struct sock->inet_sock convert question

[hu jun <duanshuidao@xxxxxxxxxxx>]

in kernel linux-2.6.16.60-0.54.5  code:

static int inet_create(struct socket *sock, int protocol)

{

struct sock *sk;

struct inet_sock *inet;

....

sk = sk_alloc(PF_INET, GFP_KERNEL, answer_prot, 1);

if (sk == NULL)

goto out;

inet = inet_sk(sk);

inet->is_icsk = (INET_PROTOSW_ICSK & answer_flags) == INET_PROTOSW_ICSK;

if (SOCK_RAW == sock->type) {

inet->num = protocol;

if (IPPROTO_RAW == protocol)

inet->hdrincl = 1;

}

if (ipv4_config.no_pmtu_disc)

inet->pmtudisc = IP_PMTUDISC_DONT;

else

inet->pmtudisc = IP_PMTUDISC_WANT;

inet->id = 0;

....

}

my question is in the red line ,  why can convert  like that?

thanks!

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