can: migrate documentation to restructured text

The kernel documentation is now restructured text. Convert the SocketCAN
documentation and include it in the toplevel kernel documentation.

This patch doesn't do any content change.

All references to can.txt in the code are converted to can.rst.

Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

8 files changed, 1442 insertions, 1314 deletions

diff --git a/Documentation/networking/00-INDEX b/Documentation/networking/00-INDEX
index f5d642c01dd3..2b89d91b376f 100644
--- a/Documentation/networking/00-INDEX
+++ b/Documentation/networking/00-INDEX
@@ -36,8 +36,6 @@ bonding.txt
 	- Linux Ethernet Bonding Driver HOWTO: link aggregation in Linux.
 bridge.txt
 	- where to get user space programs for ethernet bridging with Linux.
-can.txt
-	- documentation on CAN protocol family.
 cdc_mbim.txt
 	- 3G/LTE USB modem (Mobile Broadband Interface Model)
 checksum-offloads.txt
diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
new file mode 100644
index 000000000000..d23c51abf8c6
--- /dev/null
+++ b/Documentation/networking/can.rst
@@ -0,0 +1,1437 @@
+===================================
+SocketCAN - Controller Area Network
+===================================
+
+Overview / What is SocketCAN
+============================
+
+The socketcan package is an implementation of CAN protocols
+(Controller Area Network) for Linux.  CAN is a networking technology
+which has widespread use in automation, embedded devices, and
+automotive fields.  While there have been other CAN implementations
+for Linux based on character devices, SocketCAN uses the Berkeley
+socket API, the Linux network stack and implements the CAN device
+drivers as network interfaces.  The CAN socket API has been designed
+as similar as possible to the TCP/IP protocols to allow programmers,
+familiar with network programming, to easily learn how to use CAN
+sockets.
+
+
+.. _socketcan-motivation:
+
+Motivation / Why Using the Socket API
+=====================================
+
+There have been CAN implementations for Linux before SocketCAN so the
+question arises, why we have started another project.  Most existing
+implementations come as a device driver for some CAN hardware, they
+are based on character devices and provide comparatively little
+functionality.  Usually, there is only a hardware-specific device
+driver which provides a character device interface to send and
+receive raw CAN frames, directly to/from the controller hardware.
+Queueing of frames and higher-level transport protocols like ISO-TP
+have to be implemented in user space applications.  Also, most
+character-device implementations support only one single process to
+open the device at a time, similar to a serial interface.  Exchanging
+the CAN controller requires employment of another device driver and
+often the need for adaption of large parts of the application to the
+new driver's API.
+
+SocketCAN was designed to overcome all of these limitations.  A new
+protocol family has been implemented which provides a socket interface
+to user space applications and which builds upon the Linux network
+layer, enabling use all of the provided queueing functionality.  A device
+driver for CAN controller hardware registers itself with the Linux
+network layer as a network device, so that CAN frames from the
+controller can be passed up to the network layer and on to the CAN
+protocol family module and also vice-versa.  Also, the protocol family
+module provides an API for transport protocol modules to register, so
+that any number of transport protocols can be loaded or unloaded
+dynamically.  In fact, the can core module alone does not provide any
+protocol and cannot be used without loading at least one additional
+protocol module.  Multiple sockets can be opened at the same time,
+on different or the same protocol module and they can listen/send
+frames on different or the same CAN IDs.  Several sockets listening on
+the same interface for frames with the same CAN ID are all passed the
+same received matching CAN frames.  An application wishing to
+communicate using a specific transport protocol, e.g. ISO-TP, just
+selects that protocol when opening the socket, and then can read and
+write application data byte streams, without having to deal with
+CAN-IDs, frames, etc.
+
+Similar functionality visible from user-space could be provided by a
+character device, too, but this would lead to a technically inelegant
+solution for a couple of reasons:
+
+* **Intricate usage:**  Instead of passing a protocol argument to
+  socket(2) and using bind(2) to select a CAN interface and CAN ID, an
+  application would have to do all these operations using ioctl(2)s.
+
+* **Code duplication:**  A character device cannot make use of the Linux
+  network queueing code, so all that code would have to be duplicated
+  for CAN networking.
+
+* **Abstraction:**  In most existing character-device implementations, the
+  hardware-specific device driver for a CAN controller directly
+  provides the character device for the application to work with.
