linux-kernel - Re: [PATCH 03/17] um: don't generate asm/bpf_perf

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Message-Id: <1d998e37-926c-473f-a58a-1d47b96f882a@app.fastmail.com>
Date: Fri, 12 Jul 2024 11:13:16 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Masahiro Yamada" <masahiroy@...nel.org>,
 "Arnd Bergmann" <arnd@...nel.org>
Cc: Linux-Arch <linux-arch@...r.kernel.org>,
 "Nathan Chancellor" <nathan@...nel.org>,
 "Nicolas Schier" <nicolas@...sle.eu>, "Vineet Gupta" <vgupta@...nel.org>,
 "Russell King" <linux@...linux.org.uk>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Will Deacon" <will@...nel.org>, guoren <guoren@...nel.org>,
 "Brian Cain" <bcain@...cinc.com>, "Huacai Chen" <chenhuacai@...nel.org>,
 "WANG Xuerui" <kernel@...0n.name>, "Dinh Nguyen" <dinguyen@...nel.org>,
 "Jonas Bonn" <jonas@...thpole.se>,
 "Stefan Kristiansson" <stefan.kristiansson@...nalahti.fi>,
 "Stafford Horne" <shorne@...il.com>,
 "Paul Walmsley" <paul.walmsley@...ive.com>,
 "Palmer Dabbelt" <palmer@...belt.com>,
 "Albert Ou" <aou@...s.berkeley.edu>, "Rich Felker" <dalias@...c.org>,
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 "David S . Miller" <davem@...emloft.net>,
 "Andreas Larsson" <andreas@...sler.com>,
 "Christian Brauner" <brauner@...nel.org>,
 "Mark Rutland" <mark.rutland@....com>, linux-kbuild@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org,
 "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
 linux-hexagon@...r.kernel.org, loongarch@...ts.linux.dev,
 "linux-openrisc@...r.kernel.org" <linux-openrisc@...r.kernel.org>,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 03/17] um: don't generate asm/bpf_perf_event.h

On Fri, Jul 12, 2024, at 10:37, Masahiro Yamada wrote:
> On Thu, Jul 4, 2024 at 11:37 PM Arnd Bergmann <arnd@...nel.org> wrote:
>> --- a/arch/um/include/asm/Kbuild
>> +++ b/arch/um/include/asm/Kbuild
>> @@ -1,5 +1,4 @@
>>  # SPDX-License-Identifier: GPL-2.0
>> -generic-y += bpf_perf_event.h
>>  generic-y += bug.h
>>  generic-y += compat.h
>>  generic-y += current.h
>> diff --git a/arch/um/include/asm/bpf_perf_event.h b/arch/um/include/asm/bpf_perf_event.h
>> new file mode 100644
>> index 000000000000..0a30420c83de
>> --- /dev/null
>> +++ b/arch/um/include/asm/bpf_perf_event.h
>> @@ -0,0 +1,3 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +
>> +#include <asm-generic/bpf_perf_event.h>
>
> I guess this is a step backward.
>
> Technically, kernel-space asm/*.h files are allowed to
> wrap UAPI <asm-generic/*.h>.
> There is no reason why we ban generic-y for doing this,
> whereas check-in source is allowed.

I think in this case, the simplicity is the more important
argument: this is the only case we have of wrapping a
uapi header from a non-uapi header, and no other architecture
would need to do this.

The way the syscall-y rule works relies on enforcing some
checking for existing asm-generic headers, and I could extend
it to allow this special case, but that would make the
Makefile rule less readable  in exchange for avoiding
effectively a one-line file.

    Arnd