block: Improve empty format-specific info dump

When a block driver supports obtaining format-specific information, but
that object only contains optional fields, it is possible that none of
them are present, so that dump_qobject() (called by
bdrv_image_info_specific_dump()) will not print anything.

The callers of bdrv_image_info_specific_dump() put a header above this
information ("Format specific information:\n"), which will look strange
when there is nothing below.  Modify bdrv_image_info_specific_dump() to
print this header instead of its callers, and only if there is indeed
something to be printed.

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220620162704.80987-2-hreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
index 7a412d6512..d7e562dda6 100644
--- a/qemu-io-cmds.c
+++ b/qemu-io-cmds.c
@@ -1788,8 +1788,8 @@ static int info_f(BlockBackend *blk, int argc, char **argv)
         return -EIO;
     }
     if (spec_info) {
-        printf("Format specific information:\n");
-        bdrv_image_info_specific_dump(spec_info);
+        bdrv_image_info_specific_dump(spec_info,
+                                      "Format specific information:\n");
         qapi_free_ImageInfoSpecific(spec_info);
     }