一、引言
- hotplug：通报关于热插拔设备事件的机制
- udev： 动态地维护 /dev 下的设备文件
- inotify：监视文件系统事件的 API
在 2.6.13 之后，inotify 取代了旧有的 dnotify，克服了它的缺陷。
二、inotify
1. 用户接口
#include <sys/inotify.h>
/* 创建 inotify 实例，fd 指向一个 struct inotify_event 队列 */
int fd = inotify_init();
/* 向 fd 中添加对 path 的由 mask 指定的监视，返回监视描述符 */
int wd = inotify_add_watch(fd, path, mask);
/* 移除 fd 中的 wd 监视 */
int ret = inotify_rm_watch(fd, wd);
struct inotify_event {
int wd; /* Watch descriptor */
uint32_t mask; /* Mask describing event */
uint32_t cookie; /* cookie to synchronize two events */
uint32_t len; /* length (including nulls) of name */
char name[]; /* stub for possible name */
};
可以在函数 inotify_init() 返回的 fd 上使用 select()，poll() 或 ioctl 命令 FIONREAD 来得到当前队列的长度。另外 close(fd) 将删除所有添加到 fd 中的 watch 并做必要的清理。
2. 例子
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/inotify.h>
#include <unistd.h>
#define EVENT_NUM 12
char *event_str[EVENT_NUM] = {
"IN_ACCESS", // File was accessed
"IN_MODIFY", // File was modified
"IN_ATTRIB", // File attributes were changed
"IN_CLOSE_WRITE", // Writtable file closed
"IN_CLOSE_NOWRITE", // Unwrittable file closed
"IN_OPEN", // File was opened
"IN_MOVED_FROM", // File was moved from X
"IN_MOVED_TO", // File was moved to Y
"IN_CREATE", // Subfile was created
"IN_DELETE", // Subfile was deleted
"IN_DELETE_SELF", // Self was deleted
"IN_MOVE_SELF", // Self was moved
};
int main(int argc, char *argv[]) {
int fd, wd, len, nread;
char buf[1024];
struct inotify_event *event;
fd = inotify_init();
wd = inotify_add_watch(fd, argv[1], IN_ALL_EVENTS);
buf[sizeof(buf) - 1] = 0;
while ((len = read(fd, buf, sizeof(buf) - 1)) > 0) {
nread = 0;
while (len > nread) {
event = (struct inotify_event *)&buf[nread];
if (event->mask & IN_ISDIR) printf("Directory:\n");
for (int i = 0; i < EVENT_NUM; i++) {
if ((event->mask >> i) & 1) {
if (event->len > 0)
printf("%-20s --- %s\n", event_str[i], event->name);
else printf("%-20s --- %s\n", event_str[i], " ");
} // end if ((event->mask >> i) & 1)
} // end for (int i = 0; i < EVENT_NUM; i++)
nread = nread + sizeof(struct inotify_event) + event->len;
} // end while (len > nread)
} // end while ((len = read(fd, buf, sizeof(buf) - 1)) > 0)
return 0;
}
三、参考资料
- https://www.ibm.com/developerworks/cn/linux/l-inotifynew/index.html