[Qemu-devel] [PATCH v4 2/6] block: Get full backing filename from string

[Max Reitz <mreitz@redhat.com>]

Introduce bdrv_get_full_backing_filename_from_filename(), a function
which takes the name of the backed file and a potentially relative
backing filename to produce the full (absolute) backing filename.

Use this function from bdrv_get_full_backing_filename().

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
---
 block.c               | 16 ++++++++++++----
 include/block/block.h |  3 +++
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/block.c b/block.c
index 866c8b4..0c1be37 100644
--- a/block.c
+++ b/block.c
@@ -303,15 +303,23 @@ void path_combine(char *dest, int dest_size,
     }
 }
 
-void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz)
+void bdrv_get_full_backing_filename_from_filename(const char *backed,
+                                                  const char *backing,
+                                                  char *dest, size_t sz)
 {
-    if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) {
-        pstrcpy(dest, sz, bs->backing_file);
+    if (backing[0] == '\0' || path_has_protocol(backing)) {
+        pstrcpy(dest, sz, backing);
     } else {
-        path_combine(dest, sz, bs->filename, bs->backing_file);
+        path_combine(dest, sz, backed, backing);
     }
 }
 
+void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz)
+{
+    bdrv_get_full_backing_filename_from_filename(bs->filename, bs->backing_file,
+                                                 dest, sz);
+}
+
 void bdrv_register(BlockDriver *bdrv)
 {
     /* Block drivers without coroutine functions need emulation */
diff --git a/include/block/block.h b/include/block/block.h
index 610be9f..1c7ecaa 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -399,6 +399,9 @@ void bdrv_get_backing_filename(BlockDriverState *bs,
                                char *filename, int filename_size);
 void bdrv_get_full_backing_filename(BlockDriverState *bs,
                                     char *dest, size_t sz);
+void bdrv_get_full_backing_filename_from_filename(const char *backed,
+                                                  const char *backing,
+                                                  char *dest, size_t sz);
 int bdrv_is_snapshot(BlockDriverState *bs);
 
 int path_is_absolute(const char *path);
-- 
1.9.3