Message-ID: <20110427090011.GE757@kurt.e-circ.dyndns.org>
Date:	Wed, 27 Apr 2011 11:00:11 +0200
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	socketcan-core@...ts.berlios.de, netdev@...r.kernel.org
Subject: [PATCH v4 4/5] can-j1939: add documentation

Add documentation of the SAE J1939 protocol stack

Signed-off-by: Kurt Van Dijck <kurt.van.dijck@....be>
---
 Documentation/networking/j1939.txt |  576 ++++++++++++++++++++++++++++++++++++
 MAINTAINERS                        |    8 +
 2 files changed, 584 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/networking/j1939.txt

diff --git a/Documentation/networking/j1939.txt b/Documentation/networking/j1939.txt
new file mode 100644
index 0000000..ef0a963
--- /dev/null
+++ b/Documentation/networking/j1939.txt
@@ -0,0 +1,576 @@
+============================================================================
+
+j1939.txt
+
+Readme file for the J1939 Protocol
+
+This file contains
+
+  1 Overview / What is j1939
+    1.1 specifications used
+
+  2 Motivation
+
+  3 J1939 concepts
+    3.1 socket type
+    3.2 addressing
+    3.3 priority
+    3.4 PGN
+    3.5 filtering
+    3.6 destinations with dynamic address
+
+  4 How to use J1939
+    4.1 rtnetlink interface
+    4.2 API calls
+        4.2.1 Message flags during sendmsg
+	4.2.2 SCM_J1939_DEST_ADDR & SCM_J1939_DEST_NAME
+	4.2.3 SCM_J1939_PRIORITY
+    4.3 Dynamic addressing
+    4.4 Send Examples
+        4.4.1 Static address
+	4.4.2 Dynamic address
+	4.4.3 Mixed mode
+
+  5 socket options
+    5.1 SO_J1939_FILTER
+    5.2 SO_J1939_PROMISC
+    5.3 SO_J1939_RECV_OWN
+    5.4 SO_J1939_SEND_PRIO
+
+  6 can-j1939 procfs interface
+    6.1 /proc/net/can-j1939/ecu
+    6.2 /proc/net/can-j1939/filter
+    6.3 /proc/net/can-j1939/sock
+    6.4 /proc/net/can-j1939/transport
+
+  7 can-j1939 SYSCTL
+    7.1 /proc/sys/net/can-j1939/transport_max_payload_in_bytes
+    7.2 /proc/sys/net/can-j1939/transport_cts_nr_of_frames
+    7.3 /proc/sys/net/can-j1939/transport_tx_retry_ms
+
+  8 Credits
+
+============================================================================
+
+1. Introduction
+--------------------------------
+
+  SAE J1939 defines a higher layer protocol on CAN. It implements a more
+  sophisticated addressing scheme and extends the maximum packet size above
+  8 bytes. Several derived specifications exists, which differ from the
+  original j1939 on the application level, like MilCAN, NMEA2000 and
+  especially ISO-11783 (ISOBUS). This last one specifies the so-called ETP
+  (Extended Transport Protocol) which is has been included in this
+  implementation. This inclusion results in a maximum packet size of
+  ((2^24)-1)*7 bytes
+
+
+1.1 specifications used
+
+  SAE J1939-21 : data link layer
+  SAE J1939-81 : network management
+  ISO 11783-6  : Virtual Terminal (Extended Transport Protocol)
+
+
+2. Motivation
+--------------------------------
+
+  Given the fact there's something like SocketCAN with an API similar to BSD
+  sockets, we found some reasons to justify a kernel implementation for the
+  addressing and transport methods used by J1939.
+
+  * addressing:
+    When a process on an ECU communicates via j1939, it should not necessarily
+    know its source address. Although at least 1 process per ECU should know
+    the source address. Other processes should be able to reuse that address.
+    This way, address parameters for different processes cooperating for the
+    same ECU, are not duplicated.
+    This way of working is closely related to the unix concept where programs
+    do just 1 thing, and do it well.
