[Hurdextras-hackers] Device interface

[James A Morrison]

 Hi,

  I've thought of how I would like the upper levels talk to the
lower levels.  The obvious thing is that there needs to be at least
two functions, read and write.  I think that these functions should be
called though function pointers.  So, we would have

struct dev 
{
        error_t *(start) (dev_t this);
        error_t *(stop) (dev_t this);
        error_t *(read) (dev_t this, packet_t to_rcv);
        error_t *(write) (dev_t this, packet_t to_send);
}

struct packet
{
        size_t len;
        char *data;
}

If something tries to write a packet that is too big then write can
return E2BIG.

 I'll look into some arp stuff tommorrow, I think we might need a third
element into the packet struct that is char  *to.  I don't think it is
needed for most applications to need more than a read and a write to the
interface.  A third struct may be useful that contains the functionality
of an interface, e.g. changing the mac address of a card, setting a hard
mtu limit.

 Other things that can be added to struct dev are a get_stats function,
and set/get flags functions.

I'm getting this mostly out of reading ethernet.c in pfinet.

James A. Morrison