[C] How to use mmap


$#include <stdio.h>$
$#include <fcntl.h>$
$#include <sys/types.h>$
$#include <sys/stat.h>$
$#include <unistd.h>$
$#include <sys/io.h>$
$#include <sys/mman.h>$
int main(int argc, char const *argv[])
{
unsigned char *f;
int size;
struct stat s;
const char * file_name = argv[1];
int fd = open (argv[1], O_RDONLY);

/* Get the size of the file. */
int status = fstat (fd, & s);
size = s.st_size;

f = (char *) mmap (0, size, PROT_READ, MAP_PRIVATE, fd, 0);
for (int i = 0; i < size; i++) {
    char c;

    c = f[i];
    putchar(c);
}

return 0;

}

Reference:
- Reading a file to string with mmap

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[OpenWRT] Useful link

• asuswrt-merlin/release/src/router/httpd/
• trunk/package/nvram/src
• trunk/target/linux/brcm-2.4/files/arch/mips/bcm947xx/nvram_linux.c

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[Pipe] Example - Creating a Pipe

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

/* Read characters from the pipe and echo them to stdout. */

void
read_from_pipe (int file)
{
  FILE *stream;
  int c;
  stream = fdopen (file, "r");
  while ((c = fgetc (stream)) != EOF)
    putchar (c);
  fclose (stream);
}

/* Write some random text to the pipe. */

void
write_to_pipe (int file)
{
  FILE *stream;
  stream = fdopen (file, "w");
  fprintf (stream, "hello, world!\n");
  fprintf (stream, "goodbye, world!\n");
  fclose (stream);
}

int
main (void)
{
  pid_t pid;
  int mypipe[2];

  /* Create the pipe. */
  if (pipe (mypipe))
    {
      fprintf (stderr, "Pipe failed.\n");
      return EXIT_FAILURE;
    }

  /* Create the child process. */
  pid = fork ();
  if (pid == (pid_t) 0)
    {
    printf("child  \n");
      /* This is the child process.
         Close other end first. */
      close (mypipe[1]);
      read_from_pipe (mypipe[0]);
      return EXIT_SUCCESS;
    }
  else if (pid < (pid_t) 0)
    {
      /* The fork failed. */
      fprintf (stderr, "Fork failed.\n");
      return EXIT_FAILURE;
    }
  else
    {
    printf("parent  \n");
      /* This is the parent process.
         Close other end first. */
      close (mypipe[0]);
      write_to_pipe (mypipe[1]);
      return EXIT_SUCCESS;
    }
}

Execute Code :

./a.out 
parent  
child  
hello, world!
goodbye, world!

Reference:

• Creating a Pipe

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[C] Extract tokens from strings

Code :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define __SEC_POPEN_TOKEN " "

int main(void)
{
    char *ptr;
    char *strtokState;
    char cmdcpy[30] = "Happy Birthday";

    printf("%s \n",(ptr = strtok_r(cmdcpy, __SEC_POPEN_TOKEN, &strtokState)));
}

Execute code :

./a.out 
Happy 

Reference:

• strtok_r(3) - Linux man page
• [C] Extract tokens from strings

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[C] Extract tokens from strings

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int
main(int argc, char *argv[])
{
    char *str1, *str2, *token, *subtoken;
    char *saveptr1 = NULL, *saveptr2 = NULL;
    int j;

   if (argc != 4) {
        fprintf(stderr, "Usage: %s string delim subdelim\n",
                argv[0]);
        exit(EXIT_FAILURE);
    }   

   for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
        printf("saveptr1 = %s \n",saveptr1);
        token = strtok_r(str1, argv[2], &saveptr1);
        printf("str1 = %s, argv[2] = %s, saveptr1 = %s \n",str1, argv[2], saveptr1);
        printf("token = %s \n",token);
        if (token == NULL)
            break;
        printf("%d: %s\n", j, token);

       for (str2 = token; ; str2 = NULL) {
            subtoken = strtok_r(str2, argv[3], &saveptr2);
            if (subtoken == NULL)
                break;
            printf(" --> %s\n", subtoken);
        }
    }   

   exit(EXIT_SUCCESS);
}

Execute code :

