From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933776Ab1IONAu (ORCPT ); Thu, 15 Sep 2011 09:00:50 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:53211 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933766Ab1IONAt convert rfc822-to-8bit (ORCPT ); Thu, 15 Sep 2011 09:00:49 -0400 Message-Id: <4E72131B02000078000564AC@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 8.0.1 Date: Thu, 15 Sep 2011 14:00:43 +0100 From: "Jan Beulich" To: "Konrad Rzeszutek Wilk" Cc: "Jeremy Fitzhardinge" , , , "Jan Kara" , Subject: Re: [PATCH]: xen/blkback: Add support for old BARRIER requests - 'feature-barrier', was "Help with implementing some form of barriers in 3.0 kernels." References: <20110907174832.GN32190@dumpdata.com> <4E6F50170200007800055CF5@nat28.tlf.novell.com> <20110914085913.GB25628@phenom.oracle.com> <4E708C240200007800055FDF@nat28.tlf.novell.com> <20110914143247.GA17206@phenom.oracle.com> <20110914150102.GA18015@phenom.oracle.com> <4E70EEB302000078000561AE@nat28.tlf.novell.com> <20110915125111.GA18875@phenom.oracle.com> In-Reply-To: <20110915125111.GA18875@phenom.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 15.09.11 at 14:51, Konrad Rzeszutek Wilk wrote: >> > + if (drain) { >> > + struct request_queue *q = bdev_get_queue(preq.bdev); >> > + unsigned long flags; >> > + >> > + if (!q->elevator) { >> > + __end_block_io_op(pending_req, -EOPNOTSUPP); >> > + return -EOPNOTSUPP; >> > + } >> >> You shouldn't return here - barrier requests may be "non-empty" (i.e. >> carry data to be written), and hence you'd need to make sure the >> writes get carried out nevertheless. > > In theory (and in practice) the 'feature-barrier' is set to zero > if !q->elevator. So the frontend should not even try WRITE_BARRIER. > > I think the better approach will be to outright fail the WRITE_BARRIER > request if 'feature-barrier=0' instead of just trying (which is what > this tries). > > On a unrelated topic is what to do with devices which are bio based > but not request based. From the DM directory, only multipath is capable > of doing requests, while the rest are all bio. There is code to > quisce the bio's: dm_suspend, but it is not apparent to me how to > make it be exposed. > > >> >> Jan - this suggests that the placement isn't correct either: The >> draining of the queue - as I understand it - should be happening >> *after* these writes completed, not before they get started. > > So that looks like it should be just moved a bit, like this new patch: Looks like this is the patch after the very first modifications you made to it - I don't see anything being moved, and I no longer see any of the subsequent changes you did. Jan > commit 315c0cf1a5174b9aed494d7903133ce9ac76d6f1 > Author: Jan Kara > Date: Tue Sep 13 11:44:07 2011 +0100 > > xen: Add support for old BARRIER requests to xenblk driver > > Recent kernels do not support BARRIER operation but only FLUSH > operation. But > older xenblk frontends still use the BARRIER operation to achieve data > integrity requirements. So add support for BARRIER operation into xenblk > backend so that all guests do not corrupt their filesystem on host > crash. > > Signed-off-by: Jan Kara > Signed-off-by: Jan Beulich > [v1: Added some extra functions, and other cases] > Signed-off-by: Konrad Rzeszutek Wilk > > diff --git a/block/elevator.c b/block/elevator.c > index a3b64bc..b2143a8 100644 > --- a/block/elevator.c > +++ b/block/elevator.c > @@ -616,6 +616,7 @@ void elv_drain_elevator(struct request_queue *q) > q->elevator->elevator_type->elevator_name, q->nr_sorted); > } > } > +EXPORT_SYMBOL(elv_drain_elevator); > > /* > * Call with queue lock held, interrupts disabled > diff --git