netdev - Re: [PATCH] [RFC] C/R: inet4 and inet6 unicast routes (v2)

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Date:	Fri, 30 Apr 2010 22:02:15 -0400
From:	Oren Laadan <orenl@...columbia.edu>
To:	Dan Smith <danms@...ibm.com>
CC:	Daniel Lezcano <daniel.lezcano@...e.fr>, containers@...ts.osdl.org,
	Vlad Yasevich <vladislav.yasevich@...com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] [RFC] C/R: inet4 and inet6 unicast routes (v2)

Dan Smith wrote:
> DL> Is it possible to enter the namespace and dump / restore the
> DL> routes with NETLINK_ROUTE from userspace ? Or is it something not
> DL> possible ?
> 
> I'm sure it would be doable.  However, checkpointing the routes that
> way would:
> 
> (a) Be inconsistent with how we checkpoint all the other resources,
>     including the other network resources we handle from the kernel
>     with rtnl
> (b) Require merging of the data from the resources saved in userspace
>     with those saved in kernelspace

See below suggestion for userspace.

> (c) Eliminate the ability for an application to easily checkpoint
>     itself by making a single syscall

I can't think of a use-case of a networked application that takes
a checkpoint of itself (including live network).

Anyway, it's can still be useful to at least do the restore from
userspace (while checkpoint is done in kernel - like with pids).
We may reduce the complexity of restore (in kernel) greatly.

(BTW, instead of syscall one could have a library call that will
take care of the userspace "work").

> (d) Require this same sort of jumping back and forth between
>     namespaces by the userspace task doing the checkpoint/restart
> 

I wonder: if we could relatively simply recreate the network ns,
the interfaces in them, and then restore the routing information
all from userspace before calling sys_restart, it may be useful
in simplifying the kernel code, and allowing more flexibility for
userspace alterations.

I definitely should have asked the question much earlier when you
started the work on restoring network ns and interfaces ... (oh,
I reckon it's better late than never).

Just tossing out the idea, see what kind of thoughts it evokes.
Most likely I'll get a "that won't work because ...", but I'm
hoping for a "hmm.. maybe.. let me see.." :)

Oren.
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