linux-kernel - [PATCH 5/5] kheaders: explain why include/config/autoconf.h is excluded from md5sum

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Date:   Tue,  8 Oct 2019 21:05:56 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-kbuild@...r.kernel.org
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] kheaders: explain why include/config/autoconf.h is excluded from md5sum

This comment block explains why include/generated/compile.h is omitted,
but nothing about include/generated/autoconf.h, which might be more
difficult to understand. Add more comments.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 kernel/gen_kheaders.sh | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
index 6c5f88f3ca2d..b229a84693e5 100755
--- a/kernel/gen_kheaders.sh
+++ b/kernel/gen_kheaders.sh
@@ -32,8 +32,15 @@ fi
 all_dirs="$all_dirs $dir_list"
 
 # include/generated/compile.h is ignored because it is touched even when none
-# of the source files changed. This causes pointless regeneration, so let us
-# ignore them for md5 calculation.
+# of the source files changed.
+#
+# When Kconfig regenerates include/generated/autoconf.h, its timestamp is
+# updated, but the contents might be still the same. When any CONFIG option is
+# changed, Kconfig touches the corresponding timestamp file include/config/*.h.
+# Hence, the md5sum detects the configuration change anyway. We do not need to
+# check include/generated/autoconf.h explicitly.
+#
+# Ignore them for md5 calculation to avoid pointless regeneration.
 headers_md5="$(find $all_dirs -name "*.h"			|
 		grep -v "include/generated/compile.h"	|
 		grep -v "include/generated/autoconf.h"	|
-- 
2.17.1