How to know where does the sock->ops assigned in kernel? - linux

Question

In the code of kernel linux/net/socket.c
sock->ops->bind()
I can't find where the sock or sock->ops has been assigned in UDP program.
Thanks !

Answer 1

This is not done directly as you are expecting. If you look at the code carefully, you will find that the function sock_from_file(struct file *file, int *err) is used to assign file->f_op to socket_file_ops
It is called twice in the code
In the sockfd_lookup(int fd, int *err) function as sock = sock_from_file(file, err);
In the sockfd_lookup_light(int fd, int *err, int *fput_needed) function as sock = sock_from_file(f.file, err);
This file is then assigned to sock->file inside the sock_alloc_file(struct socket *sock, int flags, const char *dname) function.

Answer 2

The proto_ops structure is overridden in each socket implementation. If you search lxr for inet_bind you can see it.
https://elixir.bootlin.com/linux/latest/source/net/ipv4/af_inet.c#L435
int inet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
{
struct sock *sk = sock->sk;
u32 flags = BIND_WITH_LOCK;
int err;
/* If the socket has its own bind function then use it. (RAW) */
if (sk->sk_prot->bind) {
return sk->sk_prot->bind(sk, uaddr, addr_len);
}
if (addr_len < sizeof(struct sockaddr_in))
return -EINVAL;
/* BPF prog is run before any checks are done so that if the prog
* changes context in a wrong way it will be caught.
*/
err = BPF_CGROUP_RUN_PROG_INET_BIND_LOCK(sk, uaddr,
CGROUP_INET4_BIND, &flags);
if (err)
return err;
return __inet_bind(sk, uaddr, addr_len, flags);
}
EXPORT_SYMBOL(inet_bind);
That is then set in the proto_ops structure here -
https://elixir.bootlin.com/linux/latest/source/net/ipv4/af_inet.c#L1019
const struct proto_ops inet_stream_ops = {
.family = PF_INET,
.owner = THIS_MODULE,
.release = inet_release,
.bind = inet_bind,
// ...