#! /bin/bash
# SPDX-License-Identifier: GPL-2.0
# Copyright (C) 2017 CTERA Networks. All Rights Reserved.
#
# FS QA Test 034
#
# Test overlay nlink when adding lower hardlinks.
#
# nlink of overlay inode could be dropped indefinitely by adding
# unaccounted lower hardlinks underneath a mounted overlay and
# trying to remove them.
#
# The simplest way to understand this test is this:
# Imagine that you have a tool (e.g. xfs_db) with which you can add
# hardlinks, without changing the value of nlink stored on-disk for the
# inode. This is exactly what this test does when it adds lower hardlinks
# underneath a mounted overlay.
#
# Commit 5f8415d6b87e ("ovl: persistent overlay inode nlink for indexed
# inodes") fixes this issue, although the issue was never exposed in any
# released kernel.
#
# With overlayfs indexed copy up and without the fix, the test triggers
# WARN_ON(inode->i_nlink == 0) in drop_link().
#
seq=`basename $0`
seqres=$RESULT_DIR/$seq
echo "QA output created by $seq"

tmp=/tmp/$$
status=1	# failure is the default!
trap "_cleanup; exit \$status" 0 1 2 3 15

_cleanup()
{
	cd /
	rm -f $tmp.*
}

# get standard environment, filters and checks
. ./common/rc
. ./common/filter

# remove previous $seqres.full before test
rm -f $seqres.full

# real QA test starts here
_supported_fs overlay
_require_scratch
# Without overlay index feature hardlinks are broken on copy up
_require_scratch_feature index

lowerdir=$OVL_BASE_SCRATCH_MNT/$OVL_LOWER
workdir=$OVL_BASE_SCRATCH_MNT/$OVL_WORK

# Remove all files from previous tests
_scratch_mkfs

# Create lower hardlink
mkdir -p $lowerdir
touch $lowerdir/0
ln $lowerdir/0 $lowerdir/1

# Enable overlay index feature to prevent breaking hardlinks on copy up
_scratch_mount -o index=on

# Copy up lower hardlink - overlay inode nlink 2 is copied from lower
touch $SCRATCH_MNT/0

# Add lower hardlinks while overlay is mounted - overlay inode nlink
# is not being updated
ln $lowerdir/0 $lowerdir/2
ln $lowerdir/0 $lowerdir/3

# Unlink the 2 un-accounted lower hardlinks - overlay inode nlinks
# drops 2 and may reach 0 if the situation is not detected
rm $SCRATCH_MNT/2
rm $SCRATCH_MNT/3

# Check if getting ENOENT when trying to link !I_LINKABLE with nlink 0
ln $SCRATCH_MNT/0 $SCRATCH_MNT/4

# Unlink all hardlinks - if overlay inode nlink is 0, this will trigger
# WARN_ON() in drop_nlink()
rm $SCRATCH_MNT/0
rm $SCRATCH_MNT/1
rm $SCRATCH_MNT/4

# Verify that orphan index is cleaned on mount
_scratch_cycle_mount index=on
# With nfs_export=on index will contain a whiteout index entry, so allow
# chardev entries in index dir.
find $workdir/index -mindepth 1 -type c -o -print

echo "Silence is golden"
status=0
exit