From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexei Starovoitov <ast@plumgrid.com>
Subject: Re: [PATCH v2 net-next 1/2] bpf: allow extended BPF programs access
 skb fields
Date: Fri, 13 Mar 2015 21:59:43 -0700
Message-ID: <5503C03F.8020903@plumgrid.com>
References: <1426273064-4837-1-git-send-email-ast@plumgrid.com> <1426273064-4837-2-git-send-email-ast@plumgrid.com> <550392F7.9040308@iogearbox.net> <550397B0.5070409@iogearbox.net> <5503981C.6000801@plumgrid.com> <55039A0D.20000@iogearbox.net> <55039C9D.6010602@plumgrid.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Thomas Graf <tgraf@suug.ch>, linux-api@vger.kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
To: Daniel Borkmann <daniel@iogearbox.net>,
	"David S. Miller" <davem@davemloft.net>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <55039C9D.6010602@plumgrid.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: netdev.vger.kernel.org

On 3/13/15 7:27 PM, Alexei Starovoitov wrote:
> On 3/13/15 7:16 PM, Daniel Borkmann wrote:
>> On 03/14/2015 03:08 AM, Alexei Starovoitov wrote:
>>> On 3/13/15 7:06 PM, Daniel Borkmann wrote:
>>>> On 03/14/2015 02:46 AM, Daniel Borkmann wrote:
>>>> ...
>>>>> Previously, it was much more consistent, which I like better. And only
>>>>> because of the simple BUILD_BUG_ON()? :/
>>>>
>>>> Alternative is to move all of them into a central place, something like
>>>> in twsk_build_assert() or __mld2_query_bugs[].
>>>
>>> nope. that defeats the purpose of bug_on.
>>
>> Well, it doesn't. ;) It throws a build error thus the user is forced to
>> investigate that further.
>
> according to this distorted logic all build_bug_on can be in one file
> across the whole tree, since 'user is forced to investigate' ?!

also note that this case and twsk_build_assert are different.
twsk_build_assert has no other choice then to have one function
that covers logic in the whole file, whereas in this patch:
+               BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
+               *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
+                                     offsetof(struct sk_buff, mark));

the build_bug_on protect the line directly below.
Separating them just doesn't make sense at all.