+
+  * dynamic addressing:
+    Address Claiming in J1939 is time critical. Furthermore data transport
+    should be handled properly during the address negotiation. Putting these
+    functionality in the kernel eliminates this functionality as a requirement
+    for _every_ userspace process that communicates via J1939. This results in
+    a consistent J1939 bus with proper addressing.
+
+  * transport:
+    Both TP & ETP reuse some PGN's to relay big packets over them. Different
+    processes may thus use the same TP & ETP PGN's without actually knowing it.
+    The individual TP & ETP sessions _must_ be serialized (synchronised)
+    between different processes. The kernel solves this problem properly, and
+    eliminates the serialisation (synchronisation) as a requirement for
+    _every_ userspace process that communicates via J1939.
+
+  J1939 defines some other features (relaying, gateway, Fast Packet transport,
+  ...). In-kernel code for these would not contribute to protocol stability.
+  Therefore, these parts are left to userspace.
+
+  The j1939 sockets operate on CAN network devices (see SocketCAN). Any j1939
+  userspace library operating on CAN raw sockets will still operate properly.
+  Since such library does not communicate with the in-kernel implementation,
+  care must be taken that these 2 do not interfere. In practice, this means
+  they cannot share ECU addresses. A single ECU (or virtual ECU) address is
+  used by the library exclusively, or by the in-kernel system exclusively.
+
+
+3. J1939 concepts
+--------------------------------
+
+3.1 PGN
+
+  The PGN (Parameter Group Number) is a number to identify a packet. The PGN
+  is composed as follows:
+   1 bit  : Reserved Bit
+   1 bit  : Data Page
+   8 bits : PF (PDU Format)
+   8 bits : PS (PDU Specific)
+
+  In J1939-21, distinction is made between PDU1 Format (where PF < 240) and
+  PDU2 Format (where PF >= 240). Furthermore, when using PDU2 Format, the
+  PS-field contains a so-called Group Extension, which is part of the PGN.
+  When using PDU2 Format, the Group Extension is set in the PS-field.
+
+  On the other hand, when using PDU1 Format, the PS-field contains a so-called
+  Destination Address, which is _not_ part of the PGN. When communicating a
+  PGN from userspace to kernel (or visa versa) and PDU2 Format is used, the
+  PS-field of the PGN shall be set to zero. The Destination Address shall be
+  set elsewhere.
+
+  Regarding PGN mapping to 29-bit CAN identifier, the Destination Address
+  shall be get/set from/to the apropriate bits of the identifier by the kernel.
+
+
+3.2 addressing
+
+  Both static and dynamic addressing methods can be used.
+
+  For static addresses, no extra checks are made by the kernel, and provided
+  addresses are considered right. This responsibility is for the OEM or system
+  integrator.
+
+  For dynamic addressing, so-called Address Claiming, extra support is forseen
+  in the kernel. In J1939 any ECU is known by it's 64-bit NAME. At the moment
+  of succesfull address claim, the kernel keeps track of both NAME and source
+  address being claimed. This serves as a base for filter schemes. By default,
+  packets with a destination that is not locally, will be rejected soon after
+  reception.
+
+  Mixed mode packets (from a static to a dynamic address or vice versa) are
+  allowed. The BSD sockets define seperate API calls for getting/setting the
+  local & remote address and are applicable for J1939 sockets.
+
+
+3.3 Filtering
+
+  Similar to SocketCAN, j1939 defines filters per socket that a user can set
+  in order to receive a subset of the j1939 traffic. Filtering can base on
+  * SA
+  * NAME
+  * PGN
+
+  There is a semantic difference with SocketCAN with regard to filtering.
+  When multiple filters are in place for a single socket, and a packet comes
+  in that matches several of those filters, the packet is only received once
+  for that socket.
+  The rationale behind this difference originates in the filter capabilities.
+  Where SocketCAN filters on only 1 orthogonal (can id), J1939 can filter
+  on 3 orthogonal properties (sa, name, pgn).
+
+  When a filter on the SA is set, j1939 traffic with a matching SA, but with
+  its NAME set (aka having claimed SA successfully) will match, although
+  the filter would not match its NAME.
+
+  Filtering on priority is _not_ supported.
+
+
+4. How to use J1939
+--------------------------------
+
+4.1 rtnetlink interface
+
+  Per default j1939 is not active. Specifying can_ifindex != 0 in bind(2)
+  or connect(2) needs an active j1939 on that interface. You must have done
+  $ ip link set canX j1939 on
+  on that interface.
+
+  $ ip link set canX j1939 down
+  disables j1939 on canX.
+
+  Assigning addresses is done via
+  $ ip addr add dev canX j1939 0xXX
+  statically or
+  $ ip addr add dev canX j1939 name 0xXX
+  dynamically. In the latter case, address claiming must take place
+  before other traffic can leave.
+
+  Removing addresses is done similarly via
+  $ ip addr del dev canX j1939 0xXX
+  $ ip addr del dev canX j1939 name 0xXX
+
+  A static address cannot be assigned together with a 64bit name.
+
+4.2 API calls
+
+  Like TCP/IP and CAN, you first need to open a socket for communicating over a
+  CAN network. To use j1939, include <include/linux/j1939.h>. From there,
+  <include/linux/can.h> will be included too.
+  To open a socket, you would write
+
+    s = socket(PF_CAN, SOCK_DGRAM, CAN_J1939);
+
+  J1939 does use SOCK_DGRAM sockets. In the j1939 specification, connections are
+  mentioned in the context of transport protocol sessions. These still deliver
+  packets to the other end (using several CAN packets).
+  SOCK_STREAM is never appropriate.
+
+  After the successful creation of the socket, you would normally use the
+  bind(2) and/or connect(2) system call to bind the socket to a CAN interface
+  (which is different from TCP/IP due to different addressing) After binding
+  and/or connecting 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 J1939 specific socket options described
+  below.
+
+  In order to send data, a bind(2) must have succeeded. bind(2) assigns a local
+  address to a socket. For this to succeed, you can only choose addresses
+  that have been assigned earlier (see 4.1). When an empty address is assigned
+  (ie. SA=0xff && name=0), a default is taken for the device that is bound to.
+
+  Different from CAN is that the payload data is just the data that get send,
+  without it's header info. The header info is derived from the sockaddr
+  supplied to bind(2), connect(2), sendto(2) and recvfrom(2). A write(2) with
+  size 4 will result in a packet with 4 bytes.
+
+  The sockaddr structure has extensions for use with j1939 as specified below:
+      struct sockaddr_can {
+         sa_family_t can_family;
+         int         can_ifindex;
+         union {
+            struct {
+               __u64 name;
+               __u32 pgn;
+               __u8  addr;
+            } j1939;
+         } can_addr;
+      }
+
+  can_family & can_ifindex serve the same purpose as for other SocketCAN sockets.
+
+  can_addr.j1939.pgn specifies the PGN (max 0x3ffff). Individual bits are
+  specified above.
+
+  can_addr.j1939.name contains the 64-bit J1939 NAME.
+
+  can_addr.j1939.addr contains the source address.
+
+  When sending data, the source address is applied as follows: If
+  can_addr.j1939.name != 0 the NAME is looked up by the kernel and the
+  corresponding Source Address is used. If can_addr.j1939.name == 0,
+  can_addr.j1939.addr is used.
+
+  After a bind(2), the local address is assigned, i.e. the source address.
+  After a connect(2), the remote address is assigned, i.e. the destination
+  address.
+
+  Both write(2) and send(2) will send a packet with local address from bind,
+  remote address from connect(2). When the address was not set, a broadcast is
+  sent. The PGN is used from bind(2) or overruled with sendto(2), which will
+  override the destination address when valid, and the PGN when valid.
+
+  Both read(2) and recv(2) will receive packets matching the sockets filters.
+  recvfrom(2) will receive these packets with originator's address.
+
+  When creating a socket, reasonable defaults have been set. Some options can be
+  modified with setsockopt(2) & getsockopt(2).
