Re: [Xen-devel] [PATCH 4 of 4 v3] blkif.h: Define and document the request number/size/segments extension

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-02-20 at 18:07 +0000, Justin T. Gibbs wrote:
> Note: As of __XEN_INTERFACE_VERSION__ 0x00040201 the definition of
>       BLKIF_MAX_SEGMENTS_PER_REQUEST has changed.  Drivers must be updated
>       to, at minimum, use BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK, before being
>       recompiled with a __XEN_INTERFACE_VERSION greater than or equal to
>       this value.
> 
> This extension first appeared in the FreeBSD Operating System.
> 
> Signed-off-by: Justin T. Gibbs <justing@xxxxxxxxxxxxxxxx>
> 
> diff -r 09051133e2fe -r a777cbc5f48b xen/include/public/io/blkif.h
> --- a/xen/include/public/io/blkif.h   Mon Feb 20 11:02:53 2012 -0700
> +++ b/xen/include/public/io/blkif.h   Mon Feb 20 11:03:01 2012 -0700
> @@ -145,6 +145,32 @@
>   *      The maximum supported size of the request ring buffer in units of
>   *      machine pages.  The value must be a power of 2.
>   *
> + * max-requests         <uint32_t>
> + *      Default Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE)
> + *      Maximum Value:  BLKIF_MAX_RING_REQUESTS(PAGE_SIZE * max-ring-pages)
> + *
> + *      The maximum number of concurrent, logical requests that will be
> + *      issued by the backend.

by "issued" do you mean the maximum number that the backend is willing
to consume/have-in-flight at once? I guess that means issued to the
underlying storage? (backend doesn't issue requests to the frontend does
it? That's how I first read it, hence my question)

Ian.


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