Re: [Xen-devel] [PATCH 0 of 5] blkif.h: Document protocol and existing extensions

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2012-02-03 at 05:24 +0000, Justin T. Gibbs wrote:
> This patch series attempts to document the blkif PV interface and
> the various extensions to it that are out in the wild.  I assembled
> this information by reviewing xend, various versions of the Linux
> blkif drivers, fixing bugs in the FreeBSD blkfront driver, and
> writing and testing a blkback driver for FreeBSD.
> 
> Even with this experience, given this interface was previously only
> documented in source code, I'm sure there are mistakes or ommissions
> in what I've done here.  Corrections welcome.

Thanks very much for doing this Justin.

Ian.

> All but the last patch in the series is source compatible with
> existing drivers.  This final patch adds FreeBSD's extension to
> allow an I/O to span multiple ring entries.  The number of outstanding
> requests, and the max I/O size and number of segments per request,
> can all be negotiated.  Drivers offering this extension are backwards
> compatible with existing drivers, but the definition of
> BLKIF_MAX_SEGMENTS_PER_REQUEST has been changed to reflect the new
> limit of 255.  A global replacement of BLKIF_MAX_SEGMENTS_PER_REQUEST
> with BLKIF_MAX_SEGMENTS_PER_HEADER_BLOCK is all that's required to
> adjust drivers without the extension to this header change.
> 
> --
> Justin
> 
>  xen/include/public/io/blkif.h |    9 +-
>  xen/include/public/io/blkif.h |  305 
> ++++++++++++++++++++++++++++++++++-------
>  xen/include/public/io/blkif.h |   22 +++
>  xen/include/public/io/blkif.h |  101 +++++++++++-
>  xen/include/public/io/blkif.h |  106 ++++++++++++++-
>  5 files changed, 466 insertions(+), 77 deletions(-)
> 
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