linux 上热拔插事件的检测

Posted 2020-10-12 杂记

一、通过NETLINK 获得热插拨事件，此方法只适用于监测热插拨事件；（上电前SD卡或者U盘已经插上，并且系统设置为自动挂载），这样NETLINK 已经不再适用。

#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> 
#include <unistd.h> 
#include <arpa/inet.h> 
#include <netinet/in.h> 

#define UEVENT_BUFFER_SIZE 2048 

static int init_hotplug_sock() 
{ 
    const int buffersize = 1024; 
    int ret; 

    struct sockaddr_nl snl; 
    bzero(&snl, sizeof(struct sockaddr_nl)); 
    snl.nl_family = AF_NETLINK; 
    snl.nl_pid = getpid(); 
    snl.nl_groups = 1; 

    int s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT); 
    if (s == -1)  
    { 
        perror("socket"); 
        return -1; 
    } 
    setsockopt(s, SOL_SOCKET, SO_RCVBUF, &buffersize, sizeof(buffersize)); 

    ret = bind(s, (struct sockaddr *)&snl, sizeof(struct sockaddr_nl)); 
    if (ret < 0)  
    { 
        perror("bind"); 
        close(s); 
        return -1; 
    } 

    return s; 
} 

int main(int argc, char* argv[]) 
{ 
    int hotplug_sock = init_hotplug_sock(); 

    while(1) 
    { 
        /* Netlink message buffer */ 
        char buf[UEVENT_BUFFER_SIZE * 2] = {0}; 
        recv(hotplug_sock, &buf, sizeof(buf), 0); 
        printf("%s\n", buf); 
        /*不同设备的插拔会出现字符信息，通过比较不同的信息确定特定设备的插拔*/

    }
    return 0; 
}

二、通过udevmonitor获得热插拨事件，udevmonitor 的原理也是捕捉 netlink 的 socket 消息，这个消息是内核发出的。同样不适用于（上电前SD卡或者U盘已经插上，并且系统设置为自动挂载）这情况。

/*
 * Copyright (C) 2004-2006 Kay Sievers <[email protected]>
 *
 *    This program is free software; you can redistribute it and/or modify it
 *    under the terms of the GNU General Public License as published by the
 *    Free Software Foundation version 2 of the License.
 * 
 *    This program is distributed in the hope that it will be useful, but
 *    WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    General Public License for more details.
 * 
 *    You should have received a copy of the GNU General Public License along
 *    with this program; if not, write to the Free Software Foundation, Inc.,
 *    51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 */
 
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <getopt.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <linux/types.h>
#include <linux/netlink.h>
 
#include "udev.h"
#include "udevd.h"
 
static int uevent_netlink_sock = -1;
static int udev_monitor_sock = -1;
static volatile int udev_exit;
 
static int init_udev_monitor_socket(void)
{
    struct sockaddr_un saddr;
    socklen_t addrlen;
    int retval;
 
    memset(&saddr, 0x00, sizeof(saddr));
    saddr.sun_family = AF_LOCAL;
    /* use abstract namespace for socket path */
    strcpy(&saddr.sun_path[1], "/org/kernel/udev/monitor");
    addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(saddr.sun_path+1) + 1;
 
    udev_monitor_sock = socket(AF_LOCAL, SOCK_DGRAM, 0);
    if (udev_monitor_sock == -1) {
        fprintf(stderr, "error getting socket: %s\n", strerror(errno));
        return -1;
    }
 
    /* the bind takes care of ensuring only one copy running */
    retval = bind(udev_monitor_sock, (struct sockaddr *) &saddr, addrlen);
    if (retval < 0) {
        fprintf(stderr, "bind failed: %s\n", strerror(errno));
        close(udev_monitor_sock);
        udev_monitor_sock = -1;
        return -1;
    }
 
    return 0;
}
 
static int init_uevent_netlink_sock(void)
{
    struct sockaddr_nl snl;
    int retval;
 
    memset(&snl, 0x00, sizeof(struct sockaddr_nl));
    snl.nl_family = AF_NETLINK;
    snl.nl_pid = getpid();
    snl.nl_groups = 1;
 
    uevent_netlink_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
    if (uevent_netlink_sock == -1) {
        fprintf(stderr, "error getting socket: %s\n", strerror(errno));
        return -1;
    }
 
    retval = bind(uevent_netlink_sock, (struct sockaddr *) &snl,
              sizeof(struct sockaddr_nl));
    if (retval < 0) {
        fprintf(stderr, "bind failed: %s\n", strerror(errno));
        close(uevent_netlink_sock);
        uevent_netlink_sock = -1;
        return -1;
    }
 
    return 0;
}
 
static void asmlinkage sig_handler(int signum)
{
    if (signum == SIGINT || signum == SIGTERM)
        udev_exit = 1;
}
 
static const char *search_key(const char *searchkey, const char *buf, size_t buflen)
{
    size_t bufpos = 0;
    size_t searchkeylen = strlen(searchkey);
 
    while (bufpos < buflen) {
        const char *key;
        int keylen;
 
        key = &buf[bufpos];
        keylen = strlen(key);
        if (keylen == 0)
            break;
         if ((strncmp(searchkey, key, searchkeylen) == 0) && key[searchkeylen] == ‘=‘)
            return &key[searchkeylen + 1];
        bufpos += keylen + 1;
    }
    return NULL;
}
 

