[Qemu-devel] [PATCH] qcow2: Restore total_sectors value in save_vmstate

[Max Reitz <mreitz@redhat.com>]

Since df2a6f29a5, bdrv_co_do_writev increases the total_sectors value of
a growable block devices on writes after the current end. This leads to
the virtual disk apparently growing in qcow2_save_vmstate, which in turn
affects the disk size captured by the internal snapshot taken directly
afterwards through e.g. the HMP savevm command. Such a "grown" snapshot
cannot be loaded after reopening the qcow2 image, since its disk size
differs from the actual virtual disk size (writing a VM state does not
actually increase the virtual disk size).

Fix this by restoring total_sectors at the end of qcow2_save_vmstate.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index c1abaff..5c05bb5 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1939,6 +1939,7 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
                               int64_t pos)
 {
     BDRVQcowState *s = bs->opaque;
+    int64_t total_sectors = bs->total_sectors;
     int growable = bs->growable;
     int ret;
 
@@ -1946,6 +1947,10 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
     bs->growable = 1;
     ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
     bs->growable = growable;
+    // bdrv_co_do_writev will have increased the total_sectors value to include
+    // the VM state - the VM state is however not an actual part of the block
+    // device, therefore, we need to restore the old value.
+    bs->total_sectors = total_sectors;
 
     return ret;
 }
-- 
1.8.3.1