(LDD3实践)Chapter-3:字符驱动
SCULL的模型首先明确一下scull设备的模型：scull设备有qset个scull_qset结构，每个scull_qset结构维护着qset个quantum，每个quantum默认是4000，而qset默认是1000，所以一个qset的大小是4000*1000个char源代码分析：对源码的分析：http://blog.csdn.net/liuhaoyutz/article/
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SCULL的模型
首先明确一下scull设备的模型：scull设备有qset个scull_qset结构，每个scull_qset结构维护着qset个quantum，每个quantum默认是4000，而qset默认是1000，所以一个qset的大小是4000*1000个char
源代码分析：
对源码的分析：
http://blog.csdn.net/liuhaoyutz/article/details/7383313 这篇文章更为详细,不过我这里贴出来的是整个的源代码，可以直接运行的^ _ ^
scull.h :
#ifndef _SCULL_H_
#define _SCULL_H_
#ifndef SCULL_MAJOR
#define SCULL_MAJOR 0 /* dynamic major by default */
#endif
#ifndef SCULL_NR_DEVS
#define SCULL_NR_DEVS 4 /* scull0 through scull3 */
#endif
#ifndef SCULL_P_NR_DEVS
#define SCULL_P_NR_DEVS 4 /* scullpipe0 through scullpipe3 */
#endif
#ifndef SCULL_QUANTUM
#define SCULL_QUANTUM 4000
#endif
#ifndef SCULL_QSET
#define SCULL_QSET 1000
#endif
/*
* Representation of scull quantum sets.
*/
struct scull_qset {
void **data;
struct scull_qset *next;
};
struct scull_dev {
struct scull_qset *data; /* Pointer to first quantum set */
int quantum; /* the current quantum size */
int qset; /* the current array size */
unsigned long size; /* amount of data stored here */
unsigned int access_key; /* used by sculluid and scullpriv */
struct semaphore sem; /* mutual exclusion semaphore */
struct cdev cdev; /* Char device structure */
};
/*
* The different configurable parameters
*/
extern int scull_major; /* main.c */
extern int scull_nr_devs;
extern int scull_quantum;
extern int scull_qset;
int scull_trim(struct scull_dev *dev);
ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
loff_t *f_pos);
ssize_t scull_write(struct file *filp, const char __user *buf, size_t count,
loff_t *f_pos);
#endif /* _SCULL_H_ */scull.c :
/* forsakening @hdu 2013/6/16 for testing ldd3 */
//#include <linux/config.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/proc_fs.h>
#include <linux/fcntl.h> /* O_ACCMODE */
#include <linux/seq_file.h>
#include <linux/cdev.h>
#include <asm/system.h> /* cli(), *_flags */
#include <asm/uaccess.h> /* copy_*_user */
#include "scull.h" /* local definitions */
/*
* Our parameters which can be set at load time.
*/
int scull_major = SCULL_MAJOR;
int scull_minor = 0;
int scull_nr_devs = SCULL_NR_DEVS; /* number of bare scull devices */
int scull_quantum = SCULL_QUANTUM;
int scull_qset = SCULL_QSET;
/* insmod的输入参数 */
module_param(scull_major, int, S_IRUGO);
module_param(scull_minor, int, S_IRUGO);
module_param(scull_nr_devs, int, S_IRUGO);
module_param(scull_quantum, int, S_IRUGO);
module_param(scull_qset, int, S_IRUGO);
MODULE_AUTHOR("Alessandro Rubini, Jonathan Corbet");
MODULE_LICENSE("Dual BSD/GPL");
struct scull_dev *scull_devices; /* allocated in scull_init_module */
/*
* Empty out the scull device; must be called with the device
* semaphore held.
