From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:46147)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <lvivier@redhat.com>) id 1ZAfYw-0007CF-Ku
	for qemu-devel@nongnu.org; Thu, 02 Jul 2015 10:34:03 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <lvivier@redhat.com>) id 1ZAfYv-0005l6-Na
	for qemu-devel@nongnu.org; Thu, 02 Jul 2015 10:34:02 -0400
Message-ID: <55954BD1.5040406@redhat.com>
Date: Thu, 02 Jul 2015 16:33:53 +0200
From: Laurent Vivier <lvivier@redhat.com>
MIME-Version: 1.0
References: <AB4CFA84-0BE1-41D1-A825-E879FD3EF2CB@gmail.com>
	<CAJSP0QX2VOBPx=vGQVsJ+Ci8iw4k+nP9ggjivrX0xD4jaKKXKg@mail.gmail.com>
	<55952D97.7040009@redhat.com> <559540F6.9090800@redhat.com>
	<55954384.9010906@redhat.com> <559544C4.4050809@redhat.com>
	<55954836.3060700@redhat.com> <55954895.7060005@redhat.com>
In-Reply-To: <55954895.7060005@redhat.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] raw-posix.c: remove raw device access for
	cdrom
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Programmingkid <programmingkidx@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, John Snow <jsnow@redhat.com>, qemu-devel qemu-devel <qemu-devel@nongnu.org>, Qemu-block <qemu-block@nongnu.org>



On 02/07/2015 16:20, Paolo Bonzini wrote:
> 
> 
> On 02/07/2015 16:18, Laurent Vivier wrote:
>>>> I'm okay with doing the simple thing, but it needs a comment for non-BSDers.
>> So, what we have to do, in our case, for MacOS X cdrom, is something like:
>>
>> ... GetBSDPath ...
>> ...
>>     if (flags & BDRV_O_NOCACHE) {
>>         strcat(bsdPath, "r");
>>     }
>> ...
>>
>> ?
> 
> Well, what to do with Mac OS X CD-ROM is another story...  Raw access
> "seems not do work well" according to John, so we may have a comment
> there explaining why we're not adding the "r".

I think it doesn't work well because they need to be aligned, and
NOCACHE implies that (with BDRV_O_NOCACHE code will be self explicit :) )

raw_open_common()

    if ((bs->open_flags & BDRV_O_NOCACHE) != 0) {
        s->needs_alignment = true;
    }

and needs_alignment allows to probe alignment (raw_probe_alignment())

> A FIXME comment saying "we should probe for alignment here" would be
> placed where you check S_ISCHR and set need_alignment to true.

It is another case,

in the previous case (MacOS cdrom), user provides "-cdrom /dev/cdrom"
and QEMU extracts /dev/rdiskX (or now /dev/diskX) from the system DB.

In the FreeBSD case, user provides /dev/diskX or /dev/rdiskX, and QEMU
must know if it needs alignment or not. I don't think we need more
comment here.

Laurent