netdev - Re: [PATCH] veth: Cleanly handle a missing peer

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Date:	Thu, 13 Sep 2007 13:02:41 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	Stephen Hemminger <shemminger@...ux-foundation.org>
Subject: Re: [PATCH] veth: Cleanly handle a missing peer_tb argument on creation.

Eric W. Biederman wrote:
> Pavel Emelyanov <xemul@...nvz.org> writes:
> 
>> Eric W. Biederman wrote:
>>> Pavel Emelyanov <xemul@...nvz.org> writes:
>>>
>>>>> +	}
>>>>>  
>>>>> -		tbp = peer_tb;
>>>>> -	} else
>>>>> -		tbp = tb;
>>>> The intention of this part was to get the same parameters for
>>>> peer as for the first device if no "peer" argument was specified
>>>> for ip utility. Does it still work?
>>> I know it is problematic because we try to assign the same name
>>> to both network devices, if we assign a name to the primary
>>> network device.  That can't work.
>> This can - as you can see I reallocate the name lower.
> 
> Hmm. I just see:
> 	if (tbp[IFLA_IFNAME])
> 		nla_strlcpy(ifname, tbp[IFLA_IFNAME], IFNAMSIZ);
> 
> Then lower I see:
> 	if (tb[IFLA_IFNAME])
> 		nla_strlcpy(dev->name, tb[IFLA_IFNAME], IFNAMSIZ);
> 
> If (tb == tbp) then dev->name == ifname
> Unless I'm completely misreading that code.
> 
>>> Beyond that I had some really weird crashes while testing this
>>> piece of code, especially when I did not specify a peer parameter.
>> Can you please give me the exact command that caused an oops.
>> I try simple ip link add type veth and everything is just fine.
> 
> It might have been 64bit specific. 
> 
> What I have in my history is:
> ./ip/ip link add veth23 type veth
> 
> I forget exactly how it failed but as I recall it wasn't as
> nice as an oops.  My memory may be a bit foggy though.
> 
> If I haven't provided a bit enough clue I guess I can go back
> and remove the patch and try to reproduce the failure again.

Neither ip link add type veth nor your one fail on my x86_64 box.

However, maybe you didn't like that your command didn't produce
any devices. I can explain this. You order two *equal* devices with
the same name veth23. This has to fail. However if you request 
devices with generic name veth%d or with different names everything
is good.

So could you please give more clues on what's bad with veth driver.

>>> So it was just easier to avoid the problem with this patch then
>>> to completely root cause it.
>> Let me handle this problem. AFAIR this was one of wishes from 
>> Patrick that we make two equal devices in case peer is not given, 
>> not just the default peer.
> 
> Ok.  I have if we can track down the weird cases I have no problem
> if we handle this.  I think it still might be simpler if just
> copy tb onto peer_tb instead of using tbp.
> 
> Eric
> 

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