linux-kernel - Re: [PATCH] IB/mlx4: Avoid implicit enumerated type conversion

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Message-ID: <CAKwvOdkZ-0k4BhXYz0wj3wXNyy95nKFe9aYXxXveLafuviGG2w@mail.gmail.com>
Date:   Mon, 24 Sep 2018 15:29:38 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     dledford@...hat.com, jgg@...pe.ca, linux-rdma@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] IB/mlx4: Avoid implicit enumerated type conversion

On Mon, Sep 24, 2018 at 3:27 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> On Mon, Sep 24, 2018 at 03:24:36PM -0700, Nick Desaulniers wrote:
> > On Mon, Sep 24, 2018 at 12:57 PM Nathan Chancellor
> > <natechancellor@...il.com> wrote:
> > >
> > > Clang warns when one enumerated type is implicitly converted to another.
> > >
> > > drivers/infiniband/hw/mlx4/mad.c:1811:41: warning: implicit conversion
> > > from enumeration type 'enum mlx4_ib_qp_flags' to different enumeration
> > > type 'enum ib_qp_create_flags' [-Wenum-conversion]
> > >                 qp_init_attr.init_attr.create_flags = MLX4_IB_SRIOV_TUNNEL_QP;
> > >                                                     ~ ^~~~~~~~~~~~~~~~~~~~~~~
> > >
> > > drivers/infiniband/hw/mlx4/mad.c:1819:41: warning: implicit conversion
> > > from enumeration type 'enum mlx4_ib_qp_flags' to different enumeration
> > > type 'enum ib_qp_create_flags' [-Wenum-conversion]
> > >                 qp_init_attr.init_attr.create_flags = MLX4_IB_SRIOV_SQP;
> > >                                                     ~ ^~~~~~~~~~~~~~~~~
> > >
> > > The type mlx4_ib_qp_flags explicitly provides supplemental values to the
> > > type ib_qp_create_flags. Make that clear to Clang by changing the
> > > create_flags type to u32.
> > >
> > > Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> > > ---
> > >  include/rdma/ib_verbs.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
> > > index e463d3007a35..f6f4d9e3c8ed 100644
> > > --- a/include/rdma/ib_verbs.h
> > > +++ b/include/rdma/ib_verbs.h
> > > @@ -1149,7 +1149,7 @@ struct ib_qp_init_attr {
> > >         struct ib_qp_cap        cap;
> > >         enum ib_sig_type        sq_sig_type;
> > >         enum ib_qp_type         qp_type;
> > > -       enum ib_qp_create_flags create_flags;
> > > +       u32                     create_flags;
> >
> > I think it might be better to just have explicit casts at the
> > assignment.  What do the maintainers think?
> >
>
> That's fine with me, I tend to explicitly cast if it is only one
> location but it certainly makes sense in this case as well. I'll
> wait for the maintainers to weigh in before sending a v2.

Yeah, I mean my opinion on this might seem arbitrary, but based on the
pattern and the comment in ib_qp_create_flags, those enum values are
reserved to be "subclassed" in a sense, so they should always be in
sync or this code will have bigger problems.

>
> Thanks for the review,
> Nathan
>
> > >
> > >         /*
> > >          * Only needed for special QP types, or when using the RW API.
> > > --
> > > 2.19.0
> > >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers