linux-kernel - [PATCH v2 10/10] vfio: ccw: Let user wait when busy on IO

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Date:   Fri, 25 May 2018 12:21:18 +0200
From:   Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:     pasic@...ux.vnet.ibm.com, bjsdjshi@...ux.vnet.ibm.com
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, cohuck@...hat.com
Subject: [PATCH v2 10/10] vfio: ccw: Let user wait when busy on IO

In the current implementation, we do not want to start a new SSCH
command before the last one ends.

Currently the user needs to poll on the -EBUSY error to
wait before sending a new request.

Let's be friendly with global warming and let the user sleep
until he may send a new request.

Let's make the caller wait until the last SSCH ends.

Signed-off-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
---
 drivers/s390/cio/vfio_ccw_fsm.c     | 4 ++++
 drivers/s390/cio/vfio_ccw_ops.c     | 6 ++++++
 drivers/s390/cio/vfio_ccw_private.h | 1 +
 3 files changed, 11 insertions(+)

diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
index c37052d..97b74a1 100644
--- a/drivers/s390/cio/vfio_ccw_fsm.c
+++ b/drivers/s390/cio/vfio_ccw_fsm.c
@@ -200,6 +200,10 @@ static int fsm_irq(struct vfio_ccw_private *private)
 
 	if (private->io_trigger)
 		eventfd_signal(private->io_trigger, 1);
+
+	if (private->io_completion)
+		complete(private->io_completion);
+
 	return VFIO_CCW_STATE_IDLE;
 }
 
diff --git a/drivers/s390/cio/vfio_ccw_ops.c b/drivers/s390/cio/vfio_ccw_ops.c
index b202e73..39beb6e 100644
--- a/drivers/s390/cio/vfio_ccw_ops.c
+++ b/drivers/s390/cio/vfio_ccw_ops.c
@@ -183,6 +183,7 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
 	struct vfio_ccw_private *private;
 	struct ccw_io_region *region;
 	union scsw *scsw;
+	DECLARE_COMPLETION_ONSTACK(completion);
 
 	if (*ppos + count > sizeof(*region))
 		return -EINVAL;
@@ -196,6 +197,11 @@ static ssize_t vfio_ccw_mdev_write(struct mdev_device *mdev,
 	scsw = (union scsw *) &region->scsw_area;
 	switch (scsw->cmd.fctl) {
 	case SCSW_FCTL_START_FUNC:
+		if (private->state == VFIO_CCW_STATE_BUSY) {
+			private->io_completion = &completion;
+			if (wait_for_completion_interruptible(&completion))
+				return -EINTR;
+		}
 		vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_SSCH_REQ);
 		break;
 	default:
diff --git a/drivers/s390/cio/vfio_ccw_private.h b/drivers/s390/cio/vfio_ccw_private.h
index ab5e37fa..e2e4f6d 100644
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -39,6 +39,7 @@ struct vfio_ccw_private {
 	struct subchannel	*sch;
 	int			state;
 	struct completion	*completion;
+	struct completion	*io_completion;
 	atomic_t		avail;
 	struct mdev_device	*mdev;
 	struct notifier_block	nb;
-- 
2.7.4