FYI: struct sock class hierarchy

Dave,

Further info on that struct sock hierarchy stuff I'm mentioned
that I planned doing while at the netsummit, with the changes I have in one of my pending trees, things are now looking like this:

struct inet_sock {
        struct sock        sk;
        struct stream_sock *pssk;
#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
        struct ipv6_pinfo  *pinet6;
#endif
        struct inet_opt    inet;
};

I.e. inet sock is an specialization of struct sock (the pointer to any instance of both structs point to the same memory address).

Now tcp:

struct tcp_sock {
        struct inet_sock        inet;
        struct tcp_opt          tcp;
        struct stream_sock      ssk;
};

Now it is tcp_sock that is an specialization of struct inet_sock, that is, in turn, as said above, an specialization of struct sock (the pointer to any instance of the three structs points to the same memory address)

And finally struct tcp6_sock:

struct tcp6_sock {
        struct tcp_sock    tcp;
        struct ipv6_pinfo  inet6;
};

I guess you got the idea:

tcp6_sock <- tcp_sock <- inet_sock <- sock

This was done for struct udp_sock, raw6_sock, sctp_sock, etc

Using this approach we see clearly how the layouts are organized and the relations among the, ho-hum, classes, i.e. the class hierarchy.

For further eye candy please take a look at:

http://master.kernel.org/~acme/sock_class_hierarchy.ps

That has the complete struct sock class hierarchy subtree for inet protocols, including SCTP, DCCP, raw, raw6, tcp_tw_bucket, etc.

Apart from the introduction of struct stream_sock it is completely equivalent to the current state of things in Linus tree, but much clearer, IMHO, by not having all those cut'n'pasted layouts, complete with the #ifdef IPV6 optimization for when IPv6 is not compiled.

BTW, this #ifdef IPV6 is wrong, as it leads to a kernel where IPV6 can't be later compiled and loaded, but this remains a futile exercise while the other #ifdef IPV6 is scattered in the common IPV6/IPV4 code:

[acme@oldpandora stream_sock-2.6]$ grep -l IPV6 net/ipv4/*.c | wc -l 6

But this is something we'll possibly address in the future... :-)

- Arnaldo

Arnaldo,

The name struct stream_sock seems to indicate that this structure is needed only for SOCK_STREAM sockets. But in reality this structure is required for any connected sockets(ex: SOCK_SEQPACKET).
I cannot think of good name for this structure, but struct conn_sock to indicate any connected socket seems to be the best i can come up with.

Also If i understand the hierarchy correctly, stream_sock is a specialization of struct inet_sock. So can we include stream_sock also in the hierarchy as follows although i would prefer renaming stream_sock to conn_sock.

struct stream_sock {
	struct inet_sock	inet;
	struct stream_opt	sopt;
}

struct tcp_sock {
	struct stream_sock ssk;
	struct tcp_opt	 tcp;
}

Thanks
Sridhar