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can: j1939: use backquotes for code samples

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This patch adds backquotes for code samples.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Link: https://lore.kernel.org/r/20201026094442.16587-1-yegorslists@googlemail.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Yegor Yefremov 2020-10-26 10:44:42 +01:00 committed by Marc Kleine-Budde
parent ea780d39b1
commit a39372c2c5
1 changed files with 44 additions and 44 deletions
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88
Documentation/networking/j1939.rst
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@ -131,31 +131,31 @@ API Calls
---------
On CAN, you first need to open a socket for communicating over a CAN network.
To use J1939, #include <linux/can/j1939.h>. From there, <linux/can.h> will be
To use J1939, ``#include <linux/can/j1939.h>``. From there, ``<linux/can.h>`` will be
included too. To open a socket, use:
.. code-block:: C
s = socket(PF_CAN, SOCK_DGRAM, CAN_J1939);
J1939 does use SOCK_DGRAM sockets. In the J1939 specification, connections are
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 not
packets to the other end (using several CAN packets). ``SOCK_STREAM`` is not
supported.
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. 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
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. 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 been successful. bind(2) assigns a
In order to send data, a ``bind(2)`` must have been successful. ``bind(2)`` assigns a
local address to a socket.
Different from CAN is that the payload data is just the data that get sends,
without its 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
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:
@ -180,47 +180,47 @@ The sockaddr structure has extensions for use with J1939 as specified below:
} can_addr;
}
can_family & can_ifindex serve the same purpose as for other SocketCAN sockets.
``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
``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.name`` contains the 64-bit J1939 NAME.
can_addr.j1939.addr contains the address.
``can_addr.j1939.addr`` contains the address.
The bind(2) system call assigns the local address, i.e. the source address when
sending packages. If a PGN during bind(2) is set, it's used as a RX filter.
The ``bind(2)`` system call assigns the local address, i.e. the source address when
sending packages. If a PGN during ``bind(2)`` is set, it's used as a RX filter.
I.e. only packets with a matching PGN are received. If an ADDR or NAME is set
it is used as a receive filter, too. It will match the destination NAME or ADDR
of the incoming packet. The NAME filter will work only if appropriate Address
Claiming for this name was done on the CAN bus and registered/cached by the
kernel.
On the other hand connect(2) assigns the remote address, i.e. the destination
address. The PGN from connect(2) is used as the default PGN when sending
On the other hand ``connect(2)`` assigns the remote address, i.e. the destination
address. The PGN from ``connect(2)`` is used as the default PGN when sending
packets. If ADDR or NAME is set it will be used as the default destination ADDR
or NAME. Further a set ADDR or NAME during connect(2) is used as a receive
or NAME. Further a set ADDR or NAME during ``connect(2)`` is used as a receive
filter. It will match the source NAME or ADDR of the incoming packet.
Both write(2) and send(2) will send a packet with local address from bind(2) and
the remote address from connect(2). Use sendto(2) to overwrite the destination
Both ``write(2)`` and ``send(2)`` will send a packet with local address from ``bind(2)`` and the
remote address from ``connect(2)``. Use ``sendto(2)`` to overwrite the destination
address.
If can_addr.j1939.name is set (!= 0) the NAME is looked up by the kernel and
the corresponding ADDR is used. If can_addr.j1939.name is not set (== 0),
can_addr.j1939.addr is used.
If ``can_addr.j1939.name`` is set (!= 0) the NAME is looked up by the kernel and
the corresponding ADDR is used. If ``can_addr.j1939.name`` is not set (== 0),
``can_addr.j1939.addr`` is used.
When creating a socket, reasonable defaults are set. Some options can be
modified with setsockopt(2) & getsockopt(2).
modified with ``setsockopt(2)`` & ``getsockopt(2)``.
RX path related options:
- SO_J1939_FILTER - configure array of filters
- SO_J1939_PROMISC - disable filters set by bind(2) and connect(2)
- ``SO_J1939_FILTER`` - configure array of filters
- ``SO_J1939_PROMISC`` - disable filters set by ``bind(2)`` and ``connect(2)``
By default no broadcast packets can be send or received. To enable sending or
receiving broadcast packets use the socket option SO_BROADCAST:
receiving broadcast packets use the socket option ``SO_BROADCAST``:
.. code-block:: C
@ -261,26 +261,26 @@ The following diagram illustrates the RX path:
+---------------------------+
TX path related options:
SO_J1939_SEND_PRIO - change default send priority for the socket
``SO_J1939_SEND_PRIO`` - change default send priority for the socket
Message Flags during send() and Related System Calls
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
send(2), sendto(2) and sendmsg(2) take a 'flags' argument. Currently
``send(2)``, ``sendto(2)`` and ``sendmsg(2)`` take a 'flags' argument. Currently
supported flags are:
* MSG_DONTWAIT, i.e. non-blocking operation.
* ``MSG_DONTWAIT``, i.e. non-blocking operation.
recvmsg(2)
^^^^^^^^^^
In most cases recvmsg(2) is needed if you want to extract more information than
recvfrom(2) can provide. For example package priority and timestamp. The
In most cases ``recvmsg(2)`` is needed if you want to extract more information than
``recvfrom(2)`` can provide. For example package priority and timestamp. The
Destination Address, name and packet priority (if applicable) are attached to
the msghdr in the recvmsg(2) call. They can be extracted using cmsg(3) macros,
with cmsg_level == SOL_J1939 && cmsg_type == SCM_J1939_DEST_ADDR,
SCM_J1939_DEST_NAME or SCM_J1939_PRIO. The returned data is a uint8_t for
priority and dst_addr, and uint64_t for dst_name.
the msghdr in the ``recvmsg(2)`` call. They can be extracted using ``cmsg(3)`` macros,
with ``cmsg_level == SOL_J1939 && cmsg_type == SCM_J1939_DEST_ADDR``,
``SCM_J1939_DEST_NAME`` or ``SCM_J1939_PRIO``. The returned data is a ``uint8_t`` for
``priority`` and ``dst_addr``, and ``uint64_t`` for ``dst_name``.
.. code-block:: C
@ -305,12 +305,12 @@ Dynamic Addressing
Distinction has to be made between 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
``j1939.name`` member and provide it to ``bind(2)``. If the name had claimed an address
earlier, all further messages being sent will use that address. And the
j1939.addr member will be ignored.
``j1939.addr`` member will be ignored.
An exception on this is PGN 0x0ee00. This is the "Address Claim/Cannot Claim
Address" message and the kernel will use the j1939.addr member for that PGN if
Address" message and the kernel will use the ``j1939.addr`` member for that PGN if
necessary.
To claim an address following code example can be used:
@ -371,12 +371,12 @@ 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
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.
can-utils also include the j1939acd tool, so it can be used as code example or as
``can-utils`` also include the ``j1939acd`` tool, so it can be used as code example or as
default Address Claiming daemon.
Send Examples
@ -403,8 +403,8 @@ Bind:
bind(sock, (struct sockaddr *)&baddr, sizeof(baddr));
Now, the socket 'sock' is bound to the SA 0x20. Since no connect(2) was called,
at this point we can use only sendto(2) or sendmsg(2).
Now, the socket 'sock' is bound to the SA 0x20. Since no ``connect(2)`` was called,
at this point we can use only ``sendto(2)`` or ``sendmsg(2)``.
Send: