Re: [Patch net] netns: avoid allocating idr when dumping info

[Cong Wang <xiyou.wangcong@gmail.com>]

(Removing Eric from discussion since he expressed he doesn't
care this code at all in a private email.)


On Fri, Feb 27, 2015 at 4:56 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> Why? This relies on rtnetlink to dump the link after creation,
> which is not obvious at all. IOW, imagine if rtnetlink didn't do
> the dump after new link, what would happen?
>
> You are hiding it too deep, without a valid reason. It sounds
> like you want to defer the allocation as late as possible,
> but again it makes no sense: 1) we don't allocate too much,
> just one id in idr; 2) this loses the code readability and hides
> potential bugs.
>

Here we go:

This breaks veth, where veth peers are completely equal,
therefore they are links for each other. So we expect
link-netnsid shown on both side.

Your current impl. relies on rtnl_configure_link() to dump
the link to allocate the netns id after creating a link.
Unfortunately for veth, rtnl_configure_link() is called
before veth->peer is set, therefore the dump of the "peer"
does _not_ actually allocate the netns id, since its
->get_link_net() returns the same net.

I will send a patch together after I figure out another bug
I saw.