From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: veth.4 Date: Sun, 04 Nov 2012 20:11:42 -0800 Message-ID: <87vcdksn7l.fsf@xmission.com> References: <87zk2ytdbu.fsf@xmission.com> <5095C848.9000501@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <5095C848.9000501-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> (Pavel Emelyanov's message of "Sun, 04 Nov 2012 05:43:36 +0400") Sender: linux-man-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pavel Emelyanov Cc: Tomas Pospisek , "Michael Kerrisk (man-pages)" , "linux-man@vger.kernel.org" List-Id: linux-man@vger.kernel.org Pavel Emelyanov writes: > On 11/04/2012 04:35 AM, Eric W. Biederman wrote: >> Tomas Pospisek writes: >>=20 >>> Hi again Michael, Pavel, Eric and mailing list >>> >>> (Cc: to Eric, Pavel and Linux Netdev List on behalf of Michael aski= ng >>> 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 Tom=C3=A1=C5=A1 Posp=C3=AD=C5=A1ek (tpo_deb@= sourcepole.ch), >>> .\" Fri, 03 Nov 2012 22:35:33 +0100 >>> .\" >>> .\" This is free documentation; you can redistribute it and/or >>> .\" modify it under the terms of the GNU General Public License as >>> .\" published by the Free Software Foundation; either version 2 of >>> .\" the License, or (at your option) any later version. >>> .\" >>> .\" The GNU General Public License's references to "object code" >>> .\" and "executables" are to be interpreted as the output of any >>> .\" document formatting or typesetting system, including >>> .\" intermediate and printed output. >>> .\" >>> .\" This manual is distributed in the hope that it will be useful, >>> .\" but WITHOUT ANY WARRANTY; without even the implied warranty of >>> .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the >>> .\" GNU General Public License for more details. >>> .\" >>> .\" You should have received a copy of the GNU General Public >>> .\" License along with this manual; if not, write to the Free >>> .\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, = MA 02111, >>> .\" USA. >>> .\" >>> .\" >>> .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. >>=20 >> As far as understanding and using them I think this text is a bit we= ak. >> Perhaps something like: >>=20 >> 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 networ= k >> facilities of the kernel together in interesting ways. A particular= ly >> interesting use case is to place one end of a veth pair in one netwo= rk >> namespace and another end of the veth pair in another network namesp= ace >> 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= =20 > just and ifindex of the peer, and the caller can do something useful=20 > with it if the peer is still in the same net namespace as the origina= l=20 > device. But how would you find the peer device in case it already sit= s=20 > 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 brut= e 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 yo= u have found both ends of the tunnel. =46or checkpoint/restart we may need to implement something better at s= ome point. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html