#include "linux/module.h"

#include "linux/kernel.h"

#include "linux/fs.h"

#include "linux/init.h"

#include "linux/delay.h"

#include "asm/uaccess.h"

#include "asm/irq.h""

#include "asm/io.h"

#include "asm/arch/regs-gpio.h"

#include ""asm/hardware.h"

#include "linux/proc_fs.h"

#define MYLOG_BUF_LEN 1024

struct proc_dir_entry *myentry;

static char mylog_buf[MYLOG_BUF_LEN];

static char tmp_buf[MYLOG_BUF_LEN];

static int mylog_r = 0;

static int mylog_r_for_read = 0;

static int mylog_w = 0;

static DECLARE_WAIT_QUEUE_HEAD(mymsg_waitq);

static int is_mylog_empty(void)

{

return (mylog_r == mylog_w);

}

static int is_mylog_empty_for_read(void)

{

return (mylog_r_for_read == mylog_w);

}

static int is_mylog_full(void)

{

return ((mylog_w + 1)% MYLOG_BUF_LEN == mylog_r);

}

static void mylog_putc(char c)

{

if (is_mylog_full())

{

// 丟棄一個數(shù)據(jù) //

mylog_r = (mylog_r + 1) % MYLOG_BUF_LEN;

if ((mylog_r_for_read + 1) % MYLOG_BUF_LEN == mylog_r)

{

mylog_r_for_read = mylog_r;

}

}

mylog_buf[mylog_w] = c;

mylog_w = (mylog_w + 1) % MYLOG_BUF_LEN;

// 喚醒等待數(shù)據(jù)的進程 //

wake_up_interruptible(&mymsg_waitq); // 喚醒休眠的進程 //

}

static int mylog_getc(char *p)

{

if (is_mylog_empty())

{

return 0;

}

*p = mylog_buf[mylog_r];

mylog_r = (mylog_r + 1) % MYLOG_BUF_LEN;

return 1;

}

static int mylog_getc_for_read(char *p)

{

if (is_mylog_empty_for_read())

{

return 0;

}

*p = mylog_buf[mylog_r_for_read];

mylog_r_for_read = (mylog_r_for_read + 1) % MYLOG_BUF_LEN;

return 1;

}

int myprintk(const char *fmt, ...)

{

va_list args;

int i;

int j;

va_start(args, fmt);

i = vsnprintf(tmp_buf, INT_MAX, fmt, args);

va_end(args);

for (j = 0; j < i; j++)

mylog_putc(tmp_buf[j]);

return i;

}

static ssize_t mymsg_read(struct file *file, char __user *buf,

size_t count, loff_t *ppos)

{

int error = 0;

int i = 0;

char c;

// 把mylog_buf的數(shù)據(jù)copy_to_user, return //

if ((file->f_flags & O_NONBLOCK) && is_mylog_empty_for_read())

return -EAGAIN;

//printk("%s %dn", __FUNCTION__, __LINE__);

//printk("count = %dn", count);

//printk("mylog_r = %dn", mylog_r);

//printk("mylog_w = %dn", mylog_w);

error = wait_event_interruptible(mymsg_waitq, !is_mylog_empty_for_read());

//printk("%s %dn", __FUNCTION__, __LINE__);

//printk("count = %dn", count);

//printk("mylog_r = %dn", mylog_r);

//printk("mylog_w = %dn", mylog_w);

while (!error && (mylog_getc_for_read(&c)) && i < count) {

error = __put_user(c, buf);

buf++;

i++;

}

if (!error)

error = i;

return error;

}

static int mymsg_open(struct inode *inode, struct file *file)

{

mylog_r_for_read = mylog_r;

return 0;

}

const struct file_operations proc_mymsg_operations = {

.open = mymsg_open,

.read = mymsg_read,

};

static int mymsg_init(void)

{

myentry = create_proc_entry("mymsg", S_IRUSR, &proc_root);

if (myentry)

myentry->proc_fops = &proc_mymsg_operations;

return 0;

}

static void mymsg_exit(void)

{

remove_proc_entry("mymsg", &proc_root);

}

module_init(mymsg_init);

module_exit(mymsg_exit);

EXPORT_SYMBOL(myprintk);

MODULE_LICENSE("GPL");

===============================================================

解析：

當其他驅動程序調用自定義的myprintk函數(shù)打印數(shù)據(jù)時不會立即把數(shù)據(jù)打印在前臺顯示，而是把數(shù)據(jù)放在mylog_buf環(huán)形緩沖區(qū)中保存，當應用程序查看proc/mymsg時，即執(zhí)行：cat /proc/mymsg時會調用mymsg_read函數(shù)讀取環(huán)型緩沖區(qū)，如果緩沖區(qū)中有數(shù)據(jù)會調用__put_user返回，如果沒有數(shù)據(jù)系統(tǒng)會休眠。