On Thu, 13 Dec 2012, Michael Kerrisk (man-pages) wrote:
Do you have a revised version of this page taking into account the
comments of Eric and Pavel?
No I don't. I got trampled down by a horde of rabid real life tasks and am
slowly recovering from it. I'll make a new effort at some point, Eric's
and Pavel's emails still have their cosy place in my INBOX and are waiting
to be groomed.
Thanks for pinging me!
*t
On Mon, Nov 5, 2012 at 5:11 AM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
Pavel Emelyanov <xemul@xxxxxxxxxxxxx> writes:
On 11/04/2012 04:35 AM, Eric W. Biederman wrote:
Tomas Pospisek <tpo@xxxxxxxxxxxxx> writes:
Hi again Michael, Pavel, Eric and mailing list
(Cc: to Eric, Pavel and Linux Netdev List on behalf of Michael asking
for comment)
Here's the revised veth(4) man page (the inline replies to Michael's
critique are following the man page):
********************************************************************
.\" Copyright (c) 2012 Tomáš Pospíšek (tpo_deb@xxxxxxxxxxxxx),
.\" Fri, 03 Nov 2012 22:35:33 +0100
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.\"
.TH veth 4 2012-11-02 "Linux" "Linux Programmer's Manual"
.SH NAME
veth \- Virtual Ethernet Device
.SH DESCRIPTION
The
.B veth
devices are virtual Ethernet devices.
They can act as tunnels between network namespaces to create
a bridge to a physical network device in another namespace, but
can also be used as standalone network devices.
As far as understanding and using them I think this text is a bit weak.
Perhaps something like:
ip link add type veth creates a pair of directly connected ethernet
devices. What is transmited on one device is immediately received on
the other device. When either devices is down the link state of the
pair is down. veth device pairs are useful for combining the network
facilities of the kernel together in interesting ways. A particularly
interesting use case is to place one end of a veth pair in one network
namespace and another end of the veth pair in another network namespace
allowing communication between network namespaces.
Ack
ethtool can be used to test if a networking device is a veth device,
and to find the peer network interface.
This one requires clarification, I think. The ethtool will report you
just and ifindex of the peer, and the caller can do something useful
with it if the peer is still in the same net namespace as the original
device. But how would you find the peer device in case it already sits
in some other network namespace?
Until just recently the ifindex of networking devices was universally
unique so finding the other end of the device could be done with a brute
force search through network namespaces. Even without a guarantee of
global uniqueness in the ifindex performing a bidirectional comparison
of the return ifindicies of veth devices can give a strong hint that you
have found both ends of the tunnel.
For checkpoint/restart we may need to implement something better at some point.
Eric
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
