Linux Kernel Architecture

Chapter 12: Networks

<net.h>

int kernel_sendmsg(struct socket *sock, struct msghdr *msg,

struct kvec *vec, size_t num, size_t len);

int kernel_recvmsg(struct socket *sock, struct msghdr *msg,

struct kvec *vec, size_t num,

size_t len, int flags);

int kernel_bind(struct socket *sock, struct sockaddr *addr,

int addrlen);

int kernel_listen(struct socket *sock, int backlog);

int kernel_accept(struct socket *sock, struct socket **newsock,

int flags);

int kernel_connect(struct socket *sock, struct sockaddr *addr,

int addrlen, int flags);

int kernel_getsockname(struct socket *sock, struct sockaddr *addr,

int *addrlen);

int kernel_getpeername(struct socket *sock, struct sockaddr *addr,

int *addrlen);

int kernel_getsockopt(struct socket *sock, int level, int optname,

char *optval, int *optlen);

int kernel_setsockopt(struct socket *sock, int level, int optname,

char *optval, int optlen);

int kernel_sendpage(struct socket *sock, struct page *page, int offset,

size_t size, int flags);

int kernel_sock_ioctl(struct socket *sock, int cmd, unsigned long arg);

int kernel_sock_shutdown(struct socket *sock,

enum sock_shutdown_cmd how);

With the exception ofkernel_sendmsgandkernel_recvmsg, the parameters are more or less identical
with the userland API, except that sockets are not specified by socket file descriptors, but directly by a
pointer to an instance ofstruct socket. The implementation is simple since the functions work as simple
wrapper routines around the pointers stored in the protocol operationsproto_opsofstruct socket:

net/socket.c

int kernel_connect(struct socket *sock, struct sockaddr *addr, int addrlen,

int flags)

{

return sock->ops->connect(sock, addr, addrlen, flags);

}

A little care is required when the buffer space that takes received data or holds data that must be sent
is specified.kernel_sendmsgandkernel_recvmsgdo not access the data region directly viastruct
msghdras in userland, but employstruct kvec. However, the kernel automatically provides a conversion
between both representations askernel_sendmsgshows.

net/socket.c

int kernel_sendmsg(struct socket *sock, struct msghdr *msg,

struct kvec *vec, size_t num, size_t size)

{

...

int result;

...

msg->msg_iov = (struct iovec *)vec;

msg->msg_iovlen = num;