深入init进程(and5.1)
Init是系统的第一个进程，在初始化的时候会启动很多守护进程、装载文件系统、创建系统目录、初始化Android属性系统。
一、main函数
我们就来分析代码吧。
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"))//ueventd和watchdogd与init公用代码，可以在其mk文件中看到，ueventd和watchdogd只是软连接
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);//创建目录，以及mount上面是一些创建目录，挂载文件系统
close(open("/dev/.booting", O_WRONLY | O_CREAT, 0000));//创建一个空文件booting，表示正在初始化
/* 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();//创建共享区域存储属性值
get_hardware_name(hardware, &revision);
process_kernel_cmdline();//解析proc/cmdline
union selinux_callback cb;
cb.func_log = log_callback;
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");//看开机是否是关机充电模式
INFO("property init\n");
property_load_boot_defaults();//解析根目录下的default.prop文件，把文件中定义的属性值读取出来设置到属性系统中
二、解析init.rc
init_parse_config_file函数解析了init.rc文件
int init_parse_config_file(const char *fn)
{
char *data;
data = read_file(fn, 0);
if (!data) return -1;
parse_config(fn, data);
DUMP();
return 0;
}static void parse_config(const char *fn, char *s)
{
struct parse_state state;
struct listnode import_list;
struct listnode *node;
char *args[INIT_PARSER_MAXARGS];
int nargs;
nargs = 0;
state.filename = fn;
state.line = 0;
state.ptr = s;
state.nexttoken = 0;
state.parse_line = parse_line_no_op;
list_init(&import_list);
state.priv = &import_list;
for (;;) {
switch (next_token(&state)) {
case T_EOF://文件结束
state.parse_line(&state, 0, 0);
goto parser_done;
case T_NEWLINE://行结束
state.line++;
if (nargs) {
int kw = lookup_keyword(args[0]);
if (kw_is(kw, SECTION)) {//判断是否有新的section
state.parse_line(&state, 0, 0);
parse_new_section(&state, kw, nargs, args);
} else {
state.parse_line(&state, nargs, args);
}
nargs = 0;
}
break;
case T_TEXT://一个单词结束
if (nargs < INIT_PARSER_MAXARGS) {
args[nargs++] = state.text;
}
break;
}
}
parser_done:
list_for_each(node, &import_list) {
struct import *import = node_to_item(node, struct import, list);
int ret;
INFO("importing '%s'", import->filename);
ret = init_parse_config_file(import->filename);
if (ret)
ERROR("could not import file '%s' from '%s'\n",
import->filename, fn);
}
}
parse_config函数调用next_token函数就是寻找单词结束标志或行结束标志。如果是单词结束，就先存在args数组中，如果是行结束，根据第一个单词判断是否是一个section，“section”的标志是关键词on service import。如果是一个新的section，就调用parse_new_section开始一个新的section处理。
static void parse_new_section(struct parse_state *state, int kw,
int nargs, char **args)
{
printf("[ %s %s ]\n", args[0],
nargs > 1 ? args[1] : "");
switch(kw) {
case K_service://解析service
state->context = parse_service(state, nargs, args);
if (state->context) {
state->parse_line = parse_line_service;
return;
}
break;
case K_on:// 解析on
state->context = parse_action(state, nargs, args);
if (state->context) {
state->parse_line = parse_line_action;
return;
}
break;
case K_import://解析import的文件
parse_import(state, nargs, args);
break;
}
state->parse_line = parse_line_no_op;
}先看parse_service
static void *parse_service(struct parse_state *state, int nargs, char **args)
{
struct service *svc;
if (nargs < 3) {
parse_error(state, "services must have a name and a program\n");
return 0;
}
if (!valid_name(args[1])) {
parse_error(state, "invalid service name '%s'\n", args[1]);
return 0;
}
svc = service_find_by_name(args[1]);// 从service_list找，如果有了就退出
if (svc) {
parse_error(state, "ignored duplicate definition of service '%s'\n", args[1]);
return 0;
}
nargs -= 2;
svc = calloc(1, sizeof(*svc) + sizeof(char*) * nargs);
if (!svc) {
parse_error(state, "out of memory\n");
return 0;
}
svc->name = args[1];
svc->classname = "default";
memcpy(svc->args, args + 2, sizeof(char*) * nargs);
svc->args[nargs] = 0;
svc->nargs = nargs;
