Re: [Xen-devel] [PATCH] xl: Special case tap/aio for disk validation

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-01-27 at 18:35 +0000, Ian Jackson wrote: 
> Stefano Stabellini writes ("Re: [Xen-devel] [PATCH] xl: Special case tap/aio 
> for disk validation"):
> > Yeah, you can check for the presence of:
> > 
> > /sys/modules/{blkbk,xen_blkback}
> > 
> > the modules are called differently in pvops compared to traditional
> > xenolinux kernels.
> 
> No, that doesn't work because it may not be a module.

These entries appear for builtin things too (badly named directory? why
yes) if the "module" has any parameters. blkback does appear, I checked
on both types of dom0 with static blkback.

It looks like /sys/bus/xen-backend/drivers/vbd/
and /sys/bus/xen/drivers/vbd/ are also both present on systems with
blkback available and have consistent names on both classic-Xen and
pvops systems AFAICT.

One of these last two is likely to be the right answer, since the "vbd"
part of the string is the xenstore directory name too and the two are
linked.

> And we need an answer that works with 2.6.18 as well as 2.6.27 and 2.6.32 and 
> 2.6.37
> and 2.6.38 ...

2.6.18 would be the unknown here. Should be easy enough for someone to
confirm I guess.

I'm not sure that failing to detect blkback on 2.6.18 and therefore
falling back to tapdisk* and/or qemu is a huge problem but I suppose
it's best avoided.

Ian.



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