now , I see . thank you , Jeff
Subject: RE: struct sock->inet_sock convert question Date: Thu, 2 Feb 2012 10:36:03 -0800 From: [email protected] To: [email protected]; [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of hu jun Sent: Thursday, February 02, 2012 4:44 AM To: [email protected] Subject: struct sock->inet_sock convert question 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! I am not sure I understand your question, but inet_sk() is just a type cast: static inline struct inet_sock *inet_sk(const struct sock *sk){ return (struct inet_sock *)sk;} Which is valid since the first member of struct inet_sock is a struct sock: struct inet_sock { /* sk and pinet6 has to be the first two members of inet_sock */ struct sock sk; ... I haven't dived into the bowels of sk_alloc(), but I assume it allocates a big enough memory block so that after the type cast, the resultant pointer points to memory big enough to store an struct inet_sock or any other *_sock structures that get cast to struct sock. Jeff Haran _______________________________________________ Kernelnewbies mailing list [email protected] http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
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