svc->onrestart.name = "onrestart";
list_init(&svc->onrestart.commands);
list_add_tail(&service_list, &svc->slist);//将service加到service_list链表
return svc;
}如果成功将parse_line_service赋给state->parse_line 这样在parse_config中就可以解析service了
case T_NEWLINE://行结束
state.line++;
if (nargs) {
int kw = lookup_keyword(args[0]);
if (kw_is(kw, SECTION)) {//判断是否有新的section
state.parse_line(&state, 0, 0);
parse_new_section(&state, kw, nargs, args);
} else {
state.parse_line(&state, nargs, args);//利用前面的赋值函数
}
nargs = 0;
}
break;那就看看parse_line_service函数就是解析各个项
static void parse_line_service(struct parse_state *state, int nargs, char **args)
{
struct service *svc = state->context;
struct command *cmd;
int i, kw, kw_nargs;
if (nargs == 0) {
return;
}
svc->ioprio_class = IoSchedClass_NONE;
kw = lookup_keyword(args[0]);
switch (kw) {
case K_capability:
break;
case K_class:
if (nargs != 2) {
parse_error(state, "class option requires a classname\n");
} else {
svc->classname = args[1];
}
break;
case K_console:
svc->flags |= SVC_CONSOLE;
break;
case K_disabled:
svc->flags |= SVC_DISABLED;
svc->flags |= SVC_RC_DISABLED;
break;
case K_ioprio:
。。。。。。。。而解析action如下，最后将action加到action_list中
static void *parse_action(struct parse_state *state, int nargs, char **args)
{
struct action *act;
if (nargs < 2) {
parse_error(state, "actions must have a trigger\n");
return 0;
}
if (nargs > 2) {
parse_error(state, "actions may not have extra parameters\n");
return 0;
}
act = calloc(1, sizeof(*act));
act->name = args[1];
list_init(&act->commands);
list_init(&act->qlist);
list_add_tail(&action_list, &act->alist);//加到action_list中
/* XXX add to hash */
return act;
}而和service同样会把parse_line_action赋给state->parse_line ，而在parse_line_action会解析各个命令了
static void parse_line_action(struct parse_state* state, int nargs, char **args)
{
struct command *cmd;
struct action *act = state->context;
int (*func)(int nargs, char **args);
int kw, n;
if (nargs == 0) {
return;
}
kw = lookup_keyword(args[0]);
if (!kw_is(kw, COMMAND)) {
parse_error(state, "invalid command '%s'\n", args[0]);
return;
}
n = kw_nargs(kw);
if (nargs < n) {
parse_error(state, "%s requires %d %s\n", args[0], n - 1,
n > 2 ? "arguments" : "argument");
return;
}
cmd = malloc(sizeof(*cmd) + sizeof(char*) * nargs);
cmd->func = kw_func(kw);
cmd->line = state->line;
cmd->filename = state->filename;
cmd->nargs = nargs;
memcpy(cmd->args, args, sizeof(char*) * nargs);
list_add_tail(&act->commands, &cmd->clist);
}
最后parse_import，将各个import的rc文件加入import_list
static void parse_import(struct parse_state *state, int nargs, char **args)
{
struct listnode *import_list = state->priv;
struct import *import;
char conf_file[PATH_MAX];
int ret;
if (nargs != 2) {
ERROR("single argument needed for import\n");
return;
}
ret = expand_props(conf_file, args[1], sizeof(conf_file));
if (ret) {
ERROR("error while handling import on line '%d' in '%s'\n",
state->line, state->filename);
return;
}
import = calloc(1, sizeof(struct import));
import->filename = strdup(conf_file);
list_add_tail(import_list, &import->list);
INFO("found import '%s', adding to import list", import->filename);
}在parse_config函数最后会对import_list链表中的文件再次解析，这样的话是先解析当前init.rc文件再解析之前import的文件
parser_done:
list_for_each(node, &import_list) {
struct import *import = node_to_item(node, struct import, list);
int ret;
INFO("importing '%s'", import->filename);
ret = init_parse_config_file(import->filename);
if (ret)
ERROR("could not import file '%s' from '%s'\n",
import->filename, fn);
}
}
三、将action加到action_queue
在解析init.rc的时候，只是将普通的on...解析成action加到action_list中，然后只有真正加入action_queue才会真正执行。下面将分析会把哪些aciton加入action_queue
