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[Qemu-devel] Re: [PATCH] vhost-net: Do not set features for backend when


From: Jason Wang
Subject: [Qemu-devel] Re: [PATCH] vhost-net: Do not set features for backend when peer was deleted
Date: Wed, 27 Oct 2010 14:59:16 +0800

Michael S. Tsirkin writes:
 > On Wed, Oct 27, 2010 at 12:43:51AM +0800, Jason Wang wrote:
 > > When hot-unplug a virtio nic with vhost-net backend, guest may
 > > continue to program the nic even if its peer have been deleted. We can
 > > not set features at this time as vhost_net_ack_features() may still
 > > try to use the tap related vhost_net structure which have been freed
 > > in tap_cleanup(). And setting offload features for a deleted backend
 > > is also meaningless in this situation
 > > 
 > > Signed-off-by: Jason Wang <address@hidden>
 > 
 > Hmm. Actually, this is not enough.
 > We really must stop and cleanup vhost net.
 > 

But this patch just prevent the guest from programming a nic with its
vhost-net backend deleted. The vhost net was still stopped and cleaned
when the peer have been removed.

 > Two issues are 
 > 1. vhost_net_stop needs virtio device pointer
 > 2. virtio net has a vhost_started flag
 > 
 > Two ways to fix it that I see:
 > 1. add a callback in nic and invoke when peer_deleted is set
 > 2. add vhost_started and virtio device pointers in vhost
 > 
 > Path 1 seems easier ...
 > 
 > MST
 > 
 > > ---
 > >  hw/virtio-net.c |    3 +++
 > >  1 files changed, 3 insertions(+), 0 deletions(-)
 > > 
 > > diff --git a/hw/virtio-net.c b/hw/virtio-net.c
 > > index 7e1688c..68c8e48 100644
 > > --- a/hw/virtio-net.c
 > > +++ b/hw/virtio-net.c
 > > @@ -245,6 +245,9 @@ static void virtio_net_set_features(VirtIODevice 
 > > *vdev, uint32_t features)
 > >  {
 > >      VirtIONet *n = to_virtio_net(vdev);
 > >  
 > > +    if (n->nic->peer_deleted)
 > > +        return;
 > > +
 > >      n->mergeable_rx_bufs = !!(features & (1 << VIRTIO_NET_F_MRG_RXBUF));
 > >  
 > >      if (n->has_vnet_hdr) {
 > 



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