Updating dio_read_verify ZTS test (openzfs#16830)

There was a recent CI ZTS test failure on FreeBSD 14 for the
dio_read_verify test case. The failure reported there was no ARC reads
while the buffer wes being manipulated. All checksum verify errors for
Direct I/O reads are rerouted through the ARC, so there should be ARC
reads accounted for. In order to help debug any future failures of this
test case, the order of checks has been changed. First there is a check
for DIO verify failures for the reads and then ARC read counts are
checked.

This PR also contains general cleanup of the comments in the test
script.

Signed-off-by: Brian Atkinson <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>

Author: bwatkinson

tests/zfs-tests/tests/functional/direct/dio_read_verify.ksh

@@ -57,8 +57,6 @@ log_must  truncate -s $MINVDEVSIZE $DIO_VDEVS
 # while manipulating the buffer contents while the I/O is still in flight and
 # also that Direct I/O checksum verify failures and dio_verify_rd zevents are
 # reported.
-
-
 for type in "" "mirror" "raidz" "draid"; do
 	typeset vdev_type=$type
 	if [[ "${vdev_type}" == "" ]]; then
@@ -83,25 +81,28 @@ for type in "" "mirror" "raidz" "draid"; do
 	log_must manipulate_user_buffer -f "$mntpnt/direct-write.iso" \
 	    -n $NUMBLOCKS -b $BS -r
 
-	# Getting new Direct I/O and ARC Write counts.
+	# Getting new Direct I/O and ARC read counts.
 	curr_dio_rd=$(kstat_pool $TESTPOOL1 iostats.direct_read_count)
 	curr_arc_rd=$(kstat_pool $TESTPOOL1 iostats.arc_read_count)
 	total_dio_rd=$((curr_dio_rd - prev_dio_rd))
 	total_arc_rd=$((curr_arc_rd - prev_arc_rd))
 
-	log_note "Making sure there are no checksum errors with the ZPool"
-	log_must check_pool_status $TESTPOOL "errors" "No known data errors"
-
-	log_note "Making sure we have Direct I/O and ARC reads logged"
+	log_note "Making sure we have Direct I/O reads logged"
 	if [[ $total_dio_rd -lt 1 ]]; then
 		log_fail "No Direct I/O reads $total_dio_rd"
 	fi
+
+	log_note "Making sure we have Direct I/O read checksum verifies with ZPool"
+	check_dio_chksum_verify_failures "$TESTPOOL1" "$vdev_type" 1 "rd"
+
+	log_note "Making sure we have ARC reads logged"
 	if [[ $total_arc_rd -lt 1 ]]; then
 		log_fail "No ARC reads $total_arc_rd"
 	fi
 
-	log_note "Making sure we have Direct I/O write checksum verifies with ZPool"
-	check_dio_chksum_verify_failures "$TESTPOOL1" "$vdev_type" 1 "rd"
+	log_note "Making sure there are no checksum errors with the ZPool"
+	log_must check_pool_status $TESTPOOL "errors" "No known data errors"	
+
 	destroy_pool $TESTPOOL1
 done