我們平時在序列槽操作執行reboot時,系統的重新開機,與預期效果一緻,但是很多人以為是reboot這個bin檔案做了實際的動作,但事實是他隻是解析了你在reboot後面所追加的參數,發送指令,那麼最終是誰執行的呢?
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <cutils/properties.h>
#include <cutils/android_reboot.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int ret;
size_t prop_len;
char property_val[PROPERTY_VALUE_MAX];
const char *cmd = "reboot";
char *optarg = "";
opterr = 0;
do {
int c;
c = getopt(argc, argv, "p");
if (c == -1) {
break;
}
switch (c) {
case 'p':
cmd = "shutdown";
break;
case '?':
fprintf(stderr, "usage: %s [-p] [rebootcommand]\n", argv[0]);
exit(EXIT_FAILURE);
}
} while (1);
if(argc > optind + 1) {
fprintf(stderr, "%s: too many arguments\n", argv[0]);
exit(EXIT_FAILURE);
}
if (argc > optind)
optarg = argv[optind];
prop_len = snprintf(property_val, sizeof(property_val), "%s,%s", cmd, optarg);
if (prop_len >= sizeof(property_val)) {
fprintf(stderr, "reboot command too long: %s\n", optarg);
exit(EXIT_FAILURE);
}
ret = property_set(ANDROID_RB_PROPERTY, property_val);
if(ret < 0) {
perror("reboot");
exit(EXIT_FAILURE);
}
// Don't return early. Give the reboot command time to take effect
// to avoid messing up scripts which do "adb shell reboot && adb wait-for-device"
while(1) { pause(); }
fprintf(stderr, "Done\n");
return 0;
}
以上便是reboot的所有代碼,短小精悍,最重要的代碼:
ret = property_set(ANDROID_RB_PROPERTY, property_val);
這個則是在init程序中觸發的:
on property:sys.powerctl=*
powerctl ${sys.powerctl}
在init中調用
int do_powerctl(int nargs, char **args)
return android_reboot(cmd, 0, reboot_target);
然後是:
/system/core/libcutils/android_reboot.c 中的執行android_reboot();
case ANDROID_RB_RESTART2:
121 ret = __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
122 LINUX_REBOOT_CMD_RESTART2, arg); //arg = recovery
這個在bionic/libc/include/sys/reboot.h中定義的。說明這是一個标準的系統調用
extern int __reboot(int, int, int, void *);
具體到系統調用階段的我們不再贅述。