netdev - Unable to create more than 1 guest virtio-net device using vhost-net backend

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Message-Id: <1269037167.5127.12.camel@w-sridhar.beaverton.ibm.com>
Date:	Fri, 19 Mar 2010 15:19:27 -0700
From:	Sridhar Samudrala <samudrala.sridhar@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	netdev <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Unable to create more than 1 guest virtio-net device using
 vhost-net backend

When creating a guest with 2 virtio-net interfaces, i am running
into a issue causing the 2nd i/f falling back to userpace virtio
even when vhost is enabled.

After some debugging, it turned out that KVM_IOEVENTFD ioctl() 
call in qemu is failing with ENOSPC.
This is because of the NR_IOBUS_DEVS(6) limit in kvm_io_bus_register_dev()
routine in the host kernel.

I think we need to increase this limit if we want to support multiple
network interfaces using vhost-net.
Is there an alternate solution?

Thanks
Sridhar

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