make: add checkpatch to Makefile

This automatically retrieves the checkpatch.pl script from the
Linux kernel repo and runs it to check the modified or untracked
source files in the current repo.

The command can be invoke with:
$ make checkpatch

Signed-off-by: Martin Belanger <[email protected]>

Makefile

@@ -48,3 +48,19 @@ rpm: ${BUILD-DIR}
 	tar rf libnvme.tar ${BUILD-DIR}/libnvme.spec
 	gzip -f -9 libnvme.tar
 	rpmbuild -ta libnvme.tar.gz -v
+
+# Retrieve and Invoke Linux kernel's checkpatch script on modified source files
+ifeq (checkpatch,$(strip $(filter $(MAKECMDGOALS),checkpatch)))
+  MODIFIED-FILES := $(strip $(shell ./scripts/get-modified-src-files.py))
+endif
+
+${BUILD-DIR}/checkpatch.pl: ${BUILD-DIR}
+	wget "https://raw.githubusercontent.com/torvalds/linux/master/scripts/checkpatch.pl" -O $@
+	chmod +x $@
+
+.PHONY: checkpatch
+checkpatch: ${BUILD-DIR}/checkpatch.pl
+ifneq (,${MODIFIED-FILES})
+	${BUILD-DIR}/checkpatch.pl -no-tree ${MODIFIED-FILES}
+endif
+

scripts/get-modified-src-files.py

@@ -0,0 +1,25 @@
+#!/usr/bin/python3
+# SPDX-License-Identifier: LGPL-2.1-or-later
+#
+# This file is part of libnvme.
+# Copyright (c) 2023 Dell Inc.
+#
+# Authors: Martin Belanger <[email protected]>
+
+"""List source files in current git repo that have been modified or are new (untracked)"""
+
+import shutil
+import subprocess
+
+GIT = shutil.which("git")
+SRC_FILES = (".c", ".h", ".cpp", ".cc")
+
+cmd = f"{GIT} ls-files --modified --others --exclude-standard"
+p = subprocess.run(
+    cmd, stdout=subprocess.PIPE, check=True, universal_newlines=True, shell=True
+)
+
+modified_files = p.stdout.splitlines()
+modified_src_files = [fname for fname in modified_files if fname.endswith(SRC_FILES)]
+
+print(" ".join(modified_src_files))