[1/4] block: Introduce bdrv_writev_vmstate

diff --git a/block.c b/block.c
index 0ae2e93..ab1883e 100644
--- a/block.c
+++ b/block.c
@@ -3187,13 +3187,28 @@  int bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
 int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
                       int64_t pos, int size)
 {
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base   = (void *) buf,
+        .iov_len    = size,
+    };
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_writev_vmstate(bs, &qiov, pos);
+}
+
+int bdrv_writev_vmstate(BlockDriverState *bs, QEMUIOVector *qiov, int64_t pos)
+{
     BlockDriver *drv = bs->drv;
-    if (!drv)
+
+    if (!drv) {
         return -ENOMEDIUM;
-    if (drv->bdrv_save_vmstate)
-        return drv->bdrv_save_vmstate(bs, buf, pos, size);
-    if (bs->file)
-        return bdrv_save_vmstate(bs->file, buf, pos, size);
+    } else if (drv->bdrv_save_vmstate) {
+        return drv->bdrv_save_vmstate(bs, qiov, pos);
+    } else if (bs->file) {
+        return bdrv_writev_vmstate(bs->file, qiov, pos);
+    }
+
     return -ENOTSUP;
 }
 
diff --git a/block/qcow2.c b/block/qcow2.c
index 7e7d775..3dff968 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1652,18 +1652,24 @@  static void dump_refcounts(BlockDriverState *bs)
 }
 #endif
 
-static int qcow2_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
-                              int64_t pos, int size)
+static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
+                              int64_t pos)
 {
     BDRVQcowState *s = bs->opaque;
     int growable = bs->growable;
     int ret;
+    void *buf;
+
+    buf = qemu_blockalign(bs, qiov->size);
+    qemu_iovec_to_buf(qiov, 0, buf, qiov->size);
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
     bs->growable = 1;
-    ret = bdrv_pwrite(bs, qcow2_vm_state_offset(s) + pos, buf, size);
+    ret = bdrv_pwrite(bs, qcow2_vm_state_offset(s) + pos, buf, qiov->size);
     bs->growable = growable;
 
+    qemu_vfree(buf);
+
     return ret;
 }
 
diff --git a/block/sheepdog.c b/block/sheepdog.c
index 987018e..1c5b532 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -2054,12 +2054,19 @@  cleanup:
     return ret;
 }
 
-static int sd_save_vmstate(BlockDriverState *bs, const uint8_t *data,
-                           int64_t pos, int size)
+static int sd_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
+                           int64_t pos)
 {
     BDRVSheepdogState *s = bs->opaque;
+    void *buf;
+    int ret;
 
-    return do_load_save_vmstate(s, (uint8_t *)data, pos, size, 0);
+    buf = qemu_blockalign(bs, qiov->size);
+    qemu_iovec_to_buf(qiov, 0, buf, qiov->size);
+    ret = do_load_save_vmstate(s, (uint8_t *) buf, pos, qiov->size, 0);
+    qemu_vfree(buf);
+
+    return ret;
 }
 
 static int sd_load_vmstate(BlockDriverState *bs, uint8_t *data,
diff --git a/include/block/block.h b/include/block/block.h
index 9dc6aad..e5fc566 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -348,6 +348,7 @@  void path_combine(char *dest, int dest_size,
                   const char *base_path,
                   const char *filename);
 
+int bdrv_writev_vmstate(BlockDriverState *bs, QEMUIOVector *qiov, int64_t pos);
 int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
                       int64_t pos, int size);
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 0986a2d..a709ea6 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -164,8 +164,8 @@  struct BlockDriver {
                                   const char *snapshot_name);
     int (*bdrv_get_info)(BlockDriverState *bs, BlockDriverInfo *bdi);
 
-    int (*bdrv_save_vmstate)(BlockDriverState *bs, const uint8_t *buf,
-                             int64_t pos, int size);
+    int (*bdrv_save_vmstate)(BlockDriverState *bs, QEMUIOVector *qiov,
+                             int64_t pos);
     int (*bdrv_load_vmstate)(BlockDriverState *bs, uint8_t *buf,
                              int64_t pos, int size);