Add display of checksums to zdb -R

The function zdb_read_block (zdb -R) was always intended to have a :c
flag which would read the DVA and length supplied by the user, and
display the checksum. Since we don't know which checksum goes with
the data, we should calculate and display them all.

For each checksum in the table, read in the data at the supplied
DVA:length, calculate the checksum, and display it. Update the man
page and create a zfs test for the new feature.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Closes #9607

tests/zfs-tests/tests/functional/cli_root/zdb/Makefile.am

@@ -5,4 +5,5 @@ dist_pkgdata_SCRIPTS = \
 	zdb_003_pos.ksh \
 	zdb_004_pos.ksh \
 	zdb_005_pos.ksh \
-	zdb_006_pos.ksh
+	zdb_006_pos.ksh \
+	zdb_checksum.ksh

tests/zfs-tests/tests/functional/cli_root/zdb/zdb_checksum.ksh

@@ -0,0 +1,64 @@
+#!/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 Datto, Inc. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+#
+# Description:
+# zdb -c will display the same checksum as -ddddddbbbbbb
+#
+# Strategy:
+# 1. Create a pool
+# 2. Write some data to a file
+# 3. Run zdb -ddddddbbbbbb against the file
+# 4. Record the checksum and DVA of L0 block 0
+# 5. Run zdb -R with :c flag and match the checksum
+
+
+function cleanup
+{
+	datasetexists $TESTPOOL && destroy_pool $TESTPOOL
+}
+
+log_assert "Verify zdb -R generates the correct checksum."
+log_onexit cleanup
+init_data=$TESTDIR/file1
+write_count=8
+blksize=131072
+verify_runnable "global"
+verify_disk_count "$DISKS" 2
+
+default_mirror_setup_noexit $DISKS
+file_write -o create -w -f $init_data -b $blksize -c $write_count
+
+# get object number of file
+listing=$(ls -i $init_data)
+set -A array $listing
+obj=${array[0]}
+log_note "file $init_data has object number $obj"
+
+output=$(zdb -ddddddbbbbbb $TESTPOOL/$TESTFS $obj 2> /dev/null \
+    |grep -m 1 "L0 DVA" |head -n1)
+dva=$(grep -oP 'DVA\[0\]=<\K.*?(?=>)' <<< "$output")
+log_note "block 0 of $init_data has a DVA of $dva"
+cksum_expected=$(grep -oP '(?<=cksum=)[ A-Za-z0-9:]*' <<< "$output")
+log_note "expecting cksum $cksum_expected"
+output=$(zdb -R $TESTPOOL $dva:c 2> /dev/null)
+result=$(grep $cksum_expected <<< "$output")
+(( $? != 0 )) && log_fail "zdb -R failed to print the correct checksum"
+
+log_pass "zdb -R generates the correct checksum"