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Date:   Tue, 27 Jun 2023 05:31:35 +0200 (GMT+02:00)
From:   Matthieu Baerts <matthieu.baerts@tessares.net>
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Namhyung Kim <namhyung@kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        dhowells@redhat.com, acme@kernel.org, adrian.hunter@intel.com,
        alexander.shishkin@linux.intel.com, bpf@vger.kernel.org,
        davem@davemloft.net, irogers@google.com, jolsa@kernel.org,
        linux-kernel@vger.kernel.org, linux-next@vger.kernel.org,
        linux-perf-users@vger.kernel.org, mark.rutland@arm.com,
        mingo@redhat.com, netdev@vger.kernel.org, peterz@infradead.org,
        sfr@canb.auug.org.au
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Subject: Re: [PATCH net-next] perf trace: fix MSG_SPLICE_PAGES build error
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Hi Jakub, Namhyung,

@Namhyung: thank you for the explanations about the header files in the oth=
er thread!


26 Jun 2023 23:49:36 Jakub Kicinski <kuba@kernel.org>:
> On Mon, 26 Jun 2023 14:41:56 -0700 Namhyung Kim wrote:
>
>> But in general you don't need to change the copy of the tools
>> headers together.=C2=A0 It also needs to support old & new kernels
>> so different care should be taken.=C2=A0 Please separate tooling
>> changes and let us handle them.
>
> Ack, I'm not sure what makes this a special case, from Stephen's
> original report:
>
> https://lore.kernel.org/all/20230626112847.2ef3d422@canb.auug.org.au/
> > it sounded like perf won't build without the fix.

The copy of the header file is confusing :)

If I understood properly, here, we need the modification in msg_flags.c fro=
m Perf code because this file has been recently modified by David's series =
in net-next to support a new flag (not present in the system header files y=
et). Without this patch, Perf doesn't build.

Now regarding the "internal" copy of header files: we don't need to modify =
it because it is just used by Perf maintainers to monitor the modifications=
 in the original file. If I'm not mistaken, it might even be better to reve=
rt the line that has been removed in David's original series in net-next in=
 this header file. But now that Namhyung is aware of that modification, I g=
uess the revert is probably not needed. But in short, it is then better not=
 to modify this header file in the networking tree :-)

Cheers,
Matt
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