Re: [PATCH] xencommons: Attempt to load blktap driver

[George Dunlap <george.dunlap@eu.citrix.com>]

On 15/05/12 17:36, Jan Beulich wrote:
>>>> On 15.05.12 at 18:21, George Dunlap<george.dunlap@eu.citrix.com>  wrote:
>> On 15/05/12 17:16, Jan Beulich wrote:
>>>>>> On 15.05.12 at 17:49, George Dunlap<george.dunlap@eu.citrix.com>   wrote:
>>>> Older kernels, such as those found in Debian Squeeze:
>>>> * Have bugs in handling of AIO into foreign pages
>>>> * Have blktap modules, which will cause qemu not to use AIO, but
>>>> which are not loaded on boot.
>>>>
>>>> Attempt to load blktap in xencommons, to make sure modern qemu's which
>>>> use AIO will work properly on those kernels.
>>>>
>>>> Signed-off-by: George Dunlap<george.dunlap@eu.citrix.com>
>>>>
>>>> diff -r 99244350516a -r db614e92faf7 tools/hotplug/Linux/init.d/xencommons
>>>> --- a/tools/hotplug/Linux/init.d/xencommons	Tue May 15 16:48:49 2012 +0100
>>>> +++ b/tools/hotplug/Linux/init.d/xencommons	Tue May 15 16:49:32 2012 +0100
>>>> @@ -59,6 +59,7 @@ do_start () {
>>>>    	modprobe evtchn 2>/dev/null
>>>>    	modprobe gntdev 2>/dev/null
>>>>    	modprobe xen-acpi-processor 2>/dev/null
>>>> +	modprobe blktap 2>/dev/null
>>> Can we stop manually loading all kinds of drivers here? I was
>>> glad this went away with the switch to xencommons, and
>>> now this is coming back. Drivers definitely needed in all cases
>>> are acceptable imo, but backend drivers should be loaded as
>>> backends get created by the tools (similarly frontend drivers
>>> for the local attach case, though they should get auto-loaded
>>> normally anyway).
>> I tend to agree with you; I did it this way because that's what was
>> suggested to me.  But I don't at the moment know enough about the
>> backend creation stuff in xl / qemu to DTRT here.
>>
>> If you want to volunteer to do a patch that DTRT, I think it makes sense
>> to hold off.
> No, I won't.
>
>>   But if not, I suggest we accept this patch, and I'll come
>> back and try to write a proper one before the 4.2 release.  I think it's
>> really important we do something before 4.2, as it causes pretty serious
>> problems on systems which are affected (almost always a host crash,
>> possibly with some disk corruption).
> A host crash because of a driver not loaded? That would suggest
> bugs elsewhere...
Yes -- a bug in the AIO implementation for foreign pages, as the 
description states.

  -George