netdev - Re: [Patch net-next] net: allow to delete a whole device group

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Message-ID: <CAM_iQpWcuX_aVzAgOEuUEiQY5MvUJhATUARm1KdqgaXbM7Sbxg@mail.gmail.com>
Date:	Tue, 24 Mar 2015 10:21:51 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [Patch net-next] net: allow to delete a whole device group

On Tue, Mar 24, 2015 at 10:11 AM, David Miller <davem@...emloft.net> wrote:
> From: Cong Wang <xiyou.wangcong@...il.com>
> Date: Mon, 23 Mar 2015 17:04:15 -0700
>
>> +     for_each_netdev_safe(net, dev, aux) {
>> +             if (dev->group == group) {
>> +                     const struct rtnl_link_ops *ops;
>> +
>> +                     found = true;
>> +                     ops = dev->rtnl_link_ops;
>> +                     if (!ops || !ops->dellink)
>> +                             return -EOPNOTSUPP;
>> +                     ops->dellink(dev, &list_kill);
>> +             }
>
> These semantics are terrible.
>
> A netlink request should always strive (no, I'll say it _must_) either
> fully perform the requested operation for all relevant objects, or
> have no side effects and return an error.
>
> If need be you must completely unwind all partial changes before
> returning that error, or alternatively defer commiting the
> changes until you can guarantee that all of them can be performed.

Good point.

I don't see a way to unwind the dellink, I think we can scan the list
twice, once for (!ops || !ops->dellink) check, once for dellink().

Thanks.
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