[Qemu-devel] [PATCH] qcow2: Unset zero_beyond_eof in save_vmstate

[Max Reitz <mreitz@redhat.com>]

Saving the VM state is done using bdrv_pwrite. This function may perform
a read-modify-write, which in this case results in data being read from
beyond the end of the virtual disk. Since we are actually trying to
access an area which is not a part of the virtual disk, zero_beyond_eof
has to be set to false before performing the partial write, otherwise
the VM state may become corrupted.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
Follow-up to (depends on):
 - qcow2: Restore total_sectors value in save_vmstate
---
 block/qcow2.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/qcow2.c b/block/qcow2.c
index 5c05bb5..3e11f25 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1941,12 +1941,15 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
     BDRVQcowState *s = bs->opaque;
     int64_t total_sectors = bs->total_sectors;
     int growable = bs->growable;
+    bool zero_beyond_eof = bs->zero_beyond_eof;
     int ret;
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
     bs->growable = 1;
+    bs->zero_beyond_eof = false;
     ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
     bs->growable = growable;
+    bs->zero_beyond_eof = zero_beyond_eof;
     // 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.
-- 
1.8.3.1