gen_build_files.sh: rewrite with sed

The shell parsing of files is incredibly slow on many systems.  With
one report, the process was taking a minute or two which made people
thing the build was hung.  So rewrite the craziness with sed and proper
shell functions.  On an idle system, this cut the runtime by half.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

1 files changed, 47 insertions, 53 deletions

diff --git a/scripts/gen_build_files.sh b/scripts/gen_build_files.sh
index 09a95b5..1c1edcc 100755
--- a/scripts/gen_build_files.sh
+++ b/scripts/gen_build_files.sh
@@ -9,43 +9,54 @@ mkdir include 2>/dev/null
 
 srctree="$1"
 
+status() { printf '  %-8s%s\n' "$1" "$2"; }
+gen() { status "GEN" "$@"; }
+chk() { status "CHK" "$@"; }
+
+generate()
+{
+	local src="$1" dst="$2" header="$3" insert="$4"
+	#chk "${dst}"
+	(
+		echo "${header}"
+		if grep -qs '^INSERT$' "${src}"; then
+			sed -n '1,/^INSERT$/p' "${src}"
+			echo "${insert}"
+			sed -n '/^INSERT$/,$p' "${src}"
+		else
+			if [ -n "${insert}" ]; then
+				echo "ERROR: INSERT line missing in: ${src}" 1>&2
+			fi
+			cat "${src}"
+		fi
+	) | sed '/^INSERT$/d' > "${dst}.tmp"
+	if ! cmp -s "${dst}" "${dst}.tmp"; then
+		gen "${dst}"
+		mv "${dst}.tmp" "${dst}"
+	else
+		rm -f "${dst}.tmp"
+	fi
+}
+
 # (Re)generate include/applets.h
-src="$srctree/include/applets.src.h"
-dst="include/applets.h"
 s=`sed -n 's@^//applet:@@p' -- "$srctree"/*/*.c "$srctree"/*/*/*.c`
-old=`cat "$dst" 2>/dev/null`
-# Why "IFS='' read -r REPLY"??
-# This atrocity is needed to read lines without mangling.
-# IFS='' prevents whitespace trimming,
-# -r suppresses backslash handling.
-new=`echo "/* DO NOT EDIT. This file is generated from applets.src.h */"
-while IFS='' read -r REPLY; do
-	test x"$REPLY" = x"INSERT" && REPLY="$s"
-	printf "%s\n" "$REPLY"
-done <"$src"`
-if test x"$new" != x"$old"; then
-	echo "  GEN     $dst"
-	printf "%s\n" "$new" >"$dst"
-fi
+generate \
+	"$srctree/include/applets.src.h" \
+	"include/applets.h" \
+	"/* DO NOT EDIT. This file is generated from applets.src.h */" \
+	"${s}"
 
 # (Re)generate include/usage.h
-src="$srctree/include/usage.src.h"
-dst="include/usage.h"
 # We add line continuation backslash after each line,
 # and insert empty line before each line which doesn't start
 # with space or tab
 # (note: we need to use \\\\ because of ``)
 s=`sed -n -e 's@^//usage:\([ \t].*\)$@\1 \\\\@p' -e 's@^//usage:\([^ \t].*\)$@\n\1 \\\\@p' -- "$srctree"/*/*.c "$srctree"/*/*/*.c`
-old=`cat "$dst" 2>/dev/null`
-new=`echo "/* DO NOT EDIT. This file is generated from usage.src.h */"
-while IFS='' read -r REPLY; do
-	test x"$REPLY" = x"INSERT" && REPLY="$s"
-	printf "%s\n" "$REPLY"
-done <"$src"`
-if test x"$new" != x"$old"; then
-	echo "  GEN     $dst"
-	printf "%s\n" "$new" >"$dst"
-fi
+generate \
+	"$srctree/include/usage.src.h" \
+	"include/usage.h" \
+	"/* DO NOT EDIT. This file is generated from usage.src.h */" \
+	"${s}"
 
 # (Re)generate */Kbuild and */Config.in
 { cd -- "$srctree" && find . -type d; } | while read -r d; do
@@ -55,42 +66,25 @@ fi
 	dst="$d/Kbuild"
 	if test -f "$src"; then
 		mkdir -p -- "$d" 2>/dev/null
-		#echo "  CHK     $dst"
 
 		s=`sed -n 's@^//kbuild:@@p' -- "$srctree/$d"/*.c`
-
-		old=`cat "$dst" 2>/dev/null`
-		new=`echo "# DO NOT EDIT. This file is generated from Kbuild.src"
-		while IFS='' read -r REPLY; do
-			test x"$REPLY" = x"INSERT" && REPLY="$s"
-			printf "%s\n" "$REPLY"
-		done <"$src"`
-		if test x"$new" != x"$old"; then
-			echo "  GEN     $dst"
-			printf "%s\n" "$new" >"$dst"
-		fi
+		generate \
+			"${src}" "${dst}" \
+			"# DO NOT EDIT. This file is generated from Kbuild.src" \
+			"${s}"
 	fi
 
 	src="$srctree/$d/Config.src"
 	dst="$d/Config.in"
 	if test -f "$src"; then
 		mkdir -p -- "$d" 2>/dev/null
-		#echo "  CHK     $dst"
 
 		s=`sed -n 's@^//config:@@p' -- "$srctree/$d"/*.c`
-
-		old=`cat "$dst" 2>/dev/null`
-		new=`echo "# DO NOT EDIT. This file is generated from Config.src"
-		while IFS='' read -r REPLY; do
-			test x"$REPLY" = x"INSERT" && REPLY="$s"
-			printf "%s\n" "$REPLY"
-		done <"$src"`
-		if test x"$new" != x"$old"; then
-			echo "  GEN     $dst"
-			printf "%s\n" "$new" >"$dst"
-		fi
+		generate \
+			"${src}" "${dst}" \
+			"# DO NOT EDIT. This file is generated from Config.src" \
+			"${s}"
 	fi
 done
 
-# Last read failed. This is normal. Don't exit with its error code:
 exit 0