Restrict raidz faulted vdev count

Specifically, a child in a replacing vdev won't count when assessing
the dtl during a vdev_fault()

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Don Brady <don.brady@klarasystems.com>
Closes #16569

tests/runfiles/linux.run

@@ -125,7 +125,8 @@ tests = ['auto_offline_001_pos', 'auto_online_001_pos', 'auto_online_002_pos',
     'auto_replace_001_pos', 'auto_replace_002_pos', 'auto_spare_001_pos',
     'auto_spare_002_pos', 'auto_spare_multiple', 'auto_spare_ashift',
     'auto_spare_shared', 'decrypt_fault', 'decompress_fault',
-    'scrub_after_resilver', 'suspend_resume_single', 'zpool_status_-s']
+    'fault_limits', 'scrub_after_resilver', 'suspend_resume_single',
+    'zpool_status_-s']
 tags = ['functional', 'fault']
 
 [tests/functional/features/large_dnode:Linux]

tests/zfs-tests/tests/Makefile.am

@@ -1525,6 +1525,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/fault/cleanup.ksh \
 	functional/fault/decompress_fault.ksh \
 	functional/fault/decrypt_fault.ksh \
+	functional/fault/fault_limits.ksh \
 	functional/fault/scrub_after_resilver.ksh \
 	functional/fault/suspend_resume_single.ksh \
 	functional/fault/setup.ksh \

tests/zfs-tests/tests/functional/fault/fault_limits.ksh

@@ -0,0 +1,96 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+#
+# Copyright (c) 2024 by Klara, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/fault/fault.cfg
+
+#
+# DESCRIPTION: Verify that raidz children vdev fault count is restricted
+#
+# STRATEGY:
+# 1. Create a raidz2 or raidz3 pool and add some data to it
+# 2. Replace one of the child vdevs to create a replacing vdev
+# 3. While it is resilvering, attempt to fault disks
+# 4. Verify that less than parity count was faulted while replacing
+#
+
+TESTPOOL="fault-test-pool"
+PARITY=$((RANDOM%(2) + 2))
+VDEV_CNT=$((4 + (2 * PARITY)))
+VDEV_SIZ=512M
+
+function cleanup
+{
+	poolexists "$TESTPOOL" && log_must_busy zpool destroy "$TESTPOOL"
+
+	for i in {0..$((VDEV_CNT - 1))}; do
+		log_must rm -f "$TEST_BASE_DIR/dev-$i"
+	done
+}
+
+log_onexit cleanup
+log_assert "restricts raidz children vdev fault count"
+
+log_note "creating $VDEV_CNT vdevs for parity $PARITY test"
+typeset -a disks
+for i in {0..$((VDEV_CNT - 1))}; do
+	device=$TEST_BASE_DIR/dev-$i
+	log_must truncate -s $VDEV_SIZ $device
+	disks[${#disks[*]}+1]=$device
+done
+
+log_must zpool create -f ${TESTPOOL} raidz${PARITY} ${disks[1..$((VDEV_CNT - 1))]}
+
+# Add some data to the pool
+log_must zfs create $TESTPOOL/fs
+MNTPOINT="$(get_prop mountpoint $TESTPOOL/fs)"
+log_must fill_fs $MNTPOINT $PARITY 200 32768 1000 Z
+sync_pool $TESTPOOL
+
+# Replace the last child vdev to form a replacing vdev
+log_must zpool replace ${TESTPOOL} ${disks[$((VDEV_CNT - 1))]} ${disks[$VDEV_CNT]}
+# imediately offline replacement disk to keep replacing vdev around
+log_must zpool offline ${TESTPOOL} ${disks[$VDEV_CNT]}
+
+# Fault disks while a replacing vdev is still active
+for disk in ${disks[0..$PARITY]}; do
+	log_must zpool offline -tf ${TESTPOOL} $disk
+done
+
+zpool status $TESTPOOL
+
+# Count the faults that succeeded
+faults=0
+for disk in ${disks[0..$PARITY]}; do
+	state=$(zpool get -H -o value state ${TESTPOOL} ${disk})
+	if [ "$state" = "FAULTED" ] ; then
+		((faults=faults+1))
+	fi
+done
+
+log_must test "$faults" -lt "$PARITY"
+log_must test "$faults" -gt 0
+
+log_pass "restricts raidz children vdev fault count"