[PATCH] generic/793: limit number of overwrites

Testcase generic/793 overwrites a 1GB file "number of sequential zones"
times in order to trigger a bug in zoned BTRFS' garbage collection. But on
scratch devices with a huge number of sequential zones (like SMR drives)
this can cause very long runtimes.

As the testcase also limits the filesystem size to 16GB, constraint the
number of overwrite loops to the number of sequential zones in the
filesystem. This still guarantees that the file will be overwritten often
enough to trigger the bug while not exploding the overall test runtime.

Reported-by: Shin'ichiro Kawasaki <[email protected]>
Signed-off-by: Johannes Thumshirn <[email protected]>
---
 tests/generic/793 | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/tests/generic/793 b/tests/generic/793
index a59e84694309..6d48b991bedf 100755
--- a/tests/generic/793
+++ b/tests/generic/793
@@ -21,7 +21,6 @@ else
 fi
 
 _require_zoned_device "$zoned_dev"
-_require_command "$BLKZONE_PROG" blkzone
 
 # This test requires specific data space usage, skip if we have compression
 # enabled.
@@ -34,12 +33,15 @@ _fixed_by_fs_commit btrfs 258e46a6385c \
 _fixed_by_fs_commit btrfs e2a7fd22378f \
 	"btrfs: zoned: add zone reclaim flush state for DATA space_info"
 
-_scratch_mkfs_sized $((16 * 1024 * 1024 * 1024)) &>>$seqres.full
+fssize=$((16 * 1024 * 1024 * 1024))
+_scratch_mkfs_sized ${fssize} &>>$seqres.full
 _scratch_mount
 
-# Overwrite the data "number of seq zones" times, this is arbitrarily chosen
+# Overwrite the data "number of zones in fs" times, this is arbitrarily chosen
 # but triggers the original bug reliably
-loops=$($BLKZONE_PROG report $zoned_dev | grep -c "SEQ_WRITE_REQUIRED")
+qp="$(_sysfs_queue_path ${zoned_dev})"
+zsize=$(( $(cat ${qp}/chunk_sectors) << 9))
+loops=$(( fssize/zsize))
 
 for (( i = 0; i < $loops; i++ )); do
 	dd if=/dev/zero of=$SCRATCH_MNT/test bs=1M count=1024 status=none
-- 
2.53.0