linux-kernel - Re: [PATCH] uapi/netfilter: Change netfilter hook verdict code definition from macro to enum

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Message-ID: <19d2362f.5c85.18a6647817b.Coremail.00107082@163.com>
Date:   Wed, 6 Sep 2023 00:57:56 +0800 (CST)
From:   "David Wang" <00107082@....com>
To:     "Daniel Xu" <dxu@...uu.xyz>
Cc:     "Pablo Neira Ayuso" <pablo@...filter.org>,
        "Jozsef Kadlecsik" <kadlec@...filter.org>,
        "Florian Westphal" <fw@...len.de>, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH] uapi/netfilter: Change netfilter hook verdict code
 definition from macro to enum



At 2023-09-06 00:38:02, "Daniel Xu" <dxu@...uu.xyz> wrote:
>Hi David,
>
>On Mon, Sep 04, 2023 at 09:02:02PM +0800, David Wang wrote:

>>  #include <linux/in6.h>
>>  
>>  /* Responses from hook functions. */
>> -#define NF_DROP 0
>> -#define NF_ACCEPT 1
>> -#define NF_STOLEN 2
>> -#define NF_QUEUE 3
>> -#define NF_REPEAT 4
>> -#define NF_STOP 5	/* Deprecated, for userspace nf_queue compatibility. */
>> -#define NF_MAX_VERDICT NF_STOP
>> +enum {
>> +	NF_DROP        = 0,
>> +	NF_ACCEPT      = 1,
>> +	NF_STOLEN      = 2,
>> +	NF_QUEUE       = 3,
>> +	NF_REPEAT      = 4,
>> +	NF_STOP        = 5,	/* Deprecated, for userspace nf_queue compatibility. */
>> +	NF_MAX_VERDICT = NF_STOP,
>> +};
>
>Switching from macro to enum works for almost all use cases, but not
>all. If someone if #ifdefing the symbols (which is plausible) this
>change would break them.
>
>I think I've seen some other networking code define both enums and
>macros. But it was a little ugly. Not sure if that is acceptable here or
>not.
>
>[...]
>
>Thanks,
>Daniel


Thanks for the review~
I do not have a strong reasoning to deny the possibility of breaking unexpected usage of this macros,

but I also agree that it is ugly to use both enum and macro at the same time.

Kind of don't know how to proceed from here now...