[Qemu-devel] [PATCH v8 06/12] block: Add bdrv_set_backing_hd()

[Fam Zheng <famz@redhat.com>]

This is the common but non-trivial steps to assign or change the
backing_hd of BDS.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c               | 29 +++++++++++++++++++++++------
 include/block/block.h |  1 +
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index 28814f7..63a5918 100644
--- a/block.c
+++ b/block.c
@@ -958,6 +958,24 @@ fail:
     return ret;
 }
 
+void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
+{
+    if (bs->backing_hd) {
+        bdrv_unref(bs->backing_hd);
+    }
+
+    bs->backing_hd = backing_hd;
+    if (!backing_hd) {
+        return;
+    }
+    bdrv_ref(bs->backing_hd);
+
+    pstrcpy(bs->backing_file, sizeof(bs->backing_file),
+            bs->backing_hd->file->filename);
+    pstrcpy(bs->backing_format, sizeof(bs->backing_format),
+            bs->backing_hd->drv->format_name);
+}
+
 /*
  * Opens the backing file for a BlockDriverState if not yet open
  *
@@ -971,6 +989,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
     char backing_filename[PATH_MAX];
     int back_flags, ret;
     BlockDriver *back_drv = NULL;
+    BlockDriverState *backing_hd;
     Error *local_err = NULL;
 
     if (bs->backing_hd != NULL) {
@@ -994,7 +1013,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
                                        sizeof(backing_filename));
     }
 
-    bs->backing_hd = bdrv_new("");
+    backing_hd = bdrv_new("");
 
     if (bs->backing_format[0] != '\0') {
         back_drv = bdrv_find_format(bs->backing_format);
@@ -1004,20 +1023,18 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
     back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT |
                                     BDRV_O_COPY_ON_READ);
 
-    ret = bdrv_open(bs->backing_hd,
+    ret = bdrv_open(backing_hd,
                     *backing_filename ? backing_filename : NULL, options,
                     back_flags, back_drv, &local_err);
     if (ret < 0) {
-        bdrv_unref(bs->backing_hd);
-        bs->backing_hd = NULL;
+        bdrv_unref(backing_hd);
         bs->open_flags |= BDRV_O_NO_BACKING;
         error_setg(errp, "Could not open backing file: %s",
                    error_get_pretty(local_err));
         error_free(local_err);
         return ret;
     }
-    pstrcpy(bs->backing_file, sizeof(bs->backing_file),
-            bs->backing_hd->file->filename);
+    bdrv_set_backing_hd(bs, backing_hd);
     return 0;
 }
 
diff --git a/include/block/block.h b/include/block/block.h
index ac8976e..20bfcd9 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -185,6 +185,7 @@ int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_parse_discard_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename,
                    QDict *options, int flags, Error **errp);
+void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd);
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp);
 int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
               int flags, BlockDriver *drv, Error **errp);
-- 
1.8.5.1