- 为什么阻塞？
在阻塞方式下，写没有足够的空间或读时候没有数据。
※ 阻塞方式是文件读写的默认方式。没有空间或者读时没有数据返回错误。
※残留问题：
驱动程序中全局变量 在不同进程间是共享的吗？
- 阻塞型设备驱动程序
驱动代码：
1 #ifndef _MEMDEV_H_
2 #define _MEMDEV_H_
3
4 #ifndef MEMDEV_MAJOR
5 #define MEMDEV_MAJOR 0 /*预设的mem的主设备号*/
6 #endif
7
8 #ifndef MEMDEV_NR_DEVS
9 #define MEMDEV_NR_DEVS 2 /*设备数*/
10 #endif
11
12 #ifndef MEMDEV_SIZE
13 #define MEMDEV_SIZE 4096
14 #endif
15
16 /*mem设备描述结构体*/
17 struct mem_dev
18 {
19 char *data;
20 unsigned long size;
21 wait_queue_head_t inq;
22 };
23
24 #endif /* _MEMDEV_H_ */
1 #include <linux/module.h>
2 #include <linux/types.h>
3 #include <linux/fs.h>
4 #include <linux/errno.h>
5 #include <linux/mm.h>
6 #include <linux/sched.h>
7 #include <linux/init.h>
8 #include <linux/cdev.h>
9 #include <asm/io.h>
10 #include <linux/slab.h>
11 #include <asm/uaccess.h>
12
13 #include "memdev.h"
14
15 static int mem_major = MEMDEV_MAJOR;
16 bool have_data = false; /*表明设备有足够数据可供读*/
17
18 module_param(mem_major, int, S_IRUGO);
19
20 struct mem_dev *mem_devp; /*设备结构体指针*/
21
22 struct cdev cdev;
23
24 /*文件打开函数*/
25 int mem_open(struct inode *inode, struct file *filp)
26 {
27 struct mem_dev *dev;
28
29 /*获取次设备号*/
30 int num = MINOR(inode->i_rdev);
31
32 if (num >= MEMDEV_NR_DEVS)
33 return -ENODEV;
34 dev = &mem_devp[num];
35
36 /*将设备描述结构指针赋值给文件私有数据指针*/
37 filp->private_data = dev;
38
39 return 0;
40 }
41
42 /*文件释放函数*/
43 int mem_release(struct inode *inode, struct file *filp)
44 {
45 return 0;
46 }
47
48 /*读函数*/
49 static ssize_t mem_read(struct file *filp, char __user *buf, size_t size, loff_t *ppos)
50 {
51 unsigned long p = *ppos;
52 unsigned int count = size;
53 int ret = 0;
54 struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
55
56 /*判断读位置是否有效*/
57 if (p >= MEMDEV_SIZE)
58 return 0;
59 if (count > MEMDEV_SIZE - p)
60 count = MEMDEV_SIZE - p;
61
62 while (!have_data) /* 没有数据可读，考虑为什么不用if，而用while,中断信号唤醒 */
63 {
64 if (filp->f_flags & O_NONBLOCK)
65 return -EAGAIN;
66
67 wait_event_interruptible(dev->inq,have_data);
68 }
69
70
71 /*读数据到用户空间*/
72 if (copy_to_user(buf, (void*)(dev->data + p), count))
73 {
74 ret = - EFAULT;
75 }
76 else
77 {
78 *ppos += count;
79 ret = count;
80
81 printk(KERN_INFO "read %d bytes(s) from %d\n", count, p);
82 }
83
84 have_data = false; /* 表明不再有数据可读 */
85 return ret;
86 }
87
88 /*写函数*/
89 static ssize_t mem_write(struct file *filp, const char __user *buf, size_t size, loff_t *ppos)
90 {
91 unsigned long p = *ppos;
92 unsigned int count = size;
93 int ret = 0;
94 struct mem_dev *dev = filp->private_data; /*获得设备结构体指针*/
95
96 /*分析和获取有效的写长度*/
97 if (p >= MEMDEV_SIZE)
98 return 0;
99 if (count > MEMDEV_SIZE - p)
100 count = MEMDEV_SIZE - p;
101
102 /*从用户空间写入数据*/
103 if (copy_from_user(dev->data + p, buf, count))
104 ret = - EFAULT;
105 else
106 {
107 *ppos += count;
108 ret = count;
109
110 printk(KERN_INFO "written %d bytes(s) from %d\n", count, p);
111 }
112
113 have_data = true; /* 有新的数据可读 */
114
115 /* 唤醒读进程 */
116 wake_up(&(dev->inq));
117
118 return ret;
119 }
120
121 /* seek文件定位函数 */
122 static loff_t mem_llseek(struct file *filp, loff_t offset, int whence)
123 {
124 loff_t newpos;
125
126 switch(whence) {
127 case 0: /* SEEK_SET */
128 newpos = offset;
129 break;
130
131 case 1: /* SEEK_CUR */
132 newpos = filp->f_pos + offset;
133 break;
