From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [PATCH V2 2/3] xen/vm_event: Support for
 guest-requested events
Date: Mon, 06 Jul 2015 11:26:03 +0100
Message-ID: <559A73DB020000780008C9AA@mail.emea.novell.com>
References: <1434359007-9302-1-git-send-email-rcojocaru@bitdefender.com>
	<1434359007-9302-3-git-send-email-rcojocaru@bitdefender.com>
	<558D152B0200007800089FD4@mail.emea.novell.com>
	<558CFC75.9000905@bitdefender.com>
	<CAD33N+4-agvUhakTyoc=o_fRg2bZ_UpzJxoHU2CZg1jfVMPx2A@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
In-Reply-To: <CAD33N+4-agvUhakTyoc=o_fRg2bZ_UpzJxoHU2CZg1jfVMPx2A@mail.gmail.com>
Content-Disposition: inline
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Razvan Cojocaru <rcojocaru@bitdefender.com>, Tamas Lengyel <tlengyel@novetta.com>
Cc: Tim Deegan <tim@xen.org>, kevin.tian@intel.com, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Jun Nakajima <jun.nakajima@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Xen-devel <xen-devel@lists.xen.org>, eddie.dong@intel.com, Aravind.Gopalakrishnan@amd.com, suravee.suthikulpanit@amd.com, keir@xen.org, boris.ostrovsky@oracle.com, Daniel De Graaf <dgdegra@tycho.nsa.gov>
List-Id: xen-devel@lists.xenproject.org

>>> On 30.06.15 at 16:48, <tlengyel@novetta.com> wrote:
>> > --- a/xen/include/asm-x86/domain.h
> 
>> >> +++ b/xen/include/asm-x86/domain.h
>> >> @@ -342,13 +342,15 @@ struct arch_domain
>> >>
>> >>      /* Monitor options */
>> >>      struct {
>> >> -        uint16_t write_ctrlreg_enabled       : 4;
>> >> -        uint16_t write_ctrlreg_sync          : 4;
>> >> -        uint16_t write_ctrlreg_onchangeonly  : 4;
>> >> -        uint16_t mov_to_msr_enabled          : 1;
>> >> -        uint16_t mov_to_msr_extended         : 1;
>> >> -        uint16_t singlestep_enabled          : 1;
>> >> -        uint16_t software_breakpoint_enabled : 1;
>> >> +        uint32_t write_ctrlreg_enabled       : 4;
>> >> +        uint32_t write_ctrlreg_sync          : 4;
>> >> +        uint32_t write_ctrlreg_onchangeonly  : 4;
>> >> +        uint32_t mov_to_msr_enabled          : 1;
>> >> +        uint32_t mov_to_msr_extended         : 1;
>> >> +        uint32_t singlestep_enabled          : 1;
>> >> +        uint32_t software_breakpoint_enabled : 1;
>> >> +        uint32_t request_enabled             : 1;
>> >> +        uint32_t request_sync                : 1;
>> >
>> > Can you please switch to plain unsigned int if you already have to
>> > touch this? There's no reason I can see to use a fixed width integer
>> > type here.
>>
>> Ack, will make it plain int.
> 
> 
> IMHO having it fix-width is easier to read when adding new elements to see
> how many bits we have left free. I would not want this changed unless there
> is a clear benefit to doing so.

I can't see what benefit using fixed widht types here is: Best
demonstrated with uint64_t, gcc doesn't honor the type of the
field anyway. And hence counting the number of left bits (with
some unknown definition of "left") is quite pointless too - it's an
internal structure, and when a new bit field needs to be added,
it doesn't really matter whether it grows the structure (at least
no more than any other field addition).

Bottom line - no fixed width types when not really warranted,
please.

Jan