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);
/* 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");
/* Don't mount filesystems or start core system services if in charger mode. */
if (is_charger) {//是否是关机充电模式，如果是这模式，很多都不启动
action_for_each_trigger("charger", action_add_queue_tail);
} else {
action_for_each_trigger("late-init", 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先看action_for_each_trigger，看看action_list有没有当前trigger，有就用函数执行它，而这个函数就是action_add_queue_tail
void action_for_each_trigger(const char *trigger,
void (*func)(struct action *act))
{
struct listnode *node;
struct action *act;
list_for_each(node, &action_list) {
act = node_to_item(node, struct action, alist);
if (!strcmp(act->name, trigger)) {
func(act);
}
}
}而action_add_queue_tail就是将这个action加到action_queue链表中，但是比如"late-init"这个trigger，里面有好多比如"fs"，先不加到action_queue链表中，要在execute_one_command的时候解析到这个action，才会根据这个action的cmd，再把"fs"这个action加到action_queue链表中。
void action_add_queue_tail(struct action *act)
{
if (list_empty(&act->qlist)) {
list_add_tail(&action_queue, &act->qlist);
}
}而queue_builtin_action也是将新建一个action，加到action_queue，也加到action_list里面。只是这是在init里面加的，而action_for_each_trigger是原先就在init.rc中的，所以action_for_each_trigger的cmd已经解析好了。
void queue_builtin_action(int (*func)(int nargs, char **args), char *name)
{
struct action *act;
struct command *cmd;
act = calloc(1, sizeof(*act));
act->name = name;
list_init(&act->commands);
list_init(&act->qlist);
cmd = calloc(1, sizeof(*cmd));
cmd->func = func;
cmd->args[0] = name;
cmd->nargs = 1;
list_add_tail(&act->commands, &cmd->clist);
list_add_tail(&action_list, &act->alist);
action_add_queue_tail(act);
}aciton一定得通过加入到action_queue才能被init执行，因此一般在init中加入on ......是不会被执行到的，除非放在一个会被触发的on...里面，再显示的调用trigger
四、循环执行action
for(;;) {
int nr, i, timeout = -1;
execute_one_command();
restart_processes();先分析execute_one_command函数
void execute_one_command(void)
{
int ret, i;
char cmd_str[256] = "";
if (!cur_action || !cur_command || is_last_command(cur_action, cur_command)) {//取每个action，如果是最后一个cmd了，那么下次就要先去action
cur_action = action_remove_queue_head();
cur_command = NULL;
if (!cur_action)
return;
INFO("processing action %p (%s)\n", cur_action, cur_action->name);
if (!strcmp(cur_action->name, "fs")) {
queue_builtin_action(set_usb_serial_action, "set_usb_serial_action");
}
cur_command = get_first_command(cur_action);
} else {//从每个action中取cmd
cur_command = get_next_command(cur_action, cur_command);
}
if (!cur_command)
return;
ret = cur_command->func(cur_command->nargs, cur_command->args);//执行每个cmd中的func
if (klog_get_level() >= KLOG_INFO_LEVEL) {//打印而已
for (i = 0; i < cur_command->nargs; i++) {
strlcat(cmd_str, cur_command->args[i], sizeof(cmd_str));
if (i < cur_command->nargs - 1) {
strlcat(cmd_str, " ", sizeof(cmd_str));
}
}
INFO("command '%s' action=%s status=%d (%s:%d)\n",
cmd_str, cur_action ? cur_action->name : "", ret, cur_command->filename,
cur_command->line);
}
}
五、系统是如何起init.rc中的service
一开始以为service是在main函数里的restart_processes起的，最后发现不对，restart_processes只对flags是SVC_RESTARTING的service进行重启，而去看解析init.rc的service的时候没有将service的flags初始化为SVC_RESTARTING，也就是说service的启动肯定是别的方式。
于是先去搜service_start这个函数，因为service启动肯定时调这个函数，发现了service_start_if_not_disabled这个函数：
static void service_start_if_not_disabled(struct service *svc)
{
if (!(svc->flags & SVC_DISABLED)) {
service_start(svc, NULL);
} else {
svc->flags |= SVC_DISABLED_START;
}
}只要service的flags不是SVC_DISABLED就启动。
然后又在do_class_start调用这个函数
int do_class_start(int nargs, char **args)
{
/* Starting a class does not start services
* which are explicitly disabled. They must
* be started individually.
