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. This commit adds a FIXME which will be remedied by a follow-up commit. Until then, the respective piece of code will not result in any behavior that is worse than what we currently have. Signed-off-by: Max Reitz <mre...@redhat.com> --- block.c | 13 +++++++++++++ block/mirror.c | 4 ++++ blockdev.c | 16 ++++++++++++++++ include/block/block_int.h | 1 + 4 files changed, 34 insertions(+) diff --git a/block.c b/block.c index 1615f5d..438201d 100644 --- a/block.c +++ b/block.c @@ -1495,6 +1495,11 @@ 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")) { backing_filename[0] = '\0'; + + /* FIXME: Should also be set to true if @options contains other runtime + * options which control the data that is read from the backing + * BDS */ + bs->backing_overridden = true; } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) { QDECREF(options); goto free_exit; @@ -1659,6 +1664,9 @@ static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs, bdrv_ref(bs_snapshot); bdrv_append(bs_snapshot, bs); + bs_snapshot->backing_overridden = true; + bdrv_refresh_filename(bs_snapshot); + g_free(tmp_filename); return bs_snapshot; @@ -1786,6 +1794,7 @@ static BlockDriverState *bdrv_open_inherit(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"); } @@ -3959,6 +3968,10 @@ void bdrv_refresh_filename(BlockDriverState *bs) * refresh those first */ QLIST_FOREACH(child, &bs->children, next) { bdrv_refresh_filename(child->bs); + + if (child->role == &child_backing && child->bs->backing_overridden) { + bs->backing_overridden = true; + } } if (drv->bdrv_refresh_filename) { diff --git a/block/mirror.c b/block/mirror.c index 4ece624..6cb6cbd 100644 --- a/block/mirror.c +++ b/block/mirror.c @@ -891,6 +891,10 @@ static void mirror_complete(BlockJob *job, Error **errp) assert(!target->backing); bdrv_set_backing_hd(target, backing); + + /* The target image's file already has been created with the backing + * file we just set, so there is no need to set backing_overridden or + * call bdrv_refresh_filename(). */ } s->should_complete = true; diff --git a/blockdev.c b/blockdev.c index 245e1e1..7889bab 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1771,6 +1771,8 @@ static void external_snapshot_commit(BlkActionState *common) { ExternalSnapshotState *state = DO_UPCAST(ExternalSnapshotState, common, common); + TransactionAction *action = common->action; + bool image_was_existing = false; bdrv_set_aio_context(state->new_bs, state->aio_context); @@ -1783,6 +1785,20 @@ static void external_snapshot_commit(BlkActionState *common) bdrv_reopen(state->old_bs, state->old_bs->open_flags & ~BDRV_O_RDWR, NULL); } + + if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) { + BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data; + if (s->has_mode && s->mode == NEW_IMAGE_MODE_EXISTING) { + image_was_existing = true; + } + } else { + image_was_existing = true; + } + + if (image_was_existing) { + state->new_bs->backing_overridden = true; + bdrv_refresh_filename(state->new_bs); + } } static void external_snapshot_abort(BlkActionState *common) diff --git a/include/block/block_int.h b/include/block/block_int.h index 83a423c..555f3c2 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -461,6 +461,7 @@ 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]; -- 2.10.2