Re: [RFC PATCH 4/8] mm: Separate fault info out of 'struct vm_fault'

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Will Deacon <will@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	 Linux ARM <linux-arm-kernel@lists.infradead.org>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	 Andrew Morton <akpm@linux-foundation.org>,
	 "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	 Hugh Dickins <hughd@google.com>,
	Android Kernel Team <kernel-team@android.com>
Subject: Re: [RFC PATCH 4/8] mm: Separate fault info out of 'struct vm_fault'
Date: Thu, 14 Jan 2021 11:09:01 -0800	[thread overview]
Message-ID: <CAHk-=wjdJmL22+zk3_rWAfEJJCf=oDxiJ530qk-WNk_Ji0qhxw@mail.gmail.com> (raw)
In-Reply-To: <20210114190021.GB13135@willie-the-truck>

On Thu, Jan 14, 2021 at 11:00 AM Will Deacon <will@kernel.org> wrote:
>
> I tried that initially, but I found that I had to make all of the
> members const to get it to work, at which point the anonymous struct
> wasn't really adding anything. Did I just botch the syntax?

I'm not sure what you tried. But this stupid test-case sure works for me:

    struct hello {
        const struct {
                unsigned long address;
        };
        unsigned int flags;
    };

    extern int fn(struct hello *);

    int test(void)
    {
        struct hello a = {
                .address = 1,
        };
        a.flags = 0;
        return fn(&a);
    }

and because "address" is in that unnamed constant struct, you can only
set it within that initializer, and cannot do

        a.address = 0;

without an error (the way you _can_ do "a.flags = 0").

I don't see naming the struct making a difference - apart from forcing
that big rename patch, of course.

But maybe we're talking about different issues?

            Linus