block: Use bdrv_dirname() for relative filenames

bdrv_get_full_backing_filename_from_filename() breaks down when it comes
to JSON filenames. Using bdrv_dirname() as the basis is better because
since we have BDS, we can descend through the BDS tree to the protocol
layer, which gives us a greater probability of finding a non-JSON name;
also, bdrv_dirname() is more correct as it allows block drivers to
override the generation of that directory name in a protocol-specific
way.

We still need to keep bdrv_get_full_backing_filename_from_filename(),
though, because it has valid callers which need it during image creation
when no BDS is available yet.

This makes a test case in qemu-iotest 110, which was supposed to fail,
work. That is actually good, but we need to change the reference output
(and the comment in 110) accordingly.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20190201192935.18394-20-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 13 insertions, 7 deletions

diff --git a/block.c b/block.c
index 9f655c0..185475a 100644
--- a/block.c
+++ b/block.c
@@ -337,16 +337,22 @@ char *bdrv_get_full_backing_filename_from_filename(const char *backed,
 static char *bdrv_make_absolute_filename(BlockDriverState *relative_to,
                                          const char *filename, Error **errp)
 {
-    char *bs_filename;
+    char *dir, *full_name;
 
-    bdrv_refresh_filename(relative_to);
+    if (!filename || filename[0] == '\0') {
+        return NULL;
+    } else if (path_has_protocol(filename) || path_is_absolute(filename)) {
+        return g_strdup(filename);
+    }
 
-    bs_filename = relative_to->exact_filename[0]
-                      ? relative_to->exact_filename
-                      : relative_to->filename;
+    dir = bdrv_dirname(relative_to, errp);
+    if (!dir) {
+        return NULL;
+    }
 
-    return bdrv_get_full_backing_filename_from_filename(bs_filename,
-                                                        filename ?: "", errp);
+    full_name = g_strconcat(dir, filename, NULL);
+    g_free(dir);
+    return full_name;
 }
 
 char *bdrv_get_full_backing_filename(BlockDriverState *bs, Error **errp)