* Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx> [2011-08-01 01:30]:
> +static AIOPool block_queue_pool = {
> + .aiocb_size = sizeof(struct BlockDriverAIOCB),
> + .cancel = qemu_block_queue_cancel,
> +};
> +
> +static void qemu_block_queue_callback(void *opaque, int ret)
> +{
> + BlockDriverAIOCB *acb = opaque;
> +
> + qemu_aio_release(acb);
> +}
> +
So, here we really want to invoke the original commands callback, and
then free the request here (via qemu_aio_release()). see below.
> +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);
> +
> + 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)
> +{
> + int ret;
> + BlockDriverAIOCB *res;
> +
> + /* indicate this req is from block queue */
> + request->bs->req_from_queue = true;
> +
> + res = request->handler(request->bs, request->sector_num,
> + request->qiov, request->nb_sectors,
> + request->cb, request->opaque);
> +
> + if (request->acb) {
> + qemu_block_queue_callback(request->acb, 0);
> + }
> +
> + ret = (res == NULL) ? 0 : 1;
> +
> + return ret;
> +}
You don't want to malloc the BlockIORequest directly in _enqueue(), rather
you want to allocate that from your AIOPool via qemu_aio_get(). As it
is now, we're allocating two BlockIORequests (malloc and then a
aio_get()). You'll need a BlockDriverAIOCB in the BlockIORequest
structure. Then in your queue_handler, instead of passing the original
read or write callback (request->cb), you want to hook the block_queue callback
(qemu_block_queue_callback()), in that callback you can then invoke the
request callback and then release the request.
The request should be, only one malloc (via the pool which will re-use
the memory instead of incuring a malloc on every request), and then you
release the memory back to the pool once your request is complete, which
you'll know after wiring up the block_queue callback to the completion
of the request's handler. And then since we don't double allocate, you
won't need to do the qemu_free(request) in block.c in block_timer...
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@xxxxxxxxxx
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