cxl/uapi: Add warning on CXL command enum

The CXL command enum is exported to user space and must maintain
backwards compatibility.

Add comment that new defines must be added to the end of the list.

Suggested-by: Dan Williams <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Reviewed-by: Dave Jiang <[email protected]>
Signed-off-by: Ira Weiny <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dan Williams <[email protected]>

Author: weiny2

include/uapi/linux/cxl_mem.h

@@ -19,6 +19,10 @@
 #define CXL_MEM_QUERY_COMMANDS _IOR(0xCE, 1, struct cxl_mem_query_commands)
 #define CXL_MEM_SEND_COMMAND _IOWR(0xCE, 2, struct cxl_send_command)
 
+/*
+ * NOTE: New defines must be added to the end of the list to preserve
+ * compatibility because this enum is exported to user space.
+ */
 #define CXL_CMDS                                                          \
 	___C(INVALID, "Invalid Command"),                                 \
 	___C(IDENTIFY, "Identify Command"),                               \