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Date: Wed, 16 Mar 2016 12:32:13 +0100
From: Cornelia Huck <cornelia.huck@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Christian Borntraeger <borntraeger@de.ibm.com>, tubo@linux.vnet.ibm.com, Stefan Hajnoczi <stefanha@redhat.com>

On Wed, 16 Mar 2016 12:09:02 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 16/03/2016 11:49, Christian Borntraeger wrote:

> > #3  0x00000000800b713e in virtio_blk_data_plane_start (s=0xba232d80) at /home/cborntra/REPOS/qemu/hw/block/dataplane/virtio-blk.c:224
> > #4  0x00000000800b4ea0 in virtio_blk_handle_output (vdev=0xb9eee7e8, vq=0xba305270) at /home/cborntra/REPOS/qemu/hw/block/virtio-blk.c:590
> > #5  0x00000000800ef3dc in virtio_queue_notify_vq (vq=0xba305270) at /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1095
> > #6  0x00000000800f1c9c in virtio_queue_host_notifier_read (n=0xba3052c8) at /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1785
> > #7  0x00000000800f1e14 in virtio_queue_set_host_notifier_fd_handler (vq=0xba305270, assign=false, set_handler=false) at /home/cborntra/REPOS/qemu/hw/virtio/virtio.c:1817
> > #8  0x0000000080109c50 in virtio_ccw_set_guest2host_notifier (dev=0xb9eed6a0, n=0, assign=false, set_handler=false) at /home/cborntra/REPOS/qemu/hw/s390x/virtio-ccw.c:97
> > #9  0x0000000080109ef2 in virtio_ccw_stop_ioeventfd (dev=0xb9eed6a0) at /home/cborntra/REPOS/qemu/hw/s390x/virtio-ccw.c:154
> 
> One bug is here: virtio_ccw_stop_ioeventfd, in this case, should pass
> assign=true to virtio_ccw_set_guest2host_notifier.  (Assuming my
> understanding of assign=true is correct; I think it means "I'm going to
> set up another host notifier handler").

Hm... I copied these semantics from virtio-pci, and they still seem to
be the same. I wonder why we never saw this on virtio-pci?

> In dataplane, instead, all calls to
> virtio_queue_set_host_notifier_fd_handler and
> virtio_queue_aio_set_host_notifier_handler should have assign=true.  The
> ioeventfd is just being moved from one aiocontext to another.

How can a transport know where they are called from?