android系統的main函數，也稱1號進程，下面做一下簡單的分析
int main(int argc, char **argv)
{
int fd_count = 0;
struct pollfd ufds[4];
char *tmpdev;
char* debuggable;
char tmp[32];
int property_set_fd_init = 0;
int signal_fd_init = 0;
int keychord_fd_init = 0;
bool is_charger = false;
if (!strcmp(basename(argv[0]), "ueventd"))
return ueventd_main(argc, argv);
if (!strcmp(basename(argv[0]), "watchdogd"))
return watchdogd_main(argc, argv);
/* clear the umask */
umask(0);
/* Get the basic filesystem setup we need put
* together in the initramdisk on / and then we'll
* let the rc file figure out the rest.
*/
mkdir("/dev", 0755);
mkdir("/proc", 0755);
mkdir("/sys", 0755);
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
mount("proc", "/proc", "proc", 0, NULL);
mount("sysfs", "/sys", "sysfs", 0, NULL);
/* indicate that booting is in progress to background fw loaders, etc */
close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));
/* We must have some place other than / to create the
* device nodes for kmsg and null, otherwise we won't
* be able to remount / read-only later on.
* Now that tmpfs is mounted on /dev, we can actually
* talk to the outside world.
*/
open_devnull_stdio();
klog_init();
property_init();
get_hardware_name(hardware, &revision);
process_kernel_cmdline();
union selinux_callback cb;
cb.func_log = klog_write;
selinux_set_callback(SELINUX_CB_LOG, cb);
cb.func_audit = audit_callback;
selinux_set_callback(SELINUX_CB_AUDIT, cb);
selinux_initialize();
/* These directories were necessarily created before initial policy load
* and therefore need their security context restored to the proper value.
* This must happen before /dev is populated by ueventd.
*/
restorecon("/dev");
restorecon("/dev/socket");
restorecon("/dev/__properties__");
restorecon_recursive("/sys");
is_charger = !strcmp(bootmode, "charger");
INFO("property init\n");
//printk("=================[init.c] property init !\n");
if (!is_charger)
property_load_boot_defaults();
INFO("reading config file\n");
init_parse_config_file("/init.rc");
action_for_each_trigger("early-init", action_add_queue_tail);
queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(keychord_init_action, "keychord_init");
queue_builtin_action(console_init_action, "console_init");
/* execute all the boot actions to get us started */
action_for_each_trigger("init", action_add_queue_tail);
/* skip mounting filesystems in charger mode */
if (!is_charger) {
action_for_each_trigger("early-fs", action_add_queue_tail);
action_for_each_trigger("fs", action_add_queue_tail);
action_for_each_trigger("post-fs", action_add_queue_tail);
action_for_each_trigger("post-fs-data", action_add_queue_tail);
}
/* Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
* wasn't ready immediately after wait_for_coldboot_done
*/
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(property_service_init_action, "property_service_init");
queue_builtin_action(signal_init_action, "signal_init");
queue_builtin_action(check_startup_action, "check_startup");
if (is_charger) {
action_for_each_trigger("charger", action_add_queue_tail);
} else {
action_for_each_trigger("early-boot", action_add_queue_tail);
action_for_each_trigger("boot", action_add_queue_tail);
}
/* run all property triggers based on current state of the properties */
queue_builtin_action(queue_property_triggers_action, "queue_property_triggers");
#if BOOTCHART
queue_builtin_action(bootchart_init_action, "bootchart_init");
#endif
for(;;) {
int nr, i, timeout = -1;
execute_one_command();
restart_processes();
if (!property_set_fd_init && get_property_set_fd() > 0) {
ufds[fd_count].fd = get_property_set_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
property_set_fd_init = 1;
}
if (!signal_fd_init && get_signal_fd() > 0) {
ufds[fd_count].fd = get_signal_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
signal_fd_init = 1;
}
if (!keychord_fd_init && get_keychord_fd() > 0) {
ufds[fd_count].fd = get_keychord_fd();
ufds[fd_count].events = POLLIN;
ufds[fd_count].revents = 0;
fd_count++;
keychord_fd_init = 1;
}
if (process_needs_restart) {
timeout = (process_needs_restart - gettime()) * 1000;
if (timeout < 0)
timeout = 0;
}
if (!action_queue_empty() || cur_action)
timeout = 0;
#if BOOTCHART
if (bootchart_count > 0) {
if (timeout < 0 || timeout > BOOTCHART_POLLING_MS)
timeout = BOOTCHART_POLLING_MS;
if (bootchart_step() < 0 || --bootchart_count == 0) {
bootchart_finish();
bootchart_count = 0;
}
}
#endif
nr = poll(ufds, fd_count, timeout);
if (nr <= 0)
continue;
for (i = 0; i < fd_count; i++) {
if (ufds[i].revents == POLLIN) {
if (ufds[i].fd == get_property_set_fd())
handle_property_set_fd();
else if (ufds[i].fd == get_keychord_fd())
handle_keychord();
else if (ufds[i].fd == get_signal_fd())
handle_signal();
}
}
}
return 0;
}1. /* clear the umask */
umask(0);
init進程創建的文件或者目錄默認權限爲 0777
2.創建文件系統
/* Get the basic filesystem setup we need put
* together in the initramdisk on / and then we'll
* let the rc file figure out the rest.
