RDMA/core: Add helper function to retrieve driver gid context from gid attr

Adding a helper function to retrieve the driver gid context from the gid
attr.

Link: https://lore.kernel.org/r/1582107594-5180-2-git-send-email-selvin.xavier@broadcom.comSuggested-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/cache.c

@@ -972,6 +972,23 @@ int rdma_query_gid(struct ib_device *device, u8 port_num,
 }
 EXPORT_SYMBOL(rdma_query_gid);
 
+/**
+ * rdma_read_gid_hw_context - Read the HW GID context from GID attribute
+ * @attr:		Potinter to the GID attribute
+ *
+ * rdma_read_gid_hw_context() reads the drivers GID HW context corresponding
+ * to the SGID attr. Callers are required to already be holding the reference
+ * to an existing GID entry.
+ *
+ * Returns the HW GID context
+ *
+ */
+void *rdma_read_gid_hw_context(const struct ib_gid_attr *attr)
+{
+	return container_of(attr, struct ib_gid_table_entry, attr)->context;
+}
+EXPORT_SYMBOL(rdma_read_gid_hw_context);
+
 /**
  * rdma_find_gid - Returns SGID attributes if the matching GID is found.
  * @device: The device to query.

include/rdma/ib_cache.h

@@ -39,6 +39,7 @@
 
 int rdma_query_gid(struct ib_device *device, u8 port_num, int index,
 		   union ib_gid *gid);
+void *rdma_read_gid_hw_context(const struct ib_gid_attr *attr);
 const struct ib_gid_attr *rdma_find_gid(struct ib_device *device,
 					const union ib_gid *gid,
 					enum ib_gid_type gid_type,