[PATCH v2 1/2] btrfs/076: support smaller extent size limit

[Naohiro Aota <naohiro.aota@xxxxxxx>]

Running btrfs/076 on a zoned null_blk device will fail with the following error.

  - output mismatch (see /host/results/btrfs/076.out.bad)
      --- tests/btrfs/076.out     2021-02-05 01:44:20.000000000 +0000
      +++ /host/results/btrfs/076.out.bad 2023-09-15 01:49:36.000000000 +0000
      @@ -1,3 +1,3 @@
       QA output created by 076
      -80
      -80
      +83
      +83
      ...

This is because the default value of zone_append_max_bytes is 127.5 KB
which is smaller than BTRFS_MAX_UNCOMPRESSED (128K). So, the extent size is
limited to 126976 (= ROUND_DOWN(127.5K, 4096)), which makes the number of
extents larger, and fails the test.

Instead of hard-coding the number of extents, we can calculate it using the
max extent size of an extent. It is limited by either
BTRFS_MAX_UNCOMPRESSED or zone_append_max_bytes.

Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
 tests/btrfs/076     | 23 +++++++++++++++++++++--
 tests/btrfs/076.out |  3 +--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/tests/btrfs/076 b/tests/btrfs/076
index 89e9672d09e2..a5cc3eb96b2f 100755
--- a/tests/btrfs/076
+++ b/tests/btrfs/076
@@ -28,13 +28,28 @@ _supported_fs btrfs
 _require_test
 _require_scratch
 
+# An extent size can be up to BTRFS_MAX_UNCOMPRESSED
+max_extent_size=$(( 128 << 10 ))
+if _scratch_btrfs_is_zoned; then
+	zone_append_max=$(cat "/sys/block/$(_short_dev $SCRATCH_DEV)/queue/zone_append_max_bytes")
+	if [[ $zone_append_max -gt 0 && $zone_append_max -lt $max_extent_size ]]; then
+		# Round down to PAGE_SIZE
+		max_extent_size=$(( $zone_append_max / 4096 * 4096 ))
+	fi
+fi
+file_size=$(( 10 << 20 ))
+expect=$(( (file_size + max_extent_size - 1) / max_extent_size ))
+
 _scratch_mkfs >> $seqres.full 2>&1
 _scratch_mount "-o compress=lzo"
 
 $XFS_IO_PROG -f -c "pwrite 0 10M" -c "fsync" \
 	$SCRATCH_MNT/data >> $seqres.full 2>&1
 
-_extent_count $SCRATCH_MNT/data
+res=$(_extent_count $SCRATCH_MNT/data)
+if [[ $res -ne $expect ]]; then
+	_fail "Expected $expect extents, got $res"
+fi
 
 $XFS_IO_PROG -f -c "pwrite 0 $((4096*33))" -c "fsync" \
 	$SCRATCH_MNT/data >> $seqres.full 2>&1
@@ -42,7 +57,11 @@ $XFS_IO_PROG -f -c "pwrite 0 $((4096*33))" -c "fsync" \
 $XFS_IO_PROG -f -c "pwrite 0 10M" -c "fsync" \
 	$SCRATCH_MNT/data >> $seqres.full 2>&1
 
-_extent_count $SCRATCH_MNT/data
+res=$(_extent_count $SCRATCH_MNT/data)
+if [[ $res -ne $expect ]]; then
+	_fail "Expected $expect extents, got $res"
+fi
 
+echo "Silence is golden"
 status=0
 exit
diff --git a/tests/btrfs/076.out b/tests/btrfs/076.out
index b99f7eb10a16..248e095d91af 100644
--- a/tests/btrfs/076.out
+++ b/tests/btrfs/076.out
@@ -1,3 +1,2 @@
 QA output created by 076
-80
-80
+Silence is golden
-- 
2.42.0