If the backing file is overridden, this most probably does change the guest-visible data of a BDS. Therefore, we will need to consider this in bdrv_refresh_filename().
Adding a new field to the BDS is not nice, but it is very simple and exactly keeps track of whether the backing file has been overridden. Signed-off-by: Max Reitz <mre...@redhat.com> --- block.c | 2 ++ include/block/block_int.h | 1 + 2 files changed, 3 insertions(+) diff --git a/block.c b/block.c index e349e83..e178488 100644 --- a/block.c +++ b/block.c @@ -1299,6 +1299,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options, reference = qdict_get_try_str(parent_options, bdref_key); if (reference || qdict_haskey(options, "file.filename")) { + bs->backing_overridden = true; backing_filename[0] = '\0'; } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) { QDECREF(options); @@ -1589,6 +1590,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename, backing = qdict_get_try_str(options, "backing"); if (backing && *backing == '\0') { flags |= BDRV_O_NO_BACKING; + bs->backing_overridden = true; qdict_del(options, "backing"); } diff --git a/include/block/block_int.h b/include/block/block_int.h index 10d8759..d73e9ce 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -409,6 +409,7 @@ struct BlockDriverState { char backing_file[PATH_MAX]; /* if non zero, the image is a diff of this file image */ char backing_format[16]; /* if non-zero and backing_file exists */ + bool backing_overridden; /* backing file has been specified by the user */ QDict *full_open_options; char exact_filename[PATH_MAX]; -- 2.8.0