udhcp源碼剖析(五)——DHCP客戶端重要的數據結構和初始化配置


數據結構


和服務器類似,客戶端也維護著一個全局的數據結構client_config,用於所有的DHCP服務。


struct client_config_t client_config = {
/* Default options. */
abort_if_no_lease: 0,
foreground: 0,
quit_after_lease: 0,
background_if_no_lease: 0,
interface: "eth0",
pidfile: NULL,
script: DEFAULT_SCRIPT,
clientid: NULL,
hostname: NULL,
ifindex: 0,
arp: "\0\0\0\0\0\0", /* appease gcc-3.0 */
};

該結構在dhcpc.h中定義,並在dhcpc.c中設置默認值


struct client_config_t client_config = {
/* Default options. */
abort_if_no_lease: 0,
foreground: 0,
quit_after_lease: 0,
background_if_no_lease: 0,
interface: "eth0",
pidfile: NULL,
script: DEFAULT_SCRIPT,
clientid: NULL,
hostname: NULL,
ifindex: 0,
arp: "\0\0\0\0\0\0", /* appease gcc-3.0 */
};

其它全局變量


其餘所需要的重要的全局變量都以簡單數據結構給出,並沒有專門設計復雜結構。


static int state;
static unsigned long requested_ip; /* = 0,請求的IP */
static unsigned long server_addr; //服務器地址
static unsigned long timeout; //租約超時時刻
static int packet_num; /* = 0 */ //可認為是連續重復發送數據包的次數
static int fd; //本地socket監聽的fd
static int signal_pipe[2]; //本地接收signal消息的pipe fd

udhcpc_main的初始化和配置


dhcpc的初始化和dhcpd類似,但是簡化瞭很多操作,並且添加瞭對傳入參數的解析和處理。


解析arg選項


對啟動時傳遞的arg選項的解析,通過這些選項,DHCP可以選擇多種模式運行,比如傳遞參數q,即設置quit_after_lease=1,客戶端將在成功獲得lease之後退出。


enum {
OPT_c = 1 << 0,
OPT_C = 1 << 1,
OPT_V = 1 << 2,
OPT_f = 1 << 3,
OPT_b = 1 << 4,
OPT_H = 1 << 5,
OPT_h = 1 << 6,
OPT_F = 1 << 7,
OPT_i = 1 << 8,
OPT_n = 1 << 9,
OPT_p = 1 << 10,
OPT_q = 1 << 11,
OPT_R = 1 << 12,
OPT_r = 1 << 13,
OPT_s = 1 << 14,
OPT_T = 1 << 15,
OPT_t = 1 << 16,
OPT_v = 1 << 17,
OPT_S = 1 << 18,
};
#if ENABLE_GETOPT_LONG
static const char udhcpc_longopts[] ALIGN1 =
"clientid\0" Required_argument "c"
"clientid-none\0" No_argument "C"
"vendorclass\0" Required_argument "V"
"foreground\0" No_argument "f"
"background\0" No_argument "b"
"hostname\0" Required_argument "H"
"hostname\0" Required_argument "h"
"fqdn\0" Required_argument "F"
"interface\0" Required_argument "i"
"now\0" No_argument "n"
"pidfile\0" Required_argument "p"
"quit\0" No_argument "q"
"release\0" No_argument "R"
"request\0" Required_argument "r"
"script\0" Required_argument "s"
"timeout\0" Required_argument "T"
"version\0" No_argument "v"
"retries\0" Required_argument "t"
"syslog\0" No_argument "S"
;
#endif
/* Default options. */
client_config.interface = "eth0";
client_config.script = DEFAULT_SCRIPT;
client_config.retries = 3;
client_config.timeout = 3;

/* Parse command line */
opt_complementary = "c--C:C--c" // mutually exclusive
":hH:Hh"; // -h and -H are the same
#if ENABLE_GETOPT_LONG
applet_long_options = udhcpc_longopts;
#endif
opt = getopt32(argv, "c:CV:fbH:h:F:i:np:qRr:s:T:t:vS",
&str_c, &str_V, &str_h, &str_h, &str_F,
&client_config.interface, &client_config.pidfile, &str_r,
&client_config.script, &str_T, &str_t
);

if (opt & OPT_c)
client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, str_c, 0);
//if (opt & OPT_C)
if (opt & OPT_V)
client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, str_V, 0);
if (opt & OPT_f)
client_config.foreground = 1;
if (opt & OPT_b)
client_config.background_if_no_lease = 1;
if (opt & OPT_h)
client_config.hostname = alloc_dhcp_option(DHCP_HOST_NAME, str_h, 0);
if (opt & OPT_F) {
client_config.fqdn = alloc_dhcp_option(DHCP_FQDN, str_F, 3);
/* Flags: 0000NEOS
S: 1 => Client requests Server to update A RR in DNS as well as PTR
O: 1 => Server indicates to client that DNS has been updated regardless
E: 1 => Name data is DNS format, i.e. <4>host<6>domain<4>com<0> not "host.domain.com"
N: 1 => Client requests Server to not update DNS
*/
client_config.fqdn[OPT_DATA + 0] = 0x1;
/* client_config.fqdn[OPT_DATA + 1] = 0; - redundant */
/* client_config.fqdn[OPT_DATA + 2] = 0; - redundant */
}
// if (opt & OPT_i) client_config.interface = ...
if (opt & OPT_n)
client_config.abort_if_no_lease = 1;
// if (opt & OPT_p) client_config.pidfile = ...
if (opt & OPT_q)
client_config.quit_after_lease = 1;
if (opt & OPT_R)
client_config.release_on_quit = 1;
if (opt & OPT_r)
requested_ip = inet_addr(str_r);
// if (opt & OPT_s) client_config.script = ...
if (opt & OPT_T)
client_config.timeout = xatoi_u(str_T);
if (opt & OPT_t)
client_config.retries = xatoi_u(str_t);
if (opt & OPT_v) {
printf("version %s\n", BB_VER);
return 0;
}

if (opt & OPT_S) {
openlog(applet_name, LOG_PID, LOG_LOCAL0);
logmode |= LOGMODE_SYSLOG;
}

讀取接口信息和設置信號處理器


這一步和服務器的基本一致,註意這裡的不同是對clientid的初始化,以及run_script。


    if (read_interface(client_config.interface, &client_config.ifindex,
NULL, client_config.arp))
return 1;

/* Make sure fd 0,1,2 are open */
bb_sanitize_stdio();
/* Equivalent of doing a fflush after every \n */
setlinebuf(stdout);

/* Create pidfile */
write_pidfile(client_config.pidfile);
/* if (!..) bb_perror_msg("cannot create pidfile %s", pidfile); */

/* Goes to stdout and possibly syslog */
bb_info_msg("%s (v%s) started", applet_name, BB_VER);

/* if not set, and not suppressed, setup the default client ID */
if (!client_config.clientid && !(opt & OPT_C)) {
client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, "", 7);
client_config.clientid[OPT_DATA] = 1;
memcpy(client_config.clientid + OPT_DATA+1, client_config.arp, 6);
}

if (!client_config.vendorclass)
client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, "udhcp "BB_VER, 0);

/* setup the signal pipe */
udhcp_sp_setup();

state = INIT_SELECTING;
udhcp_run_script(NULL, "deconfig");
change_mode(LISTEN_RAW);
tv.tv_sec = 0;
goto jump_in;

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