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From:   Roman Kagan <rkagan@virtuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
CC:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
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        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
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        =?iso-8859-2?Q?Radim_Kr=E8m=E1=F8?= <rkrcmar@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h
Thread-Topic: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h
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Date:   Tue, 27 Nov 2018 18:48:42 +0000
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On Tue, Nov 27, 2018 at 02:10:49PM +0100, Vitaly Kuznetsov wrote:
> Roman Kagan <rkagan@virtuozzo.com> writes:
> > On Mon, Nov 26, 2018 at 04:47:29PM +0100, Vitaly Kuznetsov wrote:
> > I personally tend to prefer masks over bitfields, so I'd rather do the
> > consolidation in the opposite direction: use the definitions in
> > hyperv-tlfs.h and replace those unions/bitfields elsewhere.  (I vaguely
> > remember posting such a patchset a couple of years ago but I lacked the
> > motivation to complete it).
>=20
> Are there any known advantages of using masks over bitfields or the
> resulting binary code is the same?

Strictly speaking bitwise ops are portable while bitfields are not, but
I guess this is not much of an issue with gcc which is dependable to
produce the right thing.

I came to dislike the bitfields for the false feeling of atomicity of
assignment while most of the time they are read-modify-write operations.

And no, I don't feel strong about it, so if nobody backs me on this I
give up :)

Roman.