*/
service_for_each_class(args[1], service_start_if_not_disabled);
return 0;
}而do_class_start又在下面这个地方调用，这就是个命令对应的函数，于是去搜init.rc
KEYWORD(class, OPTION, 0, 0)
KEYWORD(class_start, COMMAND, 1, do_class_start)
KEYWORD(class_stop, COMMAND, 1, do_class_stop)
KEYWORD(class_reset, COMMAND, 1, do_class_reset)
KEYWORD(console, OPTION, 0, 0)
仔细看了init.rc发现，很多service都有class这个关键词
service ueventd /sbin/ueventd
class core
critical
seclabel u:r:ueventd:s0
service logd /system/bin/logd
#class core
socket logd stream 0666 logd logd
socket logdr seqpacket 0666 logd logd
socket logdw dgram 0222 logd logd
seclabel u:r:logd:s0
service healthd /sbin/healthd
class core
critical
seclabel u:r:healthd:s0在init.rc确实有class_start main，class_start core这样命令的section，这样就明了，肯定在解析init.rc的section的时候没有仔细分析cmd导致的，我们再分析下好了。
on nonencrypted
class_start main
class_start late_start
on property:sys.chargeonly.mode=0
class_start core
start lc-oms-sa
#add for boot mode,endparse_line_action分析每行section的命令
static void parse_line_action(struct parse_state* state, int nargs, char **args)
{
struct command *cmd;
struct action *act = state->context;
int (*func)(int nargs, char **args);
int kw, n;
if (nargs == 0) {
return;
}
kw = lookup_keyword(args[0]);//先去分析命令
if (!kw_is(kw, COMMAND)) {
parse_error(state, "invalid command '%s'\n", args[0]);
return;
}
n = kw_nargs(kw);
if (nargs < n) {
parse_error(state, "%s requires %d %s\n", args[0], n - 1,
n > 2 ? "arguments" : "argument");
return;
}
cmd = malloc(sizeof(*cmd) + sizeof(char*) * nargs);
cmd->func = kw_func(kw);
cmd->line = state->line;
cmd->filename = state->filename;
cmd->nargs = nargs;
memcpy(cmd->args, args, sizeof(char*) * nargs);
list_add_tail(&act->commands, &cmd->clist);
}
分析下lookup_keyword函数是解析每个section的cmd的
static int lookup_keyword(const char *s)
{
switch (*s++) {
case 'c'://用首字母分类
if (!strcmp(s, "opy")) return K_copy;
if (!strcmp(s, "apability")) return K_capability;
if (!strcmp(s, "hdir")) return K_chdir;
if (!strcmp(s, "hroot")) return K_chroot;
if (!strcmp(s, "lass")) return K_class;
if (!strcmp(s, "lass_start")) return K_class_start;//看到class_start了
if (!strcmp(s, "lass_stop")) return K_class_stop;
if (!strcmp(s, "lass_reset")) return K_class_reset;
if (!strcmp(s, "onsole")) return K_console;
if (!strcmp(s, "hown")) return K_chown;
if (!strcmp(s, "hmod")) return K_chmod;
if (!strcmp(s, "ritical")) return K_critical;
break;
case 'd':
if (!strcmp(s, "isabled")) return K_disabled;
if (!strcmp(s, "omainname")) return K_domainname;
。。。。。再来看看kw_func函数，获取cmd的函数时，这里巧妙运用了宏
我们来看看，kw_func只是一个结构体数组中的一个变量
#define kw_func(kw) (keyword_info[kw].func)
再来看看这个结构体，define中##代表连接在一起，一个#代表将该项变成字符串
#define KEYWORD(symbol, flags, nargs, func) \
[ K_##symbol ] = { #symbol, func, nargs + 1, flags, },
static struct {
const char *name;
int (*func)(int nargs, char **args);
unsigned char nargs;
unsigned char flags;
} keyword_info[KEYWORD_COUNT] = {
[ K_UNKNOWN ] = { "unknown", 0, 0, 0 },
#include "keywords.h"
};有意思的是在这个结构体数组定义的时候，有一个头文件引进
由于在上面已经定义过KEYWORD了，所以这边就跳过了
#ifndef KEYWORD
int do_chroot(int nargs, char **args);
int do_chdir(int nargs, char **args);
int do_class_start(int nargs, char **args);
int do_class_stop(int nargs, char **args);
int do_class_reset(int nargs, char **args);
int do_domainname(int nargs, char **args);
int do_enable(int nargs, char **args);
int do_exec(int nargs, char **args);
int do_export(int nargs, char **args);
int do_hostname(int nargs, char **args);
int do_ifup(int nargs, char **args);
