netdev - Re: [PATCH 2/4] C/R: Basic support for network namespaces and devices (v3)

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Message-ID: <20100210202509.GA23301@us.ibm.com>
Date:	Wed, 10 Feb 2010 14:25:09 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Dan Smith <danms@...ibm.com>
Cc:	containers@...ts.osdl.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/4] C/R: Basic support for network namespaces and
 devices (v3)

Quoting Dan Smith (danms@...ibm.com):
> SH> rw_lockt is effectively a spinlock, so I don't think you can sleep
> SH> here.
> 
> Yep, thanks.
> 
> >> +	for_each_netdev(net, dev) {
> >> +		if (!dev->netdev_ops->ndo_checkpoint)
> >> +			continue;
> 
> SH> Won't the checkpoint_obj() call checkpoint_netdev(), which will return
> SH> -EINVAL if ndo_checkpoint is not defined? 
> 
> Yes, but this isn't the only place that checkpoint_netdev() could be
> called (dev->peer in the veth example) so I figured that it would be
> best to test it there too before I blindly call a NULL function
> pointer.  It should never happen, but seemed prudent.
> 
> SH> But here you skip the checkpoint_obj() call (which seems wrong to
> SH> me).  Which do you want to have happen?
> 
> What the code is doing is "skipping any interfaces in a netns that
> don't have a checkpoint operation" but would fail if you called
> checkpoint_obj() on a veth peer that happened to be missing that
> operation for some reason.
> 
> I suppose you could argue that we should fail in the netns case
> instead, which will make this a bit messier for things we get for
> "free" in a new netns, like sit0.  If preferable, I can just add an
> ndo_checkpoint() to sit0 as well and simply checkpoint the presence of
> it until later when we decide if we care about it.

I think that's be better.  Right now if we checkpoint a container with
macvlan restart will be bogus, right?  We're trying to avoid any cases
where we can't tell, at checkpoint, that restart won't be right.

> SH> By hard-coding veth stuff into generic-sounding functions in
> SH> net/checkpoint_dev.c you seem to be assuming that only veth will
> SH> ever be supported for checkpoint/restart?  what about macvlan?
> SH> (Not to mention that eventually we intend to support moving
> SH> physical nics into containers)
> 
> No, that's not what I'm assuming.  The only interface type I need to
> control with RTNL is veth right now.  So, if you'd prefer a
> single-case of:
> 
>   if (type == veth)
>     do_veth_message();
>   else
>     fail();
> 
> to record the goal of having more types later I'll happily add that
> unreachable code to the patch :)

What I was asking is should do_veth_message() be in drivers/net/veth.c?

-serge
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