On Thu, Mar 31, 2016 at 7:39 PM, Stephen Hemminger
<step...@networkplumber.org> wrote:
> On Fri, 1 Apr 2016 00:28:57 +0200
> Guus Sliepen <g...@tinc-vpn.org> wrote:
>
>> On Thu, Mar 31, 2016 at 05:20:50PM -0400, David Miller wrote:
>>
>> > >> I'm trying to reduce system call overhead when reading/writing to/from a
>> > >> tun device in userspace. [...] What would be the right way to do this?
>> > >>
>> > > Personally I think tun could benefit greatly if it were implemented as
>> > > a socket instead of character interface. One thing that could be much
>> > > better is sending/receiving of meta data attached to skbuf. For
>> > > instance GSO data could be in ancillary data in a socket instead of
>> > > inline with packet data as tun seems to be doing now.
>> >
>> > Agreed.
>>
>> Ok. So how should the userspace API work? Creating an AF_PACKET socket
>> and then using a tun ioctl to create a tun interface and bind it to the
>> socket?
>>
>> int fd = socket(AF_PACKET, ...)
>> struct ifreq ifr = {...};
>> ioctl(fd, TUNSETIFF, &ifr);
>>
>
> Rather than bodge AF_PACKET onto TUN, why not just create a new device type
> and control it from something modern like netlink.Depending on the use-case, it may be sufficient to extend AF_PACKET with limited tap functionality: - add a po->xmit mode that reinjects into the kernel receive path, analogous to pktgen's M_NETIF_RECEIVE mode. - optionally drop packets in __netif_receive_skb_core and xmit_one if any of the registered packet sockets accepted the packet and has a new intercept feature flag enabled. This can be applied to a dummy device, but much more interesting is to interpose on the flow of a normal nic. It is clearly not a drop-in replacement for a tap (let alone tun) device. I have some preliminary code.