./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
saveptr1 = (null) 
str1 = a/bbb///cc, argv[2] = :;, saveptr1 = xxx:yyy: 
token = a/bbb///cc 
1: a/bbb///cc
 --> a
 --> bbb
 --> cc
saveptr1 = xxx:yyy: 
str1 = (null), argv[2] = :;, saveptr1 = yyy: 
token = xxx 
2: xxx
 --> xxx
saveptr1 = yyy: 
str1 = (null), argv[2] = :;, saveptr1 =  
token = yyy 
3: yyy
 --> yyy
saveptr1 =  
str1 = (null), argv[2] = :;, saveptr1 =  
token = (null) 

Reference:
strtok_r(3) - Linux man page

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[Compare Number] How to compare number quickly

/*
把數值放到 陣列當中，並且數值改成為 16進制
*/
    unsigned char ip[4] = {0xA0, 0xA8, 0x64, 0x01};

/*
用 For-loop 來比較
*/
    for (i = 0; i < 4; i++)
    {
        if (a(i) != ip[i])
        {
            return true;
        }
    }

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[Ipband][C] Create menu, read config, read option

Download IP Bandwidth Watchdog

According this code can learn of skill as title say.
1. Read init.c
This file can learn how to create parameter and read configuration file.

Reference:
IP Bandwidth Watchdog

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[Kernel Module] My first Kernel Module

Kernel Code 1

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
static ssize_t drv_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
{
    printk("device read\n");
    return count;
}

static ssize_t drv_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
{
    printk("device write \n");
    return count;
}

static int drv_open(struct inode *inode, struct file *filp)
{
    printk("device open \n");
    return 0;
}


int drv_ioctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
    printk("device ioctl \n");
    return 0;
}

static int drv_release(struct inode *inode, struct file *filp)
{
    printk("device close \n");
    return 0;
}

struct file_operations drv_fops = 
{
    read:               drv_read,       
    write:              drv_write,      
    compat_ioctl:       drv_ioctl,      
    open:               drv_open,       
    release:            drv_release,
};

#define MAJOR_NUM 60
#define MODULE_NAME "DEMO"
static int demo_init(void) {
 if (register_chrdev(MAJOR_NUM, "demo", &drv_fops) < 0) {
        printk("<1>%s: can't get major %d\n", MODULE_NAME, MAJOR_NUM);
            return (-EBUSY);
    }

    printk("<1>%s:started\n", MODULE_NAME);
    return 0;
}

static void demo_exit(void) {
        unregister_chrdev(MAJOR_NUM, "demo");
        printk("<1>%s: removed\n", MODULE_NAME);
}

module_init(demo_init);
module_exit(demo_exit);

Compile Kernel Module

make -C /lib/modules/3.8.0-33-generic/build M=`pwd` test.ko

User Space Code

#include <stdio.h>
int main()
{
char buf[512];
FILE *fp = fopen("/dev/demo", "w+");
if(fp == NULL) {
    printf("can't open device!\n");
    return 0;
}
fread(buf, sizeof(buf), 1, fp);
fwrite(buf, sizeof(buf), 1, fp);
fclose(fp);
return 0;
}

Compile User Space Code

gcc test.c

Execute Code

sudo ./a.out

Result

tail -n 10 /var/log/kern.log
Jul  3 12:14:36 happy-Desktop kernel: [12404.120783] device close 
Jul  3 12:14:37 happy-Desktop kernel: [12405.044410] device open 
Jul  3 12:14:37 happy-Desktop kernel: [12405.044447] device read
Jul  3 12:14:37 happy-Desktop kernel: [12405.044477] device close 
Jul  3 12:14:38 happy-Desktop kernel: [12406.056777] device open 
Jul  3 12:14:38 happy-Desktop kernel: [12406.056814] device read
Jul  3 12:14:38 happy-Desktop kernel: [12406.056839] device close 
Jul  3 12:15:10 happy-Desktop kernel: [12438.189191] device open 
Jul  3 12:15:10 happy-Desktop kernel: [12438.189233] device read
Jul  3 12:15:10 happy-Desktop kernel: [12438.189262] device close 

