Hoi Tomas, Do you have a revised version of this page taking into account the comments of Eric and Pavel? Thanks, Michael 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 >>>> .\" >>>> .\" 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. >>> >>> 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/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
