android adb源码分析(4)

本篇分析transport.c。

transport的原理是使用了fevent机制进行数据传输，atransport的定义如下：

struct atransport{    atransport *next;    atransport *prev;    int (*read_from_remote)(apacket *p, atransport *t);    int (*write_to_remote)(apacket *p, atransport *t);    void (*close)(atransport *t);    void (*kick)(atransport *t);    int fd;    int transport_socket;    fdevent transport_fde;    int ref_count;    unsigned sync_token;    int connection_state;    int online;    transport_type type;        /* usb handle or socket fd as needed */    usb_handle *usb;    int sfd;        /* used to identify transports for clients */    char *serial;    char *product;    char *model;    char *device;    char *devpath;    int adb_port; // Use for emulators (local transport)        /* a list of adisconnect callbacks called when the transport is kicked */    int          kicked;    adisconnect  disconnects;    void *key;    unsigned char token[TOKEN_SIZE];    fdevent auth_fde;    unsigned failed_auth_attempts;};

它是一个双向链表，所有的实体都保存在全局数据transport_list中：

static atransport transport_list = {    .next = &transport_list,    .prev = &transport_list,};

atransport的数据传输的两个函数是：

static intread_packet(int  fd, const char* name, apacket** ppacket){    char *p = (char*)ppacket;  /* really read a packet address */    int   r;    int   len = sizeof(*ppacket);    char  buff[8];    if (!name) {        snprintf(buff, sizeof buff, "fd=%d", fd);        name = buff;    }    while(len > 0) {        r = adb_read(fd, p, len);        if(r > 0) {            len -= r;            p   += r;        } else {            D("%s: read_packet (fd=%d), error ret=%d errno=%d: %s\n", name, fd, r, errno, strerror(errno));            if((r < 0) && (errno == EINTR)) continue;            return -1;        }    }#if ADB_TRACE    if (ADB_TRACING) {        dump_packet(name, "from remote", *ppacket);    }#endif    return 0;}static intwrite_packet(int  fd, const char* name, apacket** ppacket){    char *p = (char*) ppacket;  /* we really write the packet address */    int r, len = sizeof(ppacket);    char buff[8];    if (!name) {        snprintf(buff, sizeof buff, "fd=%d", fd);        name = buff;    }#if ADB_TRACE    if (ADB_TRACING) {        dump_packet(name, "to remote", *ppacket);    }#endif    len = sizeof(ppacket);    while(len > 0) {        r = adb_write(fd, p, len);        if(r > 0) {            len -= r;            p += r;        } else {            D("%s: write_packet (fd=%d) error ret=%d errno=%d: %s\n", name, fd, r, errno, strerror(errno));            if((r < 0) && (errno == EINTR)) continue;            return -1;        }    }    return 0;}

这是它的内部传输接口，注意传输的是apacket的数据内部。

外部接口的数据传输接口是：

static void transport_socket_events(int fd, unsigned events, void *_t){    atransport *t = _t;    D("transport_socket_events(fd=%d, events=%04x,...)\n", fd, events);    if(events & FDE_READ){        apacket *p = 0;        if(read_packet(fd, t->serial, &p)){            D("%s: failed to read packet from transport socket on fd %d\n", t->serial, fd);        } else {            handle_packet(p, (atransport *) _t);        }    }}void send_packet(apacket *p, atransport *t){    unsigned char *x;    unsigned sum;    unsigned count;    p->msg.magic = p->msg.command ^ 0xffffffff;    count = p->msg.data_length;    x = (unsigned char *) p->data;    sum = 0;    while(count-- > 0){        sum += *x++;    }    p->msg.data_check = sum;    print_packet("send", p);    if (t == NULL) {        D("Transport is null \n");        // Zap errno because print_packet() and other stuff have errno effect.        errno = 0;        fatal_errno("Transport is null");    }    if(write_packet(t->transport_socket, t->serial, &p)){        fatal_errno("cannot enqueue packet on transport socket");    }}

