From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:52893)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <sw@weilnetz.de>) id 1YROob-0007aw-Eq
	for qemu-devel@nongnu.org; Fri, 27 Feb 2015 12:35:10 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <sw@weilnetz.de>) id 1YROoa-00018z-LM
	for qemu-devel@nongnu.org; Fri, 27 Feb 2015 12:35:05 -0500
Message-ID: <54F0AAC2.6020202@weilnetz.de>
Date: Fri, 27 Feb 2015 18:34:58 +0100
From: Stefan Weil <sw@weilnetz.de>
MIME-Version: 1.0
References: <1425045947-9271-1-git-send-email-mreitz@redhat.com>
	<20150227165723.GB32542@stefanha-thinkpad.redhat.com>
	<54F0A86E.7000608@weilnetz.de> <54F0A957.5090906@redhat.com>
In-Reply-To: <54F0A957.5090906@redhat.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH v2] block/vdi: Add locking for parallel
	requests
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: Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, qemu-block@nongnu.org, qemu-stable@nongnu.org

Am 27.02.2015 um 18:28 schrieb Max Reitz:
> On 2015-02-27 at 12:25, Stefan Weil wrote:
>> block/vdi.c was never written for multi-threaded access, see my comment
>> in the header of block/vdi.c:
>>
>>   * The code is not thread safe (missing locks for changes in header and
>>   * block table, no problem with current QEMU).
>>
>> This was true in the past, but obviously later multi-threaded access was
>> introduced for QEMU. Locking was added for qcow2 and other drivers in
>> 2012 and 2013, but never for vdi.
>>
>> I must admit that I don't know which parts of the block filesystem
>> drivers potentially run in parallel threads.Ideally there would be one
>> or more test cases which test multi-threaded operations and which
>> trigger a failure with the current vdi code.
>>
>> If I had a simple test scenario, I could have a look on the problem.
>
> I have one for you. See the attached ruby script.
>
> (If there are no "Pattern verification failed" messages, everything is
> good)
>
>> The VMDK approach is fine as an intermediate work around, but please use
>> conditional compilation to allow easy tests without coarse locks (and
>> update the comments :-)).
>
> Will a macro defined in vdi.c be enough?

Yes, that would be fine. vdi.c already has several locally defined
CONFIG_VDI_... macros.

Stefan