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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From: Jeff Haran <hidden> Date: 2012-02-02 18:36:03
From: kernelnewbies-bounces@kernelnewbies.org
[mailto:kernelnewbies-bounces at kernelnewbies.org] On Behalf Of hu jun
Sent: Thursday, February 02, 2012 4:44 AM
To: kernelnewbies at kernelnewbies.org
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
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now , I see .
thank you , Jeff
Subject: RE: struct sock->inet_sock convert question
Date: Thu, 2 Feb 2012 10:36:03 -0800
From: jharan@bytemobile.com
To: duanshuidao at hotmail.com; kernelnewbies at kernelnewbies.org
From: kernelnewbies-bounces at kernelnewbies.org [mailto:kernelnewbies-bounces at kernelnewbies.org] On Behalf Of hu jun
Sent: Thursday, February 02, 2012 4:44 AM
To: kernelnewbies at kernelnewbies.org
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
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