From 68b3e533a4531486fe346f042e190fb5c426f24f Mon Sep 17 00:00:00 2001
From: Max Reitz <mreitz@redhat.com>
Date: Mon, 18 Jun 2018 16:12:05 +0200
Subject: [PATCH 29/54] block: BLK_PERM_WRITE includes ..._UNCHANGED

RH-Author: Max Reitz <mreitz@redhat.com>
Message-id: <20180618161212.14444-4-mreitz@redhat.com>
Patchwork-id: 80763
O-Subject: [RHV-7.6 qemu-kvm-rhev PATCH 03/10] block: BLK_PERM_WRITE includes ..._UNCHANGED
Bugzilla: 1518738
RH-Acked-by: John Snow <jsnow@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

Currently we never actually check whether the WRITE_UNCHANGED
permission has been taken for unchanging writes.  But the one check that
is commented out checks both WRITE and WRITE_UNCHANGED; and considering
that WRITE_UNCHANGED is already documented as being weaker than WRITE,
we should probably explicitly document WRITE to include WRITE_UNCHANGED.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20180421132929.21610-3-mreitz@redhat.com
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
(cherry picked from commit 24b7c538fea86b598e2a335f4805a0ab50a30e98)
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 include/block/block.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/block/block.h b/include/block/block.h
index cdec363..397b5e8 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -205,6 +205,9 @@ enum {
      * This permission (which is weaker than BLK_PERM_WRITE) is both enough and
      * required for writes to the block node when the caller promises that
      * the visible disk content doesn't change.
+     *
+     * As the BLK_PERM_WRITE permission is strictly stronger, either is
+     * sufficient to perform an unchanging write.
      */
     BLK_PERM_WRITE_UNCHANGED    = 0x04,
 
-- 
1.8.3.1