mdconfig_test: determine page size at run time rather than assuming 4k

Sponsored by:	Netflix
Reviewed by:	imp
Differential Revision:	https://reviews.freebsd.org/D52736

sbin/mdconfig/tests/mdconfig_test.sh

@@ -274,22 +274,23 @@ attach_size_rounddown()
 attach_size_rounddown_body()
 {
 	local md
-	local ss=8192
+	local pgsz=$(pagesize)
-	local ms=$(($ss + 4096))
+	local ss=$(($pgsz * 2))
-	local ms2=$((2 * $ss + 4096))
+	local ms=$(($ss + $pgsz))
+	local ms2=$((2 * $ss + $pgsz))
 
-	# Use a sector size that's a likely multiple of PAGE_SIZE, as md(4)
+	# Use a sector size that's a multiple of the kernel page size, as md(4)
 	# expects that for swap MDs.
 	atf_check -s exit:0 -o save:mdconfig.out -e empty \
 	    -x "mdconfig -a -t swap -S $ss -s ${ms}b"
 	md=$(cat mdconfig.out)
-	# 12288 bytes should be rounded down to one sector.
+	# one sector plus one page should be rounded down to one sector.
-	check_diskinfo "$md" 8192 1 $ss
+	check_diskinfo "$md" $ss 1 $ss
 
 	# Resize and verify that the new size was also rounded down.
 	atf_check -s exit:0 -o empty -e empty \
 	    -x "mdconfig -r -u ${md#md} -s ${ms2}b"
-	check_diskinfo "$md" 16384 2 $ss
+	check_diskinfo "$md" $((2 * $ss)) 2 $ss
 }
 attach_size_rounddown_cleanup()
 {