Android 之 ServiceManager与服务管理
是android中比较重要的一个进程,它是在init进程启动之后启动,从名字上就可以看出来它是用来管理系统中的service。比如:InputMethodService、ActivityManagerService等。在ServiceManager中有两个比较重要的方法:add_service、check_service。系统的service需要通过add_service把自己的信息注册到ServiceManager中,当需要使用时,通过check_service检查该service是否存在。
主函数(anrdroid4.0/frameworks/base/cmds/servicemanager/service_manager.c)
从它的主函数代码开始:
int main(int argc, char **argv)
{
struct binder_state *bs;
void *svcmgr = BINDER_SERVICE_MANAGER;
bs = binder_open(128*1024);
if (binder_become_context_manager(bs)) {
LOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
svcmgr_handle = svcmgr;
binder_loop(bs, svcmgr_handler);
return 0;
}
从main函数中可以看出,它主要做了三件事情:
打开/dev/binder设备,并在内存中映射128K的空间。
通知Binder设备,把自己变成context_manager
进入循环,不停的去读Binder设备,看是否有对service的请求,如果有的话,就去调用svcmgr_handler函数回调处理请求。
服务注册
再来看看ServiceManager中是怎么样去注册服务的。先来看先,当有对service的请求时,调用的回调函数svcmgr_handler:
int svcmgr_handler(struct binder_state *bs,
struct binder_txn *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
unsigned len;
void *ptr;
uint32_t strict_policy;
// LOGI("target=%p code=%d pid=%d uid=%d\n",
// txn->target, txn->code, txn->sender_pid, txn->sender_euid);
if (txn->target != svcmgr_handle)
return -1;
// Equivalent to Parcel::enforceInte易做图ce(), reading the RPC
// header with the strict mode policy mask and the inte易做图ce name.
// Note that we ignore the strict_policy and don't propagate it
// further (since we do no outbound RPCs anyway).
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s));
return -1;
}
switch(txn->code) {
case SVC_MGR_GET_SERVICE:
case SVC_MGR_CHECK_SERVICE:
s = bio_get_string16(msg, &len);
ptr = do_find_service(bs, s, len);
if (!ptr)
break;
bio_put_ref(reply, ptr);
return 0;
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
if (do_add_service(bs, s, len, ptr, txn->sender_euid))
return -1;
break;
case SVC_MGR_LIST_SERVICES: {
unsigned n = bio_get_uint32(msg);
si = svclist;
while ((n-- > 0) && si)
si = si->next;
if (si) {
bio_put_string16(reply, si->name);
return 0;
}
return -1;
}
default:
LOGE("unknown code %d\n", txn->code);
return -1;
}
bio_put_uint32(reply, 0);
return 0;
}
在该回调函数中会判断Service有什么需要,如果是请求注册service,那么久执行:
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
if (do_add_service(bs, s, len, ptr, txn->sender_euid))
return -1;
break;
我们再来看看do_add_service中做了什么事情:
int do_add_service(struct binder_state *bs,
uint16_t *s, unsigned len,
void *ptr, unsigned uid)
{
struct svcinfo *si;
// LOGI("add_service('%s',%p) uid=%d\n", str8(s), ptr, uid);
if (!ptr || (len == 0) || (len > 127))
return -1;
if (!svc_can_register(uid, s)) {
LOGE("add_service('%s',%p) uid=%d - PERMISSION DENIED\n",
str8(s), ptr, uid);
return -1;
}
si = find_svc(s, len);
if (si) {
if (si->ptr) {
LOGE("add_service('%s',%p) uid=%d - ALREADY REGISTERED\n",
str8(s), ptr, uid);
return -1;
}
si->ptr = ptr;
} else {
si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
if (!si) {
LOGE("add_service('%s',%p) uid=%d - OUT OF MEMORY\n",
&
补充:移动开发 , Android ,