breakage in blkfront with ring_pages > 1

[Justin T. Gibbs]

On 7/5/11 10:14 PM, Colin Percival wrote:
>  On 07/05/11 19:42, Colin Percival wrote:
> > On 07/05/11 19:04, Justin T. Gibbs wrote:
> >> On 7/5/11 7:14 PM, Colin Percival wrote:
> >>> Maybe the right option is to have a loader tunable dev.xn.linuxback to
> >>> control which version of the protocol is used?
> >>
> >> What a mess.
> >
> > Yep. Mess or not, shall I go ahead with having a loader tunable 
control this,
> > or can you think of a better solution?
>
>  Does anyone object to the attached patch? It keeps the differing 
behaviour to
>  a minimum -- we MUST set ring-ref with a FreeBSD blkback, and we MUST 
NOT set
>  it with a linux blkback -- but otherwise errs in the direction of 
setting more
>  variables than are needed, to maximize the possibility of a future blkback
>  being compatible with both blkback_is_linux=0 and blkback_is_linux=1.

It would be better to just change the FreeBSD blkback driver to be
compatible with the RedHat convention.

I'm still unclear on why the current FreeBSD blkfront driver believes
that it can use more than one page in your configuration given that the
RedHat blkfront doesn't advertise this capability in a way that the FreeBSD
blkfront understands (max-ring-pages isn'te set by blkback).  Did you do
something to force blkfront to use more than one page?

--
Justin