*/
/* 删除scull设备的qset内存，删除所谓的量子集群的内存 */
int scull_trim(struct scull_dev *dev)
{
struct scull_qset *next, *dptr;
int qset = dev->qset; /* "dev" is not-null */
int i;
for (dptr = dev->data; dptr; dptr = next) { /* all the list items */
if (dptr->data) {
for (i = 0; i < qset; i++)
kfree(dptr->data[i]); /* free一个quantum */
kfree(dptr->data); /* free一个qset */
dptr->data = NULL;
}
next = dptr->next;
kfree(dptr);
}
dev->size = 0;
dev->quantum = scull_quantum;
dev->qset = scull_qset;
dev->data = NULL;
return 0;
}
/*
* Open and close
*/
/* open和close方法 */
int scull_open(struct inode *inode, struct file *filp)
{
struct scull_dev *dev; /* device information */
/* 获得scull设备并保存在filp的private_data中 */
dev = container_of(inode->i_cdev, struct scull_dev, cdev);
filp->private_data = dev; /* for other methods */
/* now trim to 0 the length of the device if open was write-only */
if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) {
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
scull_trim(dev); /* ignore errors */
up(&dev->sem);
}
return 0; /* success */
}
int scull_release(struct inode *inode, struct file *filp)
{
return 0;
}
/*
* Follow the list
*/
/* scull_follow函数的作用是返回第二个参数指定的scull_qset。如果该scull_qset不存在，分配内存空间创建该scull_qset */
struct scull_qset *scull_follow(struct scull_dev *dev, int n)
{
struct scull_qset *qs = dev->data;
/* Allocate first qset explicitly if need be */
if (! qs) {
qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
if (qs == NULL)
return NULL; /* Never mind */
memset(qs, 0, sizeof(struct scull_qset));
}
/* Then follow the list */
while (n--) {
if (!qs->next) { /* 若指定的qset无数据则初始化 */
qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL);
if (qs->next == NULL)
return NULL; /* Never mind */
memset(qs->next, 0, sizeof(struct scull_qset));
}
qs = qs->next;
continue;
}
return qs;
}
/*
* Data management: read and write
*/
/* 读和写方法 */
ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, loff_t *f_pos)
{
struct scull_dev *dev = filp->private_data; /* 在open的时候将private_data置为scull设备 */
struct scull_qset *dptr;
int quantum = dev->quantum, qset = dev->qset;
int itemsize = quantum * qset; /* 一个qset的大小 */
int item, s_pos, q_pos, rest;
ssize_t retval = -ENOMEM; /* value used in "goto out" statements */
/* 获取信号量 */
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
/* find listitem, qset index and offset in the quantum */
item = (long)*f_pos / itemsize; /* 属于哪个qset */
rest = (long)*f_pos % itemsize;
s_pos = rest / quantum; /* 属于哪个quantum */
q_pos = rest % quantum; /* 在指定quantum上的偏移 */
/* follow the list up to the right position */
dptr = scull_follow(dev, item); /* 初始化指定的qset */
if (dptr == NULL)
goto out;
if (!dptr->data) { /* data是个2级指针，所以这里申请的是qset个char *的长度 */
dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL);
if (!dptr->data)
goto out;
memset(dptr->data, 0, qset * sizeof(char *));
}
if (!dptr->data[s_pos]) { /* data[i]是一级指针，填上每个quantum的首地址 */
dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL);
if (!dptr->data[s_pos])
goto out;
}
/* write only up to the end of this quantum */
/* 只在指定的quantum上面写完，若用户输入的count超过了此quantum的大小，则截断 */
if (count > quantum - q_pos)
count = quantum - q_pos;
/* 将用户态的数据保存在指定的qset上的quantum上 */
if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) {
retval = -EFAULT;
goto out;
}
*f_pos += count;
retval = count;
/* update the size */
if (dev->size < *f_pos)
dev->size = *f_pos;
out:
up(&dev->sem);
return retval;
}
ssize_t scull_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
struct scull_dev *dev = filp->private_data;
struct scull_qset *dptr; /* the first listitem */
int quantum = dev->quantum, qset = dev->qset;
int itemsize = quantum * qset; /* how many bytes in the listitem */
int item, s_pos, q_pos, rest;
ssize_t retval = 0;
if (down_interruptible(&dev->sem))
return -ERESTARTSYS;
/* 若偏移超过了scull设备的总大小则出错 */
