From 817f53312678153037928344823e2a1f11fd3a69 Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <dvlasenk@redhat.com>
Date: Thu, 5 Dec 2019 13:44:41 +0100
Subject: [PATCH] kmod.prov: fix and speed it up

For kernel builds, /usr/lib/rpm/kmod.prov is fork+execed by rpmbuild
in "Processing files:" step about 8000 times, single-threaded,
with cumulative run time of ~2 minutes.

Speed up this script, by avoiding additional fork+execing.

Tested to work, observed speedup: almost exactly 2 times faster.

While verifying correctness, noticed that old script was buggy -
it was generating a bogus "Provides:" item - kmod(modules.builtin.modinfo),
because the logic in script was filtering for */*.ko files and
for */modules.builtin* files, and wasn't prepared for
the existence of */modules.builtin.modinfo file.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
---
 kmod.prov | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/kmod.prov b/kmod.prov
index f02d8a0..bbe5aa0 100644
--- a/kmod.prov
+++ b/kmod.prov
@@ -1,17 +1,28 @@
 #!/bin/sh +x
+# Kernel build can have many thousands of modules.
+# kmod.prov is run for every one of them.
+# Try to make this script run as fast as we can.
+# For example, use shell string ops instead of external programs
+# where possible.
 
 IFS=$'\n'
 
-for i in $(grep -E '(/lib/modules/.*\.ko|/lib/modules/.*/modules.builtin)');
-do
-	kmod=$(basename $i | sed -e 's/.[xg]z//');
+read -r fname || exit
 
-	if [ $kmod == "modules.builtin" ]; then
-		for j in $(cat $i); do
-			j=$(basename $j);
-			echo "kmod($j)"
-		done
-	else
-		echo "kmod($kmod)"
-	fi
-done
+# Only process files from .../lib/modules/... subtree
+[ "${fname#*/lib/modules/*}" != "$fname" ] || exit 0
+
+kmod=${fname##*/}  # like basename, but faster
+
+if [ "$kmod" = "modules.builtin" ]; then
+        for j in $(cat -- "$fname"); do
+                echo "kmod(${j##*/})"
+        done
+        exit 0
+fi
+
+kmod=${kmod%.gz}
+kmod=${kmod%.xz}
+if [ "${kmod%.ko}" != "$kmod" ]; then
+        echo "kmod($kmod)"
+fi