rfcomm - Man Page

RFCOMM protocol

Synopsis

#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/rfcomm.h>

rfcomm_socket = socket(PF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);

Description

The RFCOMM protocol provides emulation of serial ports over the L2CAP(7) protocol. The protocol is based on the ETSI standard TS 07.10.

RFCOMM is a simple transport protocol, with additional provisions for emulating the 9 circuits of RS-232 (EIATIA-232-E) serial ports.

Socket Address

struct sockaddr_rc {
    sa_family_t rc_family;
    unsigned short rc_bdaddr;
    unsigned char rc_channel;
};

Example:

struct sockaddr_rc addr;

memset(&addr, 0, sizeof(addr));
addr.rc_family = AF_BLUETOOTH;
bacpy(&addr.rc_bdaddr, bdaddr);
addr.rc_channel = channel;

Socket Options

The socket options listed below can be set by using setsockopt(2) and read with getsockopt(2) with the socket level set to SOL_BLUETOOTH.

BT_SECURITY (since Linux 2.6.30)

Channel security level, possible values:

ValueSecurity LevelLink Key TypeEncryption
BT_SECURITY_SDP0 (SDP Only)NoneNot required
BT_SECURITY_LOW1 (Low)UnauthenticatedNot required
BT_SECURITY_MEDIUM2 (Medium - default)UnauthenticatedDesired
BT_SECURITY_HIGH3 (High)AuthenticatedRequired
BT_SECURITY_FIPS (since Linux 3.15)4 (Secure Only)Authenticated (P-256 based Secure Simple Pairing and Secure Authentication)Required

Example:

int level = BT_SECURITY_HIGH;
int err = setsockopt(rfcomm_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
                     sizeof(level));
if (err == -1) {
    perror("setsockopt");
    return 1;
}

BT_DEFER_SETUP (since Linux 2.6.30)

Channel defer connection setup, this control if the connection procedure needs to be authorized by userspace before responding which allows authorization at profile level, possible values:

ValueDescriptionAuthorization
0Disable (default)Not required
1EnableRequired

Example:

int defer_setup = 1;
int err = setsockopt(rfcomm_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
                     &defer_setup, sizeof(defer_setup));
if (err == -1) {
    perror("setsockopt");
    return err;
}

err = listen(rfcomm_socket, 5);
if (err) {
    perror("listen");
    return err;
}

struct sockaddr_rc remote_addr = {0};
socklen_t addr_len = sizeof(remote_addr);
int new_socket = accept(rfcomm_socket, (struct sockaddr*)&remote_addr,
                        &addr_len);
if (new_socket < 0) {
    perror("accept");
    return new_socket;
}

/* To complete the connection setup of new_socket read 1 byte */
char c;
struct pollfd pfd;

memset(&pfd, 0, sizeof(pfd));
pfd.fd = new_socket;
pfd.events = POLLOUT;

err = poll(&pfd, 1, 0);
if (err) {
    perror("poll");
    return err;
}

if (!(pfd.revents & POLLOUT)) {
    err = read(sk, &c, 1);
    if (err < 0) {
        perror("read");
        return err;
    }
}

BT_FLUSHABLE (since Linux 2.6.39)

Channel flushable flag, this control if the channel data can be flushed or not, possible values:

DefineValueDescription
BT_FLUSHABLE_OFF0x00 (default)Do not flush data
BT_FLUSHABLE_ON0x01Flush data

BT_POWER (since Linux 3.1)

Channel power policy, this control if the channel shall force exit of sniff mode or not, possible values:

DefineValueDescription
BT_POWER_FORCE_ACTIVE_OFF0x00 (default)Don't force exit of sniff mode
BT_POWER_FORCE_ACTIVE_ON0x01Force exit of sniff mode

BT_CHANNEL_POLICY (since Linux 3.10)

High-speed (AMP) channel policy, possible values:

DefineValueDescription
BT_CHANNEL_POLICY_BREDR_ONLY0 (default)BR/EDR only
BT_CHANNEL_POLICY_BREDR_PREFERRED1BR/EDR Preferred
BT_CHANNEL_POLICY_BREDR_PREFERRED2AMP Preferred

BT_PHY (since Linux 5.10)

Channel supported PHY(s), possible values:

DefineValueDescription
BT_PHY_BR_1M_1SLOTBIT 0BR 1Mbps 1SLOT
BT_PHY_BR_1M_3SLOTBIT 1BR 1Mbps 3SLOT
BT_PHY_BR_1M_5SLOTBIT 2BR 1Mbps 5SLOT
BT_PHY_BR_2M_1SLOTBIT 3EDR 2Mbps 1SLOT
BT_PHY_BR_2M_3SLOTBIT 4EDR 2Mbps 3SLOT
BT_PHY_BR_2M_5SLOTBIT 5EDR 2Mbps 5SLOT
BT_PHY_BR_3M_1SLOTBIT 6EDR 3Mbps 1SLOT
BT_PHY_BR_3M_3SLOTBIT 7EDR 3Mbps 3SLOT
BT_PHY_BR_3M_5SLOTBIT 8EDR 3Mbps 5SLOT

Resources

<http://www.bluez.org>

Reporting Bugs

<linux-bluetooth@vger.kernel.org>

See Also

socket(7), rctest(1)

Info

May 2024 BlueZ Linux System Administration