if (*f_pos >= dev->size)
goto out;
if (*f_pos + count > dev->size)
count = dev->size - *f_pos;
/* find listitem, qset index, and offset in the quantum */
/* 找到对应的qset和quantum和在quantum上面的偏移量 */
item = (long)*f_pos / itemsize;
rest = (long)*f_pos % itemsize;
s_pos = rest / quantum; q_pos = rest % quantum;
/* follow the list up to the right position (defined elsewhere) */
dptr = scull_follow(dev, item); /* 定位到指定的qset */
if (dptr == NULL || !dptr->data || ! dptr->data[s_pos])
goto out; /* don't fill holes */
/* read only up to the end of this quantum */
if (count > quantum - q_pos) /* 只读取一个quantum上面的数据，即使超过了，则截断读取 */
count = quantum - q_pos;
if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)) {
retval = -EFAULT;
goto out;
}
*f_pos += count; /* 更新offset */
retval = count;
out:
up(&dev->sem);
return retval;
}
/* scull设备对应的操作集 */
struct file_operations scull_fops = {
.owner = THIS_MODULE,
.read = scull_read,
.write = scull_write,
.open = scull_open,
.release = scull_release,
};
/*
* Finally, the module stuff
*/
/* module部分 */
/*
* The cleanup function is used to handle initialization failures as well.
* Thefore, it must be careful to work correctly even if some of the items
* have not been initialized
*/
/* 删除模块的操作，对于scull设备主要是删除内存 */
void scull_cleanup_module(void)
{
int i;
dev_t devno = MKDEV(scull_major, scull_minor);
/* Get rid of our char dev entries */
if (scull_devices) {
for (i = 0; i < scull_nr_devs; i++) {
scull_trim(scull_devices + i);
cdev_del(&scull_devices[i].cdev);
}
kfree(scull_devices);
}
/* cleanup_module is never called if registering failed */
/* 调用unregister_chrdev_region删除设备号 */
unregister_chrdev_region(devno, scull_nr_devs);
}
/*
* Set up the char_dev structure for this device.
*/
static void scull_setup_cdev(struct scull_dev *dev, int index)
{
int err, devno = MKDEV(scull_major, scull_minor + index);
/* 调用cdev_init和cdev_add注册一个字符设备 */
cdev_init(&dev->cdev, &scull_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &scull_fops;
err = cdev_add (&dev->cdev, devno, 1);
/* Fail gracefully if need be */
if (err)
printk(KERN_NOTICE "Error %d adding scull%d", err, index);
}
int scull_init_module(void)
{
int result, i;
dev_t dev = 0;
/*
* Get a range of minor numbers to work with, asking for a dynamic
* major unless directed otherwise at load time.
*/
if (scull_major) {
dev = MKDEV(scull_major, scull_minor); /* 静态申请设备号 */
result = register_chrdev_region(dev, scull_nr_devs, "scull");
} else { /* 动态申请设备号 */
result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs, "scull");
scull_major = MAJOR(dev);
}
if (result < 0) {
printk(KERN_WARNING "scull: can't get major %d\n", scull_major);
return result;
}
/*
* allocate the devices -- we can't have them static, as the number
* can be specified at load time
*/
scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL);
if (!scull_devices) {
result = -ENOMEM;
goto fail; /* Make this more graceful */
}
memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev));
/* Initialize each device. */
for (i = 0; i < scull_nr_devs; i++) {
scull_devices[i].quantum = scull_quantum;
scull_devices[i].qset = scull_qset;
init_MUTEX(&scull_devices[i].sem); /* 初始化信号量 */
scull_setup_cdev(&scull_devices[i], i);
}
return 0; /* succeed */
fail:
scull_cleanup_module();
return result;
}
module_init(scull_init_module);
module_exit(scull_cleanup_module);scull_load脚本：
#!/bin/sh
# $Id: scull_load,v 1.4 2004/11/03 06:19:49 rubini Exp $
module="scull"
device="scull"
mode="664"
# Group: since distributions do it differently, look for wheel or use staff
if grep -q '^staff:' /etc/group; then
group="staff"
else
group="wheel"
fi
# invoke insmod with all arguments we got
# and use a pathname, as insmod doesn't look in . by default
/sbin/insmod ./$module.ko $* || exit 1
# retrieve major number
major=$(awk "\$2==\"$module\" {print \$1}" /proc/devices)
