Fix dbufstats_001_pos

Implement a new helper within_tolerance to test if a value
is within range of a target.

Because the dbufstats and dbufs kstat file are being read
at slightly different times, it is possible for stats to be
slightly off. Use within_tolerance to determine if the value
is "close enough" to the target.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Giuseppe Di Natale <[email protected]>
Closes #7239 
Closes #7266 

2 files changed, 28 insertions, 4 deletions

diff --git a/tests/zfs-tests/include/math.shlib b/tests/zfs-tests/include/math.shlib
index 66658cdda..0c3508ec2 100644
--- a/tests/zfs-tests/include/math.shlib
+++ b/tests/zfs-tests/include/math.shlib
@@ -43,6 +43,29 @@ function within_percent
 }
 
 #
+# Return 0 if value is within +/-tolerance of target.
+# Return 1 if value exceeds our tolerance.
+# For use like this:
+#
+# Do $action if value is within the tolerance from target passed in:
+#	within_tolerance VAL TAR TOL && $action
+# Do $action if value surpasses the tolerance from target passed in:
+#	within_tolerance VAL TAR TOL || $action
+#
+function within_tolerance #value #target #tolerance
+{
+	typeset val=$1
+	typeset target=$2
+	typeset tol=$3
+
+	typeset diff=$((abs(val - target)))
+	log_note "Checking if $val is within +/-$tol of $target (diff: $diff)"
+	((diff <= tol)) && return 0
+
+	return 1
+}
+
+#
 # Return 0 if the human readable string of the form <value>[suffix] can
 # be converted to bytes.  Allow suffixes are shown in the table below.
 #
diff --git a/tests/zfs-tests/tests/functional/arc/dbufstats_001_pos.ksh b/tests/zfs-tests/tests/functional/arc/dbufstats_001_pos.ksh
index 97d370b1f..7813d263d 100755
--- a/tests/zfs-tests/tests/functional/arc/dbufstats_001_pos.ksh
+++ b/tests/zfs-tests/tests/functional/arc/dbufstats_001_pos.ksh
@@ -55,10 +55,11 @@ function testdbufstat # stat_name dbufstat_filter
 
         [[ -n "$2" ]] && filter="-F $2"
 
-        verify_eq \
-	    $(grep -w "$name" "$DBUFSTATS_FILE" | awk '{ print $3 }') \
-	    $(dbufstat.py -bxn -i "$DBUFS_FILE" "$filter" | wc -l) \
-	    "$name"
+	from_dbufstat=$(grep -w "$name" "$DBUFSTATS_FILE" | awk '{ print $3 }')
+	from_dbufs=$(dbufstat.py -bxn -i "$DBUFS_FILE" "$filter" | wc -l)
+
+	within_tolerance $from_dbufstat $from_dbufs 5 \
+	    || log_fail "Stat $name exceeded tolerance"
 }
 
 verify_runnable "both"