[libvirt] [PATCH] kvm/virtio: Set IFF_VNET_HDR when setting up tap fds

Daniel P. Berrange berrange at redhat.com
Wed Aug 13 15:01:04 UTC 2008


On Wed, Aug 13, 2008 at 03:53:27PM +0100, Mark McLoughlin wrote:
> By enabling this flag on the tap fds we create, we greatly increase
> the achievable throughput with virtio_net.
> 
> However, we need to be careful to only set the flag when a) KVM has
> support for this ABI and b) the value of the flag is queryable using
> the TUNGETIFF ioctl.

This suggests to me that QEMU should be a the one enabling this
flag, not libvirt. Its going to need todo this anyway for the
scenario where QEMU allocates the TAP fd, so it might as well
enable it for pre-allocated TAP fds passed in from external
apps.

Daniel
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