netdev - Re: [ovs-dev] [PATCH net-next V2 1/1] openvswitch: Declare ovs key structures using macros

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Date:   Tue, 5 Feb 2019 10:22:09 -0800
From:   Gregory Rose <gvrose8192@...il.com>
To:     Eli Britstein <elibr@...lanox.com>,
        David Miller <davem@...emloft.net>,
        "yihung.wei@...il.com" <yihung.wei@...il.com>
Cc:     "dev@...nvswitch.org" <dev@...nvswitch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "simon.horman@...ronome.com" <simon.horman@...ronome.com>
Subject: Re: [ovs-dev] [PATCH net-next V2 1/1] openvswitch: Declare ovs key
 structures using macros

On 2/5/2019 4:02 AM, Eli Britstein wrote:
> On 2/4/2019 10:07 PM, David Miller wrote:
>> From: Yi-Hung Wei <yihung.wei@...il.com>
>> Date: Mon, 4 Feb 2019 10:47:18 -0800
>>
>>> For example, to see how 'struct ovs_key_ipv6' is defined, now we need
>>> to trace how OVS_KEY_IPV6_FIELDS is defined, and how OVS_KEY_FIELD_ARR
>>> and OVS_KEY_FIELD defined.  I think it makes the header file to be
>>> more complicated.
>> I completely agree.
>>
>> Unless this is totally unavoidable, I do not want to apply a patch
>> which makes reading and auditing the networking code more difficult.
> This technique is discussed for example in
> https://stackoverflow.com/questions/6635851/real-world-use-of-x-macros,
> and I found existing examples of using it in the kernel tree:
>
> __BPF_FUNC_MAPPER in commit ebb676daa1a34 ("bpf: Print function name in
> addition to function id")
>
> __AAL_STAT_ITEMS and __SONET_ITEMS in commit 607ca46e97a1b ("UAPI:
> (Scripted) Disintegrate include/linux"), the successor of commit
> 1da177e4c3f4 ("Linux-2.6.12-rc2"). I didn't dig deeper to the past.
>
> I can agree it makes that H file a bit more complicated, but for sure
> less than ## macros that are widely used.
>
> However, I think the alternatives of generating such defines by some
> scripts, or having the fields in more than one place are even worse, so
> it is a kind of unavoidable.

Why is using a script to generate defines for the requirements of your 
application or driver so bad?  Your patch
turns openvswitch.h into some hardly readable code - using a script and 
having a machine output the macros
your application or driver needs seems like a much better alternative to me.

- Greg

>
> Please reconsider regarding applying this patch.
>
> _______________________________________________
> dev mailing list
> dev@...nvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-dev

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