[PATCH v3 4/6] uio_hv_generic: check that host supports monitor page

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In order for userspace application to signal host, it needs the
host to support the monitor page property. Check for the flag
and fail if this is not supported.

Signed-off-by: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
---
 drivers/uio/uio_hv_generic.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/uio/uio_hv_generic.c b/drivers/uio/uio_hv_generic.c
index dcd80aad9636..ee6d862ef4bd 100644
--- a/drivers/uio/uio_hv_generic.c
+++ b/drivers/uio/uio_hv_generic.c
@@ -133,6 +133,13 @@ hv_uio_probe(struct hv_device *dev,
 	if (ret)
 		goto fail;
 
+	/* Communicating with host has to be via shared memory not hypercall */
+	if (!dev->channel->offermsg.monitor_allocated) {
+		dev_err(&dev->device, "vmbus channel requires hypercall\n");
+		ret = -ENOTSUPP;
+		goto fail_close;
+	}
+
 	dev->channel->inbound.ring_buffer->interrupt_mask = 1;
 	set_channel_read_mode(dev->channel, HV_CALL_ISR);
 
-- 
2.15.1

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