Linux创建socket

static const struct net_proto_family inet_family_ops = {
.family = PF_INET,
.create = inet_create,
.owner = THIS_MODULE,
};

/*
 * Create an inet socket.
 */


static int inet_create(struct net *net, struct socket *sock, int protocol,
      int kern)
{
struct sock *sk;
struct inet_protosw *answer;
struct inet_sock *inet;
struct proto *answer_prot;
unsigned char answer_flags;
int try_loading_module = 0;
int err;


if (protocol < 0 || protocol >= IPPROTO_MAX)
return -EINVAL;


sock->state = SS_UNCONNECTED;


/* Look for the requested type/protocol pair. */
lookup_protocol:
err = -ESOCKTNOSUPPORT;
rcu_read_lock();
list_for_each_entry_rcu(answer, &inetsw[sock->type], list) {


err = 0;
/* Check the non-wild match. */
if (protocol == answer->protocol) {
if (protocol != IPPROTO_IP)
break;
} else {
/* Check for the two wild cases. */
if (IPPROTO_IP == protocol) {
protocol = answer->protocol;
break;
}
if (IPPROTO_IP == answer->protocol)
break;
}
err = -EPROTONOSUPPORT;
}


if (unlikely(err)) {
if (try_loading_module < 2) {
rcu_read_unlock();
/*
* Be more specific, e.g. net-pf-2-proto-132-type-1
* (net-pf-PF_INET-proto-IPPROTO_SCTP-type-SOCK_STREAM)
*/
if (++try_loading_module == 1)
request_module("net-pf-%d-proto-%d-type-%d",
      PF_INET, protocol, sock->type);
/*
* Fall back to generic, e.g. net-pf-2-proto-132
* (net-pf-PF_INET-proto-IPPROTO_SCTP)
*/
else
request_module("net-pf-%d-proto-%d",
      PF_INET, protocol);
goto lookup_protocol;
} else
goto out_rcu_unlock;
}


err = -EPERM;
if (sock->type == SOCK_RAW && !kern &&
   !ns_capable(net->user_ns, CAP_NET_RAW))
goto out_rcu_unlock;


sock->ops = answer->ops;
answer_prot = answer->prot;
answer_flags = answer->flags;
rcu_read_unlock();


WARN_ON(!answer_prot->slab);


err = -ENOBUFS;
sk = sk_alloc(net, PF_INET, GFP_KERNEL, answer_prot, kern);
if (!sk)
goto out;


err = 0;
if (INET_PROTOSW_REUSE & answer_flags)
sk->sk_reuse = SK_CAN_REUSE;


inet = inet_sk(sk);
inet->is_icsk = (INET_PROTOSW_ICSK & answer_flags) != 0;


inet->nodefrag = 0;


if (SOCK_RAW == sock->type) {
inet->inet_num = protocol;
if (IPPROTO_RAW == protocol)
inet->hdrincl = 1;
}


if (net->ipv4.sysctl_ip_no_pmtu_disc)
inet->pmtudisc = IP_PMTUDISC_DONT;
else
inet->pmtudisc = IP_PMTUDISC_WANT;


inet->inet_id = 0;


sock_init_data(sock, sk);


sk->sk_destruct  = inet_sock_destruct;
sk->sk_protocol  = protocol;
sk->sk_backlog_rcv = sk->sk_prot->backlog_rcv;


inet->uc_ttl = -1;
inet->mc_loop = 1;
inet->mc_ttl = 1;
inet->mc_all = 1;
inet->mc_index= 0;
inet->mc_list = NULL;
inet->rcv_tos = 0;


sk_refcnt_debug_inc(sk);


if (inet->inet_num) {
/* It assumes that any protocol which allows
* the user to assign a number at socket
* creation time automatically
* shares.
*/
inet->inet_sport = htons(inet->inet_num);
/* Add to protocol hash chains. */
err = sk->sk_prot->hash(sk);
if (err) {
sk_common_release(sk);
goto out;
}
}


if (sk->sk_prot->init) {
err = sk->sk_prot->init(sk);
if (err)
sk_common_release(sk);
}
out:
return err;
out_rcu_unlock:
rcu_read_unlock();
goto out;
}

/* Upon startup we insert all the elements in inetsw_array[] into
 * the linked list inetsw.
 */
static struct inet_protosw inetsw_array[] =
{
{
.type =       SOCK_STREAM,
.protocol =   IPPROTO_TCP,
.prot =       &tcp_prot,
.ops =        &inet_stream_ops,
.flags =      INET_PROTOSW_PERMANENT |
     INET_PROTOSW_ICSK,
},


{
.type =       SOCK_DGRAM,
.protocol =   IPPROTO_UDP,
.prot =       &udp_prot,
.ops =        &inet_dgram_ops,
.flags =      INET_PROTOSW_PERMANENT,
       },


       {
.type =       SOCK_DGRAM,
.protocol =   IPPROTO_ICMP,
.prot =       &ping_prot,
.ops =        &inet_dgram_ops,
.flags =      INET_PROTOSW_REUSE,
       },


       {
      .type =       SOCK_RAW,
      .protocol =   IPPROTO_IP,/* wild card */
      .prot =       &raw_prot,
      .ops =        &inet_sockraw_ops,
      .flags =      INET_PROTOSW_REUSE,
       }
};