linux驅(qū)動：[2]字符設(shè)備驅(qū)動memdev
Linux 內(nèi)存模擬字符設(shè)備 驅(qū)動程序
測試平臺： Xunlong Orange Pi Zero
代碼一覽（解析見下方）
驅(qū)動程序以及Makefile如下：
- memdev.c:
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#ifndef MEMDEV_MAJOR
#define MEMDEV_MAJOR 254
#endif
#ifndef MEMDEV_NR_DEVS
#define MEMDEV_NR_DEVS 2
#endif
#ifndef MEMDEV_SIZE
#define MEMDEV_SIZE 4096
#endif
struct mem_dev {
char *data;
unsigned long size;
};
static int mem_major = MEMDEV_MAJOR;
module_param(mem_major, int, S_IRUGO);
struct mem_dev *mem_devp;
struct cdev cdev;
int mem_open(struct inode *inode, struct file *filp)
{
struct mem_dev *dev;
int num = MINOR(inode->i_rdev);
if (num >= MEMDEV_NR_DEVS)
return -ENODEV;
dev = &mem_devp[num];
filp->private_data = dev;
return 0;
}
int mem_release(struct inode *inode, struct file *filp)
{
return 0;
}
static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *poss)
{
unsigned long p = *poss;
unsigned int count = size;
int ret = 0;
struct mem_dev *dev = filp->private_data;
if (p >= MEMDEV_SIZE)
return 0;
if (count > MEMDEV_SIZE-p)
count = MEMDEV_SIZE-p;
if(copy_to_user(buf, (void*)(dev->data + p), count)) {
ret = -EFAULT;
} else {
*poss += count;
ret = count;
printk(KERN_INFO "read %d bytes from %lu\n", count, p);
}
return ret;
}
static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *poss)
{
unsigned long p = *poss;
unsigned int count = size;
int ret = 0;
struct mem_dev *dev = filp->private_data;
if (p >= MEMDEV_SIZE)
return 0;
if (count > MEMDEV_SIZE-p)
count = MEMDEV_SIZE - p;
if (copy_from_user(dev->data + p, buf, count)) {
ret = -EFAULT;
} else {
*poss += count;
ret = count;
printk(KERN_INFO "write %d bytes from %lu\n", count, p);
}
return ret;
}
static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
{
loff_t newpos;
switch (whence) {
case 0:
newpos = offset;
break;
case 1:
newpos = filp->f_pos + offset;
break;
case 2:
newpos = MEMDEV_SIZE - 1 + offset;
break;
default:
return -EINVAL;
}
if ((newpos < 0) || (newpos > MEMDEV_SIZE))
return -EINVAL;
filp->f_pos = newpos;
return newpos;
}
static const struct file_operations mem_fops =
{
.owner = THIS_MODULE,
.llseek = mem_llseek,
.read = mem_read,
.write = mem_write,
.open = mem_open,
.release = mem_release,
};
static int memdev_init(void)
{
int result;
int i;
dev_t devno = MKDEV(mem_major, 0);
if (mem_major)
result = register_chrdev_region(devno, 2, "memdev");
else {
result = alloc_chrdev_region(&devno, 0, 2, "memdev");
mem_major = MAJOR(devno);
}
if (result < 0)
return result;
cdev_init(&cdev, &mem_fops);
cdev.owner = THIS_MODULE;
cdev.ops = &mem_fops;
cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
if (!mem_devp) {
result = -ENOMEM;
goto fail_malloc;
}
memset(mem_devp, 0, MEMDEV_NR_DEVS * sizeof(struct mem_dev));
for (i = 0; i < MEMDEV_NR_DEVS; i++) {
mem_devp[i].size = MEMDEV_SIZE;
mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
memset(mem_devp[i].data, 0, MEMDEV_SIZE);
}
printk("memdev init success\n");
return 0;
fail_malloc:
unregister_chrdev_region(devno, 2);
return result;
}
static void memdev_exit(void)
{
cdev_del(&cdev);
kfree(mem_devp);
unregister_chrdev_region(MKDEV(mem_major, 0), 2);
printk("memdev exit success\n");
}
MODULE_AUTHOR("Ziping Chen <techping.chan@gmail.com>");
MODULE_LICENSE("GPL");
module_init(memdev_init);
module_exit(memdev_exit);
- Makefile:
obj-m := memdev.o #編譯進模塊