+  This is at least very unusual in Unix systems for both, char and
+  block devices.  For example you don't have a character device for a
+  certain UART of a serial interface, a certain sound chip in your
+  computer, a SCSI or IDE controller providing access to your hard
+  disk or tape streamer device.  Instead, you have abstraction layers
+  which provide a unified character or block device interface to the
+  application on the one hand, and a interface for hardware-specific
+  device drivers on the other hand.  These abstractions are provided
+  by subsystems like the tty layer, the audio subsystem or the SCSI
+  and IDE subsystems for the devices mentioned above.
+
+  The easiest way to implement a CAN device driver is as a character
+  device without such a (complete) abstraction layer, as is done by most
+  existing drivers.  The right way, however, would be to add such a
+  layer with all the functionality like registering for certain CAN
+  IDs, supporting several open file descriptors and (de)multiplexing
+  CAN frames between them, (sophisticated) queueing of CAN frames, and
+  providing an API for device drivers to register with.  However, then
+  it would be no more difficult, or may be even easier, to use the
+  networking framework provided by the Linux kernel, and this is what
+  SocketCAN does.
+
+The use of the networking framework of the Linux kernel is just the
+natural and most appropriate way to implement CAN for Linux.
+
+
+.. _socketcan-concept:
+
+SocketCAN Concept
+=================
+
+As described in :ref:`socketcan-motivation` the main goal of SocketCAN is to
+provide a socket interface to user space applications which builds
+upon the Linux network layer. In contrast to the commonly known
+TCP/IP and ethernet networking, the CAN bus is a broadcast-only(!)
+medium that has no MAC-layer addressing like ethernet. The CAN-identifier
+(can_id) is used for arbitration on the CAN-bus. Therefore the CAN-IDs
+have to be chosen uniquely on the bus. When designing a CAN-ECU
+network the CAN-IDs are mapped to be sent by a specific ECU.
+For this reason a CAN-ID can be treated best as a kind of source address.
+
+
+.. _socketcan-receive-lists:
+
+Receive Lists
+-------------
+
+The network transparent access of multiple applications leads to the
+problem that different applications may be interested in the same
+CAN-IDs from the same CAN network interface. The SocketCAN core
+module - which implements the protocol family CAN - provides several
+high efficient receive lists for this reason. If e.g. a user space
+application opens a CAN RAW socket, the raw protocol module itself
+requests the (range of) CAN-IDs from the SocketCAN core that are
+requested by the user. The subscription and unsubscription of
+CAN-IDs can be done for specific CAN interfaces or for all(!) known
+CAN interfaces with the can_rx_(un)register() functions provided to
+CAN protocol modules by the SocketCAN core (see :ref:`socketcan-core-module`).
+To optimize the CPU usage at runtime the receive lists are split up
+into several specific lists per device that match the requested
+filter complexity for a given use-case.
+
+
+.. _socketcan-local-loopback1:
+
+Local Loopback of Sent Frames
+-----------------------------
+
+As known from other networking concepts the data exchanging
+applications may run on the same or different nodes without any
+change (except for the according addressing information):
+
+.. code::
+
+	 ___   ___   ___                   _______   ___
+	| _ | | _ | | _ |                 | _   _ | | _ |
+	||A|| ||B|| ||C||                 ||A| |B|| ||C||
+	|___| |___| |___|                 |_______| |___|
+	  |     |     |                       |       |
+	-----------------(1)- CAN bus -(2)---------------
+
+To ensure that application A receives the same information in the
+example (2) as it would receive in example (1) there is need for
+some kind of local loopback of the sent CAN frames on the appropriate
+node.
+
+The Linux network devices (by default) just can handle the
+transmission and reception of media dependent frames. Due to the
+arbitration on the CAN bus the transmission of a low prio CAN-ID
+may be delayed by the reception of a high prio CAN frame. To
+reflect the correct [*]_ traffic on the node the loopback of the sent
+data has to be performed right after a successful transmission. If
+the CAN network interface is not capable of performing the loopback for
+some reason the SocketCAN core can do this task as a fallback solution.
+See :ref:`socketcan-local-loopback1` for details (recommended).
+
+The loopback functionality is enabled by default to reflect standard
+networking behaviour for CAN applications. Due to some requests from
+the RT-SocketCAN group the loopback optionally may be disabled for each
+separate socket. See sockopts from the CAN RAW sockets in :ref:`socketcan-raw-sockets`.
+
+.. [*] you really like to have this when you're running analyser
+       tools like 'candump' or 'cansniffer' on the (same) node.
+
+
+.. _socketcan-network-problem-notifications:
+
+Network Problem Notifications
+-----------------------------
+
+The use of the CAN bus may lead to several problems on the physical
+and media access control layer. Detecting and logging of these lower
+layer problems is a vital requirement for CAN users to identify
+hardware issues on the physical transceiver layer as well as
+arbitration problems and error frames caused by the different
+ECUs. The occurrence of detected errors are important for diagnosis
+and have to be logged together with the exact timestamp. For this
+reason the CAN interface driver can generate so called Error Message
+Frames that can optionally be passed to the user application in the
+same way as other CAN frames. Whenever an error on the physical layer
+or the MAC layer is detected (e.g. by the CAN controller) the driver
+creates an appropriate error message frame. Error messages frames can
+be requested by the user application using the common CAN filter
+mechanisms. Inside this filter definition the (interested) type of
+errors may be selected. The reception of error messages is disabled
+by default. The format of the CAN error message frame is briefly
+described in the Linux header file "include/uapi/linux/can/error.h".
+
+
+How to use SocketCAN
+====================
+
+Like TCP/IP, you first need to open a socket for communicating over a
+CAN network. Since SocketCAN implements a new protocol family, you
+need to pass PF_CAN as the first argument to the socket(2) system
+call. Currently, there are two CAN protocols to choose from, the raw
+socket protocol and the broadcast manager (BCM). So to open a socket,
+you would write::
+
+    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+and::
+
+    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
+
+respectively.  After the successful creation of the socket, you would
+normally use the bind(2) system call to bind the socket to a CAN
+interface (which is different from TCP/IP due to different addressing
+- see :ref:`socketcan-concept`). After binding (CAN_RAW) or connecting (CAN_BCM)
+the socket, you can read(2) and write(2) from/to the socket or use
+send(2), sendto(2), sendmsg(2) and the recv* counterpart operations
+on the socket as usual. There are also CAN specific socket options
+described below.
+
+The basic CAN frame structure and the sockaddr structure are defined
+in include/linux/can.h:
+
+.. code-block:: C
+
+    struct can_frame {
+            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+            __u8    can_dlc; /* frame payload length in byte (0 .. 8) */
+            __u8    __pad;   /* padding */
+            __u8    __res0;  /* reserved / padding */
+            __u8    __res1;  /* reserved / padding */
+            __u8    data[8] __attribute__((aligned(8)));
+    };
+
+The alignment of the (linear) payload data[] to a 64bit boundary
+allows the user to define their own structs and unions to easily access
+the CAN payload. There is no given byteorder on the CAN bus by
+default. A read(2) system call on a CAN_RAW socket transfers a
+struct can_frame to the user space.
+
+The sockaddr_can structure has an interface index like the
+PF_PACKET socket, that also binds to a specific interface:
+
+.. code-block:: C
+
+    struct sockaddr_can {
+            sa_family_t can_family;
+            int         can_ifindex;
+            union {
+                    /* transport protocol class address info (e.g. ISOTP) */
+                    struct { canid_t rx_id, tx_id; } tp;
+
+                    /* reserved for future CAN protocols address information */
+            } can_addr;
+    };
+
+To determine the interface index an appropriate ioctl() has to
+be used (example for CAN_RAW sockets without error checking):
+
+.. code-block:: C
+
+    int s;
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+
+    s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
+
+    strcpy(ifr.ifr_name, "can0" );
+    ioctl(s, SIOCGIFINDEX, &ifr);
+
+    addr.can_family = AF_CAN;
+    addr.can_ifindex = ifr.ifr_ifindex;
+
+    bind(s, (struct sockaddr *)&addr, sizeof(addr));
+
+    (..)
+
+To bind a socket to all(!) CAN interfaces the interface index must
+be 0 (zero). In this case the socket receives CAN frames from every
+enabled CAN interface. To determine the originating CAN interface
+the system call recvfrom(2) may be used instead of read(2). To send
+on a socket that is bound to 'any' interface sendto(2) is needed to
+specify the outgoing interface.
