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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2012-05-16 at 08:47 +0100, Jan Beulich wrote:
> Finally, loading "blktap" here is the right thing for pvops, but
> wrong for legacy/forward ported kernels - blktap2 would be
> the right module name there afaict. Perhaps, if this really is to
> go in (temporarily), loading an alias (devname: or xen-backend:,
> though the latter apears to be missing from the pvops driver)
> would be better here?

George's patch doesn't seem to apply any more (hardly surprising).

>From what you say I think we want to modprobe blktap if blktap2 didn't
exist.

blktap2 isn't actually a xenbus backend driver (since it uses blkback to
do the guest facing bit) so I don't think a xen-backend: alias is
available. I can't see any other aliases defined in the code in either
the 2.6.18-xen tree, the SLES 2.6.32.12-0.7.1 kernel (which is the
latest I happen to have to hand) or a mainline kernel. If there is
something else we should be trying please let me know.

So I intend to commit the following:

8<--------------------------------------------------

xencommons: Attempt to load blktap2 driver

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>

Prefer to load blktap2 if it exists. This is the name of the driver in
classic-Xen ports, while in mainline kernels the driver is called just
blktap.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

diff -r 1126b3079bef -r 451724678dd4 tools/hotplug/Linux/init.d/xencommons
--- a/tools/hotplug/Linux/init.d/xencommons     Fri Aug 24 12:38:18 2012 +0100
+++ b/tools/hotplug/Linux/init.d/xencommons     Fri Aug 31 09:32:37 2012 +0100
@@ -68,6 +68,7 @@ do_start () {
        modprobe usbbk 2>/dev/null
        modprobe pciback 2>/dev/null
        modprobe xen-acpi-processor 2>/dev/null
+       modprobe blktap2 2>/dev/null || modprobe blktap 2>/dev/null
        mkdir -p /var/run/xen
 
        if ! `xenstore-read -s / >/dev/null 2>&1`



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