*/
mkdir("/dev", 0755);
mkdir("/proc", 0755);
mkdir("/sys", 0755);
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
mount("proc", "/proc", "proc", 0, NULL);
mount("sysfs", "/sys", "sysfs", 0, NULL);
3.創建空白設備節點和初始化日誌節點
open_devnull_stdio();
klog_init();
property_init();
get_hardware_name(hardware, &revision);
//get_hardware_name()方法用於解析/proc/cpuinfo文件獲取硬件信息，
並用於拼接成一個init.<hardware_name>.rc文件，繼續解析。
process_kernel_cmdline();
//解析/proc/cmdline文件，將其中的屬性導入Android系統全局變量
union selinux_callback cb; cb.func_log = klog_write; selinux_set_callback(SELINUX_CB_LOG, cb); cb.func_audit = audit_callback; selinux_set_callback(SELINUX_CB_AUDIT, cb);
3.創建空白設備節點和初始化日誌節點
open_devnull_stdio();
klog_init();
property_init();
get_hardware_name(hardware, &revision);
//get_hardware_name()方法用於解析/proc/cpuinfo文件獲取硬件信息，並用於拼接成一個init.<hardware_name>.rc文件，繼續解析。
process_kernel_cmdline();
//解析/proc/cmdline文件，將其中的屬性導入Android系統全局變量
union selinux_callback cb; cb.func_log = klog_write; selinux_set_callback(SELINUX_CB_LOG, cb); cb.func_audit = audit_callback; selinux_set_callback(SELINUX_CB_AUDIT, cb);
4. 解析並初始化 init.rc
INFO("reading config file\n");
init_parse_config_file("/init.rc");
action_for_each_trigger("early-init", action_add_queue_tail);
queue_builtin_action(wait_for_coldboot_done_action, "wait_for_coldboot_done");
queue_builtin_action(mix_hwrng_into_linux_rng_action, "mix_hwrng_into_linux_rng");
queue_builtin_action(keychord_init_action, "keychord_init");
queue_builtin_action(console_init_action, "console_init");
init.rc的解析結果是形成action_list（on關鍵字相關的部分），service_list（service_關鍵字相關的部分）以及action_queue（需要執行的命令或服務），以便後續流程使用。
5.主循環 循環執行並解析命令
execute_one_command();
restart_processes();
void execute_one_command(void)
{
int ret;
if (!cur_action || !cur_command || is_last_command(cur_action, cur_command)) {
cur_action = action_remove_queue_head();
cur_command = NULL;
if (!cur_action)
return;
INFO("processing action %p (%s)\n", cur_action, cur_action->name);
cur_command = get_first_command(cur_action);
} else {
cur_command = get_next_command(cur_action, cur_command);
}
if (!cur_command)
return;
ret = cur_command->func(cur_command->nargs, cur_command->args);
INFO("command '%s' r=%d\n", cur_command->args[0], ret);
}
static void restart_processes()
{
process_needs_restart = 0;
service_for_each_flags(SVC_RESTARTING,
restart_service_if_needed);
}
循環執行並解析命令,如下是init.rc的部分腳本程序
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
class main
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart media
onrestart restart netd
service drm /system/bin/drmserver
class main
user drm
group drm system inet drmrpc
service media /system/bin/mediaserver
class main
user media
group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
ioprio rt 4