[PATCH v5 1/3] common/atomicwrites: add helper for multi block atomic writes

[Catherine Hoang <catherine.hoang@oracle.com>]

Add a helper to check that we can perform multi block atomic writes. We will
use this in the following patches that add testing for large atomic writes.
This helper will prevent these tests from running on kernels that only support
single block atomic writes.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
---
 common/atomicwrites | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/common/atomicwrites b/common/atomicwrites
index 391bb6f6..ac4facc3 100644
--- a/common/atomicwrites
+++ b/common/atomicwrites
@@ -24,6 +24,27 @@ _get_atomic_write_segments_max()
         grep -w atomic_write_segments_max | grep -o '[0-9]\+'
 }
 
+_require_scratch_write_atomic_multi_fsblock()
+{
+	_require_scratch
+
+	_scratch_mkfs > /dev/null 2>&1 || \
+		_notrun "cannot format scratch device for atomic write checks"
+	_try_scratch_mount || \
+		_notrun "cannot mount scratch device for atomic write checks"
+
+	local testfile=$SCRATCH_MNT/testfile
+	touch $testfile
+
+	local bsize=$(_get_file_block_size $SCRATCH_MNT)
+	local awu_max_fs=$(_get_atomic_write_unit_max $testfile)
+
+	_scratch_unmount
+
+	test $awu_max_fs -ge $((bsize * 2)) || \
+		_notrun "multi-block atomic writes not supported by this filesystem"
+}
+
 _require_scratch_write_atomic()
 {
 	_require_scratch
-- 
2.34.1