Add link count test for root inode

Add tests for
97aa3ba44("Fix link count of root inode when snapdir is visible")
as suggested in #8727.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@osnexus.com>
Closes #8732

tests/runfiles/linux.run

@@ -635,7 +635,7 @@ tests = ['filesystem_count', 'filesystem_limit', 'snapshot_count',
 tags = ['functional', 'limits']
 
 [tests/functional/link_count]
-tests = ['link_count_001']
+tests = ['link_count_001', 'link_count_root_inode.ksh']
 tags = ['functional', 'link_count']
 
 [tests/functional/migration]

tests/zfs-tests/tests/functional/link_count/Makefile.am

@@ -2,4 +2,5 @@ pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/link_count
 dist_pkgdata_SCRIPTS = \
 	cleanup.ksh \
 	setup.ksh \
-	link_count_001.ksh
+	link_count_001.ksh \
+	link_count_root_inode.ksh

tests/zfs-tests/tests/functional/link_count/link_count_root_inode.ksh

@@ -0,0 +1,119 @@
+#!/bin/ksh
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2019 by Tomohiro Kusumi. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+#
+# DESCRIPTION:
+# Verify root inode (directory) has correct link count.
+#
+# STRATEGY:
+# 1. Create pool and fs.
+# 2. Test link count of root inode.
+# 3. Create directories and test link count of root inode.
+# 4. Delete directories and test link count of root inode.
+# 5. Create regular file and test link count of root inode.
+# 6. Delete regular file and test link count of root inode.
+#
+
+function assert_link_count
+{
+	typeset dirpath="$1"
+	typeset value="$2"
+
+	log_must test "$(ls -ld $dirpath | awk '{ print $2 }')" == "$value"
+}
+
+verify_runnable "both"
+
+log_note "Verify root inode (directory) has correct link count."
+
+# Delete a directory from link_count_001.ksh.
+if [ -d "${TESTDIR}" -a -d "${TESTDIR}/tmp" ]; then
+	log_must rm -rf ${TESTDIR}/tmp
+fi
+
+#
+# Test with hidden '.zfs' directory.
+# This also tests general directories.
+#
+log_note "Testing with snapdir set to hidden (default)"
+
+for dst in $TESTPOOL $TESTPOOL/$TESTFS
+do
+	typeset mtpt=$(get_prop mountpoint $dst)
+	log_must zfs set snapdir=hidden $dst
+	log_must test -d "$mtpt/.zfs"
+	if test -n "$(ls $mtpt)"; then
+		ls $mtpt
+		log_note "$mtpt not empty, skipping"
+		continue
+	fi
+	assert_link_count $mtpt 2
+
+	log_must mkdir $mtpt/a
+	assert_link_count $mtpt 3
+	log_must rmdir $mtpt/a
+	assert_link_count $mtpt 2
+
+	log_must mkdir -p $mtpt/a/b
+	assert_link_count $mtpt 3
+	log_must rmdir $mtpt/a/b
+	log_must rmdir $mtpt/a
+	assert_link_count $mtpt 2
+
+	log_must touch $mtpt/a
+	assert_link_count $mtpt 2
+	log_must rm $mtpt/a
+	assert_link_count $mtpt 2
+done
+
+#
+# Test with visible '.zfs' directory.
+#
+log_note "Testing with snapdir set to visible"
+
+for dst in $TESTPOOL $TESTPOOL/$TESTFS
+do
+	typeset mtpt=$(get_prop mountpoint $dst)
+	log_must zfs set snapdir=visible $dst
+	log_must test -d "$mtpt/.zfs"
+	if test -n "$(ls $mtpt)"; then
+		ls $mtpt
+		log_note "$mtpt not empty, skipping"
+		continue
+	fi
+	assert_link_count $mtpt 3
+
+	log_must mkdir $mtpt/a
+	assert_link_count $mtpt 4
+	log_must rmdir $mtpt/a
+	assert_link_count $mtpt 3
+
+	log_must mkdir -p $mtpt/a/b
+	assert_link_count $mtpt 4
+	log_must rmdir $mtpt/a/b
+	log_must rmdir $mtpt/a
+	assert_link_count $mtpt 3
+
+	log_must touch $mtpt/a
+	assert_link_count $mtpt 3
+	log_must rm $mtpt/a
+	assert_link_count $mtpt 3
+done
+
+log_pass "Verify root inode (directory) has correct link count passed"