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Re: [Qemu-devel] [RFC PATCH 4/9] linux-aio: Implement .cancel_async
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC PATCH 4/9] linux-aio: Implement .cancel_async |
Date: |
Thu, 21 Aug 2014 17:31:06 +0100 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Thu, Aug 21, 2014 at 07:56:51PM +0800, Fam Zheng wrote:
> @@ -110,6 +109,22 @@ static void qemu_laio_completion_cb(EventNotifier *e)
> }
> }
>
> +static void laio_cancel_async(BlockDriverAIOCB *blockacb)
> +{
> + struct qemu_laiocb *laiocb = (struct qemu_laiocb *)blockacb;
> + struct io_event event;
> + int ret;
> +
> + ret = io_cancel(laiocb->ctx->ctx, &laiocb->iocb, &event);
> + laiocb->ret = -ECANCELED;
> + if (!ret) {
> + /* iocb is not cancelled, cb will be called by the event loop later
> */
> + return;
> + }
No callback will be invoked if io_cancel(2) every cancels the request
immediately.
The current kernel implementation always returns -EINPROGRESS or some of
other error value. But some day it might return 0 and this would leak
the request!
> +
> + laiocb->common.cb(laiocb->common.opaque, laiocb->ret);
> +}
It would be cleaner to reuse laio_cancel_async() from laio_cancel() to
avoid code duplication. For example, there is a useful comment in
laio_cancel() explaining that io_cancel(2) doesn't cancel I/O in
practice on 2.6.31 era kernels.
pgpd3nIjuxpfy.pgp
Description: PGP signature
- [Qemu-devel] [RFC PATCH 0/9] scsi, block: Asynchronous request cancellation, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 1/9] block: Add bdrv_aio_cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 2/9] tests: Add testing code for bdrv_aio_cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 3/9] iscsi: Implement .cancel_async in acb info, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 4/9] linux-aio: Implement .cancel_async, Fam Zheng, 2014/08/21
- Re: [Qemu-devel] [RFC PATCH 4/9] linux-aio: Implement .cancel_async,
Stefan Hajnoczi <=
- [Qemu-devel] [RFC PATCH 5/9] thread-pool: Implement .cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 7/9] dma: Implement .cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 8/9] block: Implement stub bdrv_em_co_aiocb_info.cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 6/9] blkdebug: Implement .cancel_async, Fam Zheng, 2014/08/21
- [Qemu-devel] [RFC PATCH 9/9] scsi: Cancel request asynchronously, Fam Zheng, 2014/08/21