On Wed 29 Aug 2018 12:43:06 PM CEST, Max Reitz wrote: > On 2018-08-26 16:09, Alberto Garcia wrote: >> Block drivers allow opening their children using a reference to an >> existing BlockDriverState. These references remain stored in the >> 'options' and 'explicit_options' QDicts, but we don't need to keep >> them once everything is open. >> >> What is more important, these values can become wrong if the children >> change: >> >> $ qemu-img create -f qcow2 hd0.qcow2 10M >> $ qemu-img create -f qcow2 hd1.qcow2 10M >> $ qemu-img create -f qcow2 hd2.qcow2 10M >> $ $QEMU -drive if=none,file=hd0.qcow2,node-name=hd0 \ >> -drive if=none,file=hd1.qcow2,node-name=hd1,backing=hd0 \ >> -drive file=hd2.qcow2,node-name=hd2,backing=hd1 >> >> After this hd2 has hd1 as its backing file. Now let's remove it using >> block_stream: >> >> (qemu) block_stream hd2 0 hd0.qcow2 >> >> Now hd0 is the backing file of hd2, but hd2's options QDicts still >> contain backing=hd1. >> >> Signed-off-by: Alberto Garcia <be...@igalia.com> >> --- >> block.c | 12 +++++++++++- >> 1 file changed, 11 insertions(+), 1 deletion(-) > > Also, the question is, why would we discard the child options, but > keep the references (which we do not add, so we only have the ones > specified by the user).
We discussed this a couple of weeks ago: https://lists.gnu.org/archive/html/qemu-block/2018-08/msg00478.html In the end I got convinced that we didn't need to keep the child references. >> @@ -3313,6 +3317,12 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state) >> bs->open_flags = reopen_state->flags; >> bs->read_only = !(reopen_state->flags & BDRV_O_RDWR); >> >> + /* Remove child references from bs->options and bs->explicit_options */ >> + QLIST_FOREACH(child, &bs->children, next) { >> + qdict_del(bs->explicit_options, child->name); >> + qdict_del(bs->options, child->name); >> + } >> + > > Why don't you remove the child options as well? Because there's no child options here at this point. They are removed from the parent QDict in bdrv_reopen_queue_child(): QLIST_FOREACH(child, &bs->children, next) { /* ... */ child_key_dot = g_strdup_printf("%s.", child->name); qdict_extract_subqdict(explicit_options, NULL, child_key_dot); qdict_extract_subqdict(options, &new_child_options, child_key_dot); g_free(child_key_dot); bdrv_reopen_queue_child(bs_queue, child->bs, new_child_options, 0, child->role, options, flags); } Berto