int do_insmod(int nargs, char **args);
int do_mkdir(int nargs, char **args);
int do_mount_all(int nargs, char **args);
int do_mount(int nargs, char **args);
int do_powerctl(int nargs, char **args);
int do_restart(int nargs, char **args);
int do_restorecon(int nargs, char **args);
int do_restorecon_recursive(int nargs, char **args);
int do_rm(int nargs, char **args);
int do_rmdir(int nargs, char **args);
int do_setcon(int nargs, char **args);
int do_setenforce(int nargs, char **args);
int do_setkey(int nargs, char **args);
int do_setprop(int nargs, char **args);
int do_setrlimit(int nargs, char **args);
int do_setsebool(int nargs, char **args);
int do_start(int nargs, char **args);
int do_stop(int nargs, char **args);
int do_swapon_all(int nargs, char **args);
int do_trigger(int nargs, char **args);
int do_symlink(int nargs, char **args);
int do_sysclktz(int nargs, char **args);
int do_write(int nargs, char **args);
int do_copy(int nargs, char **args);
int do_chown(int nargs, char **args);
int do_chmod(int nargs, char **args);
int do_loglevel(int nargs, char **args);
int do_load_persist_props(int nargs, char **args);
int do_load_all_props(int nargs, char **args);
int do_wait(int nargs, char **args);
#define __MAKE_KEYWORD_ENUM__
#define KEYWORD(symbol, flags, nargs, func) K_##symbol,
enum {
K_UNKNOWN,
#endif//直接到这
KEYWORD(capability, OPTION, 0, 0)//再看看上面KEYWORD宏的定义这段就变成 [ K_capablity ] = { "capablity", 0 , 0 + 1, OPTION },
KEYWORD(chdir, COMMAND, 1, do_chdir)
KEYWORD(chroot, COMMAND, 1, do_chroot)
KEYWORD(class, OPTION, 0, 0)
KEYWORD(class_start, COMMAND, 1, do_class_start)// [ K_class_start ] = { "class_start", do_class_start, 1 + 1, COMMAND } ,
KEYWORD(class_stop, COMMAND, 1, do_class_stop)
KEYWORD(class_reset, COMMAND, 1, do_class_reset)
KEYWORD(console, OPTION, 0, 0)
KEYWORD(critical, OPTION, 0, 0)
KEYWORD(disabled, OPTION, 0, 0)
。。。。。。。。。
而我们前面的lookup_keyword返回的是K_class_start，而下面自然也就是do_class_start函数
#define kw_func(kw) (keyword_info[kw].func)
而其实K_class_start 是一个枚举，我们看如何实现的，
#include "keywords.h"
#define KEYWORD(symbol, flags, nargs, func) \
[ K_##symbol ] = { #symbol, func, nargs + 1, flags, },
static struct {
const char *name;
int (*func)(int nargs, char **args);
unsigned char nargs;
unsigned char flags;
} keyword_info[KEYWORD_COUNT] = {
[ K_UNKNOWN ] = { "unknown", 0, 0, 0 },
#include "keywords.h"
};
看我们在这是先引入"keywords.h"文件，然后再在结构体数组中再引入的
第一次引入的时候"keywords.h"就变成枚举了
#ifndef KEYWORD//进入，下面把函数都定义了
int do_chroot(int nargs, char **args);
int do_chdir(int nargs, char **args);
int do_class_start(int nargs, char **args);
int do_class_stop(int nargs, char **args);
int do_class_reset(int nargs, char **args);
int do_domainname(int nargs, char **args);
int do_enable(int nargs, char **args);
int do_exec(int nargs, char **args);
int do_export(int nargs, char **args);
int do_hostname(int nargs, char **args);
int do_ifup(int nargs, char **args);
int do_insmod(int nargs, char **args);
int do_mkdir(int nargs, char **args);
int do_mount_all(int nargs, char **args);
int do_mount(int nargs, char **args);
int do_powerctl(int nargs, char **args);
int do_restart(int nargs, char **args);
int do_restorecon(int nargs, char **args);
int do_restorecon_recursive(int nargs, char **args);
int do_rm(int nargs, char **args);
int do_rmdir(int nargs, char **args);
int do_setcon(int nargs, char **args);
int do_setenforce(int nargs, char **args);
int do_setkey(int nargs, char **args);
int do_setprop(int nargs, char **args);
int do_setrlimit(int nargs, char **args);
