From f5a1740117ff0ad0bdce38148e42955eee495982 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 18 Jun 2010 15:22:28 -0300
Subject: [PATCH 10/18] qcow2: Fix corruption after error in update_refcount

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <patch-9985-clone-for-rhel55-rhel55>
Patchwork-id: 10043
O-Subject: [RHEL-5.6 KVM PATCH 10/16] qcow2: Fix corruption after error in
	update_refcount
Bugzilla: 612508
RH-Acked-by: Eduardo Habkost <ehabkost@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Christoph Hellwig <chellwig@redhat.com>
RH-Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>

Bugzilla: 605701
Upstream commit: 86fa8da83771238de55dc44819a1a27bafef5353

After it is done with updating refcounts in the cache, update_refcount writes
all changed entries to disk. If a refcount block allocation fails, however,
there was no change yet and therefore first_index = last_index = -1. Don't
treat -1 as a normal sector index (resulting in a 512 byte write!) but return
without updating anything in this case.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu/block-qcow2.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/block-qcow2.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c
index 75c6759..5274f12 100644
--- a/qemu/block-qcow2.c
+++ b/qemu/block-qcow2.c
@@ -2999,6 +2999,10 @@ static int write_refcount_block_entries(BDRVQcowState *s,
     size_t size;
     int ret;
 
+    if (first_index < 0) {
+        return 0;
+    }
+
     first_index &= ~(REFCOUNTS_PER_SECTOR - 1);
     last_index = (last_index + REFCOUNTS_PER_SECTOR)
         & ~(REFCOUNTS_PER_SECTOR - 1);
-- 
1.7.0.3