Re: [PATCH] kvm: qemu: increase the size of the tap buffer [was Re: TAP MTU >= 4055 problem?]

[Avi Kivity <avi@redhat.com>]

Mark McLoughlin wrote:
> It sucks that the kernel just silently truncates and doesn't give
> userspace a chance to retry with a larger buffer. We could add that as
> an extension, I guess.
>
>   

What we want even more is to give the kernel a set of buffers (iovec) 
and have it fill them as much as it can with a number of packets, giving 
us some info as to where frames begin.  Manage the whole thing using aio 
reads.

> As debugged by Matthew Faulkner, with a 4k byte tap buffer if you
> increase the MTU on the tap device to greater than 4k, the packets
> read by qemu into the tap buffer will be truncated and the guest
> will discard the packet.
>
> With GSO enabled, we use a 64k tap buffer, so let's just use a 64k
> buffer in all cases.
>
> Also, remove the obtuse logic for figuring out the max GSO buffer
> size. We shouldn't receive IP packets larger than 64k, so let's just
> use 17 pages to make sure we've enough room for headers.
>
>   

Applied, thanks.

-- 
error compiling committee.c: too many arguments to function