sheepdog: fix return value of do_load_save_vm_state

bdrv_save_vmstate and bdrv_load_vmstate should return the vmstate size
on success, and -errno on error.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
(cherry picked from commit 6f3c714e)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

block/sheepdog.c

@@ -1957,7 +1957,7 @@ static int do_load_save_vmstate(BDRVSheepdogState *s, uint8_t *data,
                                 int64_t pos, int size, int load)
 {
     int fd, create;
-    int ret = 0;
+    int ret = 0, remaining = size;
     unsigned int data_len;
     uint64_t vmstate_oid;
     uint32_t vdi_index;
@@ -1968,11 +1968,11 @@ static int do_load_save_vmstate(BDRVSheepdogState *s, uint8_t *data,
         return fd;
     }
 
-    while (size) {
+    while (remaining) {
         vdi_index = pos / SD_DATA_OBJ_SIZE;
         offset = pos % SD_DATA_OBJ_SIZE;
 
-        data_len = MIN(size, SD_DATA_OBJ_SIZE);
+        data_len = MIN(remaining, SD_DATA_OBJ_SIZE);
 
         vmstate_oid = vid_to_vmstate_oid(s->inode.vdi_id, vdi_index);
 
@@ -1993,9 +1993,9 @@ static int do_load_save_vmstate(BDRVSheepdogState *s, uint8_t *data,
         }
 
         pos += data_len;
-        size -= data_len;
-        ret += data_len;
+        remaining -= data_len;
     }
+    ret = size;
 cleanup:
     closesocket(fd);
     return ret;