qcow2: Let vmstate call qcow2_co_preadv/pwrite directly

We don't really want to go through the block layer in order to read from
or write to the vmstate in a qcow2 image. Doing so required a few ugly
hacks like saving and restoring the old image size (because writing to
vmstate offsets would increase the image size) or disabling the "reads
after EOF = zeroes" logic. When calling the right functions directly,
these hacks aren't necessary any more.

Note that .bdrv_vmstate_load/save() return 0 instead of the number of
bytes in case of success now.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 4 insertions, 20 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index 362ada2..4718f82 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2909,36 +2909,20 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
                               int64_t pos)
 {
     BDRVQcow2State *s = bs->opaque;
-    int64_t total_sectors = bs->total_sectors;
-    bool zero_beyond_eof = bs->zero_beyond_eof;
-    int ret;
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
-    bs->zero_beyond_eof = false;
-    ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
-    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. */
-    bs->total_sectors = total_sectors;
-
-    return ret;
+    return bs->drv->bdrv_co_pwritev(bs, qcow2_vm_state_offset(s) + pos,
+                                    qiov->size, qiov, 0);
 }
 
 static int qcow2_load_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
                               int64_t pos)
 {
     BDRVQcow2State *s = bs->opaque;
-    bool zero_beyond_eof = bs->zero_beyond_eof;
-    int ret;
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_LOAD);
-    bs->zero_beyond_eof = false;
-    ret = bdrv_preadv(bs, qcow2_vm_state_offset(s) + pos, qiov);
-    bs->zero_beyond_eof = zero_beyond_eof;
-
-    return ret;
+    return bs->drv->bdrv_co_preadv(bs, qcow2_vm_state_offset(s) + pos,
+                                   qiov->size, qiov, 0);
 }
 
 /*