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 Tue, 2012-02-21 at 18:03 +0000, Justin T. Gibbs wrote:
> On Feb 21, 2012, at 7:38 AM, Ian Campbell wrote:
> 
> > 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.
> > 
> 
> I should have used the same language as in the other entries.  Does this
> make more sense?
> 
>  *      The maximum number of concurrent, logical requests supported by
>  *      the backend.

Makes sense, thanks.

Ian.

> 
> --
> Justin



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