breakage in blkfront with ring_pages > 1

[Justin T. Gibbs]

On 6/9/11 9:26 PM, Colin Percival wrote:
>  Hi all,
>
>  I'm seeing breakage with ring_pages > 1 on a blkfront; more precisely, 
request
>  #32 has a garbage response (resulting in a panic) exactly as if the 
dom0 thinks
>  we're only using a single page for the ring. Forcing ring_pages to 1 
makes the
>  problem go away.
>
>  Has anyone seen anything like this? Is it possible that there's a bug 
in how
>  our blkfront negotiates the request ring? Does anyone have ring_pages 
 > 1 in
>  use?

The only backend driver I know of that can support more than one ring page
is FreeBSD.  So, the problem likely is that blkfront is getting the
negotiation wrong and only 1 page is in use.

--
Justin