int do_setsebool(int nargs, char **args);
int do_start(int nargs, char **args);
int do_stop(int nargs, char **args);
int do_swapon_all(int nargs, char **args);
int do_trigger(int nargs, char **args);
int do_symlink(int nargs, char **args);
int do_sysclktz(int nargs, char **args);
int do_write(int nargs, char **args);
int do_copy(int nargs, char **args);
int do_chown(int nargs, char **args);
int do_chmod(int nargs, char **args);
int do_loglevel(int nargs, char **args);
int do_load_persist_props(int nargs, char **args);
int do_load_all_props(int nargs, char **args);
int do_wait(int nargs, char **args);
#define __MAKE_KEYWORD_ENUM__
#define KEYWORD(symbol, flags, nargs, func) K_##symbol,
enum {
K_UNKNOWN,
#endif
KEYWORD(capability, OPTION, 0, 0)//就变成K_capability这是枚举的2
KEYWORD(chdir, COMMAND, 1, do_chdir)
KEYWORD(chroot, COMMAND, 1, do_chroot)
KEYWORD(class, OPTION, 0, 0)
KEYWORD(class_start, COMMAND, 1, do_class_start)
KEYWORD(class_stop, COMMAND, 1, do_class_stop)
KEYWORD(class_reset, COMMAND, 1, do_class_reset)
KEYWORD(console, OPTION, 0, 0)
。。。。。
因此在init.rc中有class_start就是去调用do_class_start函数
int do_class_start(int nargs, char **args)
{
/* Starting a class does not start services
* which are explicitly disabled. They must
* be started individually.
*/
service_for_each_class(args[1], service_start_if_not_disabled);
return 0;
}service_for_each_class变量service_list中的service看有没有其classname和传入的一样，传入的class有core、main等
void service_for_each_class(const char *classname,
void (*func)(struct service *svc))
{
struct listnode *node;
struct service *svc;
list_for_each(node, &service_list) {
svc = node_to_item(node, struct service, slist);
if (!strcmp(svc->classname, classname)) {
func(svc);
}
}
}而我们在解析service的时候如果有class，会把参数赋给classname
static void parse_line_service(struct parse_state *state, int nargs, char **args)
{
struct service *svc = state->context;
struct command *cmd;
int i, kw, kw_nargs;
if (nargs == 0) {
return;
}
svc->ioprio_class = IoSchedClass_NONE;
kw = lookup_keyword(args[0]);
switch (kw) {
case K_capability:
break;
case K_class:
if (nargs != 2) {
parse_error(state, "class option requires a classname\n");
} else {
svc->classname = args[1];//把参数赋给classname
}
break;这样当执行到class_start core这个section的时候，就会去遍历service_list中service的class是core的就启动。
这样init.rc的启动service这块分析完了，继续分析。
继续分析restart_processes，restart_processes函数是重启service，也就是之前起过了
static void restart_processes()
{
process_needs_restart = 0;
service_for_each_flags(SVC_RESTARTING,
restart_service_if_needed);
}它会将service的flags是SVC_RESTARTING的service调用restart_service_if_needed
void service_for_each_flags(unsigned matchflags,
void (*func)(struct service *svc))
{
struct listnode *node;
struct service *svc;
list_for_each(node, &service_list) {
svc = node_to_item(node, struct service, slist);
if (svc->flags & matchflags) {
func(svc);
}
}
}
static void restart_service_if_needed(struct service *svc)
{
time_t next_start_time = svc->time_started + 5;
if (next_start_time <= gettime()) {
svc->flags &= (~SVC_RESTARTING);
service_start(svc, NULL);
return;
}
if ((next_start_time < process_needs_restart) ||
(process_needs_restart == 0)) {
process_needs_restart = next_start_time;
}
}service_start就不分析了，在里面会fork一个进程，然后最后将该service的flags改成running。
下面是一个poll的IO复用函数，先加fd，然后监听。
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;而各个fd是在之前queue_builtin_action的时候加入命令的,下面就是3个fd
queue_builtin_action(keychord_init_action, "keychord_init");//1
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);