# Remove stale nodes and replace them, then give gid and perms
# Usually the script is shorter, it's scull that has several devices in it.
rm -f /dev/${device}[0-3]
mknod /dev/${device}0 c $major 0
mknod /dev/${device}1 c $major 1
mknod /dev/${device}2 c $major 2
mknod /dev/${device}3 c $major 3
ln -sf ${device}0 /dev/${device}
chgrp $group /dev/${device}[0-3]
chmod $mode /dev/${device}[0-3]scull_unload脚本：
#!/bin/sh
module="scull"
device="scull"
# invoke rmmod with all arguments we got
/sbin/rmmod $module $* || exit 1
# Remove stale nodes
rm -f /dev/${device} /dev/${device}[0-3] X86测试环境：
Makefile：(x86)
和上一篇日志的makefile基本无区别~~
# To build modules outside of the kernel tree, we run "make"
# in the kernel source tree; the Makefile these then includes this
# Makefile once again.
# This conditional selects whether we are being included from the
# kernel Makefile or not.
ifeq ($(KERNELRELEASE),)
# Assume the source tree is where the running kernel was built
# You should set KERNELDIR in the environment if it's elsewhere
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
#KERNELDIR ?= /share/my_kernel/linux-2.6.30.4
# The current directory is passed to sub-makes as argument
PWD := $(shell pwd)
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install
clean:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions *.bak
.PHONY: modules modules_install clean
else
# called from kernel build system: just declare what our modules are
obj-m := scull.o
endif测试结果：
[root@zx chap3_scull]# ls
Makefile Module.markers modules.order Module.symvers scull.c scull.h scull_load scull_unload
[root@zx chap3_scull]# make clean
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions *.bak
[root@zx chap3_scull]# make
make -C /lib/modules/2.6.27.5-117.fc10.i686/build M=/share/LDD3_code/my_module/chap3_scull modules
make[1]: Entering directory `/usr/src/kernels/2.6.27.5-117.fc10.i686'
CC [M] /share/LDD3_code/my_module/chap3_scull/scull.o
Building modules, stage 2.
MODPOST 1 modules
CC /share/LDD3_code/my_module/chap3_scull/scull.mod.o
LD [M] /share/LDD3_code/my_module/chap3_scull/scull.ko
make[1]: Leaving directory `/usr/src/kernels/2.6.27.5-117.fc10.i686'
[root@zx chap3_scull]# ./scull_load
[root@zx chap3_scull]# ls /dev/scull* -l
lrwxrwxrwx 1 root root 6 06-01 18:55 /dev/scull -> scull0
crw-rw-r-- 1 root wheel 248, 0 06-01 18:55 /dev/scull0
crw-rw-r-- 1 root wheel 248, 1 06-01 18:55 /dev/scull1
crw-rw-r-- 1 root wheel 248, 2 06-01 18:55 /dev/scull2
crw-rw-r-- 1 root wheel 248, 3 06-01 18:55 /dev/scull3
[root@zx chap3_scull]# free
total used free shared buffers cached
Mem: 512580 498320 14260 0 7856 69564
-/+ buffers/cache: 420900 91680
Swap: 1048568 13568 1035000
[root@zx chap3_scull]# cat /dev/scull0
[root@zx chap3_scull]# ls > /dev/scull0
[root@zx chap3_scull]# cat /dev/scull0
Makefile
Module.markers
modules.order
Module.symvers
scull.c
scull.h
scull.ko
scull_load
scull.mod.c
