linux-kernel - Re: [PATCH net-next v2] block/drbd: use nla_put_u64

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Message-ID: <57289468.5090401@6wind.com>
Date:	Tue, 3 May 2016 14:07:04 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	netdev@...r.kernel.org, davem@...emloft.net,
	philipp.reisner@...bit.com, drbd-dev@...ts.linbit.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] block/drbd: use nla_put_u64_64bit()

Le 03/05/2016 12:06, Lars Ellenberg a écrit :
> On Tue, May 03, 2016 at 11:39:18AM +0200, Nicolas Dichtel wrote:
>> Two new handlers have been defined in genl_magic_ headers:
>>  - __field2: the corresponding nla_put() function (nla_put_flag()) takes
>>              only two args
>>  - __field4: the corresponding nla_put() function (nla_put_u64_64bit())
>>              takes four args
>>
>> __field2 allows us to define __unspec_field for padding attribute.
>> __field4 allows us to update the definition of __u64_field: the pad
>> attribute should now be specified.
> 
> Please just NOT use an additional "field",
> but always use 0 to pad.
> 
> Patch is much shorter as well, see below.
I don't think that the goal is to make the shortest patch...
But frankly, I don't care. The goal was to use the new interface in a proper
way, like every other subsystem.

> 
> Attribute type "0" is not used,
> and will never be of semantic value,
> but always be ignored in the DRBD netlink family.
> 
> Whereas using some arbitrary value will be wrong,
> and will needlessly break userland.
An application should always ignore unknown attribute, this is a golden rule.
Now if you know that this patch will break applications (which one exactly?), we
can use your proposal.


Regards,
Nicolas