tcp_sendmsg working

hello,
how tcp_sendmsg add message from application layer to socket buffer skb?

i am unable to find message field in msghdr help me. struct msghdr {
void * msg_name; /* Socket name

*/
int msg_namelen; /* Length of
name
*/
struct iovec * msg_iov; /* Data blocks

*/
__kernel_size_t msg_iovlen; /* Number of
blocks
*/
void * msg_control; /* Per
protocol magic (eg BSD
file descriptor passing) */
__kernel_size_t msg_controllen; /* Length of
cmsg list */

        unsigned        msg_flags;
};

also what is use of struct iovec? is that store actual data? if yes then how that is included in socket buffer?

regards,
linux_lover

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