Hi Andi,
On Fri, Nov 21, 2008 at 3:42 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> On Fri, Nov 21, 2008 at 11:08:22AM -0500, Michael Kerrisk wrote:
>> [CC+= Andi, this time with the right address]
>
> Just a general comment. The initial DESCRIPTION in tcp should
> be probably adapted to mentioned that Linux has pluggable
> congestion avoidance modules now and also that the defaults
> have changed (from NewReno to CUBIC etc.)
If I try to do this, I'm going to create rubbish, because I know next
to nothing about these details...
Could I ask a favor? Below is the DESCRIPTION text. Could you note
write some sentences in the rough location where you think they below,
and I will turn that into a *roff patch.
Thanks,
Michael
This is an implementation of the TCP protocol defined in
RFC 793, RFC 1122 and RFC 2001 with the NewReno and SACK
extensions. It provides a reliable, stream-oriented,
full-duplex connection between two sockets on top of
ip(7), for both v4 and v6 versions. TCP guarantees that
the data arrives in order and retransmits lost packets.
It generates and checks a per-packet checksum to catch
transmission errors. TCP does not preserve record bound-
aries.
A newly created TCP socket has no remote or local address
and is not fully specified. To create an outgoing TCP
connection use connect(2) to establish a connection to
another TCP socket. To receive new incoming connections,
first bind(2) the socket to a local address and port and
then call listen(2) to put the socket into the listening
state. After that a new socket for each incoming connec-
tion can be accepted using accept(2). A socket which has
had accept(2) or connect(2) successfully called on it is
fully specified and may transmit data. Data cannot be
transmitted on listening or not yet connected sockets.
Linux supports RFC 1323 TCP high performance extensions.
These include Protection Against Wrapped Sequence Numbers
(PAWS), Window Scaling and Timestamps. Window scaling
allows the use of large (> 64K) TCP windows in order to
support links with high latency or bandwidth. To make
use of them, the send and receive buffer sizes must be
increased. They can be set globally with the
/proc/sys/net/ipv4/tcp_wmem and
/proc/sys/net/ipv4/tcp_rmem files, or on individual sock-
ets by using the SO_SNDBUF and SO_RCVBUF socket options
with the setsockopt(2) call.
The maximum sizes for socket buffers declared via the
SO_SNDBUF and SO_RCVBUF mechanisms are limited by the
values in the /proc/sys/net/core/rmem_max and
/proc/sys/net/core/wmem_max files. Note that TCP actu-
ally allocates twice the size of the buffer requested in
the setsockopt(2) call, and so a succeeding getsockopt(2)
call will not return the same size of buffer as requested
in the setsockopt(2) call. TCP uses the extra space for
administrative purposes and internal kernel structures,
and the /proc file values reflect the larger sizes com-
pared to the actual TCP windows. On individual connec-
tions, the socket buffer size must be set prior to the
listen(2) or connect(2) calls in order to have it take
effect. See socket(7) for more information.
TCP supports urgent data. Urgent data is used to signal
the receiver that some important message is part of the
data stream and that it should be processed as soon as
possible. To send urgent data specify the MSG_OOB option
to send(2). When urgent data is received, the kernel
sends a SIGURG signal to the process or process group
that has been set as the socket "owner" using the SIOCSP-
GRP or FIOSETOWN ioctls (or the POSIX.1-2001-specified
fcntl(2) F_SETOWN operation). When the SO_OOBINLINE
socket option is enabled, urgent data is put into the
normal data stream (a program can test for its location
using the SIOCATMARK ioctl described below), otherwise it
can be only received when the MSG_OOB flag is set for
recv(2) or recvmsg(2).
Linux 2.4 introduced a number of changes for improved
throughput and scaling, as well as enhanced functional-
ity. Some of these features include support for zero-
copy sendfile(2), Explicit Congestion Notification, new
management of TIME_WAIT sockets, keep-alive socket
options and support for Duplicate SACK extensions.
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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