+
+Reading CAN frames from a bound CAN_RAW socket (see above) consists
+of reading a struct can_frame:
+
+.. code-block:: C
+
+    struct can_frame frame;
+
+    nbytes = read(s, &frame, sizeof(struct can_frame));
+
+    if (nbytes < 0) {
+            perror("can raw socket read");
+            return 1;
+    }
+
+    /* paranoid check ... */
+    if (nbytes < sizeof(struct can_frame)) {
+            fprintf(stderr, "read: incomplete CAN frame\n");
+            return 1;
+    }
+
+    /* do something with the received CAN frame */
+
+Writing CAN frames can be done similarly, with the write(2) system call::
+
+    nbytes = write(s, &frame, sizeof(struct can_frame));
+
+When the CAN interface is bound to 'any' existing CAN interface
+(addr.can_ifindex = 0) it is recommended to use recvfrom(2) if the
+information about the originating CAN interface is needed:
+
+.. code-block:: C
+
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+    socklen_t len = sizeof(addr);
+    struct can_frame frame;
+
+    nbytes = recvfrom(s, &frame, sizeof(struct can_frame),
+                      0, (struct sockaddr*)&addr, &len);
+
+    /* get interface name of the received CAN frame */
+    ifr.ifr_ifindex = addr.can_ifindex;
+    ioctl(s, SIOCGIFNAME, &ifr);
+    printf("Received a CAN frame from interface %s", ifr.ifr_name);
+
+To write CAN frames on sockets bound to 'any' CAN interface the
+outgoing interface has to be defined certainly:
+
+.. code-block:: C
+
+    strcpy(ifr.ifr_name, "can0");
+    ioctl(s, SIOCGIFINDEX, &ifr);
+    addr.can_ifindex = ifr.ifr_ifindex;
+    addr.can_family  = AF_CAN;
+
+    nbytes = sendto(s, &frame, sizeof(struct can_frame),
+                    0, (struct sockaddr*)&addr, sizeof(addr));
+
+An accurate timestamp can be obtained with an ioctl(2) call after reading
+a message from the socket:
+
+.. code-block:: C
+
+    struct timeval tv;
+    ioctl(s, SIOCGSTAMP, &tv);
+
+The timestamp has a resolution of one microsecond and is set automatically
+at the reception of a CAN frame.
+
+Remark about CAN FD (flexible data rate) support:
+
+Generally the handling of CAN FD is very similar to the formerly described
+examples. The new CAN FD capable CAN controllers support two different
+bitrates for the arbitration phase and the payload phase of the CAN FD frame
+and up to 64 bytes of payload. This extended payload length breaks all the
+kernel interfaces (ABI) which heavily rely on the CAN frame with fixed eight
+bytes of payload (struct can_frame) like the CAN_RAW socket. Therefore e.g.
+the CAN_RAW socket supports a new socket option CAN_RAW_FD_FRAMES that
+switches the socket into a mode that allows the handling of CAN FD frames
+and (legacy) CAN frames simultaneously (see :ref:`socketcan-rawfd`).
+
+The struct canfd_frame is defined in include/linux/can.h:
+
+.. code-block:: C
+
+    struct canfd_frame {
+            canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
+            __u8    len;     /* frame payload length in byte (0 .. 64) */
+            __u8    flags;   /* additional flags for CAN FD */
+            __u8    __res0;  /* reserved / padding */
+            __u8    __res1;  /* reserved / padding */
+            __u8    data[64] __attribute__((aligned(8)));
+    };
+
+The struct canfd_frame and the existing struct can_frame have the can_id,
+the payload length and the payload data at the same offset inside their
+structures. This allows to handle the different structures very similar.
+When the content of a struct can_frame is copied into a struct canfd_frame
+all structure elements can be used as-is - only the data[] becomes extended.
+
+When introducing the struct canfd_frame it turned out that the data length
+code (DLC) of the struct can_frame was used as a length information as the
+length and the DLC has a 1:1 mapping in the range of 0 .. 8. To preserve
+the easy handling of the length information the canfd_frame.len element
+contains a plain length value from 0 .. 64. So both canfd_frame.len and
+can_frame.can_dlc are equal and contain a length information and no DLC.
+For details about the distinction of CAN and CAN FD capable devices and
+the mapping to the bus-relevant data length code (DLC), see :ref:`socketcan-can-fd-driver`.
