generic/251: check min and max length and minlen for FSTRIM

Every now and then, this test fails with the following output when
running against my development tree when configured with an 8k fs block
size:

  --- a/tests/generic/251.out	2023-07-11 12:18:21.624971186 -0700
  +++ b/tests/generic/251.out.bad	2023-10-15 20:54:44.636000000 -0700
  @@ -1,2 +1,4677 @@
   QA output created by 251
   Running the test: done.
  +fstrim: /opt: FITRIM ioctl failed: Invalid argument
  +fstrim: /opt: FITRIM ioctl failed: Invalid argument
  ...
  +fstrim: /opt: FITRIM ioctl failed: Invalid argument

Dumping the exact fstrim command lines to seqres.full produces this at
the end:

  /usr/sbin/fstrim -m 32544k -o 30247k -l 4k /opt
  /usr/sbin/fstrim -m 32544k -o 30251k -l 4k /opt
  ...
  /usr/sbin/fstrim -m 32544k -o 30255k -l 4k /opt

The count of failure messages is the same as the count as the "-l 4k"
fstrim invocations.  Since this is an 8k-block filesystem, the -l
parameter is clearly incorrect.  The test computes random -m and -l
options.

Therefore, create helper functions to guess at the minimum and maximum
length and minlen parameters that can be used with the fstrim program.
In the inner loop of the test, make sure that our choices for -m and -l
fall within those constraints.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>

1 files changed, 51 insertions, 8 deletions

diff --git a/tests/generic/251 b/tests/generic/251
index 3b807df5fa..b7a15f9189 100755
--- a/tests/generic/251
+++ b/tests/generic/251
@@ -53,14 +53,46 @@ _fail()
 	kill $mypid 2> /dev/null
 }
 
-_guess_max_minlen()
+# Set FSTRIM_{MIN,MAX}_MINLEN to the lower and upper bounds of the -m(inlen)
+# parameter to fstrim on the scratch filesystem.
+set_minlen_constraints()
 {
-	mmlen=100000
-	while [ $mmlen -gt 1 ]; do
+	local mmlen
+
+	for ((mmlen = 100000; mmlen > 0; mmlen /= 2)); do
+		$FSTRIM_PROG -l $(($mmlen*2))k -m ${mmlen}k $SCRATCH_MNT &> /dev/null && break
+	done
+	test $mmlen -gt 0 || \
+		_notrun "could not determine maximum FSTRIM minlen param"
+	FSTRIM_MAX_MINLEN=$mmlen
+
+	for ((mmlen = 1; mmlen < FSTRIM_MAX_MINLEN; mmlen *= 2)); do
 		$FSTRIM_PROG -l $(($mmlen*2))k -m ${mmlen}k $SCRATCH_MNT &> /dev/null && break
-		mmlen=$(($mmlen/2))
 	done
-	echo $mmlen
+	test $mmlen -le $FSTRIM_MAX_MINLEN || \
+		_notrun "could not determine minimum FSTRIM minlen param"
+	FSTRIM_MIN_MINLEN=$mmlen
+}
+
+# Set FSTRIM_{MIN,MAX}_LEN to the lower and upper bounds of the -l(ength)
+# parameter to fstrim on the scratch filesystem.
+set_length_constraints()
+{
+	local mmlen
+
+	for ((mmlen = 100000; mmlen > 0; mmlen /= 2)); do
+		$FSTRIM_PROG -l ${mmlen}k $SCRATCH_MNT &> /dev/null && break
+	done
+	test $mmlen -gt 0 || \
+		_notrun "could not determine maximum FSTRIM length param"
+	FSTRIM_MAX_LEN=$mmlen
+
+	for ((mmlen = 1; mmlen < FSTRIM_MAX_LEN; mmlen *= 2)); do
+		$FSTRIM_PROG -l ${mmlen}k $SCRATCH_MNT &> /dev/null && break
+	done
+	test $mmlen -le $FSTRIM_MAX_LEN || \
+		_notrun "could not determine minimum FSTRIM length param"
+	FSTRIM_MIN_LEN=$mmlen
 }
 
 ##
@@ -70,13 +102,24 @@ _guess_max_minlen()
 ##
 fstrim_loop()
 {
+	set_minlen_constraints
+	set_length_constraints
+	echo "MINLEN max=$FSTRIM_MAX_MINLEN min=$FSTRIM_MIN_MINLEN" >> $seqres.full
+	echo "LENGTH max=$FSTRIM_MAX_LEN min=$FSTRIM_MIN_LEN" >> $seqres.full
+
 	trap "_destroy_fstrim; exit \$status" 2 15
 	fsize=$(_discard_max_offset_kb "$SCRATCH_MNT" "$SCRATCH_DEV")
-	mmlen=$(_guess_max_minlen)
 
 	while true ; do
-		step=$((RANDOM*$RANDOM+4))
-		minlen=$(((RANDOM*($RANDOM%2+1))%$mmlen))
+		while true; do
+			step=$((RANDOM*$RANDOM+4))
+			test "$step" -ge "$FSTRIM_MIN_LEN" && break
+		done
+		while true; do
+			minlen=$(( (RANDOM * (RANDOM % 2 + 1)) % FSTRIM_MAX_MINLEN ))
+			test "$minlen" -ge "$FSTRIM_MIN_MINLEN" && break
+		done
+
 		start=$RANDOM
 		if [ $((RANDOM%10)) -gt 7 ]; then
 			$FSTRIM_PROG $SCRATCH_MNT &