/* 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");//2
queue_builtin_action(signal_init_action, "signal_init");//3
六、如何重启service的
先来分析下signal_init_action，
static int signal_init_action(int nargs, char **args)
{
signal_init();
if (get_signal_fd() < 0) {
ERROR("signal_init() failed\n");
exit(1);
}
return 0;
}
signal_init对SIGCHIILD信号处理，处理函数为sigchld_handler，下面建立了一个pipe
void signal_init(void)
{
int s[2];
struct sigaction act;
memset(&act, 0, sizeof(act));
act.sa_handler = sigchld_handler;
act.sa_flags = SA_NOCLDSTOP;
sigaction(SIGCHLD, &act, 0);
/* create a signalling mechanism for the sigchld handler */
if (socketpair(AF_UNIX, SOCK_STREAM, 0, s) == 0) {
signal_fd = s[0];
signal_recv_fd = s[1];
fcntl(s[0], F_SETFD, FD_CLOEXEC);
fcntl(s[0], F_SETFL, O_NONBLOCK);
fcntl(s[1], F_SETFD, FD_CLOEXEC);
fcntl(s[1], F_SETFL, O_NONBLOCK);
}
handle_signal();
}而处理函数就是往管道的一侧发，那signal_recv_fd 也就有事件了
static void sigchld_handler(int s)
{
write(signal_fd, &s, 1);
}signal_recv_fd 有事件了会在init的poll函数中，调用handle_signal
void handle_signal(void)
{
char tmp[32];
/* we got a SIGCHLD - reap and restart as needed */
read(signal_recv_fd, tmp, sizeof(tmp));
while (!wait_for_one_process(0))
;
}wait_for_one_process具体不分析了，会把service的flags改成SVC_RESTARTING，下次for循环到restart_processes，就会把这个service，restart了。
七、属性系统：
java层的方法：
getProperty
setProperty
native层方法：
property_get
property_set
属性值成功修改后，init进程会检查init.rc文件中是否定义了和该属性值匹配的触发器。如果有定义，就执行该触发器。
比如：
on property:ro.debuggable=1
start console
当该属性为1，就执行了。
ro:代表只读
persist：写入data/propery开机还有
net：自动设置为最后修改的属性名
和前面的class_start类似，在init.rc中也有load_all_props
on load_all_props_action
load_all_props然后执行该action的cmd的时候会调用do_load_all_props函数
int do_load_all_props(int nargs, char **args) {
if (nargs == 1) {
load_all_props();
return 0;
}
return -1;
}load_all_props函数从下面几个不同的文件读取属性值，属性值都在这些地方定义
void load_all_props(void)
{
load_properties_from_file(PROP_PATH_SYSTEM_BUILD, NULL);
load_properties_from_file(PROP_PATH_SYSTEM_DEFAULT, NULL);
load_properties_from_file(PROP_PATH_VENDOR_BUILD, NULL);
load_properties_from_file(PROP_PATH_FACTORY, "ro.*");
load_override_properties();
/* Read persistent properties after all default values have been loaded. */
load_persistent_properties();
}在上面这些函数最后都会调到property_set函数
int property_set(const char *name, const char *value)
{
prop_info *pi;
int ret;
size_t namelen = strlen(name);
size_t valuelen = strlen(value);
if (!is_legal_property_name(name, namelen)) return -1;
if (valuelen >= PROP_VALUE_MAX) return -1;
pi = (prop_info*) __system_property_find(name);
if(pi != 0) {
/* ro.* properties may NEVER be modified once set */
if(!strncmp(name, "ro.", 3)) return -1;
__system_property_update(pi, value, valuelen);
} else {
ret = __system_property_add(name, namelen, value, valuelen);
if (ret < 0) {
ERROR("Failed to set '%s'='%s'\n", name, value);
return ret;
}
}
/* If name starts with "net." treat as a DNS property. */
if (strncmp("net.", name, strlen("net.")) == 0) {
if (strcmp("net.change", name) == 0) {
return 0;
}
/*
* The 'net.change' property is a special property used track when any
* 'net.*' property name is updated. It is _ONLY_ updated here. Its value
* contains the last updated 'net.*' property.
*/
property_set("net.change", name);
} else if (persistent_properties_loaded &&
strncmp("persist.", name, strlen("persist.")) == 0) {
/*
* Don't write properties to disk until after we have read all default properties
* to prevent them from being overwritten by default values.