+
+The length of the two CAN(FD) frame structures define the maximum transfer
+unit (MTU) of the CAN(FD) network interface and skbuff data length. Two
+definitions are specified for CAN specific MTUs in include/linux/can.h:
+
+.. code-block:: C
+
+  #define CAN_MTU   (sizeof(struct can_frame))   == 16  => 'legacy' CAN frame
+  #define CANFD_MTU (sizeof(struct canfd_frame)) == 72  => CAN FD frame
+
+
+.. _socketcan-raw-sockets:
+
+RAW Protocol Sockets with can_filters (SOCK_RAW)
+------------------------------------------------
+
+Using CAN_RAW sockets is extensively comparable to the commonly
+known access to CAN character devices. To meet the new possibilities
+provided by the multi user SocketCAN approach, some reasonable
+defaults are set at RAW socket binding time:
+
+- The filters are set to exactly one filter receiving everything
+- The socket only receives valid data frames (=> no error message frames)
+- The loopback of sent CAN frames is enabled (see :ref:`socketcan-local-loopback2`)
+- The socket does not receive its own sent frames (in loopback mode)
+
+These default settings may be changed before or after binding the socket.
+To use the referenced definitions of the socket options for CAN_RAW
+sockets, include <linux/can/raw.h>.
+
+
+.. _socketcan-rawfilter:
+
+RAW socket option CAN_RAW_FILTER
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The reception of CAN frames using CAN_RAW sockets can be controlled
+by defining 0 .. n filters with the CAN_RAW_FILTER socket option.
+
+The CAN filter structure is defined in include/linux/can.h:
+
+.. code-block:: C
+
+    struct can_filter {
+            canid_t can_id;
+            canid_t can_mask;
+    };
+
+A filter matches, when:
+
+.. code-block:: C
+
+    <received_can_id> & mask == can_id & mask
+
+which is analogous to known CAN controllers hardware filter semantics.
+The filter can be inverted in this semantic, when the CAN_INV_FILTER
+bit is set in can_id element of the can_filter structure. In
+contrast to CAN controller hardware filters the user may set 0 .. n
+receive filters for each open socket separately:
+
+.. code-block:: C
+
+    struct can_filter rfilter[2];
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = CAN_SFF_MASK;
+    rfilter[1].can_id   = 0x200;
+    rfilter[1].can_mask = 0x700;
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
+
+To disable the reception of CAN frames on the selected CAN_RAW socket:
+
+.. code-block:: C
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, NULL, 0);
+
+To set the filters to zero filters is quite obsolete as to not read
+data causes the raw socket to discard the received CAN frames. But
+having this 'send only' use-case we may remove the receive list in the
+Kernel to save a little (really a very little!) CPU usage.
+
+CAN Filter Usage Optimisation
+.............................
+
+The CAN filters are processed in per-device filter lists at CAN frame
+reception time. To reduce the number of checks that need to be performed
+while walking through the filter lists the CAN core provides an optimized
+filter handling when the filter subscription focusses on a single CAN ID.
+
+For the possible 2048 SFF CAN identifiers the identifier is used as an index
+to access the corresponding subscription list without any further checks.
+For the 2^29 possible EFF CAN identifiers a 10 bit XOR folding is used as
+hash function to retrieve the EFF table index.
+
+To benefit from the optimized filters for single CAN identifiers the
+CAN_SFF_MASK or CAN_EFF_MASK have to be set into can_filter.mask together
+with set CAN_EFF_FLAG and CAN_RTR_FLAG bits. A set CAN_EFF_FLAG bit in the
+can_filter.mask makes clear that it matters whether a SFF or EFF CAN ID is
+subscribed. E.g. in the example from above:
+
+.. code-block:: C
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = CAN_SFF_MASK;
+
+both SFF frames with CAN ID 0x123 and EFF frames with 0xXXXXX123 can pass.
+
+To filter for only 0x123 (SFF) and 0x12345678 (EFF) CAN identifiers the
+filter has to be defined in this way to benefit from the optimized filters:
+
+.. code-block:: C
+
+    struct can_filter rfilter[2];
+
+    rfilter[0].can_id   = 0x123;
+    rfilter[0].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_SFF_MASK);
+    rfilter[1].can_id   = 0x12345678 | CAN_EFF_FLAG;
+    rfilter[1].can_mask = (CAN_EFF_FLAG | CAN_RTR_FLAG | CAN_EFF_MASK);
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_FILTER, &rfilter, sizeof(rfilter));
+
+
+RAW Socket Option CAN_RAW_ERR_FILTER
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As described in :ref:`socketcan-network-problem-notifications` the CAN interface driver can generate so
+called Error Message Frames that can optionally be passed to the user
+application in the same way as other CAN frames. The possible
+errors are divided into different error classes that may be filtered
+using the appropriate error mask. To register for every possible
+error condition CAN_ERR_MASK can be used as value for the error mask.
