[Bluez-devel] L2CAP sockets, SDP

["Meenakshi Seeballack" <meena2010@gmail.com>]

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Hello,
I have tried to understand how to open an L2CAP socket, and have used the
BlueZ API. This is what I have got so far:
/*
 * l2cap_listen(l2cap_channel)
 * Use this channel as a listening post
 */
static int l2cap_listen(const bdaddr_t *bdaddr, unsigned short psm, int lm,
int backlog)
{
    struct sockaddr_l2 addr;
    struct l2cap_options opts;
    int sk;

    /* allocate a free socket */
    if ((sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP)) < 0)
        return -1;

    /* open connection to remote device */
    memset(&addr, 0, sizeof(addr));
    addr.l2_family = AF_BLUETOOTH;
    bacpy(&addr.l2_bdaddr, bdaddr); /* update source address of socket */
    addr.l2_psm = htobs(psm);

    /* bind socket to newly formed socket */
    if (bind(sk, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
        perror("ERROR: Could not bind socket");
        close(sk);
        return -1;
    }

    setsockopt(sk, SOL_L2CAP, L2CAP_LM, &lm, sizeof(lm));

    memset(&opts, 0, sizeof(opts));
    opts.imtu = HIDP_DEFAULT_MTU;
    opts.omtu = HIDP_DEFAULT_MTU;
    opts.flush_to = 0xffff;

    setsockopt(sk, SOL_L2CAP, L2CAP_OPTIONS, &opts, sizeof(opts));

    /* backlog: specifies the number of unaccepted connection
     * that the system will allow before refusing new connections
     */
    if (listen(sk, backlog) < 0) {
        close(sk);
        return -1;
    }

    return sk;
}

/*
 * l2cap_connect_req()
 * Establishes connection with specific socket
 * Request to establish connection from remote
 * communication partner.
 * Such a socket has to have been previously created
 * by an application with the command listen.
 */
static int l2cap_connect(bdaddr_t *src, bdaddr_t *dst, unsigned short psm)
{
    struct sockaddr_l2 addr;
    struct l2cap_options opts;
    int sk;

    /* socket allocation */
    if ((sk = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP)) < 0)
        perror("ERROR: Could not create socket");
        return -1;

    memset(&addr, 0, sizeof(addr));
    addr.l2_family  = AF_BLUETOOTH;
    bacpy(&addr.l2_bdaddr, src); /*update source address of socket */

    /* binds socket to psm */
    if (bind(sk, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
        close(sk);
        return -1;
    }

    memset(&opts, 0, sizeof(opts));
    opts.imtu = HIDP_DEFAULT_MTU;
    opts.omtu = HIDP_DEFAULT_MTU;
    opts.flush_to = 0xffff;

    setsockopt(sk, SOL_L2CAP, L2CAP_OPTIONS, &opts, sizeof(opts));

    memset(&addr, 0, sizeof(addr));
    addr.l2_family  = AF_BLUETOOTH;
    bacpy(&addr.l2_bdaddr, dst);
    addr.l2_psm = htobs(psm);

    if (connect(sk, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
        close(sk);
        return -1;
    }

    return sk;
}

/*
 * l2cap_accept()
 * (Permits incoming connection)
 * Blocks and accepts incoming connection
 * Function switches from BT_LISTEN to BT_CONNECTED
 */
static int l2cap_accept(int sk, bdaddr_t *bdaddr)
{
    struct sockaddr_l2 addr;
    socklen_t addrlen;
    int nsk;

    memset(&addr, 0, sizeof(addr));
    addrlen = sizeof(addr);

    // accept one connection
    if ((nsk = accept(sk, (struct sockaddr *) &addr, &addrlen)) < 0)
        return -1;

    if (bdaddr)
        bacpy(bdaddr, &addr.l2_bdaddr);

    return nsk;
}
--------------------
I am eventually aiming to register the mouse HID events, and send it via the
L2CAP socket to "control" another bluetooth-enabled PC.
How do I use an SDP service in conjunction with the existing L2CAP code? How
do I use the control channel (L2CAP_PSM_HIDP_CTRL 0x11) and the interrupt
channel (L2CAP_PSM_HIDP_INTR 0x13)
I think the control channel is used by SDP for signalling, (device
discovery); the interrupt channel is used for data transfer (service
discovery)
Thanks in advance for any help!

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