[PATCH 0 of 4 v4] 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 v4:

patch 2 (blkif.h: Provide more complete documentation of the blkif interface.):
  o Fix typo "discard-aligment" -> "discard-alignment"
  o Fix typo "unamp" -> "unmap"
  o Fix typo "formated" -> "formatted"
  o Clarify the text for "params".
  o Clarify the text for "sector-size".

patch 4 (blkif.h: Define and document the request number/size/segments
        extension.)
  o Insert space in "Red Hat".
  o Clarify the text for "max-requests" in the backend section.

Changes in v3:

patch 3 (blkif.h: Document the Red Hat and Citrix blkif multi-page
        ring extensions.):
 o Mark the Red Hat/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 Red Hat and Citrix blkif multi-page
        ring extensions.):
 o Correct node names for the Red Hat/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