+The values for the error mask are defined in linux/can/error.h:
+
+.. code-block:: C
+
+    can_err_mask_t err_mask = ( CAN_ERR_TX_TIMEOUT | CAN_ERR_BUSOFF );
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_ERR_FILTER,
+               &err_mask, sizeof(err_mask));
+
+
+RAW Socket Option CAN_RAW_LOOPBACK
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To meet multi user needs the local loopback is enabled by default
+(see :ref:`socketcan-local-loopback1` for details). But in some embedded use-cases
+(e.g. when only one application uses the CAN bus) this loopback
+functionality can be disabled (separately for each socket):
+
+.. code-block:: C
+
+    int loopback = 0; /* 0 = disabled, 1 = enabled (default) */
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_LOOPBACK, &loopback, sizeof(loopback));
+
+
+RAW socket option CAN_RAW_RECV_OWN_MSGS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When the local loopback is enabled, all the sent CAN frames are
+looped back to the open CAN sockets that registered for the CAN
+frames' CAN-ID on this given interface to meet the multi user
+needs. The reception of the CAN frames on the same socket that was
+sending the CAN frame is assumed to be unwanted and therefore
+disabled by default. This default behaviour may be changed on
+demand:
+
+.. code-block:: C
+
+    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
+
+    setsockopt(s, SOL_CAN_RAW, CAN_RAW_RECV_OWN_MSGS,
+               &recv_own_msgs, sizeof(recv_own_msgs));
+
+
+.. _socketcan-rawfd:
+
+RAW Socket Option CAN_RAW_FD_FRAMES
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+CAN FD support in CAN_RAW sockets can be enabled with a new socket option
+CAN_RAW_FD_FRAMES which is off by default. When the new socket option is
+not supported by the CAN_RAW socket (e.g. on older kernels), switching the
+CAN_RAW_FD_FRAMES option returns the error -ENOPROTOOPT.
+
+Once CAN_RAW_FD_FRAMES is enabled the application can send both CAN frames
+and CAN FD frames. OTOH the application has to handle CAN and CAN FD frames
+when reading from the socket:
+
+.. code-block:: C
+
+    CAN_RAW_FD_FRAMES enabled:  CAN_MTU and CANFD_MTU are allowed
+    CAN_RAW_FD_FRAMES disabled: only CAN_MTU is allowed (default)
+
+Example:
+
+.. code-block:: C
+
+    [ remember: CANFD_MTU == sizeof(struct canfd_frame) ]
+
+    struct canfd_frame cfd;
+
+    nbytes = read(s, &cfd, CANFD_MTU);
+
+    if (nbytes == CANFD_MTU) {
+            printf("got CAN FD frame with length %d\n", cfd.len);
+            /* cfd.flags contains valid data */
+    } else if (nbytes == CAN_MTU) {
+            printf("got legacy CAN frame with length %d\n", cfd.len);
+            /* cfd.flags is undefined */
+    } else {
+            fprintf(stderr, "read: invalid CAN(FD) frame\n");
+            return 1;
+    }
+
+    /* the content can be handled independently from the received MTU size */
+
+    printf("can_id: %X data length: %d data: ", cfd.can_id, cfd.len);
+    for (i = 0; i < cfd.len; i++)
+            printf("%02X ", cfd.data[i]);
+
+When reading with size CANFD_MTU only returns CAN_MTU bytes that have
+been received from the socket a legacy CAN frame has been read into the
+provided CAN FD structure. Note that the canfd_frame.flags data field is
+not specified in the struct can_frame and therefore it is only valid in
+CANFD_MTU sized CAN FD frames.
+
+Implementation hint for new CAN applications:
+
+To build a CAN FD aware application use struct canfd_frame as basic CAN
+data structure for CAN_RAW based applications. When the application is
+executed on an older Linux kernel and switching the CAN_RAW_FD_FRAMES
+socket option returns an error: No problem. You'll get legacy CAN frames
+or CAN FD frames and can process them the same way.
+
+When sending to CAN devices make sure that the device is capable to handle
+CAN FD frames by checking if the device maximum transfer unit is CANFD_MTU.
