Commit b9dd2bea authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by David S. Miller

docs: networking: convert kcm.txt to ReST

- add SPDX header;
- adjust titles and chapters, adding proper markups;
- mark code blocks and literals as such;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 82a07bf3
...@@ -73,6 +73,7 @@ Contents: ...@@ -73,6 +73,7 @@ Contents:
ipv6 ipv6
ipvlan ipvlan
ipvs-sysctl ipvs-sysctl
kcm
.. only:: subproject and html .. only:: subproject and html
......
.. SPDX-License-Identifier: GPL-2.0
=============================
Kernel Connection Multiplexor Kernel Connection Multiplexor
----------------------------- =============================
Kernel Connection Multiplexor (KCM) is a mechanism that provides a message based Kernel Connection Multiplexor (KCM) is a mechanism that provides a message based
interface over TCP for generic application protocols. With KCM an application interface over TCP for generic application protocols. With KCM an application
can efficiently send and receive application protocol messages over TCP using can efficiently send and receive application protocol messages over TCP using
datagram sockets. datagram sockets.
KCM implements an NxM multiplexor in the kernel as diagrammed below: KCM implements an NxM multiplexor in the kernel as diagrammed below::
+------------+ +------------+ +------------+ +------------+ +------------+ +------------+ +------------+ +------------+
| KCM socket | | KCM socket | | KCM socket | | KCM socket | | KCM socket | | KCM socket | | KCM socket | | KCM socket |
+------------+ +------------+ +------------+ +------------+ +------------+ +------------+ +------------+ +------------+
| | | | | | | |
+-----------+ | | +----------+ +-----------+ | | +----------+
| | | | | | | |
...@@ -20,16 +23,16 @@ KCM implements an NxM multiplexor in the kernel as diagrammed below: ...@@ -20,16 +23,16 @@ KCM implements an NxM multiplexor in the kernel as diagrammed below:
| | | | | | | | | |
+---------+ | | | ------------+ +---------+ | | | ------------+
| | | | | | | | | |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+
| Psock | | Psock | | Psock | | Psock | | Psock | | Psock | | Psock | | Psock | | Psock | | Psock |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+
| | | | | | | | | |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+
| TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock | | TCP sock |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+ +----------+
KCM sockets KCM sockets
----------- ===========
The KCM sockets provide the user interface to the multiplexor. All the KCM sockets The KCM sockets provide the user interface to the multiplexor. All the KCM sockets
bound to a multiplexor are considered to have equivalent function, and I/O bound to a multiplexor are considered to have equivalent function, and I/O
...@@ -37,7 +40,7 @@ operations in different sockets may be done in parallel without the need for ...@@ -37,7 +40,7 @@ operations in different sockets may be done in parallel without the need for
synchronization between threads in userspace. synchronization between threads in userspace.
Multiplexor Multiplexor
----------- ===========
The multiplexor provides the message steering. In the transmit path, messages The multiplexor provides the message steering. In the transmit path, messages
written on a KCM socket are sent atomically on an appropriate TCP socket. written on a KCM socket are sent atomically on an appropriate TCP socket.
...@@ -45,14 +48,14 @@ Similarly, in the receive path, messages are constructed on each TCP socket ...@@ -45,14 +48,14 @@ Similarly, in the receive path, messages are constructed on each TCP socket
(Psock) and complete messages are steered to a KCM socket. (Psock) and complete messages are steered to a KCM socket.
TCP sockets & Psocks TCP sockets & Psocks
-------------------- ====================
TCP sockets may be bound to a KCM multiplexor. A Psock structure is allocated TCP sockets may be bound to a KCM multiplexor. A Psock structure is allocated
for each bound TCP socket, this structure holds the state for constructing for each bound TCP socket, this structure holds the state for constructing
messages on receive as well as other connection specific information for KCM. messages on receive as well as other connection specific information for KCM.
Connected mode semantics Connected mode semantics
------------------------ ========================
Each multiplexor assumes that all attached TCP connections are to the same Each multiplexor assumes that all attached TCP connections are to the same
destination and can use the different connections for load balancing when destination and can use the different connections for load balancing when
...@@ -60,7 +63,7 @@ transmitting. The normal send and recv calls (include sendmmsg and recvmmsg) ...@@ -60,7 +63,7 @@ transmitting. The normal send and recv calls (include sendmmsg and recvmmsg)
can be used to send and receive messages from the KCM socket. can be used to send and receive messages from the KCM socket.
Socket types Socket types
------------ ============
KCM supports SOCK_DGRAM and SOCK_SEQPACKET socket types. KCM supports SOCK_DGRAM and SOCK_SEQPACKET socket types.