+
+4.2.1 Message flags during sendmsg
+
+  send(2), sendto(2) and sendmsg(2) take a 'flags' argument. J1939 interpretes
+  these flags during outgoing traffic:
+
+  * MSG_DONTWAIT determines nonblocking operation. When a packet must wait for
+    any reason, -EAGAIN is returned.
+
+  * MSG_SYN
+    Packets flagged with MSG_SYN will wait for all pending packets on a socket
+    to be sent before trying to send. This means that if a socket just started
+    a Transport Protocol session, a packet with MSG_SYN will wait for that
+    session to complete before proceeding.
+    Traffic without MSG_SYN (on that very same socket) will still continue.
+
+4.2.2 SCM_J1939_DEST_ADDR & SCM_J1939_DEST_NAME
+
+  Different received j1939 packets could have had different destionations:
+  - broadcast packet, i.e. no destination address
+  - destination address that matches the sockets local address
+  - destination address that matches _a_ local address on the system, and the
+    socket had no local address defined.
+  - SO_J1939_PROMISC was set
+
+  The destination address & destination name (if applicable) are attached
+  to the msghdr in the recvmsg(2) call. It can be extracted using cmsg(3) macros,
+  with cmsg_level == SOL_J1939 && cmsg_type == SCM_J1939_DEST_ADDR
+  or SCM_J1939_DEST_NAME. The returned data is a uint8_t/uint64_t.
+
+4.2.3 SCM_J1939_PRIORITY
+
+  Attached to the msghdr is also the packet's priority on the bus. This is a
+  uint8_t, packed as cmsg_type == SCM_J1939_PRIORITY.
+
+4.3 Dynamic Addressing
+
+  Distinction has to be made in and using the claimed address and doing an
+  address claim. To use an already claimed address, one has to fill in the
+  j1939.name member and provide it to bind(2). If the name had claimed an
+  address earlier, all further PGN's being sent will use that address. And the
+  j1939.addr member will be ignored.
+
+  An exception on this is pgn 0x0ee00. This is the "Address Claim/Cannot Claim
+  Address" message and when the kernel will use the j1939.addr member for that
+  pgn if necessary.
+
+  To claim an address, bind(2) with:
+  j1939.pgn  set to 0x0ee00
+  j1939.addr set to the desired Source Address.
+  j1939.name set to the NAME you want the Source Address to claim to.
+
+  Afterwards do a write(2) with data set to the NAME (Little Endian). If the
+  NAME provided, does not match the j1939.name provided to bind(2), EPROTO
+  will be returned. One might use sendto(2) also to send the Addres Claim. In
+  that case, the j1939.addr member must be set to the broadcast address (255)
+  and the j1939.pgn must be set to 0x0ee00. If This combination is not given,
+  EPROTO is returned.
+
+  If no-one else contest the address claim within 250ms after transmission, the
+  kernel marks the NAME-SA assignment as valid. The valid assignment will be
+  kept, among other valid NAME-SA assignments. From that point, any socket
+  bound to the NAME can send packets.
+
+  If another ECU claims the address, the kernel will mark the NAME-SA expired.
+  No socket bound to the NAME can send packets (other than address claims).
+  To claim another address, some socket bound to NAME, must bind(2) again,
+  but with only j1939.addr changed to the new SA, and must then send a
+  valid address claim packet. This restarts the state machine in the kernel
+  (and any other participant on the bus) for this NAME.
+
+
+4.4 Send Examples
+
+4.4.1 Static addressing
+
+  This example will send a pgn (0x12300) from SA 0x20 to DA 0x30.
+
+  Add the address to the system:
+  $ ip addr add j1939 0x20 dev can0
+
+  Bind:
+    struct sockaddr_can addr;
+
+    memset(&addr, 0, sizeof(addr));
+    addr.can_ifindex = ifindex("can0"); // ifindex is a substitute.
+    addr.can_addr.j1939.name = J1939_NO_NAME;
+    addr.can_addr.j1939.addr = 0x20;
+    addr.can_addr.j1939.pgn = J1939_NO_PGN;
+
+    bind(sk, (void *)&addr, sizeof(addr));
+
+  Now, the socket 'sk' is bound to the address 0x20. Since no pgn
+  was specified during bound, a pgn will be necessary during sendto() operations.
