u-boot环境变量

在u-boot命令行中输入print会得到所以的环境变量，这些环境变量都是在哪里定义的呢？？

先看看print命令在哪里实现

U_BOOT_CMD(printenv, CONFIG_SYS_MAXARGS, 1,do_env_print,"print environment variables","\n    - print values of all environment variables\n""printenv name ...\n""    - print value of environment variable 'name'");

文件common/Cmd_nvedit.c 定义了printenv命令，我们来看看它是从哪里打印的

int do_env_print (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]){int i;int rcode = 0;if (argc == 1) {/* print all env vars */rcode = env_print(NULL);if (!rcode)return 1;printf("\nEnvironment size: %d/%ld bytes\n",rcode, (ulong)ENV_SIZE);return 0;}/* print selected env vars */for (i = 1; i < argc; ++i) {int rc = env_print(argv[i]);if (!rc) {printf("## Error: \"%s\" not defined\n", argv[i]);++rcode;}}return rcode;}

env_print中

char *res = NULL;size_t len;/* print whole list */len = hexport('\n', &res, 0);if (len > 0) {puts(res);free(res);return len;}

再看hexport

ssize_t hexport(const char sep, char **resp, size_t size){return hexport_r(&htab, sep, resp, size);}

最终在函数hexport_r中找到这么一段

for (i = 1, n = 0, totlen = 0; i <= htab->size; ++i) {if (htab->table[i].used) {ENTRY *ep = &htab->table[i].entry;list[n++] = ep;totlen += strlen(ep->key) + 2;if (sep == '\0') {totlen += strlen(ep->data);} else {/* check if escapes are needed */char *s = ep->data;while (*s) {++totlen;/* add room for needed escape chars */if ((*s == sep) || (*s == '\\'))++totlen;++s;}}totlen += 2;/* for '=' and 'sep' char */}}

将结构体htab中的table结构体中的entry项的地址给ep

然后把ep的地址给数组list，在下文打印出list数组

for (i = 0, p = res; i < n; ++i) {char *s;s = list[i]->key;while (*s)*p++ = *s++;*p++ = '=';s = list[i]->data;while (*s) {if ((*s == sep) || (*s == '\\'))*p++ = '\\';/* escape */*p++ = *s++;}*p++ = sep;}

我们来搜索一下看看谁定义并填充了htab结构体

在同一个文件中找到htab的定义

static struct hsearch_data htab;

那么猜测填充这个htab的函数也在这个文件中

果然在同文件中找到函数hcreate

int hcreate(size_t nel){return hcreate_r(nel, &htab);}

int hcreate_r(size_t nel, struct hsearch_data *htab){/* Test for correct arguments.  */if (htab == NULL) {__set_errno(EINVAL);return 0;}/* There is still another table active. Return with error. */if (htab->table != NULL)return 0;/* Change nel to the first prime number not smaller as nel. */nel |= 1;/* make odd */while (!isprime(nel))nel += 2;htab->size = nel;htab->filled = 0;/* allocate memory and zero out */htab->table = (_ENTRY *) calloc(htab->size + 1, sizeof(_ENTRY));if (htab->table == NULL)return 0;/* everything went alright */return 1;}

搜索一下看看谁调用hcreate

竟然没有人调用hcreate？？这什么情况？不按套路出牌啊！

记得board_init_r函数中调用了一个环境变量初始化函数

/* initialize environment */env_relocate();

env_relocate中有

</pre><pre name="code" class="cpp">env_relocate_spec ();

结果弄了一堆env_relocate_spec ()不知道u-boot用的哪个,郁闷

最后根据编译u-boot时候的输出信息，common目录下包含了env_auto.o知道env_relocate_spec ()是在env_auto.c中定义

env_relocate_spec ()中

use_default();

找到use_default()

static void use_default(){char boot_cmd[100];puts("*** Warning - using default environment\n\n");if (default_environment_size > CONFIG_ENV_SIZE) {puts("*** Error - default environment is too large\n\n");return;}memset (env_ptr, 0, sizeof(env_t));memcpy (env_ptr->data,default_environment,default_environment_size);env_ptr->crc = crc32(0, env_ptr->data, ENV_SIZE);gd->env_valid = 1;env_import((const char *)env_ptr, 1);}

在这里用的缺省环境变量设置

我们来看看default_environment

uchar default_environment[] = {#ifdefCONFIG_BOOTARGS"bootargs="CONFIG_BOOTARGS"\0"#endif#ifdefCONFIG_BOOTCOMMAND"bootcmd="CONFIG_BOOTCOMMAND"\0"#endif#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)"bootdelay="MK_STR(CONFIG_BOOTDELAY)"\0"#endif#if defined(CONFIG_BAUDRATE) && (CONFIG_BAUDRATE >= 0)"baudrate="MK_STR(CONFIG_BAUDRATE)"\0"#endif#ifdefCONFIG_ETHADDR"ethaddr="MK_STR(CONFIG_ETHADDR)"\0"#endif#ifdefCONFIG_IPADDR"ipaddr="MK_STR(CONFIG_IPADDR)"\0"#endif#ifdefCONFIG_SERVERIP"serverip="MK_STR(CONFIG_SERVERIP)"\0"#endif#ifdefCONFIG_GATEWAYIP"gatewayip="MK_STR(CONFIG_GATEWAYIP)"\0"#endif#ifdefCONFIG_NETMASK"netmask="MK_STR(CONFIG_NETMASK)"\0"#endif"\0"};

再看看配置文件

#define CONFIG_ETHADDR00:40:5c:26:0a:5b#define CONFIG_NETMASK          255.255.255.0#define CONFIG_IPADDR192.168.0.20#define CONFIG_SERVERIP192.168.0.10#define CONFIG_GATEWAYIP192.168.0.1#define CONFIG_BOOTDELAY3/* Default boot commands for Android booting. */#define CONFIG_BOOTCOMMAND"movi read kernel 0 40008000;movi read rootfs 0 41000000 100000;bootm 40008000 41000000"#define CONFIG_BOOTARGS""

默认的环境变量为

bootargs= bootcmd=        movi read kernel 0 40008000;movi read rootfs 0 41000000 100000;bootm 40008000 41000000bootdelay=3baudrate=115200ethaddr=00:40:5c:26:0a:5bipaddr=        192.168.0.20serverip=192.168.0.10gatewayip=192.168.0.1netmask=255.255.255.0