*/
write_persistent_property(name, value);
} else if (strcmp("selinux.reload_policy", name) == 0 &&
strcmp("1", value) == 0) {
selinux_reload_policy();
}
property_changed(name, value);//最总也会调用property_changed函数
return 0;
}这里有一个property_triggers_enabled变量的判断，这个变量初始为0，在queue_property_triggers_action会把它置为1
void property_changed(const char *name, const char *value)
{
if (property_triggers_enabled)
queue_property_triggers(name, value);
}
queue_property_triggers_action函数
static int queue_property_triggers_action(int nargs, char **args)
{
queue_all_property_triggers();
/* enable property triggers */
property_triggers_enabled = 1;
return 0;
}下面是遍历所有的action的所有事待property的，看属性值满足要求就把这个action加入action_queue。这个queue_property_triggers_action只会执行一遍，因为从action_queue拿出来就删了。
void queue_all_property_triggers()
{
struct listnode *node;
struct action *act;
list_for_each(node, &action_list) {
act = node_to_item(node, struct action, alist);
if (!strncmp(act->name, "property:", strlen("property:"))) {
/* parse property name and value
syntax is property:= */
const char* name = act->name + strlen("property:");
const char* equals = strchr(name, '=');
if (equals) {
char prop_name[PROP_NAME_MAX + 1];
char value[PROP_VALUE_MAX];
int length = equals - name;
if (length > PROP_NAME_MAX) {
ERROR("property name too long in trigger %s", act->name);
} else {
int ret;
memcpy(prop_name, name, length);
prop_name[length] = 0;
/* does the property exist, and match the trigger value? */
ret = property_get(prop_name, value);
if (ret > 0 && (!strcmp(equals + 1, value) ||
!strcmp(equals + 1, "*"))) {
action_add_queue_tail(act);
}
}
}
}
}
} 下面继续看property_changed的queue_property_triggers函数，遍历所有的action，哪个属性值是满足，就将其action加入action_queue
void queue_property_triggers(const char *name, const char *value)
{
struct listnode *node;
struct action *act;
list_for_each(node, &action_list) {
act = node_to_item(node, struct action, alist);
if (!strncmp(act->name, "property:", strlen("property:"))) {
const char *test = act->name + strlen("property:");
int name_length = strlen(name);
if (!strncmp(name, test, name_length) &&
test[name_length] == '=' &&
(!strcmp(test + name_length + 1, value) ||
!strcmp(test + name_length + 1, "*"))) {
action_add_queue_tail(act);
}
}
}
}
再来看poll监听的系统属性，property_service_init_action函数，先建了一个socket，并获取fd
static int property_service_init_action(int nargs, char **args)
{
/* read any property files on system or data and
* fire up the property service. This must happen
* after the ro.foo properties are set above so
* that /data/local.prop cannot interfere with them.
*/
start_property_service();
if (get_property_set_fd() < 0) {
ERROR("start_property_service() failed\n");
exit(1);
}
return 0;
}poll监听到这个fd的事件后，也就是上层或者native谁设置了属性，就会往init发socket信息。
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();handle_property_set_fd函数如果发下来的属性是ctl.start ctl.stop ctl.restart，检查属性后启动或者停止指定的service；而如果是其他属性就直接设置了。设置属性最后也会去遍历所有的action，符合要求把这个action加入action_queue
void handle_property_set_fd()
{
.............
if(memcmp(msg.name,"ctl.",4) == 0) {
// Keep the old close-socket-early behavior when handling
// ctl.* properties.
close(s);
if (check_control_mac_perms(msg.value, source_ctx)) {
handle_control_message((char*) msg.name + 4, (char*) msg.value);//执行开启service还是暂停
} else {
ERROR("sys_prop: Unable to %s service ctl [%s] uid:%d gid:%d pid:%d\n",
msg.name + 4, msg.value, cr.uid, cr.gid, cr.pid);
}
} else {
if (check_perms(msg.name, source_ctx)) {
property_set((char*) msg.name, (char*) msg.value);//设置属性
} else {
ERROR("sys_prop: permission denied uid:%d name:%s\n",
cr.uid, msg.name);
}
// Note: bionic's property client code assumes that the
// property server will not close the socket until *AFTER*
// the property is written to memory.
close(s);
}
freecon(source_ctx);
break;
default:
close(s);
break;
}
}看看handle_control_message函数根据不同命令执行
void handle_control_message(const char *msg, const char *arg)
{
if (!strcmp(msg,"start")) {
msg_start(arg);
} else if (!strcmp(msg,"stop")) {
msg_stop(arg);
} else if (!strcmp(msg,"restart")) {
msg_restart(arg);
} else {
ERROR("unknown control msg '%s'\n", msg);
}
}
这样整个init就分析完了！