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Re: [Qemu-devel] [PATCH v3 13/16] block: Implement bdrv_append() without
From: |
Alberto Garcia |
Subject: |
Re: [Qemu-devel] [PATCH v3 13/16] block: Implement bdrv_append() without bdrv_swap() |
Date: |
Tue, 13 Oct 2015 11:01:34 +0200 |
User-agent: |
Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.2.1 (i486-pc-linux-gnu) |
On Tue 13 Oct 2015 10:39:22 AM CEST, Kevin Wolf <address@hidden> wrote:
>> > +static void change_parent_backing_link(BlockDriverState *from,
>> > + BlockDriverState *to)
>> > +{
>> > + BdrvChild *c, *next;
>> > +
>> > + QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
>> > + assert(c->role != &child_backing);
>> > + c->bs = to;
>> > + QLIST_REMOVE(c, next_parent);
>> > + QLIST_INSERT_HEAD(&to->parents, c, next_parent);
>> > + bdrv_ref(to);
>> > + bdrv_unref(from);
>> > + }
>> > + if (from->blk) {
>> > + blk_set_bs(from->blk, to);
>> > + if (!to->device_list.tqe_prev) {
>> > + QTAILQ_INSERT_BEFORE(from, to, device_list);
>> > + }
>>
>> Is it even possible that this last condition is false? In what case
>> would 'to' be already in bdrv_states?
>>
>> I understand that it would mean that it would already be attached to
>> a BlockBackend, but that's not possible in this case.
>
> Yes, I think it's not possible currently (hopefully, because that
> would cause other bugs), just being careful. Eventually we'll allow
> more than one BlockBackend pointing to the same BDS, and then this is
> a scenario that could happen.
blk_set_bs() already asserts that to->blk == NULL, so if this is not
possible here wouldn't it be better to use another assertion instead?
When I was reviewing the code I kept wondering in what kind of scenario
this condition could be false.
Berto
- [Qemu-devel] [PATCH v3 03/16] blkverify: Convert s->test_file to BdrvChild, (continued)
- [Qemu-devel] [PATCH v3 03/16] blkverify: Convert s->test_file to BdrvChild, Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 04/16] quorum: Convert to BdrvChild, Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 09/16] block: Split bdrv_move_feature_fields(), Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 12/16] block: Introduce parents list, Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 13/16] block: Implement bdrv_append() without bdrv_swap(), Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 01/16] block: Introduce BDS.file_child, Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 10/16] block/io: Make bdrv_requests_pending() public, Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 08/16] block: Manage backing file references in bdrv_set_backing_hd(), Kevin Wolf, 2015/10/09
- [Qemu-devel] [PATCH v3 02/16] vmdk: Use BdrvChild instead of BDS for references to extents, Kevin Wolf, 2015/10/10
- [Qemu-devel] [PATCH v3 07/16] block: Convert bs->backing_hd to BdrvChild, Kevin Wolf, 2015/10/10