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

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Message-ID: <1538087622.226558.8.camel@acm.org>
Date:   Thu, 27 Sep 2018 15:33:42 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        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, 2018-09-27 at 16:28 -0600, Jason Gunthorpe wrote:
> 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.

Hi Jason,

Are you perhaps confusing C and C++? For C++, an enumeration whose underlying
type is not fixed, the underlying type is an integral type that can represent
all the enumerator values defined in the enumeration. For C however I think
that enumeration values are restricted to what fits in an int.

Bart.