On Wed, Aug 27, 2014 at 10:49:10AM +0800, Fam Zheng wrote:
> +/* Async version of aio cancel. The caller is not blocked if the acb
> implements
> + * cancel_async, otherwise fall back to bdrv_aio_cancel. In both cases,
> acb->cb
> + * is guarenteed to be called, before or after function returns. */
> +void bdrv_aio_cancel_async(BlockDriverAIOCB *acb)
> +{
> + if (acb->aiocb_info->cancel_async) {
> + acb->aiocb_info->cancel_async(acb);
> + } else {
> + /* Mask the cb and cancel, we'll call it manually once the
> synchronous
> + * cancel is done. */
> + BlockDriverCompletionFunc *cb = acb->cb;
> + void *opaque = acb->opaque;
> + acb->cb = bdrv_aio_cancel_cb_nop;
> + acb->opaque = NULL;
> + qemu_aio_ref(acb);
> + acb->aiocb_info->cancel(acb);
> + cb(opaque, -ECANCELED);
> + qemu_aio_release(acb);
> + }
> +}It is not totally obvious why we hijack the callback. If you respin, please rephrase the comment along the lines of: /* bdrv_aio_cancel() does not guarantee to invoke cb() so mask it during * bdrv_aio_cancel() and always invoke it ourselves. */ Stefan
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