linux-kernel - Re: [PATCH] md/md-multipath: Convert "struct mpconf" to flexible array

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Message-ID: <CAPhsuW5F1aRrCRW-ad5Sq=cgxHX+QgXgYZyMX17Zj4Mj=Jnhjw@mail.gmail.com>
Date:   Fri, 8 Dec 2023 10:11:10 -0800
From:   Song Liu <song@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-raid@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] md/md-multipath: Convert "struct mpconf" to flexible array

On Fri, Dec 8, 2023 at 9:27 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Dec 07, 2023 at 09:33:17PM -0800, Song Liu wrote:
> > On Mon, Dec 4, 2023 at 2:20 PM Kees Cook <keescook@...omium.org> wrote:
> > >
> > > On Sun, Dec 03, 2023 at 08:48:06PM +0100, Christophe JAILLET wrote:
> > > > The 'multipaths' field of 'struct mpconf' can be declared as a flexible
> > > > array.
> > > >
> > > > The advantages are:
> > > >    - 1 less indirection when accessing to the 'multipaths' array
> > > >    - save 1 pointer in the structure
> > > >    - improve memory usage
> > > >    - give the opportunity to use __counted_by() for additional safety
> > > >
> > > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > >
> > > This looks like a really nice conversion. I haven't run-tested this, but
> > > it reads correct to me.
> >
> > Agreed this is a good optimization. However, since MD_MULTIPATH is
> > already marked as deprecated. I don't think we should ship further
> > changes to it.
>
> Hm, that seems like a weird catch-22 to me. I would say we should
> continue to improve any code in the kernel that people spend time to
> work on, or we should remove that code entirely. Should MD_MULTIPATH be
> removed? How long has it been deprecated? (We just had an LTS release,
> so doing removal now is a good time...)

We marked it as deprecated about 2.5 years ago. But to be honest,
I currently don't have a plan to remove it. I guess I should start thinking
about it.

Thanks,
Song