Re: [RFC] Support of non-indirect grant backend on 64KB guest

[Julien Grall <julien.grall@citrix.com>]

On 20/08/2015 10:42, David Vrabel wrote:
>> When using 64KB page, a Linux block request (struct *request) may
>> contain up to 64KB of data. This is because the block segment size
>> must at least be the size of a Linux page.
>
> You should ensure you configure the request queue with the limits that
> are currently supported.  In particular:
>
> 	/* Each segment in a request is up to an aligned page in
>             size. */
> 	blk_queue_segment_boundary(rq, PAGE_SIZE - 1);
> 	blk_queue_max_segment_size(rq, PAGE_SIZE);
>
> Is obviously wrong with PAGE_SIZE > 44 KiB.
>
> Get the block later to split requests and don't do it in blkfront.

I may not have been enough clear in the paragraph you quoted. I said 
that the minimum size supported by the block framework is a linux page 
size. It means that if you pass a value smaller than that it will 
replace with the page linux granularity.

It would have been handy that the block framework supports smaller size 
but it's not the case, give a look to the implementation of both function.

Cheers,

-- 
Julien Grall