From 9bffc974294d823d42b4b4d51e44abd26f7147a6 Mon Sep 17 00:00:00 2001

From: Max Reitz <mreitz@redhat.com>

Date: Sat, 13 Jun 2015 16:22:33 +0200

Subject: [PATCH 39/42] qcow2: Respect new_block in alloc_refcount_block()

Message-id: <1434212556-3927-40-git-send-email-mreitz@redhat.com>

Patchwork-id: 66058

O-Subject: [RHEL-7.2 qemu-kvm PATCH 39/42] qcow2: Respect new_block in alloc_refcount_block()

Bugzilla: 1129893

RH-Acked-by: Jeffrey Cody <jcody@redhat.com>

RH-Acked-by: Fam Zheng <famz@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

BZ: 1129893

When choosing a new place for the refcount table, alloc_refcount_block()

tries to infer the number of clusters used so far from its argument

cluster_index (which comes from the idea that if any cluster with an

index greater than cluster_index was in use, the refcount table would

have to be big enough already to describe cluster_index).

However, there is a cluster that may be at or after cluster_index, and

which is not covered by the refcount structures, and that is the new

refcount block new_block. Therefore, it should be taken into account for

the blocks_used calculation.

Also, because new_block already describes (or is intended to describe)

cluster_index, we may not put the new refcount structures there.

Signed-off-by: Max Reitz <mreitz@redhat.com>

Message-id: 1423598552-24301-2-git-send-email-mreitz@redhat.com

Reviewed-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Signed-off-by: Max Reitz <mreitz@redhat.com>

(cherry picked from commit 14a58a4e0c2e98a7d9232e1c229a531ca231133b)

Signed-off-by: Max Reitz <mreitz@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 block/qcow2-refcount.c | 16 ++++++++++++++--

 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c

index 87b932c..cee5b1f 100644

--- a/block/qcow2-refcount.c

+++ b/block/qcow2-refcount.c

@@ -319,8 +319,20 @@ static int alloc_refcount_block(BlockDriverState *bs,

      */

     BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_GROW);

-    /* Calculate the number of refcount blocks needed so far */

-    uint64_t blocks_used = DIV_ROUND_UP(cluster_index, s->refcount_block_size);

+    /* Calculate the number of refcount blocks needed so far; this will be the

+     * basis for calculating the index of the first cluster used for the

+     * self-describing refcount structures which we are about to create.

+     *

+     * Because we reached this point, there cannot be any refcount entries for

+     * cluster_index or higher indices yet. However, because new_block has been

+     * allocated to describe that cluster (and it will assume this role later

+     * on), we cannot use that index; also, new_block may actually have a higher

+     * cluster index than cluster_index, so it needs to be taken into account

+     * here (and 1 needs to be added to its value because that cluster is used).

+     */

+    uint64_t blocks_used = DIV_ROUND_UP(MAX(cluster_index + 1,

+                                            (new_block >> s->cluster_bits) + 1),

+                                        s->refcount_block_size);

     if (blocks_used > QCOW_MAX_REFTABLE_SIZE / sizeof(uint64_t)) {

         return -EFBIG;

-- 

1.8.3.1