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Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop


From: Cornelia Huck
Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
Date: Wed, 16 Mar 2016 12:52:01 +0100

On Wed, 16 Mar 2016 12:32:13 +0100
Cornelia Huck <address@hidden> wrote:

> On Wed, 16 Mar 2016 12:09:02 +0100
> Paolo Bonzini <address@hidden> 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?

Hm^2... I looked at virtio-scsi dataplane, and I noticed that it
acquires the aio context prior to calling ->set_host_notifiers(). Does
virtio-blk dataplane need to do this as well, or is virtio-scsi
dataplane wrong/different?




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