libnetutils 中的ｄｈｃｐ_ｕｔｉｌｓ.ｃ，用来控制 dhcpcd_eth0 守护进程

最新推荐文章于 2022-02-25 17:25:14 发布

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#interface #cmd #null #server #system #properties

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本文介绍了一个用于管理DHCP客户端守护进程的实用程序，包括启动、停止DHCP客户端、请求IP地址更新、释放租约等功能，并详细解释了相关函数的工作原理。

1. 全局变量初始化：

/* Utilities for managing the dhcpcd DHCP client daemon */

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

#include <cutils/properties.h>

static const char DAEMON_NAME[]        = "dhcpcd";
static const char DAEMON_PROP_NAME[]   = "init.svc.dhcpcd";
static const char HOSTNAME_PROP_NAME[] = "net.hostname";
static const char DHCP_PROP_NAME_PREFIX[]  = "dhcp";
static const int NAP_TIME = 200;   /* wait for 200ms at a time */
                                  /* when polling for property values */
static const char DAEMON_NAME_RENEW[]  = "iprenew";
static char errmsg[100];
/* interface suffix on dhcpcd */
#define MAX_DAEMON_SUFFIX 25

2. dhcp_do_request(), 开始DHCP之后，会首先调用这个函数：

/*
 * Start the dhcp client daemon, and wait for it to finish
 * configuring the interface.
 */
int dhcp_do_request(const char *interface,
                    char *ipaddr,
                    char *gateway,
                    uint32_t *prefixLength,
                    char *dns1,
                    char *dns2,
                    char *server,
                    uint32_t  *lease)
{
    char result_prop_name[PROPERTY_KEY_MAX];
    char daemon_prop_name[PROPERTY_KEY_MAX];
    char prop_value[PROPERTY_VALUE_MAX] = {'\0'};
    char daemon_cmd[PROPERTY_VALUE_MAX * 2];
    const char *ctrl_prop = "ctl.start";
    const char *desired_status = "running";  //用来判断running状态
    char daemon_suffix[MAX_DAEMON_SUFFIX];

    get_daemon_suffix(interface, daemon_suffix);

    snprintf(result_prop_name, sizeof(result_prop_name), "%s.%s.result",
            DHCP_PROP_NAME_PREFIX,
            interface);

    snprintf(daemon_prop_name, sizeof(daemon_prop_name), "%s_%s",
            DAEMON_PROP_NAME,
            daemon_suffix);

    /* Erase any previous setting of the dhcp result property */
    property_set(result_prop_name, "");

    /* Start the daemon and wait until it's ready */
    if (property_get(HOSTNAME_PROP_NAME, prop_value, NULL) && (prop_value[0] != '\0'))
        snprintf(daemon_cmd, sizeof(daemon_cmd), "%s_%s:-h %s %s", DAEMON_NAME, daemon_suffix,
                 prop_value, interface);
    else
        snprintf(daemon_cmd, sizeof(daemon_cmd), "%s_%s:%s", DAEMON_NAME, daemon_suffix, interface);
    memset(prop_value, '\0', PROPERTY_VALUE_MAX);
    property_set(ctrl_prop, daemon_cmd);
    if (wait_for_property(daemon_prop_name, desired_status, 10) < 0) {
        snprintf(errmsg, sizeof(errmsg), "%s", "Timed out waiting for dhcpcd to start");
        return -1;
    }

    /* Wait for the daemon to return a result */
    if (wait_for_property(result_prop_name, NULL, 30) < 0) {
        snprintf(errmsg, sizeof(errmsg), "%s", "Timed out waiting for DHCP to finish");
        return -1;
    }

    if (!property_get(result_prop_name, prop_value, NULL)) {
        /* shouldn't ever happen, given the success of wait_for_property() */
        snprintf(errmsg, sizeof(errmsg), "%s", "DHCP result property was not set");
        return -1;
    }
    if (strcmp(prop_value, "ok") == 0) {
        char dns_prop_name[PROPERTY_KEY_MAX];
        if (fill_ip_info(interface, ipaddr, gateway, prefixLength, dns1, dns2, server, lease)
                == -1) {
            return -1;
        }

