[Xen-changelog] [xen-3.4-testing] blkif: Clarify units for 'sector'-sized blkif request params.

["Xen patchbot-3.4-testing" <patchbot-3.4-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1243863673 -3600
# Node ID a19637a356c361d852fcee5c4357a0c6c4caa206
# Parent  9b8d56a338a2989bf0871a3e475e6d5c912e9d7e
blkif: Clarify units for 'sector'-sized blkif request params.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
xen-unstable changeset:   19640:cc682927d123
xen-unstable date:        Tue May 26 10:01:54 2009 +0100
---
 xen/include/public/io/blkif.h |    7 +++++++
 1 files changed, 7 insertions(+)

diff -r 9b8d56a338a2 -r a19637a356c3 xen/include/public/io/blkif.h
--- a/xen/include/public/io/blkif.h     Mon Jun 01 14:40:46 2009 +0100
+++ b/xen/include/public/io/blkif.h     Mon Jun 01 14:41:13 2009 +0100
@@ -84,6 +84,13 @@
  */
 #define BLKIF_MAX_SEGMENTS_PER_REQUEST 11
 
+/* 
+ * NB. first_sect and last_sect in blkif_request_segment, as well as
+ * sector_number in blkif_request, are always expressed in 512-byte units.
+ * However they must be properly aligned to the real sector size of the
+ * physical disk, which is reported in the "sector-size" node in the backend
+ * xenbus info. Also the xenbus "sectors" node is expressed in 512-byte units.
+ */
 struct blkif_request_segment {
     grant_ref_t gref;        /* reference to I/O buffer frame        */
     /* @first_sect: first sector in frame to transfer (inclusive).   */

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