scull.mod.o
scull.o
scull_unload
[root@zx chap3_scull]# free
total used free shared buffers cached
Mem: 512580 498320 14260 0 7888 69564
-/+ buffers/cache: 420868 91712
Swap: 1048568 13568 1035000
[root@zx chap3_scull]# TQ2440-ARM9测试环境：
Makefile:(arm9)
#hello_makefile ARM
obj-m :=scull.o
KRNELDIR :=/share/my_kernel/linux-2.6.30.4-tq2440
CROSS_COMPILE =arm-linux-
CC :=$(CROSS_COMPILE)gcc
LD :=$(CROSS_COMPILE)ld
PWD :=$(shell pwd)
all:
make -C $(KRNELDIR) M=$(PWD) modules
.PHONY :clean
clean:
rm -rf *.o *ko运行测试：(交叉编译)
[root@zx chap3_scull]# ls
Makefile Makefile-x86 Module.markers modules.order Module.symvers scull.c scull.h scull_load scull_unload
[root@zx chap3_scull]# make
make -C /share/my_kernel/linux-2.6.30.4-tq2440 M=/share/LDD3_code/my_module/chap3_scull modules
make[1]: Entering directory `/share/my_kernel/linux-2.6.30.4-tq2440'
CC [M] /share/LDD3_code/my_module/chap3_scull/scull.o
Building modules, stage 2.
MODPOST 1 modules
CC /share/LDD3_code/my_module/chap3_scull/scull.mod.o
LD [M] /share/LDD3_code/my_module/chap3_scull/scull.ko
make[1]: Leaving directory `/share/my_kernel/linux-2.6.30.4-tq2440'
[root@zx chap3_scull]# 运行测试：(开发板)
[root@EmbedSky /modules_test]# mkdir chap3
[root@EmbedSky /modules_test]# ls
arm_hello.ko chap3
[root@EmbedSky /modules_test]# cd chap3/
[root@EmbedSky chap3]# ls
[root@EmbedSky chap3]# rx scull.ko
C
Starting xmodem transfer. Press Ctrl+C to cancel.
Transferring scull.ko...
100% 6 KB 2 KB/s 00:00:03 0 Errors
100% 6 KB 2 KB/s 00:00:03 0 Errors
root@EmbedSky chap3]# rx scull_load
C
Starting xmodem transfer. Press Ctrl+C to cancel.
Transferring scull_load...
100% 891 bytes 148 bytes/s 00:00:06 0 Errors
root@EmbedSky chap3]# rx scull_unload
C
Starting xmodem transfer. Press Ctrl+C to cancel.
Transferring scull_unload...
100% 185 bytes 37 bytes/s 00:00:05 0 Errors
root@EmbedSky chap3]# chmod 777 ./*
[root@EmbedSky chap3]# ./scull_load
chgrp: unknown group wheel
[root@EmbedSky chap3]# lsmod
Not tainted
scull 5028 0 - Live 0xbf050000
EmbedSky_irq 3068 1 - Live 0xbf04a000
ov9650 11088 0 - Live 0xbf042000
zd1211rw 67168 0 - Live 0xbf02c000
mac80211 144260 1 zd1211rw, Live 0xbf003000
input_polldev 3464 0 - Live 0xbf000000
[root@EmbedSky chap3]# free
total used free shared buffers
Mem: 60164 21184 38980 0 0
Swap: 0 0 0
Total: 60164 21184 38980
[root@EmbedSky chap3]# ls /dev/scull* -l
lrwxrwxrwx 1 root root 6 Nov 14 12:22 /dev/scull -> scull0
crw-rw-r-- 1 root root 252, 0 Nov 14 12:22 /dev/scull0
crw-rw-r-- 1 root root 252, 1 Nov 14 12:22 /dev/scull1
crw-rw-r-- 1 root root 252, 2 Nov 14 12:22 /dev/scull2
crw-rw-r-- 1 root root 252, 3 Nov 14 12:22 /dev/scull3
[root@EmbedSky chap3]# ls > /dev/scull0
[root@EmbedSky chap3]# cat /dev/scull0
scull.ko
scull_load
scull_unload
[root@EmbedSky chap3]# free
total used free shared buffers
Mem: 60164 21184 38980 0 0
Swap: 0 0 0
Total: 60164 21184 38980
[root@EmbedSky chap3]# lsmod > /dev/scull0
