int mdev_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int mdev_main(int argc UNUSED_PARAM, char **argv)
{
RESERVE_CONFIG_BUFFER(temp, PATH_MAX + SCRATCH_SIZE);

INIT_G();

if ENABLE_FEATURE_MDEV_CONF

G.filename = "/etc/mdev.conf";

endif

bb_sanitize_stdio();

umask(0);

xchdir("/dev");--------------------------------------------------?????????/dev??

if (argv[1] && strcmp(argv[1], "-s") == 0) {---------------------mdev -s?????/sys/dev???????
    /*
     * Scan: mdev -s
     */
    struct stat st;

if ENABLE_FEATURE_MDEV_CONF

    /* Same as xrealloc_vector(NULL, 4, 0): */
    G.rule_vec = xzalloc((1 << 4) * sizeof(*G.rule_vec));

endif

    xstat("/", &st);
    G.root_major = major(st.st_dev);
    G.root_minor = minor(st.st_dev);

    putenv((char*)"ACTION=add");

    /* Create all devices from /sys/dev hierarchy */
    recursive_action("/sys/dev",
             ACTION_RECURSE | ACTION_FOLLOWLINKS,
             fileAction, dirAction, temp, 0);----------------????????????/sys/dev??????????dev??????/etc/mdev.con??????????
} else {
    char *fw;
    char *seq;
    char *action;
    char *env_devname;
    char *env_devpath;
    unsigned my_pid;
    unsigned seqnum = seqnum; /* for compiler */
    int seq_fd;
    smalluint op;

    /* Hotplug:
     * env ACTION=... DEVPATH=... SUBSYSTEM=... [SEQNUM=...] mdev
     * ACTION can be "add", "remove", "change"
     * DEVPATH is like "/block/sda" or "/class/input/mice"
     */
    env_devname = getenv("DEVNAME"); /* can be NULL */----------????kobject_uevent_env()?????????????????do_execve()????mdev????getenv????
    G.subsystem = getenv("SUBSYSTEM");
    action = getenv("ACTION");
    env_devpath = getenv("DEVPATH");
    if (!action || !env_devpath /*|| !G.subsystem*/)
        bb_show_usage();
    fw = getenv("FIRMWARE");
    seq = getenv("SEQNUM");
    op = index_in_strings(keywords, action);--------------------keywords???add?remove???op???OP_add?OP_remove?

...
snprintf(temp, PATH_MAX, "/sys%s", env_devpath);
if (op == OP_remove) {
/* Ignoring "remove firmware". It was reported
* to happen and to cause erroneous deletion
* of device nodes. */
if (!fw)
make_device(env_devname, temp, op);-----------------?temp????????env_devnam??????
}
else {
make_device(env_devname, temp, op);---------------------??temp??????env_devname????
if (ENABLE_FEATURE_MDEV_LOAD_FIRMWARE) {
if (op == OP_add && fw)
load_firmware(fw, temp);------------------------?fw?????temp????
}
}
...
}

if (ENABLE_FEATURE_CLEAN_UP)
    RELEASE_CONFIG_BUFFER(temp);

return EXIT_SUCCESS;

}