a/drivers/block/xen-blkback/blkback.c > b/drivers/block/xen-blkback/blkback.c > index 9713d5a..1df773c 100644 > --- a/drivers/block/xen-blkback/blkback.c > +++ b/drivers/block/xen-blkback/blkback.c > @@ -464,6 +464,11 @@ static void __end_block_io_op(struct pending_req > *pending_req, int error) > pr_debug(DRV_PFX "flush diskcache op failed, not supported\n"); > xen_blkbk_flush_diskcache(XBT_NIL, pending_req->blkif->be, 0); > pending_req->status = BLKIF_RSP_EOPNOTSUPP; > + } else if ((pending_req->operation == BLKIF_OP_WRITE_BARRIER) && > + (error == -EOPNOTSUPP)) { > + pr_debug(DRV_PFX "write barrier op failed, not supported\n"); > + xen_blkbk_barrier(XBT_NIL, pending_req->blkif->be, 0); > + pending_req->status = BLKIF_RSP_EOPNOTSUPP; > } else if (error) { > pr_debug(DRV_PFX "Buffer not up-to-date at end of operation," > " error=%d\n", error); > @@ -590,6 +595,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif, > struct bio *biolist[BLKIF_MAX_SEGMENTS_PER_REQUEST]; > int i, nbio = 0; > int operation; > + bool drain = false; > struct blk_plug plug; > > switch (req->operation) { > @@ -601,6 +607,8 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif, > blkif->st_wr_req++; > operation = WRITE_ODIRECT; > break; > + case BLKIF_OP_WRITE_BARRIER: > + drain = true; > case BLKIF_OP_FLUSH_DISKCACHE: > blkif->st_f_req++; > operation = WRITE_FLUSH; > @@ -609,7 +617,6 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif, > blkif->st_ds_req++; > operation = REQ_DISCARD; > break; > - case BLKIF_OP_WRITE_BARRIER: > default: > operation = 0; /* make gcc happy */ > goto fail_response; > @@ -668,6 +675,17 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif, > } > } > > + if (drain) { > + struct request_queue *q = bdev_get_queue(preq.bdev); > + unsigned long flags; > + > + /* Emulate the original behavior of write barriers */ > + spin_lock_irqsave(q->queue_lock, flags); > + elv_drain_elevator(q); > + __blk_run_queue(q); > + spin_unlock_irqrestore(q->queue_lock, flags); > + } > + > /* > * If we have failed at this point, we need to undo the M2P override, > * set gnttab_set_unmap_op on all of the grant references and perform > diff --git a/drivers/block/xen-blkback/common.h > b/drivers/block/xen-blkback/common.h > index bfb532e..42b0e46 100644 > --- a/drivers/block/xen-blkback/common.h > +++ b/drivers/block/xen-blkback/common.h > @@ -228,6 +228,8 @@ int xen_blkif_schedule(void *arg); > > int xen_blkbk_flush_diskcache(struct xenbus_transaction xbt, > struct backend_info *be, int state); > +int xen_blkbk_barrier(struct xenbus_transaction xbt, > + struct backend_info *be, int state); > > struct xenbus_device *xen_blkbk_xenbus(struct backend_info *be); > > diff --git a/drivers/block/xen-blkback/xenbus.c > b/drivers/block/xen-blkback/xenbus.c > index 2b3aef0..b477aee 100644 > --- a/drivers/block/xen-blkback/xenbus.c > +++ b/drivers/block/xen-blkback/xenbus.c > @@ -421,6 +421,20 @@ int xen_blkbk_flush_diskcache(struct xenbus_transaction > xbt, > return err; > } > > +int xen_blkbk_barrier(struct xenbus_transaction xbt, > + struct backend_info *be, int state) > +{ > + struct xenbus_device *dev = be->dev; > + int err; > + > + err = xenbus_printf(xbt, dev->nodename, "feature-barrier", > + "%d", state); > + if (err) > + xenbus_dev_fatal(dev, err, "writing feature-barrier"); > + > + return err; > +} > + > int xen_blkbk_discard(struct xenbus_transaction xbt, struct backend_info > *be) > { > struct xenbus_device *dev = be->dev; > @@ -706,6 +720,8 @@ again: > if (err) > goto abort; > > + err = xen_blkbk_barrier(xbt, be, be->blkif->vbd.flush_support); > + > err = xen_blkbk_discard(xbt, be); > > err = xenbus_printf(xbt, dev->nodename, "sectors", "%llu",