Provided by: libbluetooth-dev_5.77-0ubuntu2_amd64 
NAME
l2cap - L2CAP protocol
SYNOPSIS
#include <sys/socket.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/l2cap.h>
l2cap_socket = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_L2CAP);
DESCRIPTION
L2CAP is a protocol that provides an interface for higher-level protocols to send and receive data over a
Bluetooth connection. L2CAP sits on top of the Bluetooth Host Controller Interface (HCI) and provides a
set of channels that can be used by higher-level protocols to transmit data.
L2CAP provides a number of services to higher-level protocols, including segmentation and reassembly of
large data packets and flow control to prevent overloading of the receiver. L2CAP also supports multiple
channels per connection, allowing for concurrent data transmission using different protocols.
SOCKET ADDRESS
struct sockaddr_l2 {
sa_family_t l2_family;
unsigned short l2_psm;
bdaddr_t l2_bdaddr;
unsigned short l2_cid;
uint8_t l2_bdaddr_type;
};
Example:
struct sockaddr_l2 addr;
memset(&addr, 0, sizeof(addr));
addr.l2_family = AF_BLUETOOTH;
bacpy(&addr.l2_bdaddr, bdaddr);
if (cid)
addr.l2_cid = htobs(cid);
else
addr.l2_psm = htobs(psm);
addr.l2_bdaddr_type = bdaddr_type;
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: ┌───────────────────┬──────────────────────┬────────────────────────┬──────────────┐ │Value │ Security Level │ Link Key Type │ Encryption │ ├───────────────────┼──────────────────────┼────────────────────────┼──────────────┤ │BT_SECURITY_SDP │ 0 (SDP Only) │ None │ Not required │ ├───────────────────┼──────────────────────┼────────────────────────┼──────────────┤ │BT_SECURITY_LOW │ 1 (Low) │ Unauthenticated │ Not required │ ├───────────────────┼──────────────────────┼────────────────────────┼──────────────┤ │BT_SECURITY_MEDIUM │ 2 (Medium - default) │ Unauthenticated │ Desired │ ├───────────────────┼──────────────────────┼────────────────────────┼──────────────┤ │BT_SECURITY_HIGH │ 3 (High) │ Authenticated │ Required │ ├───────────────────┼──────────────────────┼────────────────────────┼──────────────┤ │BT_SECURITY_FIPS │ 4 (Secure Only) │ Authenticated (P-256 │ Required │ │(since Linux 3.15) │ │ based Secure Simple │ │ │ │ │ Pairing and Secure │ │ │ │ │ Authentication) │ │ └───────────────────┴──────────────────────┴────────────────────────┴──────────────┘ Example: int level = BT_SECURITY_HIGH; int err = setsockopt(l2cap_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: ┌──────┬───────────────────┬───────────────┐ │Value │ Description │ Authorization │ ├──────┼───────────────────┼───────────────┤ │0 │ Disable (default) │ Not required │ ├──────┼───────────────────┼───────────────┤ │1 │ Enable │ Required │ └──────┴───────────────────┴───────────────┘ Example: int defer_setup = 1; int err = setsockopt(l2cap_socket, SOL_BLUETOOTH, BT_DEFER_SETUP, &defer_setup, sizeof(defer_setup)); if (err == -1) { perror("setsockopt"); return err; } err = listen(l2cap_socket, 5); if (err) { perror("listen"); return err; } struct sockaddr_l2 remote_addr = {0}; socklen_t addr_len = sizeof(remote_addr); int new_socket = accept(l2cap_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: ┌─────────────────┬────────────────┬───────────────────┐ │Define │ Value │ Description │ ├─────────────────┼────────────────┼───────────────────┤ │BT_FLUSHABLE_OFF │ 0x00 (default) │ Do not flush data │ ├─────────────────┼────────────────┼───────────────────┤ │BT_FLUSHABLE_ON │ 0x01 │ Flush 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: ┌──────────────────────────┬────────────────┬──────────────────────────────┐ │Define │ Value │ Description │ ├──────────────────────────┼────────────────┼──────────────────────────────┤ │BT_POWER_FORCE_ACTIVE_OFF │ 0x00 (default) │ Don't force exit of sniff │ │ │ │ mode │ ├──────────────────────────┼────────────────┼──────────────────────────────┤ │BT_POWER_FORCE_ACTIVE_ON │ 0x01 │ Force exit of sniff mode │ └──────────────────────────┴────────────────┴──────────────────────────────┘ BT_CHANNEL_POLICY (since Linux 3.10) High-speed (AMP) channel policy, possible values: ┌──────────────────────────────────┬─────────────┬──────────────────┐ │Define │ Value │ Description │ ├──────────────────────────────────┼─────────────┼──────────────────┤ │BT_CHANNEL_POLICY_BREDR_ONLY │ 0 (default) │ BR/EDR only │ ├──────────────────────────────────┼─────────────┼──────────────────┤ │BT_CHANNEL_POLICY_BREDR_PREFERRED │ 1 │ BR/EDR Preferred │ ├──────────────────────────────────┼─────────────┼──────────────────┤ │BT_CHANNEL_POLICY_BREDR_PREFERRED │ 2 │ AMP Preferred │ └──────────────────────────────────┴─────────────┴──────────────────┘ BT_PHY (since Linux 5.10) Channel supported PHY(s), possible values: ┌───────────────────┬────────┬─────────────────┐ │Define │ Value │ Description │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_1M_1SLOT │ BIT 0 │ BR 1Mbps 1SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_1M_3SLOT │ BIT 1 │ BR 1Mbps 3SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_1M_5SLOT │ BIT 2 │ BR 1Mbps 5SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_2M_1SLOT │ BIT 3 │ EDR 2Mbps 1SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_2M_3SLOT │ BIT 4 │ EDR 2Mbps 3SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_2M_5SLOT │ BIT 5 │ EDR 2Mbps 5SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_3M_1SLOT │ BIT 6 │ EDR 3Mbps 1SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_3M_3SLOT │ BIT 7 │ EDR 3Mbps 3SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_BR_3M_5SLOT │ BIT 8 │ EDR 3Mbps 5SLOT │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_1M_TX │ BIT 9 │ LE 1Mbps TX │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_1M_RX │ BIT 10 │ LE 1Mbps RX │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_2M_TX │ BIT 11 │ LE 2Mbps TX │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_2M_RX │ BIT 12 │ LE 2Mbps RX │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_CODED_TX │ BIT 13 │ LE Coded TX │ ├───────────────────┼────────┼─────────────────┤ │BT_PHY_LE_CODED_RX │ BIT 14 │ LE Coded RX │ └───────────────────┴────────┴─────────────────┘ BT_MODE (since Linux 5.10) Channel Mode, possible values: ┌────────────────────┬────────────────┬────────────────────────┬────────┐ │Define │ Value │ Description │ Link │ ├────────────────────┼────────────────┼────────────────────────┼────────┤ │BT_MODE_BASIC │ 0x00 (default) │ Basic mode │ Any │ ├────────────────────┼────────────────┼────────────────────────┼────────┤ │BT_MODE_ERTM │ 0x01 │ Enhanced │ BR/EDR │ │ │ │ Retransmission mode │ │ ├────────────────────┼────────────────┼────────────────────────┼────────┤ │BT_MODE_STREAM │ 0x02 │ Stream mode │ BR/EDR │ ├────────────────────┼────────────────┼────────────────────────┼────────┤ │BT_MODE_LE_FLOWCTL │ 0x03 │ Credit based flow │ LE │ │ │ │ control mode │ │ ├────────────────────┼────────────────┼────────────────────────┼────────┤ │BT_MODE_EXT_FLOWCTL │ 0x04 │ Extended Credit based │ Any │ │ │ │ flow control mode │ │ └────────────────────┴────────────────┴────────────────────────┴────────┘
RESOURCES
<http://www.bluez.org>
REPORTING BUGS
<linux-bluetooth@vger.kernel.org>
SEE ALSO
socket(7), l2test(1)
COPYRIGHT
Free use of this software is granted under ther terms of the GNU Lesser General Public Licenses (LGPL).