[Click] Re: driver hacking and packet annotations

[Eddie Kohler]

Hi John,

> Hi Everyone,
> I've been doing a lot of hacking on some of the wireless drivers so
> that we can do some cool things in click that used to require cumbersome
> hacks.
> 
> For instance, when the prism2 driver receives a packet, it can mark
> a packet annotation with the signal and noise that the packet was
> recieved with, and then you process that information in click since
> the annotations are stored in sk_buff->cb.  
> 
> Here is the packet_anno.h file that I put in the linux-2.4.20/include/linux
> dir and I have been using.  It's basically stuff taken out of 
> click/include/click/packet.hh. 
> 
> I don't know that this is something that you want to include in the patches,
> but I wondered if you had any thoughts or feedback.
> 
> --john

I like this approach, but would suggest something different, more like the
rest of Linux. Why not define a structure, and cast the 'cb' to have that
structure type? Like in <linux/atmdev.h>:

struct atm_skb_data {
       struct atm_vcc	*vcc;		/* ATM VCC */
       int		iovcnt;		   /* 0 for "normal" operation */
       unsigned long	atm_options;	   /* ATM layer options */
};

#define ATM_SKB(skb) (((struct atm_skb_data *) (skb)->cb))


Or tcp_skb_cb in <net/tcp.h>, etc. For instance you could do:


struct wifi_skb_cb {
       unsigned char	padding[10];
       unsigned char	wifi_tx_success;
       unsigned char	wifi_tx_power;
       unsigned char	wifi_rate;
       unsigned char	wifi_retries;
       unsigned char	wifi_signal;
       unsigned char	wifi_noise;
};

#define WIFI_SKB_CB(__skb) ((struct wifi_skb_cb *)((__skb)->cb))


Anyway, if you decide to do it using packet_anno.h instead, you probably
want to declare the functions as "static inline".

Eddie