From 64a58b0c174552396630862e4556d904d61509b2 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Thu, 21 Jan 2010 14:03:05 -0200
Subject: [PATCH 07/10] qcow2: Improve error handling in update_refcount

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <1264082588-10273-8-git-send-email-kwolf@redhat.com>
Patchwork-id: 6516
O-Subject: [RHEL-5.5 KVM PATCH 07/10] qcow2: Improve error handling in
	update_refcount
Bugzilla: 537077
RH-Acked-by: Christoph Hellwig <chellwig@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Gleb Natapov <gleb@redhat.com>
RH-Acked-by: Markus Armbruster <armbru@redhat.com>

Bugzilla: 537077
Upstream status: Submitted

If update_refcount fails, try to undo any changes made so far to avoid
inconsistencies in the image file.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu/block-qcow2.c |   32 +++++++++++++++++++++++++-------
 1 files changed, 25 insertions(+), 7 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/block-qcow2.c |   32 +++++++++++++++++++++++++-------
 1 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c
index e0d60b7..4dc2886 100644
--- a/qemu/block-qcow2.c
+++ b/qemu/block-qcow2.c
@@ -2788,6 +2788,7 @@ static int update_refcount(BlockDriverState *bs,
     int64_t refcount_block_offset = 0;
     int64_t table_index = -1, old_table_index;
     int first_index = -1, last_index = -1;
+    int ret;
 
 #ifdef DEBUG_ALLOC2
     printf("update_refcount: offset=%lld size=%lld addend=%d\n",
@@ -2802,6 +2803,7 @@ static int update_refcount(BlockDriverState *bs,
     {
         int block_index, refcount;
         int64_t cluster_index = cluster_offset >> s->cluster_bits;
+        int64_t new_block;
 
         /* Only write refcount block to disk when we are done with it */
         old_table_index = table_index;
@@ -2819,10 +2821,12 @@ static int update_refcount(BlockDriverState *bs,
         }
 
         /* Load the refcount block and allocate it if needed */
-        refcount_block_offset = alloc_refcount_block(bs, cluster_index);
-        if (refcount_block_offset < 0) {
-            return refcount_block_offset;
+        new_block = alloc_refcount_block(bs, cluster_index);
+        if (new_block < 0) {
+            ret = new_block;
+            goto fail;
         }
+        refcount_block_offset = new_block;
 
         /* we can update the count and save it */
         block_index = cluster_index &
@@ -2836,24 +2840,38 @@ static int update_refcount(BlockDriverState *bs,
 
         refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
         refcount += addend;
-        if (refcount < 0 || refcount > 0xffff)
-            return -EINVAL;
+        if (refcount < 0 || refcount > 0xffff) {
+            ret = -EINVAL;
+            goto fail;
+        }
         if (refcount == 0 && cluster_index < s->free_cluster_index) {
             s->free_cluster_index = cluster_index;
         }
         s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
     }
 
+    ret = 0;
+fail:
+
     /* Write last changed block to disk */
     if (refcount_block_offset != 0) {
         if (write_refcount_block_entries(s, refcount_block_offset,
             first_index, last_index) < 0)
         {
-            return -EIO;
+            return ret < 0 ? ret : -EIO;
         }
     }
 
-    return 0;
+    /*
+     * Try do undo any updates if an error is returned (This may succeed in
+     * some cases like ENOSPC for allocating a new refcount block)
+     */
+    if (ret < 0) {
+        int dummy;
+        dummy = update_refcount(bs, offset, cluster_offset - offset, -addend);
+    }
+
+    return ret;
 }
 
 /*
-- 
1.6.3.rc4.29.g8146