1BinderServiceManager

int main(int argc, char** argv)
{
    struct binder_state *bs;
    union selinux_callback cb;
    char *driver;

    if (argc > 1) {
        driver = argv[1];
    } else {
        driver = "/dev/binder";
    }

    bs = binder_open(driver, 128*1024);//1
    
    if (binder_become_context_manager(bs)) {//2
        ALOGE("cannot become context manager (%s)\n", strerror(errno));
        return -1;
    }
    
    binder_loop(bs, svcmgr_handler);//3

    return 0;
}

int svcmgr_handler(struct binder_state *bs,
                   struct binder_transaction_data *txn,
                   struct binder_io *msg,
                   struct binder_io *reply)
{
    switch(txn->code) {
    case SVC_MGR_GET_SERVICE:
    case SVC_MGR_CHECK_SERVICE:
        s = bio_get_string16(msg, &len);
        handle = do_find_service(s, len, txn->sender_euid, txn->sender_pid);
        if (!handle)
            break;
        bio_put_ref(reply, handle);
        return 0;

    case SVC_MGR_ADD_SERVICE:
        s = bio_get_string16(msg, &len);
        handle = bio_get_ref(msg);
        allow_isolated = bio_get_uint32(msg) ? 1 : 0;
        dumpsys_priority = bio_get_uint32(msg);
        if (do_add_service(bs, s, len, handle, txn->sender_euid, allow_isolated, dumpsys_priority,
                           txn->sender_pid))
            return -1;
        break;

    case SVC_MGR_LIST_SERVICES: {
        uint32_t n = bio_get_uint32(msg);
        uint32_t req_dumpsys_priority = bio_get_uint32(msg);

        if (!svc_can_list(txn->sender_pid, txn->sender_euid)) {
            ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
                    txn->sender_euid);
            return -1;
        }
        si = svclist;
        // walk through the list of services n times skipping services that
        // do not support the requested priority
        while (si) {
            if (si->dumpsys_priority & req_dumpsys_priority) {
                if (n == 0) break;
                n--;
            }
            si = si->next;
        }
        if (si) {
            bio_put_string16(reply, si->name);
            return 0;
        }
        return -1;
    }
    default:
        ALOGE("unknown code %d\n", txn->code);
        return -1;
    }

    bio_put_uint32(reply, 0);
    return 0;
}

int do_add_service(struct binder_state *bs, const uint16_t *s, size_t len, uint32_t handle,
                   uid_t uid, int allow_isolated, uint32_t dumpsys_priority, pid_t spid) {
    struct svcinfo *si;
    if (!handle || (len == 0) || (len > 127))
    return -1;

    if (!svc_can_register(s, len, spid, uid)) {
        ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
             str8(s, len), handle, uid);
        return -1;
    }
    
    si = find_svc(s, len);
    if (si) {
        if (si->handle) {
            ALOGE("add_service('%s',%x) uid=%d - ALREADY REGISTERED, OVERRIDE\n",
                 str8(s, len), handle, uid);
            svcinfo_death(bs, si);
        }
        si->handle = handle;
    } else {
        si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
        if (!si) {
            ALOGE("add_service('%s',%x) uid=%d - OUT OF MEMORY\n",
                 str8(s, len), handle, uid);
            return -1;
        }
        si->handle = handle;
        si->len = len;
        memcpy(si->name, s, (len + 1) * sizeof(uint16_t));
        si->name[len] = '\0';
        si->death.func = (void*) svcinfo_death;
        si->death.ptr = si;
        si->allow_isolated = allow_isolated;
        si->dumpsys_priority = dumpsys_priority;
        si->next = svclist;
        svclist = si;
    }

    binder_acquire(bs, handle);
    binder_link_to_death(bs, handle, &si->death);
    return 0;
}

uint32_t do_find_service(const uint16_t *s, size_t len, uid_t uid, pid_t spid)
{
    struct svcinfo *si = find_svc(s, len);
    if (!si || !si->handle) {
        return 0;
    }
    if (!si->allow_isolated) {
        // If this service doesn't allow access from isolated processes,
        // then check the uid to see if it is isolated.
        uid_t appid = uid % AID_USER;
        if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
            return 0;
        }
    }
    if (!svc_can_find(s, len, spid, uid)) {
        return 0;
    }
    return si->handle;
}

struct svcinfo
{
    struct svcinfo *next;
    uint32_t handle;
    struct binder_death death;
    int allow_isolated;
    uint32_t dumpsys_priority;
    size_t len;
    uint16_t name[0];
};

struct svcinfo *find_svc(const uint16_t *s16, size_t len)
{
    struct svcinfo *si;

    for (si = svclist; si; si = si->next) {
        if ((len == si->len) &&
            !memcmp(s16, si->name, len * sizeof(uint16_t))) {
            return si;
        }
    }
    return NULL;
}

struct binder_state *binder_open(const char* driver, size_t mapsize)
{
    struct binder_state *bs;
    struct binder_version vers;
    
    bs->fd = open(driver, O_RDWR | O_CLOEXEC);
    ioctl(bs->fd, BINDER_VERSION, &vers)
    bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, 0);
}

