/proc/net/tcp documentation

[Arnout Engelen <arnouten@bzzt.net>]

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Hi,

I noticed there doesn't seem to be any documentation for /proc/net/tcp,
so i whipped up the attached description. 

Maybe someone could add this to /Documentation/networking? I wrote it
for 2.4.26, but the code doesn't seem to have changed relevantly since
then.


(please cc me in replies as i won't be constantly monitoring the list)

Kind regards,

-- 
Arnout Engelen <arnouten@bzzt.net>

  "If it sounds good, it /is/ good."
          -- Duke Ellington

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/proc/net/tcp and /proc/net/tcp6

These /proc interfaces provide information about currently active TCP 
connections, and are implemented by tcp_get_info() in net/ipv4/tcp_ipv4.c and
tcp6_get_info() 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 treshold
    |          |    |     |    |     |  | |  |      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 field will contain data.
  4  zero window probe timer is pending