canfd socket

### CAN FD Socket Programming and Configuration

#### Overview of CAN FD Protocol
CAN FD (Controller Area Network with Flexible Data-Rate) extends the classic CAN protocol to support higher data rates and larger payloads. This allows for more efficient communication on automotive networks.

In Linux, CAN FD is supported through the socket CAN interface which provides a Berkeley socket API for CAN devices[^1].

#### Setting Up CAN Interface
To configure a CAN interface for CAN FD operation:

sudo ip link set can0 up type can bitrate 500000 dbitrate 2000000 fd on

This command sets `can0` into CAN FD mode with nominal bit rate at 500kbps and data phase bit rate at 2Mbps.

#### Creating CAN FD Sockets
For applications wishing to communicate over CAN FD interfaces, sockets must be created using AF_CAN address family as follows:

#include <sys/socket.h>
#include <linux/can.h>
#include <linux/can/raw.h>

int sock;
struct sockaddr_can addr;
struct ifreq ifr;

sock = socket(PF_CAN, SOCK_RAW, CAN_RAW);

strcpy(ifr.ifr_name, "can0");
ioctl(sock, SIOCGIFINDEX, &ifr);
addr.can_family = AF_CAN;
addr.can_ifindex = ifr.ifr_ifindex;

bind(sock, (struct sockaddr *)&addr, sizeof(addr));

The above C code snippet demonstrates how to create a raw CAN socket bound to a specific network interface (`can0`) configured earlier for CAN FD operations.

When sending frames via this socket, ensure that struct `canfd_frame` instead of regular `can_frame` structures are used when dealing specifically with CAN FD messages due to their capability of carrying extended payload sizes beyond standard CAN frame limits.

#### Sending and Receiving Messages
Messages sent should use appropriate flags indicating whether they're part of classical CAN or CAN FD format depending upon message structure size requirements.

Reception involves reading from the file descriptor associated with the socket where received packets conforming either traditional CAN formats or enhanced ones defined by CAN FD specification will appear based on what was transmitted across bus connected peers supporting such standards.

--related questions--

1. How does one interpret error states reported during CAN FD transmissions?
2. What tools exist within Linux distributions aimed towards debugging issues related to CAN/CAN-FD communications?
3. Are there any significant differences between implementing CAN vs CAN FD protocols concerning security aspects?
4. Can you provide an example scenario illustrating advantages gained through adoption of CAN FD over conventional CAN implementations?