From c659199f9bf37c798bd741ddd151db213d5d73f8 Mon Sep 17 00:00:00 2001
From: Jeffrey Cody <jcody@redhat.com>
Date: Tue, 11 Feb 2014 16:14:25 +0100
Subject: [PATCH 19/28] block: resize backing file image during offline commit, if necessary

RH-Author: Jeffrey Cody <jcody@redhat.com>
Message-id: <54cb47d8cd589585e9788df80b9612ea527e193d.1392134912.git.jcody@redhat.com>
Patchwork-id: 57215
O-Subject: [RHEL7 qemu-kvm PATCH 1/6] block: resize backing file image during offline commit, if necessary
Bugzilla: 1047254
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Markus Armbruster <armbru@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

Currently, if an image file is logically larger than its backing file,
committing it via 'qemu-img commit' will fail.

For instance, if we have a base image with a virtual size 10G, and a
snapshot image of size 20G, then committing the snapshot offline with
'qemu-img commit' will likely fail.

This will automatically attempt to resize the base image, if the
snapshot image to be committed is larger.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit 72706ea4cd38bfcb151265df0178ba21863d7518)
---
 block.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block.c |   28 +++++++++++++++++++++++++---
 1 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/block.c b/block.c
index 1b57236..c7aa285 100644
--- a/block.c
+++ b/block.c
@@ -1947,10 +1947,10 @@ int bdrv_check(BlockDriverState *bs, BdrvCheckResult *res, BdrvCheckMode fix)
 int bdrv_commit(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
-    int64_t sector, total_sectors;
+    int64_t sector, total_sectors, length, backing_length;
     int n, ro, open_flags;
     int ret = 0;
-    uint8_t *buf;
+    uint8_t *buf = NULL;
     char filename[PATH_MAX];
 
     if (!drv)
@@ -1975,7 +1975,29 @@ int bdrv_commit(BlockDriverState *bs)
         }
     }
 
-    total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
+    length = bdrv_getlength(bs);
+    if (length < 0) {
+        ret = length;
+        goto ro_cleanup;
+    }
+
+    backing_length = bdrv_getlength(bs->backing_hd);
+    if (backing_length < 0) {
+        ret = backing_length;
+        goto ro_cleanup;
+    }
+
+    /* If our top snapshot is larger than the backing file image,
+     * grow the backing file image if possible.  If not possible,
+     * we must return an error */
+    if (length > backing_length) {
+        ret = bdrv_truncate(bs->backing_hd, length);
+        if (ret < 0) {
+            goto ro_cleanup;
+        }
+    }
+
+    total_sectors = length >> BDRV_SECTOR_BITS;
     buf = g_malloc(COMMIT_BUF_SECTORS * BDRV_SECTOR_SIZE);
 
     for (sector = 0; sector < total_sectors; sector += n) {
-- 
1.7.1