block: introduce bdrv_open_file_child() helper

Almost all drivers call bdrv_open_child() similarly. Let's create a
helper for this.

The only not updated drivers that call bdrv_open_child() to set
bs->file are raw-format and snapshot-access:
    raw-format sometimes want to have filtered child but
        don't set drv->is_filter to true.
    snapshot-access wants only DATA | PRIMARY

Possibly we should implement drv->is_filter_func() handler, to consider
raw-format as filter when it works as filter.. But it's another story.

Note also, that we decrease assignments to bs->file in code: it helps
us restrict modifying this field in further commit.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220726201134.924743-3-vsementsov@yandex-team.ru>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/block.c b/block.c
index c8374dac4f..25a596a612 100644
--- a/block.c
+++ b/block.c
@@ -3674,6 +3674,27 @@ BdrvChild *bdrv_open_child(const char *filename,
 }
 
 /*
+ * Wrapper on bdrv_open_child() for most popular case: open primary child of bs.
+ */
+int bdrv_open_file_child(const char *filename,
+                         QDict *options, const char *bdref_key,
+                         BlockDriverState *parent, Error **errp)
+{
+    BdrvChildRole role;
+
+    /* commit_top and mirror_top don't use this function */
+    assert(!parent->drv->filtered_child_is_backing);
+
+    role = parent->drv->is_filter ?
+        (BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY) : BDRV_CHILD_IMAGE;
+
+    parent->file = bdrv_open_child(filename, options, bdref_key, parent,
+                                   &child_of_bds, role, false, errp);
+
+    return parent->file ? 0 : -EINVAL;
+}
+
+/*
  * TODO Future callers may need to specify parent/child_class in order for
  * option inheritance to work. Existing callers use it for the root node.
  */