Original address: http://bbs.chinaunix.net/thread-1940094-1-1.html
Most Linux kernel-state programs need to exchange data with user-space processes, but Linux kernel states cannot provide enough support for traditional methods of synchronizing and communicating between Linux processes. This article summarizes the common IPC,
Getsockopt/setsockopt mmap netlink/socket proc/seq copy_from_user/copy_to_user file. After the introduction of the test code before the way, NetLink and proc because Jianggo and Duan brother have written better I posted a link ... Okay, no more nonsense, start.
I. getsockopt/setsockopt
Recently looked at Ebtables source code, found that with the kernel of IPC is the use of getsockopt, the implementation is in the kernel with the NF_REGISTER_SOCKOPT function to register a NF_SOCKOPT_OPS structure, such as said:
static struct Nf_sockopt_ops NSO = {
. PF = pf_inet,//protocol family
. Set_optmin = constant,//define minimum SET command word
. Set_optmax = constant +n,//define maximum SET command word
. Set = Do_nso_set,//define Set handler function
. Get_optmin = constant,//define minimum GET command word
. Get_optmax = constant +n,//define MAX GET command word
. get = Do_nso_get,//define Set handler function
}; Copy Code
Where the command word cannot be duplicated with the system's existing command word. The Set/get handler function is called directly by the set/getsockopt function of the user space.
From this diagram can be seen, the essence of this method is the call is the Copy_from_user ()/copy_to_user () method to complete the kernel and user communication, which is not efficient, more use in the Transfer Control option information, not suitable for a large number of data transmission. Copy_from_user ()/copy_to_user () I'll explain in the following ... Of course for Linux anything is a file then I think should also be able to define their own ioctl, this in the back of the
Copy_xx_user in the block device
Setsockopt/getsockopt kernel part of the code:
static int recv_msg (struct sock *sk, int cmd, void *user, unsigned int len)
{
int ret = 0;
PRINTK (Kern_info "sockopt:recv_msg () \ n");
/*
Switch (CMD)
{
Case Imp1_set:
{
Char umsg[64];
memset (umsg, 0, sizeof (char) *64);
Copy_from_user (umsg, user, sizeof (char) *64);
PRINTK ("Umsg:%s", umsg);
}
Break
}
*/
if (cmd = = socket_ops_set)
{
Char umsg[64];
int len = sizeof (char) *64;
memset (umsg, 0, Len);
ret = Copy_from_user (umsg, user, Len);
PRINTK ("recv_msg:umsg =%s. ret =%d\n", umsg, ret);
}
return 0;
}
static int send_msg (struct sock *sk, int cmd, void *user, int *len)
{
int ret = 0;
PRINTK (Kern_info "sockopt:send_msg () \ n");
if (cmd = = socket_ops_get)
{
ret = copy_to_user (user, kmsg, kmsg_len);
PRINTK ("send_msg:umsg =%s. Ret =%d. success\n", kmsg, ret);
}
return 0;
}
static struct Nf_sockopt_ops Test_sockops =
{
. PF = Pf_inet,
. set_optmin = Socket_ops_set,
. Set_optmax = Socket_ops_max,
. set = Recv_msg,
. get_optmin = Socket_ops_get,
. Get_optmax = Socket_ops_max,
. get = Send_msg,
};
Copy Code
Setsockopt/getsockopt User Part code:
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