---

1. 第一次寫Linux Driver就上手 - RSWiki ↩

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[Kernel Module] Make own kernel module

Code 1

#include <linux/init.h> 
#include <linux/module.h> 
MODULE_LICENSE("Dual BSD/GPL"); static char *book_name = "dissecting Linux Device Driver"; static int num = 4000; static int param[8] = {1, 2, 3, 4, 5, 6, 7, 8}; static int param_len = 8; static int book_init(void) { 
    int i; 
    printk(KERN_ALERT " book name: %s\n", book_name); 
    printk(KERN_ALERT " book num: %d\n", num); 
    for(i = 0; i < 8; i++)  
    { 
        printk(KERN_ALERT "param[%d] = %d \n", i, param[i]); 
    } 
    return 0; } 
static void book_exit(void) { 
    printk(KERN_ALERT " Book module exit\n"); } 

module_init(book_init); 
module_exit(book_exit); 
module_param(num, int, S_IRUGO); 
module_param(book_name, charp, S_IRUGO); 
module_param_array(param, int, &param_len, S_IRUGO); 


MODULE_AUTHOR("Jimmy, fightingjimmy@gmail.com"); 
MODULE_DESCRIPTION("A simple Module for testing module params"); 
MODULE_VERSION("v1.0");

Compile

make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
                         |
                         V
make -C /lib/modules/3.8.0-33-generic/build M=`pwd` test.ko

insmod

sudo insmod test.ko book_name='GoodBook' num=5000

Result

Jul  3 07:48:16 happy-Desktop kernel: [10874.385886]  book num: 5000
Jul  3 07:48:16 happy-Desktop kernel: [10874.385891] param[0] = 1 Jul  3 07:48:16 happy-Desktop kernel: [10874.385897] param[1] = 2 Jul  3 07:48:16 happy-Desktop kernel: [10874.385901] param[2] = 3 Jul  3 07:48:16 happy-Desktop kernel: [10874.385933] param[3] = 4 Jul  3 07:48:16 happy-Desktop kernel: [10874.385938] param[4] = 5 Jul  3 07:48:16 happy-Desktop kernel: [10874.385943] param[5] = 6 Jul  3 07:48:16 happy-Desktop kernel: [10874.385947] param[6] = 7 Jul  3 07:48:16 happy-Desktop kernel: [10874.385951] param[7] = 8 

Reference

1. l​i​n​u​x​ ​模​块​层​叠​技​术​和​多​个​k​o​的​编​译 ↩

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[Linux Program] Linux System program by example - fork and dup

/* ch09-pipeline.c --- fork two processes into their own pipeline. 
   Minimal error checking for brevity. */  

#include <stdio.h>  
#include <errno.h>  
#include <sys/types.h>  
#include <sys/wait.h>  
#include <unistd.h>  

int pipefd[2];  

extern void left_child(void), right_child(void);  

/* main --- fork children, wait for them to finish */  

int main(int argc, char **argv)  
{  
    pid_t left_pid, right_pid;  
    pid_t ret;  
    int status;  

    if (pipe(pipefd) < 0) {      /* create pipe, very first thing */  
        perror("pipe");  
        exit(1);  
    }  

    if ((left_pid = fork()) < 0) {   /* fork left-hand child */  
        perror("fork");  
        exit(1);  
    } else if (left_pid == 0)  
        left_child();  

    if ((right_pid = fork()) < 0) {  /* fork right-hand child */  
        perror("fork");  
        exit(1);  
    } else if (right_pid == 0)  
        right_child();  

