netdev - Re: [PATCH] veth: replace iflink by a dedicated symlink in sysfs

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Message-ID: <87bne38oj7.fsf@zoro.exoscale.ch>
Date:	Wed, 19 Aug 2015 14:13:00 +0200
From:	Vincent Bernat <vincent@...nat.im>
To:	Jiri Benc <jbenc@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: Re: [PATCH] veth: replace iflink by a dedicated symlink in sysfs

 ❦ 19 août 2015 13:00 +0200, Jiri Benc <jbenc@...hat.com> :

>> While the documentation doesn't say exactly what kind of relationship
>> iflink should represent, until a45253, only lower devices were
>> advertised this way. While veth cannot have a lower device, using iflink
>> to advertise the peer may create infinite loops in programs using iflink
>> to discover device topology.
>> 
>> Instead of advertising the peer link with iflink, a symbolic link "peer"
>> is added to each peer.
>
> By removing veth_get_iflink, you're also stopping IFLA_LINK being
> advertised in netlink messages, which consequently makes impossible to
> reliably match veth peers across name spaces again. This would be a
> huge step backwards.

That's the main goal of this patch: advertising the peer link as
IFLA_LINK attribute triggers an infinite loop in userland software when
they follow iflink to discover network devices topology. iflink has
always been the index of a lower device. If a sysfs symbolic link is not
good enough, I can propose a new IFLA_PEER attribute instead.
-- 
How apt the poor are to be proud.
		-- William Shakespeare, "Twelfth-Night"
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