[Qemu-devel] [PATCH v9 06/11] block: Add backing_blocker in BlockDriverState

[Fam Zheng <famz@redhat.com>]

This makes use of op_blocker and blocks all the operations except for
commit target, on each BlockDriverState->backing_hd.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c                   | 16 ++++++++++++++--
 include/block/block_int.h |  3 +++
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index ff25749..907c483 100644
--- a/block.c
+++ b/block.c
@@ -961,13 +961,22 @@ fail:
 void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
 {
     if (bs->backing_hd) {
+        assert(error_is_set(&bs->backing_blocker));
+        bdrv_op_unblock_all(bs->backing_hd, bs->backing_blocker);
         bdrv_unref(bs->backing_hd);
+    } else if (backing_hd) {
+        error_setg(&bs->backing_blocker,
+                   "device is used as backing hd of '%s'",
+                   bs->device_name);
     }
 
     bs->backing_hd = backing_hd;
     if (!backing_hd) {
         bs->backing_file[0] = '\0';
         bs->backing_format[0] = '\0';
+        if (error_is_set(&bs->backing_blocker)) {
+            error_free(bs->backing_blocker);
+        }
         return;
     }
     pstrcpy(bs->backing_file, sizeof(bs->backing_file), backing_hd->filename);
@@ -975,6 +984,10 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
             backing_hd->drv ? backing_hd->drv->format_name : "");
     bdrv_ref(bs->backing_hd);
 
+    bdrv_op_block_all(bs->backing_hd, bs->backing_blocker);
+    /* Otherwise we won't be able to commit due to check in bdrv_commit */
+    bdrv_op_unblock(bs->backing_hd, BLOCK_OP_TYPE_COMMIT,
+                    bs->backing_blocker);
     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
             bs->backing_hd->file->filename);
     pstrcpy(bs->backing_format, sizeof(bs->backing_format),
@@ -1481,8 +1494,7 @@ void bdrv_close(BlockDriverState *bs)
 
     if (bs->drv) {
         if (bs->backing_hd) {
-            bdrv_unref(bs->backing_hd);
-            bs->backing_hd = NULL;
+            bdrv_set_backing_hd(bs, NULL);
         }
         bs->drv->bdrv_close(bs);
         g_free(bs->opaque);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 2f6556d..1ac17d5 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -341,6 +341,9 @@ struct BlockDriverState {
     BlockJob *job;
 
     QDict *options;
+
+    /* The error object in use for blocking operations on backing_hd */
+    Error *backing_blocker;
 };
 
 int get_tmp_filename(char *filename, int size);
-- 
1.8.5.1