From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:44506)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1V3nOR-0005Yg-Pe
	for qemu-devel@nongnu.org; Mon, 29 Jul 2013 09:21:50 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1V3nOL-0007XR-PU
	for qemu-devel@nongnu.org; Mon, 29 Jul 2013 09:21:43 -0400
Received: from mx1.redhat.com ([209.132.183.28]:34919)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kwolf@redhat.com>) id 1V3nOL-0007XD-J2
	for qemu-devel@nongnu.org; Mon, 29 Jul 2013 09:21:37 -0400
Date: Mon, 29 Jul 2013 15:21:29 +0200
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20130729132129.GE10467@dhcp-200-207.str.redhat.com>
References: <1374762197-7261-1-git-send-email-pbonzini@redhat.com>
	<1374762197-7261-6-git-send-email-pbonzini@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1374762197-7261-6-git-send-email-pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 05/19] block: make bdrv_co_is_allocated
	static
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>
Cc: pl@kamp.de, qemu-devel@nongnu.org, stefanha@redhat.com, Charlie Shepherd <charlie@ctshepherd.com>

Am 25.07.2013 um 16:23 hat Paolo Bonzini geschrieben:
> bdrv_is_allocated can detect coroutine context and go through a fast
> path, similar to other block layer functions.
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

It can, but why is this a good idea?

The other block layer functions do this because existing drivers call
bdrv_(p)read/write(v) and we don't want them to block the vcpu. So it's
basically just a method of avoiding massive changes to existing callers.

The only such caller of bdrv_is_allocated() that I can see is vvfat, and
I don't think optimising that is our top priority.

Charlie is working in exactly the opposite direction, namely splitting
the existing functions in a coroutine-only and a synchronous-only part.
We should be clear what we really want here.

Kevin