From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:59958)
	by lists.gnu.org with esmtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1UzhIq-0005Zz-4I
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 02:03:02 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pl@kamp.de>) id 1UzhIn-0004HQ-Mj
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 02:03:00 -0400
Received: from mx.ipv6.kamp.de ([2a02:248:0:51::16]:33409 helo=mx01.kamp.de)
	by eggs.gnu.org with smtp (Exim 4.71) (envelope-from <pl@kamp.de>)
	id 1UzhIn-0004HI-Cw
	for qemu-devel@nongnu.org; Thu, 18 Jul 2013 02:02:57 -0400
Message-ID: <51E78512.2090407@kamp.de>
Date: Thu, 18 Jul 2013 08:02:58 +0200
From: Peter Lieven <pl@kamp.de>
MIME-Version: 1.0
References: <1373885705-13722-1-git-send-email-pl@kamp.de>
	<20130718050330.GA26971@stefanha-thinkpad.redhat.com>
In-Reply-To: <20130718050330.GA26971@stefanha-thinkpad.redhat.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCHv3] block-migration: efficiently encode zero
	blocks
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: Stefan Hajnoczi <stefanha@redhat.com>
Cc: kwolf@redhat.com, pbonzini@redhat.com, owasserm@redhat.com, qemu-devel@nongnu.org, quintela@redhat.com

On 18.07.2013 07:03, Stefan Hajnoczi wrote:
> On Mon, Jul 15, 2013 at 12:55:05PM +0200, Peter Lieven wrote:
>> @@ -114,16 +115,29 @@ static void blk_mig_unlock(void)
>>   static void blk_send(QEMUFile *f, BlkMigBlock * blk)
>>   {
>>       int len;
>> +    uint64_t flags = BLK_MIG_FLAG_DEVICE_BLOCK;
>> +
>> +    if (migrate_zero_blocks() && buffer_is_zero(blk->buf, BLOCK_SIZE)) {
> [...]
>> +bool migrate_zero_blocks(void)
>> +{
>> +    MigrationState *s;
>> +
>> +    s = migrate_get_current();
>> +
>> +    return s->enabled_capabilities[MIGRATION_CAPABILITY_ZERO_BLOCKS];
>> +}
> blk_send() is called without locks held.  It would be safer and cleaner
> to stash bool migrate_zero_blocks in BlkMigBlock in init_blk_migration()
> instead of accessing migrate_get_current() without locks held.
>
> This eliminates the assumption that accessing migrate_get_current() is
> safe without locks.
>
> Besides this locking issue I'm happy with the code.
Thank you,

I will sent a v4 shortly. I have to rebase it anyway.

Peter