On 12/23/2015 06:04 PM, Stefan Hajnoczi wrote:
> On Thu, Dec 17, 2015 at 02:22:14PM +0800, Wen Congyang wrote:
>> Stefan:Ping...
>>
>> What about this feature? I have worked for it about 1 year, but it is still
>> in the
>> way...
>
> The code still has TODOs. What is the plan for supporting replication
> after failover? This feature seems critical because anyone who wants FT
> won't be able to use this code unless it supports FT after the first
> failure.
We have implemented it based on an old version qemu. To keep the logical
simple, we don't post them now. We will post them after this feature is merged
into qemu.
>
> ---
>
> Adding new block layer APIs that are replication-specific is not clean.
> Only the replication block driver cares about the start/stop/checkpoint
> interface.
>
> It is cleaner to have a separate API and data structure for block
> replication.
>
> The replication code should define its own BlockReplicationOps struct
> and allow objects to register themselves. Then it's no longer necessary
> to modify the core block layer to forward start/stop/checkpoint calls.
>
> Something like:
>
> typedef struct BlockReplicationOps BlockReplicationOps;
> typedef struct BlockReplicationState {
> const BlockReplicationOps *ops;
> QLIST_ENTRY(BlockReplicationState) list;
> } BlockReplicationState;
>
> typedef struct {
> void start(BlockReplicationState *brs, Error **errp);
> void stop(BlockReplicationState *brs, Error **errp);
> void checkpoint(BlockReplicationState *brs, Error **errp);
> } BlockReplicationOps;
>
> static QLIST_HEAD(BlockReplicationState) block_replication_states;
>
> void block_replication_add(BlockReplicationState *brs);
> void block_replication_remove(BlockReplicationState *brs);
>
> The replication block driver would add/remove itself. The quorum block
> driver probably doesn't need to be modified (I think in your current
> patches you modify it just to forward the start/stop/checkpoint calls to
> a particular quorum child).
Yes, it is the major purpose. We also do some check in the quorum driver:
we don't allow more than one child support block replication.
Thanks
Wen Congyang
>
> Stefan
>