 int main(int argc, char *argv[])
{
    struct sigaction act;
    int option;
    int env = 0;
    int kernel = 0;
    int udev = 0;
    fd_set readfds;
    int retval = 0;
 
    static const struct option options[] = {
        { "environment", 0, NULL, ‘e‘ },
        { "kernel", 0, NULL, ‘k‘ },
        { "udev", 0, NULL, ‘u‘ },
        { "help", 0, NULL, ‘h‘ },
        {}
    };
 
    while (1) {
        option = getopt_long(argc, argv, "ekuh", options, NULL);
        if (option == -1)
            break;
 
        switch (option) {
        case ‘e‘:
            env = 1;
            break;
        case ‘k‘:
            kernel = 1;
            break;
        case ‘u‘:
            udev = 1;
            break;
        case ‘h‘:
            printf("Usage: udevmonitor [--environment] [--kernel] [--udev] [--help]\n"
                   "  --env    print the whole event environment\n"
                   "  --kernel print kernel uevents\n"
                   "  --udev   print udev events\n"
                   "  --help   print this help text\n\n");
        default:
            goto out;
        }
    }
 
    if (!kernel && !udev) {
        kernel = 1;
        udev =1;
    }
 
    if (getuid() != 0 && kernel) {
        fprintf(stderr, "root privileges needed to subscribe to kernel events\n");
        goto out;
    }
 
    /* set signal handlers */
    memset(&act, 0x00, sizeof(struct sigaction));
    act.sa_handler = (void (*)(int)) sig_handler;
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_RESTART;
    sigaction(SIGINT, &act, NULL);
    sigaction(SIGTERM, &act, NULL);
 
    printf("udevmonitor will print the received events for:\n");
    if (udev) {
        retval = init_udev_monitor_socket();
        if (retval)
            goto out;
        printf("UDEV the event which udev sends out after rule processing\n");
    }
    if (kernel) {
        retval = init_uevent_netlink_sock();
        if (retval)
            goto out;
        printf("UEVENT the kernel uevent\n");
    }
    printf("\n");
 
    while (!udev_exit) {
        char buf[UEVENT_BUFFER_SIZE*2];
        ssize_t buflen;
        ssize_t bufpos;
        ssize_t keys;
        int fdcount;
        struct timeval tv;
        struct timezone tz;
        char timestr[64];
        const char *source = NULL;
        const char *devpath, *action, *subsys;
 
        buflen = 0;
        FD_ZERO(&readfds);
        if (uevent_netlink_sock >= 0)
            FD_SET(uevent_netlink_sock, &readfds);
        if (udev_monitor_sock >= 0)
            FD_SET(udev_monitor_sock, &readfds);
 
        fdcount = select(UDEV_MAX(uevent_netlink_sock, udev_monitor_sock)+1, &readfds, NULL, NULL, NULL);
        if (fdcount < 0) {
            if (errno != EINTR)
                fprintf(stderr, "error receiving uevent message: %s\n", strerror(errno));
            continue;
        }
 
        if (gettimeofday(&tv, &tz) == 0) {
            snprintf(timestr, sizeof(timestr), "%llu.%06u",
                 (unsigned long long) tv.tv_sec, (unsigned int) tv.tv_usec);
        } else
            timestr[0] = ‘\0‘;
 
        if ((uevent_netlink_sock >= 0) && FD_ISSET(uevent_netlink_sock, &readfds)) {
            buflen = recv(uevent_netlink_sock, &buf, sizeof(buf), 0);
            if (buflen <= 0) {
                fprintf(stderr, "error receiving uevent message: %s\n", strerror(errno));
                continue;
            }
            source = "UEVENT";
        }
 
        if ((udev_monitor_sock >= 0) && FD_ISSET(udev_monitor_sock, &readfds)) {
            buflen = recv(udev_monitor_sock, &buf, sizeof(buf), 0);
            if (buflen <= 0) {
                fprintf(stderr, "error receiving udev message: %s\n", strerror(errno));
                continue;
            }
            source = "UDEV  ";
        }
 
        if (buflen == 0)
            continue;
 
        keys = strlen(buf) + 1; /* start of payload */
        devpath = search_key("DEVPATH", &buf[keys], buflen);
        action = search_key("ACTION", &buf[keys], buflen);
        subsys = search_key("SUBSYSTEM", &buf[keys], buflen);
        printf("%s[%s] %-8s %s (%s)\n", source, timestr, action, devpath, subsys);
 
        /* print environment */
        bufpos = keys;
        if (env) {
            while (bufpos < buflen) {
                int keylen;
                char *key;
 
                key = &buf[bufpos];
                keylen = strlen(key);
                if (keylen == 0)
                    break;
                printf("%s\n", key);
                bufpos += keylen + 1;
            }
            printf("\n");
        }
    }
 
out:
    if (uevent_netlink_sock >= 0)
        close(uevent_netlink_sock);
    if (udev_monitor_sock >= 0)
        close(udev_monitor_sock);
 
    if (retval)
        return 1;
    return 0;
}

 

ps:不要在udev规则下调用的脚本去创建文件或文件夹，如果一开机的情况下就SD卡或U盘在位；
    创建将失败，应该是权限问题。系统起来后的热拔插不存在这问题。

ps:/proc/scsi/usb-storage-0目录下有U盘挂载信息

对于 （上电前SD卡或者U盘已经插上，并且系统设置为自动挂载）情况下NETLINK不适用的情况，可参考statfs解决。在上一篇中有介绍。