    close(pipefd[0]);       /* close parent's read copy of pipe */  
    close(pipefd[1]);       /* close parent's write copy of pipe */

    while ((ret = wait(& status)) > 0) { /* wait for children */  
        if (ret == left_pid)  /* If left_pid match then ...*/
            printf("left child terminated, status: %x\n", status);  
        else if (ret == right_pid) /* If right_pid match then ...*/  
            printf("right child terminated, status: %x\n", status);  
        else  
            printf("yow! unknown child %d terminated, status %x\n",  
              ret, status);  
    }  

    return 0;  
}  

/* 0 (read)  ---Pipe--> 1 (write) */


/* left_child --- do the work for the left child */  

void left_child(void)  
{  
/* fork - have parent source, so need to close some parameter */
    static char *left_argv[]  = { "echo", "hi", "there", NULL };  

    close(pipefd[0]);  /* Left_child don't need to read */
    close(1);  /* Close standard output */
    dup(pipefd[1]);  /* Copy left_child write to parent's write */
    close(pipefd[1]);  /* Copy parent's write*/ 

    execvp("echo", left_argv);  
    _exit(errno == ENOENT ? 127 : 126);  
}  

/* right_child --- do the work for the right child */  

void right_child(void)  
{  
/* fork - have parent source, so need to close some parameter */    
    static char *right_argv[] = { "sed", "s/hi/hello/g", NULL };  

    close(pipefd[1]);  /* right_child don't need to write */
    close(0);  /* Close standard input */
    dup(pipefd[0]);  
    close(pipefd[0]);  

    execvp("sed", right_argv);  
    _exit(errno == ENOENT ? 127 : 126);  
}  

Reference
1. Linux System programming by example (Example download)

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[Linux Program] IPC (Interprocess Communication)

Process

• Related process - The relation like (parent - Child)


• unrelated process - Don’t have any relation like (parent - Child)

Method

• shared memory


• pipes,FIFOs


• sockets


• mapped memory

Pipes

[Related process]

Use (file descriptor) to do IPC

FIFOs (Named Pipe)

[unrelated process]

Use (shared file) to do IPC

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[Linux coding][make menuconfig] How to use ext4 filesystem in Embedded system

[Linux coding][make menuconfig] How to use ext4 filesystem in Embedded system

Open ext4 filesystem support

Kernel Configuration  --->

File systems  --->

<*> The Extended 4 (ext4) filesystem

[*]   Use ext4 for ext2/ext3 file systems

[*]   Ext4 extended attributes

[ ]     Ext4 POSIX Access Control Lists

[ ]     Ext4 Security Labels

[ ]   EXT4 debugging support



Q: EXT4-fs (sda): Filesystem with huge files cannot be mounted RDWR without CONFIG_LBDAF

A:

Search LBDAF



Kernel Configuration  --->

[*] Enable the block layer  --->

Support for large (2TB+) block devices and files



Reference :

• 
  内核编译后 重启错误 请教了 谢谢

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[GCC library compare] GCC static and share

[GCC library compare] GCC static and share

hello.h

void hello(); 

hello.c

#include <stdio.h>

void hello(){

    printf("hello world\n");

}

main.c

#include <stdio.h>

#include "hello.h"



int main(){

    printf("call hello()");

    hello();

}

 

##############################

Share library

gcc -fPIC -shared hello.c -o libhello.so

gcc main.c -L. -lhello -o main



Q:

./main

./main: error while loading shared libraries: libhello.so: cannot open shared object file: No such file or directory



A:

sudo cp libhello.so /usr/lib/

./main

call hello()hello world



##############################

Static library

gcc -c hello.c -o hello.o



ar -r libhello.a hello.o   # put *.o to *.a. This command like tar.



gcc main.c -lhello -L. -static -o main

./main

call hello()hello world



Reference :

• 
  Linux GCC编译使用动态、静态链接库

 

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[Linux][Program] Linux Program List

[Linux][Program] Linux Program List

Download Advanced Linux Programming

linux programming

 

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