How to load backend drivers in 4.2

[Olaf Hering <olaf@aepfle.de>]

The xencommons runlevel script has a few modprobe calls to load drivers
for dom0. Recently also the backend drivers for vbd and vif were added.
Unfortunately without an explanation why that is (suddenly) needed.

Now that I have been hitting such missing backend driver issue as well
with a xenlinux based dom0 kernel I wonder how to handle the situation.

The pvops kernel has 3 backend drivers which have module aliases:
  xen-netback ; alias:          xen-backend:vif
  xen-blkback ; alias:          xen-backend:vbd
  xen-pciback ; alias:          xen-backend:pci
These aliases have been in the tree since at least 3.2, which is a long
time.

The sles11sp2 kernel has more backend drivers, but they have no alias:
  netbk
  blkbk
  xen-scsibk
  usbbk
  tpmbk
  pciback

I'm sure adding ad a MODULE_ALIAS() entry to netbk, blkbk and pciback to
match mainline is trivial.

I wonder why libxl does not do a 'modprobe xen-backend:vif &>/dev/null' if
it is about to configure an interface for the first time? The current
error message when a backend driver is missing is just not helpful.

So what should be done in xencommons for 4.2? Add a dumb loop like this?

for m in xen-backend:{vif,vbd,pci} netbk blkbk pciback xen-scsibk usbbk tpmbk
do
        modprobe $m &> /dev/null
done

Or should rather libxl take care of loading these things?


Olaf