docs: networking: convert proc_net_tcp.txt to ReST

- add SPDX header;
- add a document title;
- mark code blocks and literals as such;
- mark tables as such;
- adjust identation, whitespaces and blank lines where needed;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 57 insertions, 0 deletions

diff --git a/Documentation/networking/proc_net_tcp.rst b/Documentation/networking/proc_net_tcp.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+============================================
+The proc/net/tcp and proc/net/tcp6 variables
+============================================
+
+This document describes the interfaces /proc/net/tcp and /proc/net/tcp6.
+Note that these interfaces are deprecated in favor of tcp_diag.
+
+These /proc interfaces provide information about currently active TCP
+connections, and are implemented by tcp4_seq_show() in net/ipv4/tcp_ipv4.c
+and tcp6_seq_show() in net/ipv6/tcp_ipv6.c, respectively.
+
+It will first list all listening TCP sockets, and next list all established
+TCP connections. A typical entry of /proc/net/tcp would look like this (split
+up into 3 parts because of the length of the line)::
+
+   46: 010310AC:9C4C 030310AC:1770 01
+   |      |      |      |      |   |--> connection state
+   |      |      |      |      |------> remote TCP port number
+   |      |      |      |-------------> remote IPv4 address
+   |      |      |--------------------> local TCP port number
+   |      |---------------------------> local IPv4 address
+   |----------------------------------> number of entry
+
+   00000150:00000000 01:00000019 00000000
+      |        |     |     |       |--> number of unrecovered RTO timeouts
+      |        |     |     |----------> number of jiffies until timer expires
+      |        |     |----------------> timer_active (see below)
+      |        |----------------------> receive-queue
+      |-------------------------------> transmit-queue
+
+   1000        0 54165785 4 cd1e6040 25 4 27 3 -1
+    |          |    |     |    |     |  | |  | |--> slow start size threshold,
+    |          |    |     |    |     |  | |  |      or -1 if the threshold
+    |          |    |     |    |     |  | |  |      is >= 0xFFFF
+    |          |    |     |    |     |  | |  |----> sending congestion window
+    |          |    |     |    |     |  | |-------> (ack.quick<<1)|ack.pingpong
+    |          |    |     |    |     |  |---------> Predicted tick of soft clock
+    |          |    |     |    |     |              (delayed ACK control data)
+    |          |    |     |    |     |------------> retransmit timeout
+    |          |    |     |    |------------------> location of socket in memory
+    |          |    |     |-----------------------> socket reference count
+    |          |    |-----------------------------> inode
+    |          |----------------------------------> unanswered 0-window probes
+    |---------------------------------------------> uid
+
+timer_active:
+
+ ==  ================================================================
+  0  no timer is pending
+  1  retransmit-timer is pending
+  2  another timer (e.g. delayed ack or keepalive) is pending
+  3  this is a socket in TIME_WAIT state. Not all fields will contain
+     data (or even exist)
+  4  zero window probe timer is pending
+ ==  ================================================================