int binder_become_context_manager(struct binder_state *bs)
{
    return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);
}

void binder_loop(struct binder_state *bs, binder_handler func)
{
    int res;
    struct binder_write_read bwr;
    uint32_t readbuf[32];

    bwr.write_size = 0;
    bwr.write_consumed = 0;
    bwr.write_buffer = 0;

    readbuf[0] = BC_ENTER_LOOPER;
    binder_write(bs, readbuf, sizeof(uint32_t));

    for (;;) {
        bwr.read_size = sizeof(readbuf);
        bwr.read_consumed = 0;
        bwr.read_buffer = (uintptr_t) readbuf;

        res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);

        res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
    }
}

int binder_write(struct binder_state *bs, void *data, size_t len)
{
    struct binder_write_read bwr;
    int res;

    bwr.write_size = len;
    bwr.write_consumed = 0;
    bwr.write_buffer = (uintptr_t) data;
    bwr.read_size = 0;
    bwr.read_consumed = 0;
    bwr.read_buffer = 0;
    res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
    return res;
}

int binder_parse(struct binder_state *bs, struct binder_io *bio,
                 uintptr_t ptr, size_t size, binder_handler func)
{
        while (ptr < end) {
        uint32_t cmd = *(uint32_t *) ptr;
        ptr += sizeof(uint32_t);
        switch(cmd) {
            case BR_TRANSACTION: {
            struct binder_transaction_data *txn = (struct binder_transaction_data *) ptr;
            if ((end - ptr) < sizeof(*txn)) {
                ALOGE("parse: txn too small!\n");
                return -1;
            }
            binder_dump_txn(txn);
            if (func) {
                unsigned rdata[256/4];
                struct binder_io msg;
                struct binder_io reply;
                int res;

                bio_init(&reply, rdata, sizeof(rdata), 4);
                bio_init_from_txn(&msg, txn);
                res = func(bs, txn, &msg, &reply);//callback method svcmgr_handler
                if (txn->flags & TF_ONE_WAY) {
                    binder_free_buffer(bs, txn->data.ptr.buffer);
                } else {
                    binder_send_reply(bs, &reply, txn->data.ptr.buffer, res);
                }
            }
            ptr += sizeof(*txn);
            break;
        }
}

struct binder_io
{
    char *data;            /* pointer to read/write from */
    binder_size_t *offs;   /* array of offsets */
    size_t data_avail;     /* bytes available in data buffer */
    size_t offs_avail;     /* entries available in offsets array */

    char *data0;           /* start of data buffer */
    binder_size_t *offs0;  /* start of offsets buffer */
    uint32_t flags;
    uint32_t unused;
};

void bio_init_from_txn(struct binder_io *bio, struct binder_transaction_data *txn)
{
    bio->data = bio->data0 = (char *)(intptr_t)txn->data.ptr.buffer;
    bio->offs = bio->offs0 = (binder_size_t *)(intptr_t)txn->data.ptr.offsets;
    bio->data_avail = txn->data_size;
    bio->offs_avail = txn->offsets_size / sizeof(size_t);
    bio->flags = BIO_F_SHARED;
}

uint16_t *bio_get_string16(struct binder_io *bio, size_t *sz)
{
    size_t len;

    /* Note: The payload will carry 32bit size instead of size_t */
    len = (size_t) bio_get_uint32(bio);
    if (sz)
        *sz = len;
    return bio_get(bio, (len + 1) * sizeof(uint16_t));
}

uint32_t bio_get_uint32(struct binder_io *bio)
{
    uint32_t *ptr = bio_get(bio, sizeof(*ptr));
    return ptr ? *ptr : 0;
}

static void *bio_get(struct binder_io *bio, size_t size)
{
    size = (size + 3) & (~3);

    if (bio->data_avail < size){
        bio->data_avail = 0;
        bio->flags |= BIO_F_OVERFLOW;
        return NULL;
    }  else {
        void *ptr = bio->data;
        bio->data += size;
        bio->data_avail -= size;
        return ptr;
    }
}

uint32_t bio_get_ref(struct binder_io *bio)
{
    struct flat_binder_object *obj;

    obj = _bio_get_obj(bio);
    if (!obj)
        return 0;

    if (obj->hdr.type == BINDER_TYPE_HANDLE)
        return obj->handle;

    return 0;
}

void bio_put_ref(struct binder_io *bio, uint32_t handle)
{
    struct flat_binder_object *obj;

    if (handle)
        obj = bio_alloc_obj(bio);
    else
        obj = bio_alloc(bio, sizeof(*obj));

    if (!obj)
        return;

    obj->flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
    obj->hdr.type = BINDER_TYPE_HANDLE;
    obj->handle = handle;
    obj->cookie = 0;
}

static struct flat_binder_object *_bio_get_obj(struct binder_io *bio)
{
    size_t n;
    size_t off = bio->data - bio->data0;

    for (n = 0; n < bio->offs_avail; n++) {
        if (bio->offs[n] == off)
            return bio_get(bio, sizeof(struct flat_binder_object));
    }

    bio->data_avail = 0;
    bio->flags |= BIO_F_OVERFLOW;
    return NULL;
}