+  Alternatively, specifying addr.can_addr.j1939.pgn during bind() allows
+  for using send() & write(), since a default pgn (the pgn specified during bind())
+  can be used then.
+
+  Send:
+    struct sockaddr_can addr;
+
+    memset(&addr, 0, sizeof(addr));
+    addr.can_addr.j1939.name = J1939_NO_NAME;
+    addr.can_addr.j1939.addr = 0x30;
+    addr.can_addr.j1939.pgn = 0x12300;
+    // addr.can_ifindex is not necessary here.
+
+    sendto(sk, data, sizeof(data), 0, (void *)&addr, sizeof(addr));
+
+4.4.2 Dynamic addressing
+
+  This example will send a pgn (0x12300) from 12345678 to 9ABCDEF
+
+  Add the name to the system:
+  $ ip addr add j1939 name 12345678 dev can0
+
+  Start an address claiming daemon (e.g. jacd)
+  $ jacd -r 0x20-0x30 12345678 can0 &
+
+  Bind:
+    struct sockaddr_can addr;
+
+    memset(&addr, 0, sizeof(addr));
+    addr.can_ifindex = ifindex("can0"); // ifindex is a substitute.
+    addr.can_addr.j1939.name = 0x12345678ULL;
+    addr.can_addr.j1939.addr = J1939_NO_ADDR;
+    addr.can_addr.j1939.pgn = J1939_NO_PGN;
+
+    bind(sk, (void *)&addr, sizeof(addr));
+
+  Send:
+    struct sockaddr_can addr;
+
+    memset(&addr, 0, sizeof(addr));
+    addr.can_addr.j1939.name = 0x9ABCDEFULL;
+    addr.can_addr.j1939. = J1939_NO_ADDR;
+    addr.can_addr.j1939.pgn = 0x12300;
+
+    sendto(sk, data, sizeof(data), 0, (void *)&addr, sizeof(addr));
+
+4.4.3 Mixed mode
+
+  A scenario that sends a packet from a static address to a dynamic address
+  or vice versa is called 'mixed mode' here.
+
+  Combining the setup of the static address with a sendto() to a dynamic
+  address from the above examples is legal, and implements such mixed mode
+  addressing. The same applies for the setup of the dynamic address combined
+  with the sendto() towards a dynamic address.
+
+
+5 Socket Options
+--------------------------------
+
+  j1939 sockets have some options that are configurable via setsockopt(2).
+  Each of those options is initialized with a reasonable default.
+
+
+5.1 SO_J1939_FILTER
+
+  As mentioned above, J1939 supports filtering in both NAME, Source Address
+  and PGN. All members must match.
+
+   struct j1939_filter filter = {
+      .name         = ...
+      .name_mask   = ...
+      .addr         = ...
+      .addr_mask   = ...
+      .pgn         = ...
+      .pgn_mask   = ...
+   }
+
+    setsockopt(s, SOL_CAN_J1939, SO_J1939_FILTER, &filter, sizeof(filter));
+
+
+5.2 SO_J1939_PROMISC
+
+  When set, j1939 will receive all packets, not just those with a destination
+  on the local system.
+  default off.
+
+    int promisc = 1; /* 0 = disabled (default), 1 = enabled */
+
+    setsockopt(s, SOL_CAN_J1939, SO_J1939_PROMISC, &promisc, sizeof(promisc));
+
+
+5.3 SO_J1939_RECV_OWN
+
+  All the sent j1939 packets are looped back in the system.
+  The reception of the j1939 packets on the same socket that was
+  sending the j1939 packet is assumed to be unwanted and therefore
+  disabled by default. This default behaviour may be changed on
+  demand:
+
+    int recv_own_msgs = 1; /* 0 = disabled (default), 1 = enabled */
+
+    setsockopt(s, SOL_CAN_J1939, SO_J1939_RECV_OWN,
+               &recv_own_msgs, sizeof(recv_own_msgs));
+
+
+5.4 SO_J1939_SEND_PRIO
+
+  To set the priority field for outgoing packets, the SO_J1939_SEND_PRIO can
+  be changed. This int field specifies the priority that will be used.