[root@EmbedSky chap3]# cat /dev/scull0
Not tainted
scull 5028 2 - Live 0xbf050000
EmbedSky_irq 3068 1 - Live 0xbf04a000
ov9650 11088 0 - Live 0xbf042000
zd1211rw 67168 0 - Live 0xbf02c000
mac80211 144260 1 zd1211rw, Live 0xbf003000
input_polldev 3464 0 - Live 0xbf000000
[root@EmbedSky chap3]# free
total used free shared buffers
Mem: 60164 21184 38980 0 0
Swap: 0 0 0
//add at 6/16
用户态测试scull：
/* forsakening @hdu 2013/6/16 fot testing scull */
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h> /* open */
#include <unistd.h> /* write */
#include <stdlib.h> /* malloc */
#include <stdio.h>
int main(int argc, char *argv[])
{
int fd = open("/dev/scull0", O_APPEND);
if (!fd)
{
printf("open error!\n");
return 1;
}
else
printf("open fd is: %d\n", fd);
/*
if (!write(fd, "This is from user!", 1000))
{
printf("write error!\n");
return 1;
}
*/
/* scull设备在读取的时候一次最多只能读取1000.cat命令是循环实现的？ */
char *read_buf = malloc(1000);
int read_length = 0;
if ((read_length = read(fd, read_buf, 1000)))
{
printf("This is from kernel!\n--------------\n");
printf("%s-----------\nread_length:%d\n", read_buf, read_length);
}
else
{
printf("read error!\n");
free(read_buf);
}
free(read_buf);
return 0;
}PC测试：
[root@zx chap3_scull]# gcc -Wall -o user-scull user-scull.c
[root@zx chap3_scull]# echo '' > /dev/scull
[root@zx chap3_scull]# ./user-scull
open fd is: 3
This is from kernel!
--------------
-----------
read_length:1
[root@zx chap3_scull]# echo 'forsakening' > /dev/scull
[root@zx chap3_scull]# ./user-scull
open fd is: 3
This is from kernel!
--------------
forsakening
-----------
read_length:12
[root@zx chap3_scull]# cat /dev/scull
forsakening
[root@zx chap3_scull]# ARM测试：
在pc上执行
arm-linux-gcc -Wall -o user-scull user-scull.c 得到arm开发板的可执行文件
[root@EmbedSky chap3]# ls
scull.ko scull_load scull_unload
[root@EmbedSky chap3]# lsmod
Not tainted
EmbedSky_irq 3068 1 - Live 0xbf04a000
ov9650 11088 0 - Live 0xbf042000
zd1211rw 67168 0 - Live 0xbf02c000
mac80211 144260 1 zd1211rw, Live 0xbf003000
input_polldev 3464 0 - Live 0xbf000000
[root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]# ./scull_load
chgrp: unknown group wheel
[root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]# rx user-scull
CC
Starting xmodem transfer. Press Ctrl+C to cancel.
Transferring user-scull...
100% 6 KB 1 KB/s 00:00:05 0 Errors
root@EmbedSky chap3]#
[root@EmbedSky chap3]#
[root@EmbedSky chap3]# ls
scull.ko scull_load scull_unload user-scull
[root@EmbedSky chap3]# chmod 777 ./*
[root@EmbedSky chap3]# ./user-scull
open fd is: 3
read error!
*** glibc detected *** ./user-scull: double free or corruption (top): 0x00011008 ***
Aborted
[root@EmbedSky chap3]# ls > /dev/scull
[root@EmbedSky chap3]# ./user-scull
open fd is: 3
This is from kernel!
--------------
scull.ko
scull_load
scull_unload
user-scull
-----------
read_length:44
[root@EmbedSky chap3]# 
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