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From: Jeff Xu <jeffxu@chromium.org>
Date: Mon, 15 Apr 2024 12:06:24 -0700
Message-ID: <CABi2SkW+X4+m2odCHKVDzYYWPgvebxX_mr97NsKCRfkx641sHA@mail.gmail.com>
Subject: Re: [PATCH v10 1/5] mseal: Wire up mseal syscall
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>, akpm@linux-foundation.org, 
	keescook@chromium.org, jannh@google.com, sroettger@google.com, 
	willy@infradead.org, gregkh@linuxfoundation.org, corbet@lwn.net, 
	Liam.Howlett@oracle.com, surenb@google.com, merimus@google.com, 
	rdunlap@infradead.org, jeffxu@google.com, jorgelo@chromium.org, 
	groeck@chromium.org, linux-kernel@vger.kernel.org, 
	linux-kselftest@vger.kernel.org, linux-mm@kvack.org, pedro.falcato@gmail.com, 
	dave.hansen@intel.com, linux-hardening@vger.kernel.org, deraadt@openbsd.org
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On Mon, Apr 15, 2024 at 11:21=E2=80=AFAM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, 15 Apr 2024 at 11:11, Muhammad Usama Anjum
> <usama.anjum@collabora.com> wrote:
> >
> > It isn't logical to wire up something which isn't present
>
> Actually, with system calls, the rules end up being almost opposite.
>
> There's no point in adding the code if it's not reachable. So adding
> the system call code before adding the wiring makes no sense.
>
> So you have two cases: add the stubs first, or add the code first.
> Neither does anything without the other.
>
> So then you go "add both in the same commit" option, which ends up
> being horrible from a "review the code" standpoint. The two parts are
> entirely different and mixing them up makes the patch very unclear
> (and has very different target audiences for reviewing it - the MM
> people really shouldn't have to look at the architecture wiring
> parts).
>
> End result: there are no "this is the logical ordering" cases.
>
> But the "wire up system calls" part actually has some reasons to be first=
:
>
>  - it reserves the system call number
>
>  - it adds the "when system call isn't enabled, return -ENOSYS"
> conditional system call logic
>
> so I actually tend prefer this ordering when it comes to system calls.
>
I confirm that the wire up change can be merged by its own, i.e. build
will pass, and  -ENOSYS will be returned at runtime.

Thanks Linus for clarifying this.
-Jeff


>                 Linus