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Date: Wed, 14 Sep 2011 05:30:19 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Jan Beulich <JBeulich@...e.com>, jaxboe@...ionio.com
Cc: Jeremy Fitzhardinge <jeremy@...p.org>, hch@...radead.org,
Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org
Subject: Re: Help with implementing some form of barriers in 3.0 kernels.
> >> Below is what Jan Kara came up with for addressing this - what do
> >> you think?
Jens,
Could you take a look at the block/elevator patch below?
> >
> > It looks like it would do it. I modified it a bit, testing it now.
> >
> >
> > commit 315c0cf1a5174b9aed494d7903133ce9ac76d6f1
> > Author: Jan Kara <jack@...e.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@...e.cz>
> > Signed-off-by: Jan Beulich <JBeulich@...e.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.
<nods> Which is OK - but you might want to migrate in the the 'feature-write-flush'
>
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.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()?
The rest of that file had EXPORT_SYMBOL.. so I figured I will follow
the same appearance. But I am OK doing it via EXPORT_SYMBOL_GPL. Lets
ask Jens.
>
> 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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