Reopening a node's backing child needs a bit of special handling because the "backing" child has different defaults than all other children (among other things). Adding filter support here is a bit more difficult than just using the child access functions. In fact, we often have to directly use bs->backing because these functions are about the "backing" child (which may or may not be the COW backing file).
Signed-off-by: Max Reitz <mre...@redhat.com> --- block.c | 36 +++++++++++++++++++++++++++++------- 1 file changed, 29 insertions(+), 7 deletions(-) diff --git a/block.c b/block.c index 505b3e9a01..db2759c10d 100644 --- a/block.c +++ b/block.c @@ -3542,17 +3542,39 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state, } } + /* + * Ensure that @bs can really handle backing files, because we are + * about to give it one (or swap the existing one) + */ + if (bs->drv->is_filter) { + /* Filters always have a file or a backing child */ + if (!bs->backing) { + error_setg(errp, "'%s' is a %s filter node that does not support a " + "backing child", bs->node_name, bs->drv->format_name); + return -EINVAL; + } + } else if (!bs->drv->supports_backing) { + error_setg(errp, "Driver '%s' of node '%s' does not support backing " + "files", bs->drv->format_name, bs->node_name); + return -EINVAL; + } + /* * Find the "actual" backing file by skipping all links that point * to an implicit node, if any (e.g. a commit filter node). + * We cannot use any of the bdrv_skip_*() functions here because + * those return the first explicit node, while we are looking for + * its overlay here. */ overlay_bs = bs; - while (backing_bs(overlay_bs) && backing_bs(overlay_bs)->implicit) { - overlay_bs = backing_bs(overlay_bs); + while (bdrv_filtered_bs(overlay_bs) && + bdrv_filtered_bs(overlay_bs)->implicit) + { + overlay_bs = bdrv_filtered_bs(overlay_bs); } /* If we want to replace the backing file we need some extra checks */ - if (new_backing_bs != backing_bs(overlay_bs)) { + if (new_backing_bs != bdrv_filtered_bs(overlay_bs)) { /* Check for implicit nodes between bs and its backing file */ if (bs != overlay_bs) { error_setg(errp, "Cannot change backing link if '%s' has " @@ -3560,8 +3582,8 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state, return -EPERM; } /* Check if the backing link that we want to replace is frozen */ - if (bdrv_is_backing_chain_frozen(overlay_bs, backing_bs(overlay_bs), - errp)) { + if (bdrv_is_backing_chain_frozen(overlay_bs, + child_bs(overlay_bs->backing), errp)) { return -EPERM; } reopen_state->replace_backing_bs = true; @@ -3712,7 +3734,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue, * its metadata. Otherwise the 'backing' option can be omitted. */ if (drv->supports_backing && reopen_state->backing_missing && - (backing_bs(reopen_state->bs) || reopen_state->bs->backing_file[0])) { + (reopen_state->bs->backing || reopen_state->bs->backing_file[0])) { error_setg(errp, "backing is missing for '%s'", reopen_state->bs->node_name); ret = -EINVAL; @@ -3857,7 +3879,7 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state) * from bdrv_set_backing_hd()) has the new values. */ if (reopen_state->replace_backing_bs) { - BlockDriverState *old_backing_bs = backing_bs(bs); + BlockDriverState *old_backing_bs = child_bs(bs->backing); assert(!old_backing_bs || !old_backing_bs->implicit); /* Abort the permission update on the backing bs we're detaching */ if (old_backing_bs) { -- 2.21.0