Re: [Qemu-devel] [PATCH 5/10] Add network announce function

[Chris Lalancette]

Anthony Liguori wrote:
> +static int announce_self_create(uint8_t *buf, 
> +                             uint8_t *mac_addr)
> +{
> +    uint32_t magic = EXPERIMENTAL_MAGIC;
> +    uint16_t proto = htons(ETH_P_EXPERIMENTAL);
> +
> +    /* FIXME: should we send a different packet (arp/rarp/ping)? */
> +
> +    memset(buf, 0xff, 6);         /* h_dst */
> +    memcpy(buf + 6, mac_addr, 6); /* h_src */
> +    memcpy(buf + 12, &proto, 2);  /* h_proto */
> +    memcpy(buf + 14, &magic, 4);  /* magic */
> +
> +    return 18; /* len */
> +}
> +
> +void qemu_announce_self(void)
> +{
> +    int i, j, len;
> +    VLANState *vlan;
> +    VLANClientState *vc;
> +    uint8_t buf[256];
> +
> +    for (i = 0; i < nb_nics; i++) {
> +        len = announce_self_create(buf, nd_table[i].macaddr);
> +        vlan = nd_table[i].vlan;
> +        for(vc = vlan->first_client; vc != NULL; vc = vc->next) {
> +            if (vc->fd_read == tap_receive)  /* send only if tap */
> +                for (j=0; j < SELF_ANNOUNCE_ROUNDS; j++)
> +                    vc->fd_read(vc->opaque, buf, len);
> +        }
> +    }
> +}
> +

This one is yucky, as the FIXME points out.  First, I'm guessing the point of
this is to do an ARP poison on the switch?  If so, we probably want to do some
kind of ARP packet, although I'm not an expert on this.  Also, why are we trying
 SELF_ANNOUNCE_ROUNDS times?  Is there some issue where some of these get
dropped, or is it just being safe about it?

Chris Lalancette