netdev - Re: [PATCH RFC net-next] net: Allow name change of IFF

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Message-ID: <87efskye74.fsf@vitty.brq.redhat.com>
Date:   Wed, 09 Aug 2017 17:05:03 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
Cc:     network dev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH RFC net-next] net: Allow name change of IFF_UP interfaces

吉藤英明 <hideaki.yoshifuji@...aclelinux.com> writes:

> 2017-08-09 19:42 GMT+09:00 Vitaly Kuznetsov <vkuznets@...hat.com>:
>> What happens is: __netvsc_vf_setup() does dev_open() for the VF device and
>> the consecutive dev_change_name() fails with -EBUSY because of the
>> (dev->flags & IFF_UP) check. The history of this code predates git so I
>> wasn't able to figure out when and why the check was added, everything
>> seems to work fine without it. dev_change_name() has only two call sites,
>> both hold rtnl_lock.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  RFC: I'm probably miossing something obvious and the check can't be just
>>  dropped. Stephen suggested a different solution to the isuue:
>>  https://www.spinics.net/lists/netdev/msg448243.html but it has its own
>>  drawbacks.
>> ---
>>  net/core/dev.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 1d75499add72..c608e233a78a 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1186,8 +1186,6 @@ int dev_change_name(struct net_device *dev, const char *newname)
>>         BUG_ON(!dev_net(dev));
>>
>>         net = dev_net(dev);
>> -       if (dev->flags & IFF_UP)
>> -               return -EBUSY;
>>
>>         write_seqcount_begin(&devnet_rename_seq);
>
> I think people expect the name won't change while up
> and I don't think it is a good idea to allow changing the
> name while the interface is up.

I understand the 'legacy' concern but at the same time we don't want to
have aftificial limitations too. Name change, in particular, doesn't
happen 'under the hood' -- someone privileged enough needs to request
the change.

Can you think of any particular real world scenarios which are broken by
the change?

-- 
  Vitaly