Messages in this thread | | | Date | Wed, 14 Sep 2011 10:12:36 +0100 | From | "Jan Beulich" <> | Subject | Re: Help with implementing some form of barriers in 3.0 kernels. |
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>>> On 14.09.11 at 10:59, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote: > On Tue, Sep 13, 2011 at 11:44:07AM +0100, Jan Beulich wrote: >> >>> On 07.09.11 at 19:48, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote: >> > Hey Christoph, >> > >> > I was wondering what you think is the proper way of implementing a >> > backend to support the 'barrier' type requests? We have this issue were >> > there are 2.6.36 type guests that still use barriers and we would like >> > to support them properly. But in 3.0 there are no barriers - hence >> > the question whether WRITE_fLUSH_FUA would be equal to WRITE_BARRIER? >> > >> > Or is there some other things that we should take in consideration? >> > >> > Thanks! >> >> Below is what Jan Kara came up with for addressing this - what do >> you think? > > It looks like it would do it. I modified it a bit, testing it now. > > > commit 315c0cf1a5174b9aed494d7903133ce9ac76d6f1 > Author: Jan Kara <jack@suse.cz> > 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 <jack@suse.cz> > Signed-off-by: Jan Beulich <JBeulich@suse.com> > [v1: Added some extra functions, and other cases]
Ah, yes, of course - Jan probably didn't pay attention because in our variant of the driver these functions never got removed.
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> > > 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);
Now, if you modify it anyway, how about making this an EXPORT_SYMBOL_GPL()?
Jan
> > /* > * 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",
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