Re: Q: (ab)using zerocopy for drivers with alignment contraints

["David S. Miller" <davem@xxxxxxxxxx>]

Manfred Spraul writes:
 > Several cheap busmaster nics only accept tx buffers that are 32-bit
 > aligned.

I'm going to assume that it is safe to bet that such cards cannot take
multiple buffers for a TX packet too.

Because if they could, then we could do something like copy the header
forward a few bytes to get it aligned, and set up two buffer pointers
into the packet such that the 32-bit alignment requirement is met.

There'd be some difficulty with SKB sharing...

BTW, a routine exists already doing what you propose, only to user
space.  Make skb_copy_datagram{,_iovec}_kernel(), export these
routines to modules, and I'd be more than happy to accept that patch.

Later,
David S. Miller
davem@xxxxxxxxxx