From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [Xen-devel] Re: [PATCH 3/3] xen-blkfront: If no barrier or flush is supported, use invalid operation. Date: Fri, 16 Sep 2011 15:15:15 -0400 Message-ID: <20110916191514.GA31818@phenom.oracle.com> References: <1315593060-20031-1-git-send-email-konrad.wilk@oracle.com> <1315593060-20031-3-git-send-email-konrad.wilk@oracle.com> <4E6DD8750200007800055ADA@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4E6DD8750200007800055ADA@nat28.tlf.novell.com> Sender: linux-kernel-owner@vger.kernel.org To: Jan Beulich Cc: axboe@kernel.dk, xen-devel@lists.xensource.com, jeremy.fitzhardinge@citrix.com, stable@kernel.org, linux-kernel@vger.kernel.org List-Id: xen-devel@lists.xenproject.org On Mon, Sep 12, 2011 at 09:01:25AM +0100, Jan Beulich wrote: > >>> On 09.09.11 at 20:31, Konrad Rzeszutek Wilk wrote: > > By default we would set the info->flush_op=0, and zero maps > > to BLKIF_OP_READ request code. So if the backend did not support > > either barrier ('feature-barrier') or flush ('feature-flush-cache') > > we would end up using that opcode for the flush/barrier request, meaning > > we actually do a READ request. Fortunatly for us, __generic_make_request > > checks q->flush_flags and realizes that we don't do FLUSH and removes > > the REQ_FLUSH | REQ_FUA so we never end up issuing a READ request > > for a flush request. However, other third party implementations of > > __make_request might not be so smart, so lets fix this up. > > Wouldn't it be better to simply have blkif_queue_request() fail in that > case (and then it doesn't matter whether flush_op is set to 0 or -1)? > Not the least because older (forward-port) backends stall the incoming > queue and are possibly verbose for invalid requests seen. So like this: diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index 468bfec..e9d301c 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -380,7 +380,9 @@ static void do_blkif_request(struct request_queue *rq) blk_start_request(req); - if (req->cmd_type != REQ_TYPE_FS) { + if ((req->cmd_type != REQ_TYPE_FS) || + ((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) && + !info->flush_op)) { __blk_end_request_all(req, -EIO); continue; }