tools/golang/xenlight: Rework gengotypes.py and generation of *.gen.go

gengotypes.py creates both "types.gen.go" and "helpers.gen.go", but
make can start gengotypes.py twice. Rework the rules so that
gengotypes.py is executed only once.

Also, add the ability to provide a path to tell gengotypes.py where to
put the files. This doesn't matter yet but it will when for example
the script will be run from tools/ to generate the targets.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

tools/golang/xenlight/Makefile

@@ -15,8 +15,10 @@ all: build
 
 GOXL_GEN_FILES = types.gen.go helpers.gen.go
 
-%.gen.go: gengotypes.py $(LIBXL_SRC_DIR)/libxl_types.idl $(LIBXL_SRC_DIR)/idl.py
-	LIBXL_SRC_DIR=$(LIBXL_SRC_DIR) $(PYTHON) gengotypes.py $(LIBXL_SRC_DIR)/libxl_types.idl
+# This exploits the 'multi-target pattern rule' trick.
+# gentypes.py should be executed only once to make all the targets.
+$(subst .gen.,.%.,$(GOXL_GEN_FILES)): gengotypes.py $(LIBXL_SRC_DIR)/libxl_types.idl $(LIBXL_SRC_DIR)/idl.py
+	LIBXL_SRC_DIR=$(LIBXL_SRC_DIR) $(PYTHON) gengotypes.py $(LIBXL_SRC_DIR)/libxl_types.idl $(@D)/types.gen.go $(@D)/helpers.gen.go
 
 # Go will do its own dependency checking, and not actuall go through
 # with the build if none of the input files have changed.

tools/golang/xenlight/gengotypes.py

@@ -1,5 +1,7 @@
 #!/usr/bin/python
 
+from __future__ import print_function
+
 import os
 import sys
 
@@ -723,7 +725,13 @@ def xenlight_golang_fmt_name(name, exported = True):
     return words[0] + ''.join(x.title() for x in words[1:])
 
 if __name__ == '__main__':
+    if len(sys.argv) != 4:
+        print("Usage: gengotypes.py <idl> <types.gen.go> <helpers.gen.go>", file=sys.stderr)
+        sys.exit(1)
+
     idlname = sys.argv[1]
+    path_types = sys.argv[2]
+    path_helpers = sys.argv[3]
 
     (builtins, types) = idl.parse(idlname)
 
@@ -735,9 +743,11 @@ if __name__ == '__main__':
 // source: {}
 
 """.format(os.path.basename(sys.argv[0]),
-           ' '.join([os.path.basename(a) for a in sys.argv[1:]]))
+           os.path.basename(sys.argv[1]))
 
     xenlight_golang_generate_types(types=types,
+                                   path=path_types,
                                    comment=header_comment)
     xenlight_golang_generate_helpers(types=types,
+                                     path=path_helpers,
                                      comment=header_comment)