[Qemu-block] [PATCH v4 15/25] block: Use bdrv_dirname() for relative filenames

[Max Reitz]

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 <address@hidden>
---
 block.c                    | 20 +++++++++++++++-----
 tests/qemu-iotests/110     |  3 ++-
 tests/qemu-iotests/110.out |  2 +-
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/block.c b/block.c
index e591e326c5..f3d4436c9e 100644
--- a/block.c
+++ b/block.c
@@ -214,12 +214,22 @@ 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 = relative_to->exact_filename[0]
-                        ? relative_to->exact_filename
-                        : relative_to->filename;
+    char *dir, *full_name;
 
-    return bdrv_get_full_backing_filename_from_filename(bs_filename, filename,
-                                                        errp);
+    if (filename[0] == '\0' || path_has_protocol(filename) ||
+        path_is_absolute(filename))
+    {
+        return g_strdup(filename);
+    }
+
+    dir = bdrv_dirname(relative_to, errp);
+    if (!dir) {
+        return NULL;
+    }
+
+    full_name = g_strconcat(dir, filename, NULL);
+    g_free(dir);
+    return full_name;
 }
 
 char *bdrv_get_full_backing_filename(BlockDriverState *bs, Error **errp)
diff --git a/tests/qemu-iotests/110 b/tests/qemu-iotests/110
index 9de7369f3a..ba1b3c6c7d 100755
--- a/tests/qemu-iotests/110
+++ b/tests/qemu-iotests/110
@@ -61,7 +61,8 @@ echo '=== Non-reconstructable filename ==='
 echo
 
 # Across blkdebug without a config file, you cannot reconstruct filenames, so
-# qemu is incapable of knowing the directory of the top image
+# qemu is incapable of knowing the directory of the top image from the filename
+# alone. However, using bdrv_dirname(), it should still work.
 TEST_IMG="json:{
     'driver': '$IMGFMT',
     'file': {
diff --git a/tests/qemu-iotests/110.out b/tests/qemu-iotests/110.out
index b3584ff87f..5370bc1d26 100644
--- a/tests/qemu-iotests/110.out
+++ b/tests/qemu-iotests/110.out
@@ -14,7 +14,7 @@ backing file: t.IMGFMT.base (actual path: 
TEST_DIR/t.IMGFMT.base)
 image: json:{"driver": "IMGFMT", "file": {"set-state.0.event": "read_aio", 
"image": {"driver": "file", "filename": "TEST_DIR/t.IMGFMT"}, "driver": 
"blkdebug", "set-state.0.new_state": 42}}
 file format: IMGFMT
 virtual size: 64M (67108864 bytes)
-backing file: t.IMGFMT.base (cannot determine actual path)
+backing file: t.IMGFMT.base (actual path: TEST_DIR/t.IMGFMT.base)
 
 === Backing name is always relative to the backed image ===
 
-- 
2.11.0