[PATCH fstests v2] generic/755: test that inode's ctime is updated on unlink

[Jeff Layton <jlayton@kernel.org>]

I recently found and fixed a bug in btrfs where it wasn't updating the
citme on the target inode when unlinking [1]. Add a fstest for this.

[1]: https://lore.kernel.org/linux-btrfs/20240812-btrfs-unlink-v1-1-ee5c2ef538eb@kernel.org/

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
HCH suggested I roll a fstest for this problem that I found in btrfs the
other day. This just creates a file and a hardlink to it, statx's it and
then unlinks the hardlink and statx's it again. The ctimes are then
compared.
---
Changes in v2:
- Turn it into a shell script.
- Link to v1: https://lore.kernel.org/r/20240813-master-v1-1-862678cc4000@kernel.org
---
 tests/generic/755     | 38 ++++++++++++++++++++++++++++++++++++++
 tests/generic/755.out |  2 ++
 2 files changed, 40 insertions(+)

diff --git a/tests/generic/755 b/tests/generic/755
new file mode 100755
index 000000000000..68da3b20073f
--- /dev/null
+++ b/tests/generic/755
@@ -0,0 +1,38 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024, Jeff Layton <jlayton@kernel.org>
+#
+# FS QA Test No. 755
+#
+# Create a file, stat it and then unlink it. Does the ctime of the
+# target inode change?
+#
+. ./common/preamble
+_begin_fstest auto quick
+
+_require_test
+_require_test_program unlink-ctime
+
+testfile="$TEST_DIR/unlink-ctime1.$$"
+testlink="$TEST_DIR/unlink-ctime2.$$"
+
+rm -f $testfile $testlink
+touch $testfile
+ln $testfile $testlink
+
+time1=$(stat -c "%Z" $testfile)
+
+sleep 2
+unlink $testlink
+
+time2=$(stat -c "%Z" $testfile)
+
+unlink $testfile
+
+if [ $time1 -eq $time2 ]; then
+	echo "Target's ctime did not change after unlink!"
+fi
+
+echo Silence is golden
+status=0
+exit
diff --git a/tests/generic/755.out b/tests/generic/755.out
new file mode 100644
index 000000000000..7c9ea51cd298
--- /dev/null
+++ b/tests/generic/755.out
@@ -0,0 +1,2 @@
+QA output created by 755
+Silence is golden

---
base-commit: f5ada754d5838d29fd270257003d0d123a9d1cd2
change-id: 20240813-master-e3b46de630bd

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>