134
135 case 2: /* SEEK_END */
136 newpos = MEMDEV_SIZE -1 + offset;
137 break;
138
139 default: /* can‘t happen */
140 return -EINVAL;
141 }
142 if ((newpos<0) || (newpos>MEMDEV_SIZE))
143 return -EINVAL;
144
145 filp->f_pos = newpos;
146 return newpos;
147
148 }
149
150 /*文件操作结构体*/
151 static const struct file_operations mem_fops =
152 {
153 .owner = THIS_MODULE,
154 .llseek = mem_llseek,
155 .read = mem_read,
156 .write = mem_write,
157 .open = mem_open,
158 .release = mem_release,
159 };
160
161 /*设备驱动模块加载函数*/
162 static int memdev_init(void)
163 {
164 int result;
165 int i;
166
167 dev_t devno = MKDEV(mem_major, 0);
168
169 /* 静态申请设备号*/
170 if (mem_major)
171 result = register_chrdev_region(devno, 2, "memdev");
172 else /* 动态分配设备号 */
173 {
174 result = alloc_chrdev_region(&devno, 0, 2, "memdev");
175 mem_major = MAJOR(devno);
176 }
177
178 if (result < 0)
179 return result;
180
181 /*初始化cdev结构*/
182 cdev_init(&cdev, &mem_fops);
183 cdev.owner = THIS_MODULE;
184 cdev.ops = &mem_fops;
185
186 /* 注册字符设备 */
187 cdev_add(&cdev, MKDEV(mem_major, 0), MEMDEV_NR_DEVS);
188
189 /* 为设备描述结构分配内存*/
190 mem_devp = kmalloc(MEMDEV_NR_DEVS * sizeof(struct mem_dev), GFP_KERNEL);
191 if (!mem_devp) /*申请失败*/
192 {
193 result = - ENOMEM;
194 goto fail_malloc;
195 }
196 memset(mem_devp, 0, sizeof(struct mem_dev));
197
198 /*为设备分配内存*/
199 for (i=0; i < MEMDEV_NR_DEVS; i++)
200 {
201 mem_devp[i].size = MEMDEV_SIZE;
202 mem_devp[i].data = kmalloc(MEMDEV_SIZE, GFP_KERNEL);
203 memset(mem_devp[i].data, 0, MEMDEV_SIZE);
204
205 /*初始化等待队列*/
206 init_waitqueue_head(&(mem_devp[i].inq));
207 }
208
209 return 0;
210
211 fail_malloc:
212 unregister_chrdev_region(devno, 1);
213
214 return result;
215 }
216
217 /*模块卸载函数*/
218 static void memdev_exit(void)
219 {
220 cdev_del(&cdev); /*注销设备*/
221 kfree(mem_devp); /*释放设备结构体内存*/
222 unregister_chrdev_region(MKDEV(mem_major, 0), 2); /*释放设备号*/
223 }
224
225 MODULE_AUTHOR("David Xie");
226 MODULE_LICENSE("GPL");
227
228 module_init(memdev_init);
229 module_exit(memdev_exit);
ifneq ($(KERNELRELEASE),)
obj-m := memdev.o
else
KDIR := /home/rpi/RpiLinux
all:
make -C $(KDIR) M=$(PWD) modules ARCH=arm CROSS_COMPILE=/home/rpi/RpiTools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-bcm2708hardfp-linux-gnueabi-
clean:
rm -f *.ko *.o *.mod.o *.mod.c *.symvers modul*
endif
测试程序：
1 #include <stdio.h>
2
3 int main()
4 {
5 FILE *fp = NULL;
6 char Buf[128];
7
8
9 /*打开设备文件*/
10 fp = fopen("/dev/memdev0","r+");
11 if (fp == NULL)
12 {
13 printf("Open Dev memdev0 Error!\n");
14 return -1;
15 }
16
17 /*写入设备*/
18 strcpy(Buf,"memdev is char dev!");
19 printf("Write BUF: %s\n",Buf);
20 fwrite(Buf, sizeof(Buf), 1, fp);
21
22 sleep(5);
23 fclose(fp);
24
25 return 0;
26
27 }
1 #include <stdio.h>
2
3 int main()
4 {
5 FILE *fp = NULL;
6 char Buf[128];
7
8 /*初始化Buf*/
9 strcpy(Buf,"memdev is char dev!");
10 printf("BUF: %s\n",Buf);
11
12 /*打开设备文件*/
13 fp = fopen("/dev/memdev0","r+");
14 if (fp == NULL)
15 {
16 printf("Open memdev0 Error!\n");
17 return -1;
18 }
19
20 /*清除Buf*/
21 strcpy(Buf,"Buf is NULL!");
22 printf("Read BUF1: %s\n",Buf);
23
24 /*读出数据*/
25 fread(Buf, sizeof(Buf), 1, fp);
26
27 /*检测结果*/
28 printf("Read BUF2: %s\n",Buf);
29
30 fclose(fp);
31
32 return 0;
33
34 }
测试结果：
时间： 2024-08-21 22:25:07