[Qemu-devel] [PATCH v4 5/7] block: Parse "backing" option to reference existing BDS

[Fam Zheng]

Signed-off-by: Fam Zheng <f...@redhat.com>
---
 block.c                   | 37 ++++++++++++++++++++++++++++++++-----
 include/block/block_int.h |  3 +++
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/block.c b/block.c
index 3bf4c8a..a5da656 100644
--- a/block.c
+++ b/block.c
@@ -1166,11 +1166,33 @@ int bdrv_open(BlockDriverState *bs, const char 
*filename, QDict *options,
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
         QDict *backing_options;
-
-        qdict_extract_subqdict(options, &backing_options, "backing.");
-        ret = bdrv_open_backing_file(bs, backing_options, &local_err);
-        if (ret < 0) {
-            goto close_and_fail;
+        const char *backing_bs;
+
+        backing_bs = qdict_get_try_str(options, "backing");
+        if (backing_bs) {
+            bs->backing_hd = bdrv_find(backing_bs);
+            qdict_del(options, "backing");
+            if (bs->backing_hd) {
+                bdrv_ref(bs->backing_hd);
+                assert(!bs->backing_blocker);
+                error_setg(&bs->backing_blocker,
+                           "device is used as backing hd of '%s'",
+                           bs->device_name);
+                bdrv_op_block_all(bs->backing_hd, bs->backing_blocker);
+                pstrcpy(bs->backing_file, sizeof(bs->backing_file),
+                        bs->backing_hd->filename);
+                pstrcpy(bs->backing_format, sizeof(bs->backing_format),
+                        bs->backing_hd->drv->format_name);
+            } else {
+                error_setg(errp, "Backing device not found: %s", backing_bs);
+                goto close_and_fail;
+            }
+        } else {
+            qdict_extract_subqdict(options, &backing_options, "backing.");
+            ret = bdrv_open_backing_file(bs, backing_options, &local_err);
+            if (ret < 0) {
+                goto close_and_fail;
+            }
         }
     }
 
@@ -1461,6 +1483,11 @@ void bdrv_close(BlockDriverState *bs)
 
     if (bs->drv) {
         if (bs->backing_hd) {
+            if (error_is_set(&bs->backing_blocker)) {
+                bdrv_op_unblock_all(bs->backing_hd,
+                                    bs->backing_blocker);
+                error_free(bs->backing_blocker);
+            }
             bdrv_unref(bs->backing_hd);
             bs->backing_hd = NULL;
         }
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 60edc80..6db30c9 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -316,6 +316,9 @@ struct BlockDriverState {
     BlockJob *job;
 
     QDict *options;
+
+    /* For backing reference, block the operations of named backing device */
+    Error *backing_blocker;
 };
 
 int get_tmp_filename(char *filename, int size);
-- 
1.8.4.2