Drivers: hv: vmbus: Introduce functions for estimating room in the ring buffer

Introduce separate functions for estimating how much can be read from
and written to the ring buffer.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/hyperv.h

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index aa0fadc..66226ce 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -151,6 +151,33 @@
 	*read = dsize - *write;
 }
 
+static inline u32 hv_get_bytes_to_read(struct hv_ring_buffer_info *rbi)
+{
+	u32 read_loc, write_loc, dsize, read;
+
+	dsize = rbi->ring_datasize;
+	read_loc = rbi->ring_buffer->read_index;
+	write_loc = READ_ONCE(rbi->ring_buffer->write_index);
+
+	read = write_loc >= read_loc ? (write_loc - read_loc) :
+		(dsize - read_loc) + write_loc;
+
+	return read;
+}
+
+static inline u32 hv_get_bytes_to_write(struct hv_ring_buffer_info *rbi)
+{
+	u32 read_loc, write_loc, dsize, write;
+
+	dsize = rbi->ring_datasize;
+	read_loc = READ_ONCE(rbi->ring_buffer->read_index);
+	write_loc = rbi->ring_buffer->write_index;
+
+	write = write_loc >= read_loc ? dsize - (write_loc - read_loc) :
+		read_loc - write_loc;
+	return write;
+}
+
 /*
  * VMBUS version is 32 bit entity broken up into
  * two 16 bit quantities: major_number. minor_number.