...@@ -110,19 +113,19 @@ User interface ...@@ -110,19 +113,19 @@ User interface
Creating a multiplexor Creating a multiplexor
---------------------- ----------------------
A new multiplexor and initial KCM socket is created by a socket call: A new multiplexor and initial KCM socket is created by a socket call::
socket(AF_KCM, type, protocol) socket(AF_KCM, type, protocol)
- type is either SOCK_DGRAM or SOCK_SEQPACKET - type is either SOCK_DGRAM or SOCK_SEQPACKET
- protocol is KCMPROTO_CONNECTED - protocol is KCMPROTO_CONNECTED
Cloning KCM sockets Cloning KCM sockets
------------------- -------------------
After the first KCM socket is created using the socket call as described After the first KCM socket is created using the socket call as described
above, additional sockets for the multiplexor can be created by cloning above, additional sockets for the multiplexor can be created by cloning
a KCM socket. This is accomplished by an ioctl on a KCM socket: a KCM socket. This is accomplished by an ioctl on a KCM socket::
/* From linux/kcm.h */ /* From linux/kcm.h */
struct kcm_clone { struct kcm_clone {
...@@ -142,7 +145,7 @@ Attach transport sockets ...@@ -142,7 +145,7 @@ Attach transport sockets
------------------------ ------------------------
Attaching of transport sockets to a multiplexor is performed by calling an Attaching of transport sockets to a multiplexor is performed by calling an
ioctl on a KCM socket for the multiplexor. e.g.: ioctl on a KCM socket for the multiplexor. e.g.::
/* From linux/kcm.h */ /* From linux/kcm.h */
struct kcm_attach { struct kcm_attach {
...@@ -160,14 +163,15 @@ ioctl on a KCM socket for the multiplexor. e.g.: ...@@ -160,14 +163,15 @@ ioctl on a KCM socket for the multiplexor. e.g.:
ioctl(kcmfd, SIOCKCMATTACH, &info); ioctl(kcmfd, SIOCKCMATTACH, &info);
The kcm_attach structure contains: The kcm_attach structure contains:
fd: file descriptor for TCP socket being attached
bpf_prog_fd: file descriptor for compiled BPF program downloaded - fd: file descriptor for TCP socket being attached
- bpf_prog_fd: file descriptor for compiled BPF program downloaded
Unattach transport sockets Unattach transport sockets
-------------------------- --------------------------
Unattaching a transport socket from a multiplexor is straightforward. An Unattaching a transport socket from a multiplexor is straightforward. An
"unattach" ioctl is done with the kcm_unattach structure as the argument: "unattach" ioctl is done with the kcm_unattach structure as the argument::
/* From linux/kcm.h */ /* From linux/kcm.h */
struct kcm_unattach { struct kcm_unattach {
...@@ -190,7 +194,7 @@ When receive is disabled, any pending messages in the socket's ...@@ -190,7 +194,7 @@ When receive is disabled, any pending messages in the socket's
receive buffer are moved to other sockets. This feature is useful receive buffer are moved to other sockets. This feature is useful
if an application thread knows that it will be doing a lot of if an application thread knows that it will be doing a lot of
work on a request and won't be able to service new messages for a work on a request and won't be able to service new messages for a
while. Example use: while. Example use::
int val = 1; int val = 1;
...@@ -200,7 +204,7 @@ BFP programs for message delineation ...@@ -200,7 +204,7 @@ BFP programs for message delineation
------------------------------------ ------------------------------------
BPF programs can be compiled using the BPF LLVM backend. For example, BPF programs can be compiled using the BPF LLVM backend. For example,
the BPF program for parsing Thrift is: the BPF program for parsing Thrift is::
#include "bpf.h" /* for __sk_buff */ #include "bpf.h" /* for __sk_buff */
#include "bpf_helpers.h" /* for load_word intrinsic */ #include "bpf_helpers.h" /* for load_word intrinsic */
...@@ -250,6 +254,7 @@ based on groups, or batches of messages, can be beneficial for performance. ...@@ -250,6 +254,7 @@ based on groups, or batches of messages, can be beneficial for performance.
On transmit, there are three ways an application can batch (pipeline) On transmit, there are three ways an application can batch (pipeline)
messages on a KCM socket. messages on a KCM socket.
1) Send multiple messages in a single sendmmsg. 1) Send multiple messages in a single sendmmsg.
2) Send a group of messages each with a sendmsg call, where all messages 2) Send a group of messages each with a sendmsg call, where all messages
except the last have MSG_BATCH in the flags of sendmsg call. except the last have MSG_BATCH in the flags of sendmsg call.
......
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