generic: test XFS forkoff miscalcution on 32-bit platform

There is a regression that recent XFS_LITINO(mp) update causes
xfs_attr_shortform_bytesfit() returns maxforkoff rather than 0.

Therefore, one result is
  "ASSERT(new_size <= XFS_IFORK_SIZE(ip, whichfork));"

Add a regression test in fstests generic to look after that since
the testcase itself isn't xfs-specific.

Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/618

@@ -0,0 +1,75 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2020 Red Hat, Inc. All Rights Reserved.
+#
+# FS QA Test 618
+#
+# Verify that forkoff can be returned as 0 properly if it isn't
+# able to fit inline for XFS.
+# However, this test is fs-neutral and can be done quickly so
+# leave it in generic
+# This test verifies the problem fixed in kernel with commit
+# ada49d64fb35 ("xfs: fix forkoff miscalculation related to XFS_LITINO(mp)")
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+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
+. ./common/attr
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+_supported_fs generic
+_require_scratch
+_require_attrs user
+
+if [ $FSTYP = "xfs" ]; then
+	# avoid crashing the system if possible
+	_require_no_xfs_bug_on_assert
+
+	# Use fixed inode size 512, so both v4 and v5 can be tested,
+	# and also make sure the issue can be triggered if the default
+	# inode size is changed later.
+	MKFS_OPTIONS="$MKFS_OPTIONS -i size=512"
+fi
+
+_scratch_mkfs > $seqres.full 2>&1
+_scratch_mount
+
+localfile="${SCRATCH_MNT}/testfile"
+touch $localfile
+
+# value cannot exceed XFS_ATTR_SF_ENTSIZE_MAX (256) or it will turn into leaf
+# form directly; the following combination can trigger the issue for both v4
+# (XFS_LITINO = 412) & v5 (XFS_LITINO = 336) fses, in details the 2nd setattr
+# causes an integer underflow that is incorrectly typecast, leading to the
+# assert triggering.
+"${SETFATTR_PROG}" -n user.0 -v "`seq 0 80`" "${localfile}"
+"${SETFATTR_PROG}" -n user.1 -v "`seq 0 80`" "${localfile}"
+
+# Make sure that changes are written to disk
+_scratch_cycle_mount
+
+# getfattr won't succeed with the expected result if fails
+_getfattr --absolute-names -ebase64 -d $localfile | tail -n +2 | sort
+
+_scratch_unmount
+status=0
+exit

tests/generic/618.out

@@ -0,0 +1,4 @@
+QA output created by 618
+
+user.0=0sMAoxCjIKMwo0CjUKNgo3CjgKOQoxMAoxMQoxMgoxMwoxNAoxNQoxNgoxNwoxOAoxOQoyMAoyMQoyMgoyMwoyNAoyNQoyNgoyNwoyOAoyOQozMAozMQozMgozMwozNAozNQozNgozNwozOAozOQo0MAo0MQo0Mgo0Mwo0NAo0NQo0Ngo0Nwo0OAo0OQo1MAo1MQo1Mgo1Mwo1NAo1NQo1Ngo1Nwo1OAo1OQo2MAo2MQo2Mgo2Mwo2NAo2NQo2Ngo2Nwo2OAo2OQo3MAo3MQo3Mgo3Mwo3NAo3NQo3Ngo3Nwo3OAo3OQo4MA==
+user.1=0sMAoxCjIKMwo0CjUKNgo3CjgKOQoxMAoxMQoxMgoxMwoxNAoxNQoxNgoxNwoxOAoxOQoyMAoyMQoyMgoyMwoyNAoyNQoyNgoyNwoyOAoyOQozMAozMQozMgozMwozNAozNQozNgozNwozOAozOQo0MAo0MQo0Mgo0Mwo0NAo0NQo0Ngo0Nwo0OAo0OQo1MAo1MQo1Mgo1Mwo1NAo1NQo1Ngo1Nwo1OAo1OQo2MAo2MQo2Mgo2Mwo2NAo2NQo2Ngo2Nwo2OAo2OQo3MAo3MQo3Mgo3Mwo3NAo3NQo3Ngo3Nwo3OAo3OQo4MA==

tests/generic/group

@@ -620,3 +620,4 @@
 615 auto rw
 616 auto rw io_uring stress
 617 auto rw io_uring stress
+618 auto quick attr