" attribute 
from the <driver> tag of <disk> xml
made it work even on tmpfs , since qemu uses O_DIRECT only when cache=none

>
> Daniel