+  j1939 defines a priority between 0 and 7 inclusive,
+  with 7 the lowest priority.
+  Per default, the priority is set to 6 (conforming J1939).
+  This priority socket option operates on the same value that is modified
+  with
+
+    setsockopt(s, SOL_SOCKET, SO_PRIORITY, &pri, sizeof(pri))
+
+  socketoption, with a difference that SOL_SOCKET/SO_PRIORITY is defined with
+  0 the lowest priority. SOL_CAN_J1939/SO_J1939_SEND_PRIO inverts this value
+  for you.
+
+
+6. /proc/net/can-j1939 Interface.
+--------------------------------
+
+  Files giving you a view on the in-kernel operation of J1939 are located at:
+  /proc/net/j1939.
+
+6.1 /proc/net/can-j1939/ecu
+
+  This file gives an overview of the known ECU's to the kernel.
+  - iface : network interface they operate on.
+  - SA : current address.
+  - name : 64bit NAME
+  - flags : 'L' = local, 'R' = remote
+
+6.2 /proc/net/can-j1939/filter
+
+6.3 /proc/net/can-j1939/sock
+
+  This file gives a list of all j1939 sockets currently open.
+  - iface : network interface
+  - flags :
+    'b' : bound
+    'c' : connected
+    'P' : PROMISC
+    'o' : RECV_OWN
+    'd' : RECV_DEST
+    'p' : RECV_PRIO
+  - local: [NAME],SA
+  - remote: [NAME]/MASK,DA
+  - pgn : PGN
+  - prio : priority
+  - pending : # packets pending (see MSG_SYN on 4.2.1)
+
+6.4 /proc/net/can-j1939/transport
+
+  This file shows a list of pending transport sessions
+  - iface
+  - src : XX (addr) or XXXXXXXXXXXXXXXX (name)
+  - dst : XX or XXXXXXXXXXXXXXXX or '-' (broadcast)
+  - pgn :
+  - done/total : current # transferred bytes / total
+
+
+7. /proc/sys/net/can-j1939 - SYSCTL
+--------------------------------
+
+  Via these sysctl files, some parameters of the j1939 module can be tuned.
+
+7.1 /proc/sys/net/can-j1939/transport_max_payload_in_bytes [int]
+
+  Is the maximum packet size to accept on both transmit & receive side.
+  Bigger packets will be rejected (local sender), aborted (local receiver)
+  or ignored (broadcasts & remote recievers in PROMISC).
+
+7.2 /proc/sys/net/can-j1939/transport_cts_nr_frames [int]
+
+  Controls the number of packets to allow between consecutive CTS frames
+  (default 255).
+  This number is communicated within the CTS frame from receiver to transmitter.
+  Setting this has effect on received transport sessions only.
+
+7.3 /proc/sys/net/can-j1939/transport_tx_retry_ms [int]
+
+  Controls how many time to wait before retrying to send an individual TP
+  flow or data packet after transmission failure (default 20).
+
+
+8. Credits
+--------------------------------
+
+  Kurt Van Dijck (j1939 core, transport protocol, API)
+  Pieter Beyens (j1939 core, address claiming)
+
diff --git a/MAINTAINERS b/MAINTAINERS
index b5266ad..ec7b016 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1648,6 +1648,14 @@ F:	include/linux/can/error.h
 F:	include/linux/can/netlink.h
 F:	include/linux/can/platform/
 
+CAN-J1939 NETWORK LAYER
+M:	Kurt Van Dijck <kurt.van.dijck@....be>
+L:	socketcan-core@...ts.berlios.de
+L:	netdev@...r.kernel.org
+S:	Maintained
+F:	net/can/j1939/
+F:	include/linux/can/j1939.h
+
 CELL BROADBAND ENGINE ARCHITECTURE
 M:	Arnd Bergmann <arnd@...db.de>
 L:	linuxppc-dev@...ts.ozlabs.org
-- 
1.7.2.5

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