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

[Pierre Morel]

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 <pmo...@linux.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