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

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Message-ID: <20180927222821.GC28301@ziepe.ca>
Date:   Thu, 27 Sep 2018 16:28:21 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>, dledford@...hat.com,
        linux-rdma@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] IB/mlx4: Avoid implicit enumerated type conversion

On Thu, Sep 27, 2018 at 01:34:16PM -0700, Nick Desaulniers wrote:

> > Neither ib_qp_create_flags nor mlx4_ib_qp_flags have negative values, is
> > signedness necessary?
>
> enums are by default restricted to the range of ints.  

That's not quite right, the compiler sizes the enum to be able to fit
the largest value contained within, today that is int, but if we added
1<<31, then it would become larger.

Values intended to hold bitfields should always be unsigned, so u32 is
an appropriate for flags where the flags are defined in an enum.

Jason