        /* copy dns data to system properties - TODO - remove this after we have async
         * notification of renewal's */
        snprintf(dns_prop_name, sizeof(dns_prop_name), "net.%s.dns1", interface);
        property_set(dns_prop_name, *dns1 ? ipaddr_to_string(*dns1) : "");
        snprintf(dns_prop_name, sizeof(dns_prop_name), "net.%s.dns2", interface);
        property_set(dns_prop_name, *dns2 ? ipaddr_to_string(*dns2) : "");
        return 0;
    } else {
        snprintf(errmsg, sizeof(errmsg), "DHCP result was %s", prop_value);
        return -1;
    }
}

a. wait_for_property():

/*
 * Wait for a system property to be assigned a specified value.
 * If desired_value is NULL, then just wait for the property to
 * be created with any value. maxwait is the maximum amount of
 * time in seconds to wait before giving up.
 */
static int wait_for_property(const char *name, const char *desired_value, int maxwait)
{
    char value[PROPERTY_VALUE_MAX] = {'\0'};
    int maxnaps = (maxwait * 1000) / NAP_TIME;

    if (maxnaps < 1) {
        maxnaps = 1;
    }

    while (maxnaps-- > 0) {
        usleep(NAP_TIME * 1000);
        if (property_get(name, value, NULL)) {
            if (desired_value == NULL ||
                    strcmp(value, desired_value) == 0) {
                return 0;
            }
        }
    }
    return -1; /* failure */
}

b. fill_ip_info():填充IP 数据

static int fill_ip_info(const char *interface,
                     char *ipaddr,
                     char *gateway,
                     uint32_t *prefixLength,
                     char *dns1,
                     char *dns2,
                     char *server,
                     uint32_t  *lease)
{
    char prop_name[PROPERTY_KEY_MAX];
    char prop_value[PROPERTY_VALUE_MAX];

    snprintf(prop_name, sizeof(prop_name), "%s.%s.ipaddress", DHCP_PROP_NAME_PREFIX, interface);
    property_get(prop_name, ipaddr, NULL);

    snprintf(prop_name, sizeof(prop_name), "%s.%s.gateway", DHCP_PROP_NAME_PREFIX, interface);
    property_get(prop_name, gateway, NULL);

    snprintf(prop_name, sizeof(prop_name), "%s.%s.server", DHCP_PROP_NAME_PREFIX, interface);
    property_get(prop_name, server, NULL);

    //TODO: Handle IPv6 when we change system property usage
    if (strcmp(gateway, "0.0.0.0") == 0) {
        //DHCP server is our best bet as gateway
        strncpy(gateway, server, PROPERTY_VALUE_MAX);
    }

    snprintf(prop_name, sizeof(prop_name), "%s.%s.mask", DHCP_PROP_NAME_PREFIX, interface);
    if (property_get(prop_name, prop_value, NULL)) {
        int p;
        // this conversion is v4 only, but this dhcp client is v4 only anyway
        in_addr_t mask = ntohl(inet_addr(prop_value));
        // Check netmask is a valid IP address.  ntohl gives NONE response (all 1's) for
        // non 255.255.255.255 inputs.  if we get that value check if it is legit..
        if (mask == INADDR_NONE && strcmp(prop_value, "255.255.255.255") != 0) {
            snprintf(errmsg, sizeof(errmsg), "DHCP gave invalid net mask %s", prop_value);
            return -1;
        }
        for (p = 0; p < 32; p++) {
            if (mask == 0) break;
            // check for non-contiguous netmask, e.g., 255.254.255.0
            if ((mask & 0x80000000) == 0) {
                snprintf(errmsg, sizeof(errmsg), "DHCP gave invalid net mask %s", prop_value);
                return -1;
            }
            mask = mask << 1;
        }
        *prefixLength = p;
    }
    snprintf(prop_name, sizeof(prop_name), "%s.%s.dns1", DHCP_PROP_NAME_PREFIX, interface);
    property_get(prop_name, dns1, NULL);

    snprintf(prop_name, sizeof(prop_name), "%s.%s.dns2", DHCP_PROP_NAME_PREFIX, interface);
    property_get(prop_name, dns2, NULL);

    snprintf(prop_name, sizeof(prop_name), "%s.%s.leasetime", DHCP_PROP_NAME_PREFIX, interface);
    if (property_get(prop_name, prop_value, NULL)) {
        *lease = atol(prop_value);
    }
    return 0;
}

3. stop_dhcp() --- 停止DHCP 时，会调用这个函数

/**
 * Stop the DHCP client daemon.
 */
int dhcp_stop(const char *interface)
{
    char result_prop_name[PROPERTY_KEY_MAX];
    char daemon_prop_name[PROPERTY_KEY_MAX];
    char daemon_cmd[PROPERTY_VALUE_MAX * 2];
    const char *ctrl_prop = "ctl.stop";
    const char *desired_status = "stopped";

    char daemon_suffix[MAX_DAEMON_SUFFIX];

    get_daemon_suffix(interface, daemon_suffix);

    snprintf(result_prop_name, sizeof(result_prop_name), "%s.%s.result",
            DHCP_PROP_NAME_PREFIX,
            interface);

    snprintf(daemon_prop_name, sizeof(daemon_prop_name), "%s_%s",
            DAEMON_PROP_NAME,
            daemon_suffix);

    snprintf(daemon_cmd, sizeof(daemon_cmd), "%s_%s", DAEMON_NAME, daemon_suffix);

    /* Stop the daemon and wait until it's reported to be stopped */
    property_set(ctrl_prop, daemon_cmd);
    if (wait_for_property(daemon_prop_name, desired_status, 5) < 0) {
        return -1;
    }
    property_set(result_prop_name, "failed");
    return 0;
}

4. dhcp_do_request_renew（）

/**
 * Run WiMAX dhcp renew service.
 * "wimax_renew" service shoud be included in init.rc.
 */
int dhcp_do_request_renew(const char *interface,
                    in_addr_t *ipaddr,
                    in_addr_t *gateway,
                    uint32_t *prefixLength,
                    in_addr_t *dns1,
                    in_addr_t *dns2,
                    in_addr_t *server,
                    uint32_t  *lease)
{
    char result_prop_name[PROPERTY_KEY_MAX];
    char prop_value[PROPERTY_VALUE_MAX] = {'\0'};
    char daemon_cmd[PROPERTY_VALUE_MAX * 2];
    const char *ctrl_prop = "ctl.start";

    char daemon_suffix[MAX_DAEMON_SUFFIX];

    get_daemon_suffix(interface, daemon_suffix);

    snprintf(result_prop_name, sizeof(result_prop_name), "%s.%s.result",
            DHCP_PROP_NAME_PREFIX,
            interface);

    /* Erase any previous setting of the dhcp result property */
    property_set(result_prop_name, "");

    /* Start the renew daemon and wait until it's ready */
    snprintf(daemon_cmd, sizeof(daemon_cmd), "%s_%s:%s", DAEMON_NAME_RENEW,
            daemon_suffix, interface);
    memset(prop_value, '\0', PROPERTY_VALUE_MAX);
    property_set(ctrl_prop, daemon_cmd);

    /* Wait for the daemon to return a result */
    if (wait_for_property(result_prop_name, NULL, 30) < 0) {
        snprintf(errmsg, sizeof(errmsg), "%s", "Timed out waiting for DHCP Renew to finish");
        return -1;
    }

    if (!property_get(result_prop_name, prop_value, NULL)) {
        /* shouldn't ever happen, given the success of wait_for_property() */
        snprintf(errmsg, sizeof(errmsg), "%s", "DHCP Renew result property was not set");
        return -1;
    }
    if (strcmp(prop_value, "ok") == 0) {
        fill_ip_info(interface, ipaddr, gateway, prefixLength, dns1, dns2, server, lease);
        return 0;
    } else {
        snprintf(errmsg, sizeof(errmsg), "DHCP Renew result was %s", prop_value);
        return -1;
    }
}

5. dhcp_release_lease(const char *interface)

/**
 * Release the current DHCP client lease.
 */
int dhcp_release_lease(const char *interface)
{
    char daemon_prop_name[PROPERTY_KEY_MAX];
    char daemon_cmd[PROPERTY_VALUE_MAX * 2];
    const char *ctrl_prop = "ctl.stop";
    const char *desired_status = "stopped";

    char daemon_suffix[MAX_DAEMON_SUFFIX];

    get_daemon_suffix(interface, daemon_suffix);

    snprintf(daemon_prop_name, sizeof(daemon_prop_name), "%s_%s",
            DAEMON_PROP_NAME,
            daemon_suffix);

    snprintf(daemon_cmd, sizeof(daemon_cmd), "%s_%s", DAEMON_NAME, daemon_suffix);

    /* Stop the daemon and wait until it's reported to be stopped */
    property_set(ctrl_prop, daemon_cmd);
    if (wait_for_property(daemon_prop_name, desired_status, 5) < 0) {
        return -1;
    }
    return 0;
}