On Wed, 09/10 17:09, Bin Wu wrote: > On 2014/9/10 13:59, Fam Zheng wrote: > >v5: Fix IDE callback. (Paolo) > > Fix blkdebug. (Paolo) > > Drop the DMA fix which is independent of this series. (Paolo) > > Incorperate Yuan's patch on quorum_aio_cancel. (Benoît) > > Commit message wording fix. (Benoît) > > Rename qemu_aio_release to qemu_aio_unref. (Benoît) > > > >v4: Drop AIOCBInfo.cancel. > > > >This series adds a new block layer API: > > > > void bdrv_aio_cancel_async(BlockDriverAIOCB *acb); > > > >And use it to emulate bdrv_aio_cancel. > > > >The function is similar to bdrv_aio_cancel in that it cancels an AIO request, > >but different that it doesn't block until the request is completely cancelled > >or done. > > > >More importantly, the completion callback, BlockDriverAIOCB.cb, is guaranteed > >to be called, so that the cb can take care of resource releasing and status > >reporting to guest, etc. > > > >In the following work, scsi emulation code will be shifted to use the async > >cancelling. > > > >One major benefit would be that when guest tries to cancel a request, where > >the > >request cannot be cancelled easily, (due to throttled BlockDriverState, a > >lost > >connection, or a large request queue), we don't need to block the whole vm > >with > >a busy loop, which is how bdrv_aio_cancel is implemented now. > > First, I think this series is really useful. However, I tested the v4 series > and found virtio-scsi disk(scsi-hd) was still blocked when the IO could not > come back because of virtio_scsi_do_tmf->scsi_cancel_io->bdrv_aio_cancel. > can we just change the bdrv_aio_cancel to bdrv_aio_cancel_async to solve > this problem?
We can't just change it yet. We need to take care of the scsi_req_unref there, if we unref right after bdrv_aio_cancel_async, in the cb it will access dangling pointer. It's not trivial enough to do in this series, I will work on that on top, as said below. For now, the user visible behavior of io cancellation is still the same. Thanks for testing. Fam > > > >Later, we will change scsi device code to make this asynchronous, on top of > >bdrv_aio_cancel_async.
