Am 04.05.2023 um 21:53 hat Stefan Hajnoczi geschrieben:
> This patch is part of an effort to remove the aio_disable_external()
> API because it does not fit in a multi-queue block layer world where
> many AioContexts may be submitting requests to the same disk.
>
> The SCSI emulation code is already in good shape to stop using
> aio_disable_external(). It was only used by commit 9c5aad84da1c
> ("virtio-scsi: fixed virtio_scsi_ctx_check failed when detaching scsi
> disk") to ensure that virtio_scsi_hotunplug() works while the guest
> driver is submitting I/O.
>
> Ensure virtio_scsi_hotunplug() is safe as follows:
>
> 1. qdev_simple_device_unplug_cb() -> qdev_unrealize() ->
> device_set_realized() calls qatomic_set(&dev->realized, false) so
> that future scsi_device_get() calls return NULL because they exclude
> SCSIDevices with realized=false.
>
> That means virtio-scsi will reject new I/O requests to this
> SCSIDevice with VIRTIO_SCSI_S_BAD_TARGET even while
> virtio_scsi_hotunplug() is still executing. We are protected against
> new requests!
>
> 2. scsi_device_unrealize() already contains a call to
I think you mean scsi_qdev_unrealize(). Can be fixed while applying.
> scsi_device_purge_requests() so that in-flight requests are cancelled
> synchronously. This ensures that no in-flight requests remain once
> qdev_simple_device_unplug_cb() returns.
>
> Thanks to these two conditions we don't need aio_disable_external()
> anymore.
>
> Cc: Zhengui Li <lizhen...@huawei.com>
> Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
> Reviewed-by: Daniil Tatianin <d-tatia...@yandex-team.ru>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Kevin
