[PATCH 0 of 4 v3] blkif.h: Document protocol and existing extensions

["Justin T. Gibbs" <justing@spectralogic.com>]

This patch series attempts to document the blkif PV interface and
the various extensions to it that are out in the wild.

Changes in v3:

patch 3 (blkif.h: Document the RedHat and Citrix blkif multi-page
         ring extensions.):
  o Mark the RedHat/Amazon EC2 ring extension nodes as deprecated.  While
    there is nothing fundamentally wrong with the method used there, it
    was not publicly documented (not even in patch form), and differs from
    the "page-order" large ring XenBus node convention used for other
    drivers.

patch 4 (blkif.h: Define and document the request number/size/segments
         extension.)
   o Fix typo "max-ring_pages" -> "max-ring-pages".

Changes in v2:

patch 2 (blkif.h: Provide more complete documentation of the blkif interface.):
  o Mark backend device identification section as private to the
    backend driver.
  o Refer to docs/misc/vbd-interface.txt for the format of the
    virtual-device front-end node.
  o Correct field size for the virtual-device front-end node.

patch 3 (blkif.h: Document the RedHat and Citrix blkif multi-page
         ring extensions.):
  o Correct node names for the RedHat/Amazon multi-ring extension.  The
    previous patch mistakenly documented the now defunct FreeBSD extension.
  o Clarify the note on multi-page ring interoperability to indicate that
    identical ring parameters should be published to the XenStore for
    all supported schemes.

v1 patch 4 (Deleted):
  o Remove patch that added the XEN_*_MAJOR definitions.

patch 4 (blkif.h: Define and document the request number/size/segments
         extension.)
  o Bump __XEN_LATEST_INTERFACE_VERSION to 0x00040201 and use this version
    to guard the change to BLKIF_MAX_SEGMENTS_PER_REQUEST.

--
Justin