标签：android启动优化 android init init android 启动流程 android 启动速度
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LOCAL_MODULE:= init LOCAL_FORCE_STATIC_EXECUTABLE := true LOCAL_MODULE_PATH := $(TARGET_ROOT_OUT) LOCAL_UNSTRIPPED_PATH := $(TARGET_ROOT_OUT_UNSTRIPPED) LOCAL_STATIC_LIBRARIES := libfs_mgr liblogwrap libcutils liblog libc libselinux libmincrypt libext4_utils_static LOCAL_ADDITIONAL_DEPENDENCIES += $(LOCAL_PATH)/Android.mk include $(BUILD_EXECUTABLE)我们发现，init的代码其实是被编译成了一个可执行的程序：
include $(BUILD_EXECUTABLE)
LOCAL_MODULE:= init
878 if (!ramdisk_execute_command)
879 ramdisk_execute_command = "/init";
880
881 if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
882 ramdisk_execute_command = NULL;
883 prepare_namespace();
884 }
我们发现，ramdisk_execute_command被初始化为了initsys_access((const char __user *) ramdisk_execute_command, 0)判断系统中是否存在/init的命令，如果不存在的话，会将ramdisk_execute_command置为NUll
init_post();而这个函数的实现如下：
795/* This is a non __init function. Force it to be noinline otherwise gcc
796 * makes it inline to init() and it becomes part of init.text section
797 */
798static noinline int init_post(void)
799{
800 /* need to finish all async __init code before freeing the memory */
801 async_synchronize_full();
802 free_initmem();
803 mark_rodata_ro();
804 system_state = SYSTEM_RUNNING;
805 numa_default_policy();
806
807
808 current->signal->flags |= SIGNAL_UNKILLABLE;
809
810 if (ramdisk_execute_command) {
811 run_init_process(ramdisk_execute_command);
812 printk(KERN_WARNING "Failed to execute %s\n",
813 ramdisk_execute_command);
814 }
815
816 /*
817 * We try each of these until one succeeds.
818 *
819 * The Bourne shell can be used instead of init if we are
820 * trying to recover a really broken machine.
821 */
822 if (execute_command) {
823 run_init_process(execute_command);
824 printk(KERN_WARNING "Failed to execute %s. Attempting "
825 "defaults...\n", execute_command);
826 }
827 run_init_process("/sbin/init");
828 run_init_process("/etc/init");
829 run_init_process("/bin/init");
830 run_init_process("/bin/sh");
831
832 panic("No init found. Try passing init= option to kernel. "
833 "See Linux Documentation/init.txt for guidance.");
834}
可以看到，当ramdisk_execute_command不为NULL的时候，就会去run run_init_process.<pre name="code" class="cpp" style="font-size: 13.63636302948px; line-height: 25.9943180084229px;">789static void run_init_process(const char *init_filename)
790{
791 argv_init[0] = init_filename;
792 kernel_execve(init_filename, argv_init, envp_init);
793}
794
标签：android启动优化 android init init android 启动流程 android 启动速度
原文地址：http://blog.csdn.net/chaoy1116/article/details/44724417
