Re: [Xen-devel] [PATCH] xencommons: Attempt to load blktap driver

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.05.12 at 18:21, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 15/05/12 17:16, Jan Beulich wrote:
>>>>> On 15.05.12 at 17:49, George Dunlap<george.dunlap@xxxxxxxxxxxxx>  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@xxxxxxxxxxxxx>
>>>
>>> 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...

Jan


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