下面說一下在用戶空間調用open/close/dup跟驅動中的open和release的對應。
下面是測試驅動：
1 #include <linux/module.h>
2 #include <linux/miscdevice.h>
3 #include <linux/fs.h>
4
5
6 static int misc_demo_open(struct inode *nodp, struct file *filp)
7 {
8 printk("%s enter, nodp: %p, filp: %p.\n", __func__, nodp, filp);
9
10 return 0;
11 }
12
13 static int misc_demo_release(struct inode *nodp, struct file *filp)
14 {
15 printk("%s enter, nodp: %p, filp: %p.\n", __func__, nodp, filp);
16
17 return 0;
18 }
19
20 static struct file_operations misc_demo_fops = {
21 .owner = THIS_MODULE,
22 .open = misc_demo_open,
23 .release = misc_demo_release,
24 };
25
26 static struct miscdevice misc_demo_dev = {
27 .minor = MISC_DYNAMIC_MINOR,
28 .name = "misc_demo",
29 .fops = &misc_demo_fops
30 };
31
32 static __init int misc_demo_init(void)
33 {
34 int ret;
35
36 ret = misc_register(&misc_demo_dev);
37
38 return ret;
39 }
40
41 static __exit void misc_demo_exit(void)
42 {
43 misc_deregister(&misc_demo_dev);
44
45 return;
46 }
47
48 module_init(misc_demo_init);
49 module_exit(misc_demo_exit);
50 MODULE_LICENSE("GPL");
下面是用戶空間測試代碼：
1 #include <stdio.h>
2 #include <sys/types.h>
3 #include <sys/stat.h>
4 #include <fcntl.h>
5 #include <unistd.h>
6
7
8 int main(int argc, const char *argv[])
9 {
10 int fd[3], fd2[3], i;
11
12 printf("Begin open.\n");
13 for (i=0; i<3; i++) {
14 fd[i] = open("/dev/misc_demo", O_RDONLY);
15 printf("open: %d\n", fd[i]);
16 fd2[i] = dup(fd[i]);
17 printf("dup: %d\n", fd2[i]);
18 sleep(1);
19 }
20
21 sleep(5);
22
23 printf("Begin close.\n");
24 for (i=0; i<3; i++) {
25 printf("close: %d\n", fd[i]);
26 close(fd[i]);
27 sleep(1);
28 }
29
30 sleep(2);
31
32 printf("Begin close dup.\n");
33 for (i=0; i<3; i++) {
34 printf("close dup: %d\n", fd2[i]);
35 close(fd2[i]);
36 sleep(1);
37 }
38
39 return 0;
40 }
下面是輸出的log：
Begin open. [ 4628.805135] misc_demo_open enter, nodp: c3b88a18, filp: c3859060. open: 3 dup: 4 [ 4629.809860] misc_demo_open enter, nodp: c3b88a18, filp: c3859c40. open: 5 dup: 6 [ 4630.814891] misc_demo_open enter, nodp: c3b88a18, filp: c3859ec0. open: 7 dup: 8 Begin close. close: 3 close: 5 close: 7 Begin close dup. close dup: 4 [ 4641.845172] misc_demo_release enter, nodp: c3b88a18, filp: c3859060. close dup: 6 [ 4642.850183] misc_demo_release enter, nodp: c3b88a18, filp: c3859c40. close dup: 8 [ 4643.855123] misc_demo_release enter, nodp: c3b88a18, filp: c3859ec0.
通過分析log，我們得出結論， 用戶空間每調用一次open，驅動中的open都會被執行一次，而在調用dup的時候，只是將struct file的引用計數加1，而沒有產生新的struct file，所以返回的新的fd跟老的fd對應的是同一個struct file，同時也沒用調用open。在close的時候，只有struct file對應的所有fd都被關閉或者說struct file的引用計數爲0的時候，驅動中的release纔會被執行。
完。
时间： 2024-11-04 16:08:52