[Qemu-block] [PATCH v3 5/5] block/qapi: allow best-effort query

[John Snow]

For more complex BDS trees that can be created under normal circumstances,
we lose the ability to issue query commands because of our inability to
re-construct the absolute filename.

Instead, omit this field when it is a problem and present as much information
as we can.

This will change the expected output in iotest 110, where we will now see a
json filename and the lack of an absolute filename instead of an error.

Signed-off-by: John Snow <address@hidden>
---
 block/qapi.c               | 7 ++++---
 tests/qemu-iotests/110.out | 5 ++++-
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/block/qapi.c b/block/qapi.c
index c61fb30..9c6c02d 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -245,10 +245,11 @@ void bdrv_query_image_info(BlockDriverState *bs,
         info->has_backing_filename = true;
         bdrv_get_full_backing_filename(bs, backing_filename2, PATH_MAX, &err);
         if (err) {
-            error_propagate(errp, err);
-            qapi_free_ImageInfo(info);
+            /* Can't reconstruct the full backing filename, so we must omit
+             * this field and apply a Best Effort to this query. */
             g_free(backing_filename2);
-            return;
+            backing_filename2 = NULL;
+            error_free(err);
         }
 
         /* Always report the full_backing_filename if present, even if it's the
diff --git a/tests/qemu-iotests/110.out b/tests/qemu-iotests/110.out
index 0270980..b3584ff 100644
--- a/tests/qemu-iotests/110.out
+++ b/tests/qemu-iotests/110.out
@@ -11,7 +11,10 @@ backing file: t.IMGFMT.base (actual path: 
TEST_DIR/t.IMGFMT.base)
 
 === Non-reconstructable filename ===
 
-qemu-img: Cannot use relative backing file names for '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}}'
+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 name is always relative to the backed image ===
 
-- 
2.4.3