獲得U盤的插入或者拔取得信息的傳統方法是在內核級運行hotplug程序,相關參數通過環境變量傳遞過來,再由hotplug通知其他關注hotplug的應用程序。這樣的做法效率有些低,現在通過一種特殊類型的socket netlink實現獲取U盤拔插的信息。netlink專門用於內核空間和用戶空間的異步通信。
下面的例子可以監聽內核的hotplug事件,源代碼如下:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/un.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <Linux/types.h>
#include <Linux/netlink.h>
#include <errno.h>
#define UEVENT_BUFFER_SIZE 2048
static int init_hotplug_sock(void);
int main(int argc, char* argv[])
{
int hotplug_sock = init_hotplug_sock();
while(1){
char buf[UEVENT_BUFFER_SIZE*2] = {0};
recv(hotplug_sock, &buf, sizeof(buf), 0);
printf("%s\n", buf);
}
return 0;
}
static int init_hotplug_sock(void)
{
struct sockaddr_nl snl;
const int buffersize = 16 * 1024 * 1024;
int retval;
memset(&snl, 0x00, sizeof(struct sockaddr_nl));
snl.nl_family = AF_NETLINK;
snl.nl_pid = getpid();
snl.nl_groups = 1;
int hotplug_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
if (hotplug_sock == -1) {
printf("error getting socket: %s", strerror(errno));
return -1;
}
/* set receive buffersize */
setsockopt(hotplug_sock, SOL_SOCKET, SO_RCVBUFFORCE, &buffersize, sizeof(buffersize));
retval = bind(hotplug_sock, (struct sockaddr *) &snl, sizeof(struct sockaddr_nl));
if (retval < 0) {
printf("bind failed: %s", strerror(errno));
close(hotplug_sock);
hotplug_sock = -1;
return -1;
}
return hotplug_sock;
}