KERNELDIR := /lib/modules/4.11.0-rc4-00064-g89970a0-dirty/build #此處為linux內(nèi)核庫目錄
PWD := $(shell pwd) #獲取當(dāng)前目錄
OUTPUT := $(obj-m) $(obj-m:.o=.ko) $(obj-m:.o=.mod.o) $(obj-m:.o=.mod.c) modules.order Module.symvers
modules:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
clean:
rm -rf $(OUTPUT)
在shell中使用以下命令裝載驅(qū)動程序：
<font color="red">(這里以主設(shè)備號為181進行測試)</font>
$ make
$ insmod memdev.ko mem_major=181
$ mknod /dev/memdev0 c 181 0
使用linux c進行測試：
- memapp.c:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
int main()
{
int fd;
char buf[4096];
strcpy(buf,"memory simulate char device test...\n");
printf("original buf:%s\n",buf);
fd = open("/dev/memdev0",O_RDWR);
if (fd == -1) {
printf("open memdev failed!\n");
return -1;
}
write(fd, buf, sizeof(buf));
lseek(fd, 0, SEEK_SET);
strcpy(buf, "nothing here");
read(fd, buf, sizeof(buf));
printf("read buf:%s\n", buf);
return 0;
}
進行編譯坐儿、測試：
$ gcc -o memapp memapp.c
實驗成功！
代碼解析：
一、分配設(shè)備號
if (mem_major)
result = register_chrdev_region(devno, 2, "memdev");
else {
result = alloc_chrdev_region(&devno, 0, 2, "memdev");
mem_major = MAJOR(devno);
}
如果定義的參數(shù)mem_major不為0(上面測試用了181),則進行靜態(tài)分配
register_chrdev_region(devno, 2, "memdev");//靜態(tài)分配設(shè)備號為devno的設(shè)備
如果mem_major為0則進行動態(tài)分配
alloc_chrdev_region(&devno, 0, 2, "memdev");//動態(tài)分配主設(shè)備號為devno絮短，次設(shè)備號為0的設(shè)備
二萎庭、初始化cdev結(jié)構(gòu)
/linux/include/linux/cdev.h:
struct cdev {
struct kobject kobj;//每個 cdev 都是一個 kobject
struct module *owner;//指向?qū)崿F(xiàn)驅(qū)動的模塊
const struct file_operations *ops;//操縱這個字符設(shè)備文件的方法
struct list_head list;//與 cdev 對應(yīng)的字符設(shè)備文件的 inode->i_devices 的鏈表頭
dev_t dev;//起始設(shè)備編號
unsigned int count;//設(shè)備范圍號大小
};
一個 cdev 一般它有兩種定義初始化方式：靜態(tài)的和動態(tài)的刘离。
靜態(tài)內(nèi)存定義初始化：
struct cdev my_cdev;
cdev_init(&my_cdev, &fops);
my_cdev.owner = THIS_MODULE;
動態(tài)內(nèi)存定義初始化：
struct cdev *my_cdev = cdev_alloc();
my_cdev->ops = &fops;
my_cdev->owner = THIS_MODULE;
兩種使用方式的功能是一樣的垢揩，只是使用的內(nèi)存區(qū)不一樣因谎，一般視實際的數(shù)據(jù)結(jié)構(gòu)需求而定闹获。
源碼分析：
struct cdev *cdev_alloc(void)
{
struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
if (p) {
INIT_LIST_HEAD(&p->list);
kobject_init(&p->kobj, &ktype_cdev_dynamic);
}
return p;
}
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
memset(cdev, 0, sizeof *cdev);
INIT_LIST_HEAD(&cdev->list);
kobject_init(&cdev->kobj, &ktype_cdev_default);
cdev->ops = fops;
}
可見期犬，兩個函數(shù)完成都功能基本一致。
三避诽、添加cdev
初始化 cdev 后龟虎，需要把它添加到系統(tǒng)中去。為此可以調(diào)用 cdev_add() 函數(shù)茎用。傳入 cdev 結(jié)構(gòu)的指針遣总，起始設(shè)備編號睬罗，以及設(shè)備編號范圍。
int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
p->dev = dev;
p->count = count;
return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}
簡單地說旭斥，設(shè)備驅(qū)動程序通過調(diào)用cdev_add把它所管理的設(shè)備對象的指針嵌入到一個類型為struct probe的節(jié)點之中容达，然后再把該節(jié)點加入到cdev_map所實現(xiàn)的哈希鏈表中。
對系統(tǒng)而言垂券，當(dāng)設(shè)備驅(qū)動程序成功調(diào)用了cdev_add之后花盐，就意味著一個字符設(shè)備對象已經(jīng)加入到了系統(tǒng)，在需要的時候菇爪，系統(tǒng)就可以找到它算芯。對用戶態(tài)的程序而言，cdev_add調(diào)用之后凳宙，就已經(jīng)可以通過文件系統(tǒng)的接口調(diào)用到我們的驅(qū)動程序熙揍。
四、卸載cdev
當(dāng)一個字符設(shè)備驅(qū)動不再需要的時候（比如模塊卸載）氏涩，就可以用 cdev_del() 函數(shù)來釋放 cdev 占用的內(nèi)存届囚。
void cdev_del(struct cdev *p)
{
cdev_unmap(p->dev, p->count);
kobject_put(&p->kobj);
}
其中 cdev_unmap() 調(diào)用 kobj_unmap() 來釋放 cdev_map 散列表中的對象。kobject_put() 釋放 cdev 結(jié)構(gòu)本身是尖。
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