物理接口到atransport的接口是：

/* The transport is opened by transport_register_func before** the input and output threads are started.**** The output thread issues a SYNC(1, token) message to let** the input thread know to start things up.  In the event** of transport IO failure, the output thread will post a** SYNC(0,0) message to ensure shutdown.**** The transport will not actually be closed until both** threads exit, but the input thread will kick the transport** on its way out to disconnect the underlying device.*/static void *output_thread(void *_t){    atransport *t = _t;    apacket *p;    D("%s: starting transport output thread on fd %d, SYNC online (%d)\n",       t->serial, t->fd, t->sync_token + 1);    p = get_apacket();    p->msg.command = A_SYNC;    p->msg.arg0 = 1;    p->msg.arg1 = ++(t->sync_token);    p->msg.magic = A_SYNC ^ 0xffffffff;    if(write_packet(t->fd, t->serial, &p)) {        put_apacket(p);        D("%s: failed to write SYNC packet\n", t->serial);        goto oops;    }    D("%s: data pump started\n", t->serial);    for(;;) {        p = get_apacket();        if(t->read_from_remote(p, t) == 0){            D("%s: received remote packet, sending to transport\n",              t->serial);            if(write_packet(t->fd, t->serial, &p)){                put_apacket(p);                D("%s: failed to write apacket to transport\n", t->serial);                goto oops;            }        } else {            D("%s: remote read failed for transport\n", t->serial);            put_apacket(p);            break;        }    }    D("%s: SYNC offline for transport\n", t->serial);    p = get_apacket();    p->msg.command = A_SYNC;    p->msg.arg0 = 0;    p->msg.arg1 = 0;    p->msg.magic = A_SYNC ^ 0xffffffff;    if(write_packet(t->fd, t->serial, &p)) {        put_apacket(p);        D("%s: failed to write SYNC apacket to transport", t->serial);    }oops:    D("%s: transport output thread is exiting\n", t->serial);    kick_transport(t);    transport_unref(t);    return 0;}static void *input_thread(void *_t){    atransport *t = _t;    apacket *p;    int active = 0;    D("%s: starting transport input thread, reading from fd %d\n",       t->serial, t->fd);    for(;;){        if(read_packet(t->fd, t->serial, &p)) {            D("%s: failed to read apacket from transport on fd %d\n",               t->serial, t->fd );            break;        }        if(p->msg.command == A_SYNC){            if(p->msg.arg0 == 0) {                D("%s: transport SYNC offline\n", t->serial);                put_apacket(p);                break;            } else {                if(p->msg.arg1 == t->sync_token) {                    D("%s: transport SYNC online\n", t->serial);                    active = 1;                } else {                    D("%s: transport ignoring SYNC %d != %d\n",                      t->serial, p->msg.arg1, t->sync_token);                }            }        } else {            if(active) {                D("%s: transport got packet, sending to remote\n", t->serial);                t->write_to_remote(p, t);            } else {                D("%s: transport ignoring packet while offline\n", t->serial);            }        }        put_apacket(p);    }    // this is necessary to avoid a race condition that occured when a transport closes    // while a client socket is still active.    close_all_sockets(t);    D("%s: transport input thread is exiting, fd %d\n", t->serial, t->fd);    kick_transport(t);    transport_unref(t);    return 0;}

这里，源码做了一个物理到抽象的转换。最上层还有一层是tmsg的传输（作者为什么要这么绕，实在是看得不明白）：

void init_transport_registration(void){    int s[2];    if(adb_socketpair(s)){        fatal_errno("cannot open transport registration socketpair");    }    transport_registration_send = s[0];    transport_registration_recv = s[1];    fdevent_install(&transport_registration_fde,                    transport_registration_recv,                    transport_registration_func,                    0);    fdevent_set(&transport_registration_fde, FDE_READ);}/* the fdevent select pump is single threaded */static void register_transport(atransport *transport){    tmsg m;    m.transport = transport;    m.action = 1;    D("transport: %s registered\n", transport->serial);    if(transport_write_action(transport_registration_send, &m)) {        fatal_errno("cannot write transport registration socket\n");    }}static void remove_transport(atransport *transport){    tmsg m;    m.transport = transport;    m.action = 0;    D("transport: %s removed\n", transport->serial);    if(transport_write_action(transport_registration_send, &m)) {        fatal_errno("cannot write transport registration socket\n");    }}

tmsg的作用是用于atransport的管理。