Dr. VIjay Gokhale sir unix notes

UNIX Internals
https://drive.google.com/open?id=0B-kWNNOlNjLJbEowX3M1NTdxWjg

Kernel module

        

         ************Linux Kernel Module*************

what is kernel module?

kernel module is a piece of code which added when we are used upon kernel demand.

it is use for the extend the functionality of kernel.

***.#make  command is use for the compile the kernel module.***

1).#lsmod command is use for the display list of kernel module.

2).#insmod command is use for the load the kernel module.

3).printk() is used for print the message in your logfile.

4).#dmesg is used for display message which present in logfile

5).#rmmod command is use for the remove the kernel module.

our first Kernel module

*********************************************************************************

 hello.c - The simplest kernel module.

#include <linux/module.h> /* Needed by all modules */#include <linux/kernel.h> /* Needed for KERN_INFO */

int init_module(void)

{      printk(KERN_INFO "Hello world 1.\n");

/*

* A non 0 return means init_module failed;

* module can't be loaded

*/

return 0;

}

void cleanup_module(void)

{

printk(KERN_INFO "Goodbye world 1.\n");

}

module_init(init_module);

module_exit(cleanup_module);

Note:

Now create Makefile and keep our hello.c and Makefile in a folder and that folder keep on desktop.

just copy and paste below code in Makefile

obj-m += hello.o all: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

save file and run #make command for compile the kernel module

Socket Programming in C

                        Socket Programming in C

What is socket programming? 
Socket programming is a way of connecting two nodes on a network to communicate with each other. One socket(node) listens on a particular port at an IP, while other socket reaches out to the other to form a connection. Server forms the listener socket while client reaches out to the server.

// Server side C program to demonstrate Socket programming

#include <stdio.h>

#include <sys/socket.h>

#include <stdlib.h>

#include <netinet/in.h>

#include <string.h>

#define PORT 8080

int main(int argc, char const *argv[])

{

    int server_fd, new_socket, valread;

    struct sockaddr_in address;

    int opt = 1;

    int addrlen = sizeof(address);

    char buffer[1024] = {0};

    char *hello = "Hello from server";

      

    // Creating socket file descriptor

    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)

    {

        perror("socket failed");

        exit(EXIT_FAILURE);

    }

      

    // Forcefully attaching socket to the port 8080

    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,

                                                  &opt, sizeof(opt)))

    {

        perror("setsockopt");

        exit(EXIT_FAILURE);

    }

    address.sin_family = AF_INET;

    address.sin_addr.s_addr = INADDR_ANY;

    address.sin_port = htons( PORT );

      

    // Forcefully attaching socket to the port 8080

    if (bind(server_fd, (struct sockaddr *)&address,

                                 sizeof(address))<0)

    {

        perror("bind failed");

        exit(EXIT_FAILURE);

    }

    if (listen(server_fd, 3) < 0)

    {

        perror("listen");

        exit(EXIT_FAILURE);

    }

    if ((new_socket = accept(server_fd, (struct sockaddr *)&address,

                       (socklen_t*)&addrlen))<0)

    {

        perror("accept");

        exit(EXIT_FAILURE);

    }

    valread = read( new_socket , buffer, 1024);

    printf("%s\n",buffer );

    send(new_socket , hello , strlen(hello) , 0 );

    printf("Hello message sent\n");

    return 0;

}










// Client side C program to demonstrate Socket programming




#include <stdio.h>

#include <sys/socket.h>

#include <stdlib.h>

#include <netinet/in.h>

#include <string.h>

#define PORT 8080

  

int main(int argc, char const *argv[])

{

    struct sockaddr_in address;

    int sock = 0, valread;

    struct sockaddr_in serv_addr;

    char *hello = "Hello from client";

    char buffer[1024] = {0};

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)

    {

        printf("\n Socket creation error \n");

        return -1;

    }

  

    memset(&serv_addr, '0', sizeof(serv_addr));

  

    serv_addr.sin_family = AF_INET;

    serv_addr.sin_port = htons(PORT);

      

    // Convert IPv4 and IPv6 addresses from text to binary form

    if(inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr)<=0)

    {

        printf("\nInvalid address/ Address not supported \n");

        return -1;

    }

  

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)

    {

        printf("\nConnection Failed \n");

        return -1;

    }

    send(sock , hello , strlen(hello) , 0 );

    printf("Hello message sent\n");

    valread = read( sock , buffer, 1024);

    printf("%s\n",buffer );

    return 0;

}




output:

Client:Hello message sent
Hello from server
Server:Hello from client
Hello message sent 

compile both file together..