+The CAN device MTU can be retrieved e.g. with a SIOCGIFMTU ioctl() syscall.
+
+
+RAW socket option CAN_RAW_JOIN_FILTERS
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The CAN_RAW socket can set multiple CAN identifier specific filters that
+lead to multiple filters in the af_can.c filter processing. These filters
+are indenpendent from each other which leads to logical OR'ed filters when
+applied (see :ref:`socketcan-rawfilter`).
+
+This socket option joines the given CAN filters in the way that only CAN
+frames are passed to user space that matched *all* given CAN filters. The
+semantic for the applied filters is therefore changed to a logical AND.
+
+This is useful especially when the filterset is a combination of filters
+where the CAN_INV_FILTER flag is set in order to notch single CAN IDs or
+CAN ID ranges from the incoming traffic.
+
+
+RAW Socket Returned Message Flags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When using recvmsg() call, the msg->msg_flags may contain following flags:
+
+MSG_DONTROUTE:
+	set when the received frame was created on the local host.
+
+MSG_CONFIRM:
+	set when the frame was sent via the socket it is received on.
+	This flag can be interpreted as a 'transmission confirmation' when the
+	CAN driver supports the echo of frames on driver level, see
+	:ref:`socketcan-local-loopback1` and :ref:`socketcan-local-loopback2`.
+	In order to receive such messages, CAN_RAW_RECV_OWN_MSGS must be set.
+
+
+Broadcast Manager Protocol Sockets (SOCK_DGRAM)
+-----------------------------------------------
+
+The Broadcast Manager protocol provides a command based configuration
+interface to filter and send (e.g. cyclic) CAN messages in kernel space.
+
+Receive filters can be used to down sample frequent messages; detect events
+such as message contents changes, packet length changes, and do time-out
+monitoring of received messages.
+
+Periodic transmission tasks of CAN frames or a sequence of CAN frames can be
+created and modified at runtime; both the message content and the two
+possible transmit intervals can be altered.
+
+A BCM socket is not intended for sending individual CAN frames using the
+struct can_frame as known from the CAN_RAW socket. Instead a special BCM
+configuration message is defined. The basic BCM configuration message used
+to communicate with the broadcast manager and the available operations are
+defined in the linux/can/bcm.h include. The BCM message consists of a
+message header with a command ('opcode') followed by zero or more CAN frames.
+The broadcast manager sends responses to user space in the same form:
+
+.. code-block:: C
+
+    struct bcm_msg_head {
+            __u32 opcode;                   /* command */
+            __u32 flags;                    /* special flags */
+            __u32 count;                    /* run 'count' times with ival1 */
+            struct timeval ival1, ival2;    /* count and subsequent interval */
+            canid_t can_id;                 /* unique can_id for task */
+            __u32 nframes;                  /* number of can_frames following */
+            struct can_frame frames[0];
+    };
+
+The aligned payload 'frames' uses the same basic CAN frame structure defined
+at the beginning of :ref:`socketcan-rawfd` and in the include/linux/can.h include. All
+messages to the broadcast manager from user space have this structure.
+
+Note a CAN_BCM socket must be connected instead of bound after socket
+creation (example without error checking):
+
+.. code-block:: C
+
+    int s;
+    struct sockaddr_can addr;
+    struct ifreq ifr;
+
+    s = socket(PF_CAN, SOCK_DGRAM, CAN_BCM);
+
+    strcpy(ifr.ifr_name, "can0");
+    ioctl(s, SIOCGIFINDEX, &ifr);
+
+    addr.can_family = AF_CAN;
+    addr.can_ifindex = ifr.ifr_ifindex;
+
+    connect(s, (struct sockaddr *)&addr, sizeof(addr));
+
+    (..)
+
+The broadcast manager socket is able to handle any number of in flight
+transmissions or receive filters concurrently. The different RX/TX jobs are
+distinguished by the unique can_id in each BCM message. However additional
+CAN_BCM sockets are recommended to communicate on multiple CAN interfaces.
+When the broadcast manager socket is bound to 'any' CAN interface (=> the
+interface index is set to zero) the configured receive filters apply to any
+CAN interface unless the sendto() syscall is used to overrule the 'any' CAN
+interface index. When using recvfrom() instead of read() to retrieve BCM
+socket messages the originating CAN interface is provided in can_ifindex.
