Re: [PATCH 2/3] kvm: qemu: handle link status in qemu_sendv_packet()

[Mark McLoughlin <markmc@redhat.com>]

On Tue, 2008-12-09 at 08:57 -0600, Anthony Liguori wrote:
> Mark McLoughlin wrote:
> > Signed-off-by: Mark McLoughlin <markmc@redhat.com>
> > ---
> >  qemu/net.c |   18 +++++++++++++++++-
> >  1 files changed, 17 insertions(+), 1 deletions(-)
> >
> > diff --git a/qemu/net.c b/qemu/net.c
> > index 16a0990..f23a17f 100644
> > --- a/qemu/net.c
> > +++ b/qemu/net.c
> > @@ -400,6 +400,17 @@ static ssize_t vc_sendv_compat(VLANClientState *vc, const struct iovec *iov,
> >      return offset;
> >  }
> >  
> > +static ssize_t calc_iov_length(const struct iovec *iov, int iovcnt)
> > +{
> > +    size_t offset = 0;
> > +    int i;
> > +
> > +    for (i = 0; i < iovcnt; i++)
> > +	offset += iov[i].iov_len;
> > +
> > +    return offset;
> > +}
> > +
> >  ssize_t qemu_sendv_packet(VLANClientState *vc1, const struct iovec *iov,
> >  			  int iovcnt)
> >  {
> > @@ -407,13 +418,18 @@ ssize_t qemu_sendv_packet(VLANClientState *vc1, const struct iovec *iov,
> >      VLANClientState *vc;
> >      ssize_t max_len = 0;
> >  
> > +    if (vc1->link_down)
> > +	return calc_iov_length(iov, iovcnt);
> > +
> >      for (vc = vlan->first_client; vc != NULL; vc = vc->next) {
> >  	ssize_t len = 0;
> >  
> >  	if (vc == vc1)
> >  	    continue;
> >  
> > -	if (vc->fd_readv)
> > +	if (vc->link_down)
> > +	    len = calc_iov_length(iov, iovcnt);
> >   
> 
> Instead of returning a success and silently dropping the packet, maybe 
> it would be better to return an error and let the card deal with 
> dropping the packet.
> 
> In real hardware, the link down would mean the TX queue would fill up 
> because packets aren't able to be sent.

I failed to figure out for real what typical hardware would do, e.g. by
reading the e1000 spec, but I figure the current behaviour is good
enough for now?

Re-based patches follow.

Cheers,
Mark.