linux-kernel - Re: [PATCH v13 2/3] cachestat: implement cachestat syscall

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Message-Id: <315e7ec2-169c-4c4b-93df-485380bc0852@app.fastmail.com>
Date:   Sat, 06 May 2023 19:35:05 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Andrew Morton" <akpm@...ux-foundation.org>,
        "Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:     "Nhat Pham" <nphamcs@...il.com>,
        "Johannes Weiner" <hannes@...xchg.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, bfoster@...hat.com,
        "Matthew Wilcox" <willy@...radead.org>, linux-api@...r.kernel.org,
        kernel-team@...a.com
Subject: Re: [PATCH v13 2/3] cachestat: implement cachestat syscall

On Fri, May 5, 2023, at 22:34, Andrew Morton wrote:
> On Thu, 4 May 2023 19:26:11 +0200 Geert Uytterhoeven 
> <geert@...ux-m68k.org> wrote:
>
>> >  arch/x86/entry/syscalls/syscall_32.tbl |   1 +
>> >  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
>> 
>> This should be wired up on each and every architecture.
>> Currently we're getting
>> 
>>     <stdin>:1567:2: warning: #warning syscall cachestat not implemented [-Wcpp]
>> 
>> in linux-next for all the missing architectures.
>
> Is that wise?  We risk adding a syscall to an architecture without the
> arch maintainers and testers even knowing about it.
>
> The compile-time nag is there to inform the arch maintainers that a new
> syscall is available and that they should wire it up, run the selftest
> and then ship the code if they're happy with the result.

The usual approach is for the author of a new syscall to
include a patch with all the architecture specific changes
and Cc the architecture maintainers for that.

Note that half the architectures get the entry from
include/uapi/asm-generic/unistd.h, so adding it there
does not necessarily trigger adding each maintainer
from scripts/get_maintainer.pl.

The only real risk in adding a new syscall is passing __u64
register arguments that behave differently across
architectures, or using pointers to data structures that
require a compat handler on some architectures. I watch out
for those as they get sent to me or the linux-arch list,
and this one is fine.

     Arnd