On Tue, Aug 9, 2011 at 8:49 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote:
> On Tue, Aug 9, 2011 at 5:17 AM, Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx> wrote:
>> +/* The APIs for block request queue on qemu block layer.
>> + */
>> +
>> +static void qemu_block_queue_cancel(BlockDriverAIOCB *acb)
>> +{
>> + qemu_aio_release(acb);
>> +}
>> +
>> +static AIOPool block_queue_pool = {
>> + .aiocb_size = sizeof(struct BlockDriverAIOCB),
>> + .cancel = qemu_block_queue_cancel,
>> +};
>
> The lifecycle of block_queue_pool acbs should be like this:
>
> When a request is queued we need a BlockQueue acb because we have no
> real acb yet. So we get an acb from block_queue_pool.
>
> If the acb is cancelled before being dispatched we need to release the
> acb and remove the request from the queue. (This patch does not
> remove the request from the queue on cancel.)
>
> When the acb is dispatched we need to keep track of the real acb (e.g.
> from qcow2). The caller will only ever see our acb because there is
> no way to give them the pointer to the new acb after dispatch. That
> means we need to keep the our acb alive for the entire lifetime of the
> request. (This patch currently releases our acb when the request is
> dispatched.)
>
> If the acb is cancelled after being dispatched we need to first cancel
> the real acb and then release our acb.
>
> When the acb is dispatched we need to pass qemu_block_queue_callback
> as the cb function to handler. Inside qemu_block_queue_callback we
> invoke the request cb and then release our acb. This is how our acb
> should be freed.
To the point, very good.
>
>> +BlockDriverAIOCB *qemu_block_queue_enqueue(BlockQueue *queue,
>> + BlockDriverState *bs,
>> + BlockRequestHandler *handler,
>> + int64_t sector_num,
>> + QEMUIOVector *qiov,
>> + int nb_sectors,
>> + BlockDriverCompletionFunc *cb,
>> + void *opaque)
>> +{
>> + BlockIORequest *request;
>> + BlockDriverAIOCB *acb;
>> +
>> + request = qemu_malloc(sizeof(BlockIORequest));
>> + request->bs = bs;
>> + request->handler = handler;
>> + request->sector_num = sector_num;
>> + request->qiov = qiov;
>> + request->nb_sectors = nb_sectors;
>> + request->cb = cb;
>> + request->opaque = opaque;
>> +
>> + QTAILQ_INSERT_TAIL(&queue->requests, request, entry);
>
> It would be simpler to define BlockQueueAIOCB and using it as our acb
> instead of managing an extra BlockIORequest structure. That way you
> don't need to worry about extra mallocs and frees.
Sorry, i don't get what you mean. how to define it? Can you elaborate?
>
>> +
>> + acb = qemu_aio_get(&block_queue_pool, bs,
>> + qemu_block_queue_callback, opaque);
>> +
>> + request->acb = acb;
>> +
>> + return acb;
>> +}
>> +
>> +int qemu_block_queue_handler(BlockIORequest *request)
>
> This function can be static.
Sure.
>
> Stefan
>
--
Regards,
Zhi Yong Wu
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