IB/core: Introduce counters read verb

The user supplies counters instance and a reference to an output array of
uint64_t. The driver reads the hardware counters values and writes them
to the output index location in the user supplied array. All counters
values are represented as uint64_t types.

To be able to successfully read the data the counters must be first bound
to an IB object.

Downstream patches will present binding method for flow counters.

Reviewed-by: Yishai Hadas <[e-mail]>
Signed-off-by: Raed Salem <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

include/rdma/ib_verbs.h

···
 	atomic_t	usecnt;
 };
 
+enum ib_read_counters_flags {
+	/* prefer read values from driver cache */
+	IB_READ_COUNTERS_ATTR_PREFER_CACHED = 1 << 0,
+};
+
+struct ib_counters_read_attr {
+	u64	*counters_buff;
+	u32	ncounters;
+	u32	flags; /* use enum ib_read_counters_flags */
+};
+
 struct uverbs_attr_bundle;
 
 struct ib_device {
···
 	struct ib_counters *	(*create_counters)(struct ib_device *device,
 						   struct uverbs_attr_bundle *attrs);
 	int	(*destroy_counters)(struct ib_counters	*counters);
+	int	(*read_counters)(struct ib_counters *counters,
+				 struct ib_counters_read_attr *counters_read_attr,
+				 struct uverbs_attr_bundle *attrs);
 
 	/**
 	 * rdma netdev operation