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

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. 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).


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