backup-files: Quick exit when unlinking is not needed

The "check for hard links" use case is almost always a no-op. Check
if any work is needed at all first, and only if this is the case,
walk the list of files and unlink the faulty files. This approach
results in a huge performance gain in the most common case, and a
very small performance loss in the uncommon case.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Raphael Hertzog <hertzog@debian.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/quilt/scripts/backup-files.in b/quilt/scripts/backup-files.in
index 5ee3c4f..8a8fb6c 100644
--- a/quilt/scripts/backup-files.in
+++ b/quilt/scripts/backup-files.in
@@ -187,6 +187,13 @@ noop_nolinks()
 	fi
 }
 
+# Test if some backed up files have a link count greater than 1
+some_files_have_links()
+{
+	(cd "$OPT_PREFIX" && find . -type f -print0) \
+	| xargs -0 stat @STAT_HARDLINK@ 2> /dev/null | grep -qv '^1$'
+}
+
 
 ECHO=echo
 while [ $# -gt 0 ]; do
@@ -256,6 +263,13 @@ if [ "$1" = - ]; then
 		exit
 	fi
 
+	# We typically expect the link count of backed up files to be 1
+	# already, so check quickly that this is the case, and only if not,
+	# take the slow path and walk the file list in search of files to fix.
+	if [ "$OPT_WHAT" = noop_nolinks ] && ! some_files_have_links; then
+		exit
+	fi
+
 	find "$OPT_PREFIX" -type f -print \
 	| while read
 	do