+
+
+Broadcast Manager Operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The opcode defines the operation for the broadcast manager to carry out,
+or details the broadcast managers response to several events, including
+user requests.
+
+Transmit Operations (user space to broadcast manager):
+
+TX_SETUP:
+	Create (cyclic) transmission task.
+
+TX_DELETE:
+	Remove (cyclic) transmission task, requires only can_id.
+
+TX_READ:
+	Read properties of (cyclic) transmission task for can_id.
+
+TX_SEND:
+	Send one CAN frame.
+
+Transmit Responses (broadcast manager to user space):
+
+TX_STATUS:
+	Reply to TX_READ request (transmission task configuration).
+
+TX_EXPIRED:
+	Notification when counter finishes sending at initial interval
+	'ival1'. Requires the TX_COUNTEVT flag to be set at TX_SETUP.
+
+Receive Operations (user space to broadcast manager):
+
+RX_SETUP:
+	Create RX content filter subscription.
+
+RX_DELETE:
+	Remove RX content filter subscription, requires only can_id.
+
+RX_READ:
+	Read properties of RX content filter subscription for can_id.
+
+Receive Responses (broadcast manager to user space):
+
+RX_STATUS:
+	Reply to RX_READ request (filter task configuration).
+
+RX_TIMEOUT:
+	Cyclic message is detected to be absent (timer ival1 expired).
+
+RX_CHANGED:
+	BCM message with updated CAN frame (detected content change).
+	Sent on first message received or on receipt of revised CAN messages.
+
+
+Broadcast Manager Message Flags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When sending a message to the broadcast manager the 'flags' element may
+contain the following flag definitions which influence the behaviour:
+
+SETTIMER:
+	Set the values of ival1, ival2 and count
+
+STARTTIMER:
+	Start the timer with the actual values of ival1, ival2
+	and count. Starting the timer leads simultaneously to emit a CAN frame.
+
+TX_COUNTEVT:
+	Create the message TX_EXPIRED when count expires
+
+TX_ANNOUNCE:
+	A change of data by the process is emitted immediately.
+
+TX_CP_CAN_ID:
+	Copies the can_id from the message header to each
+	subsequent frame in frames. This is intended as usage simplification. For
+	TX tasks the unique can_id from the message header may differ from the
+	can_id(s) stored for transmission in the subsequent struct can_frame(s).
+
+RX_FILTER_ID:
+	Filter by can_id alone, no frames required (nframes=0).
+
+RX_CHECK_DLC:
+	A change of the DLC leads to an RX_CHANGED.
+
+RX_NO_AUTOTIMER:
+	Prevent automatically starting the timeout monitor.
+
+RX_ANNOUNCE_RESUME:
+	If passed at RX_SETUP and a receive timeout occurred, a
+	RX_CHANGED message will be generated when the (cyclic) receive restarts.
+
+TX_RESET_MULTI_IDX:
+	Reset the index for the multiple frame transmission.
+
+RX_RTR_FRAME:
+	Send reply for RTR-request (placed in op->frames[0]).
+
+
+Broadcast Manager Transmission Timers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Periodic transmission configurations may use up to two interval timers.
+In this case the BCM sends a number of messages ('count') at an interval
+'ival1', then continuing to send at another given interval 'ival2'. When
+only one timer is needed 'count' is set to zero and only 'ival2' is used.
+When SET_TIMER and START_TIMER flag were set the timers are activated.
+The timer values can be altered at runtime when only SET_TIMER is set.
+
+
+Broadcast Manager message sequence transmission
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Up to 256 CAN frames can be transmitted in a sequence in the case of a cyclic
+TX task configuration. The number of CAN frames is provided in the 'nframes'
+element of the BCM message head. The defined number of CAN frames are added
+as array to the TX_SETUP BCM configuration message:
+
+.. code-block:: C
+
+    /* create a struct to set up a sequence of four CAN frames */
+    struct {
+            struct bcm_msg_head msg_head;
+            struct can_frame frame[4];
+    } mytxmsg;
+
+    (..)
+    mytxmsg.msg_head.nframes = 4;
+    (..)
+
+    write(s, &mytxmsg, sizeof(mytxmsg));
+
+With every transmission the index in the array of CAN frames is increased
+and set to zero at index overflow.
+
+
+Broadcast Manager Receive Filter Timers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The timer values ival1 or ival2 may be set to non-zero values at RX_SETUP.
+When the SET_TIMER flag is set the timers are enabled:
+