From ab2ef6c7b0c99840a5b530899076998a7bbdf5df Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Mon, 15 Jan 2018 11:23:35 +0100
Subject: [PATCH 10/12] block: Don't use BLK_PERM_CONSISTENT_READ for format
 probing

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <20180115112337.20885-2-kwolf@redhat.com>
Patchwork-id: 78573
O-Subject: [RHV-7.5 qemu-kvm-rhev PATCH 1/3] block: Don't use BLK_PERM_CONSISTENT_READ for format probing
Bugzilla: 1515604
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

For format probing, we don't really care whether all of the image
content is consistent. The only thing we're looking at is the image
header, and specifically the magic numbers that are expected to never
change, no matter how inconsistent the guest visible disk content is.

Therefore, don't request BLK_PERM_CONSISTENT_READ. This allows to use
format probing, e.g. in the context of 'qemu-img info', even while the
guest visible data in the image is inconsistent during a running block
job.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
(cherry picked from commit dacaa16238cc5915a609ddaab4b7f81c4bceb9ae)
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 17629ab..90a60bc 100644
--- a/block.c
+++ b/block.c
@@ -2540,7 +2540,10 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
             goto fail;
         }
         if (file_bs != NULL) {
-            file = blk_new(BLK_PERM_CONSISTENT_READ, BLK_PERM_ALL);
+            /* Not requesting BLK_PERM_CONSISTENT_READ because we're only
+             * looking at the header to guess the image format. This works even
+             * in cases where a guest would not see a consistent state. */
+            file = blk_new(0, BLK_PERM_ALL);
             blk_insert_bs(file, file_bs, &local_err);
             bdrv_unref(file_bs);
             if (local_err) {
-- 
1.8.3.1