netdev - Re: [PATCH 08/20] octeontx2-af: Alloc and config NPC MCAM entry at a time

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Date:   Fri, 9 Nov 2018 22:06:07 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sunil Kovvuri <sunil.kovvuri@...il.com>
Cc:     Networking <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>, linux-soc@...r.kernel.org,
        Sunil Goutham <sgoutham@...vell.com>
Subject: Re: [PATCH 08/20] octeontx2-af: Alloc and config NPC MCAM entry at a time

On Fri, Nov 9, 2018 at 6:13 PM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:
> On Fri, Nov 9, 2018 at 4:32 PM Arnd Bergmann <arnd@...db.de> wrote:
> > On Fri, Nov 9, 2018 at 5:21 AM Sunil Kovvuri <sunil.kovvuri@...il.com> wrote:

> >
> > Since b is aligned to four bytes, you get padding between a and b.
> > On top of that, you also get padding after c to make the size of
> > structure itself be a multiple of its alignment. For interfaces, we
> > should avoid both kinds of padding. This can be done by marking
> > members as __packed (usually I don't recommend that), by
> > changing the size of members, or by adding explicit 'reserved'
> > fields in place of the padding.
> >
> > > > I also noticed a similar problem in struct mbox_msghdr. Maybe
> > > > use the 'pahole' tool to check for this kind of padding in the
> > > > API structures.
>
> Got your point now and agree that padding has to be avoided.
> But this is a big change and above pointed structure is not
> the only one as this applies to all structures in the file.
>
> Would it be okay if I submit a separate patch after this series
> addressing all structures ?

It depends on how you want to address it. If you want to
change the structure layout, then I think it would be better
integrated into the series as that is an incompatible interface
change. If you just want to add reserved members to make
the padding explicit, that could be a follow-up.

        Arnd