标签：linu license this include nod void return dynamic release
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。
标签：linu license this include nod void return dynamic release
原文地址：http://www.cnblogs.com/pengdonglin137/p/5990558.html
