From 57e68bd5c6bb93be7ef64e847ac51dc0d1e678f3 Mon Sep 17 00:00:00 2001
From: Filipe Manana <fdmanana@suse.com>
Date: Thu, 24 Jul 2025 13:05:59 +0100
Subject: [PATCH] generic/211: verify if the filesystem being tested supports
 in place writes

The test currently assumes the filesystem can do in place writes (no
Copy-On-Write, no allocation of new extents) when overwriting a file.
While that is the case for most filesystems in most configurations, there
are exceptions such as zoned xfs where overwriting results in allocating
new extents for the new data.

So make the test check that in place writes are supported and skip the
test if they are not supported.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>
---
 common/rc         | 71 +++++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/211 |  9 ++----
 2 files changed, 73 insertions(+), 7 deletions(-)

diff --git a/common/rc b/common/rc
index 96578d15..b9292a78 100644
--- a/common/rc
+++ b/common/rc
@@ -5873,6 +5873,77 @@ _require_program() {
 	_have_program "$1" || _notrun "$tag required"
 }
 
+_force_inplace_writes()
+{
+	local file=$1
+
+	if [ -z "$file" ]; then
+		_fail "Usage: _force_inplace_writes <file path>"
+	fi
+
+	case "$FSTYP" in
+	"btrfs")
+		# Set the file to NOCOW mode on btrfs, which must be done while
+		# the file is empty, otherwise it fails with -EINVAL.
+		_require_chattr C
+		$CHATTR_PROG +C "$file"
+		;;
+	esac
+}
+
+# Test that a filesystem can do writes to a file in place (without allocating
+# new extents, without Copy-On-Write semantics).
+_require_inplace_writes()
+{
+	_require_xfs_io_command "fiemap"
+
+	local target=$1
+	local test_file="${target}/test_inplace_writes"
+	local fiemap_before
+	local fiemap_after
+
+	if [ -z "$target" ]; then
+		_fail "Usage: _require_inplace_writes <filesystem path>"
+	fi
+
+	rm -f "$test_file"
+	touch "$test_file"
+	_force_inplace_writes "$test_file"
+
+	$XFS_IO_PROG -c "pwrite 0 128K" -c "fsync" "$test_file" &> /dev/null
+	if [ $? -ne 0 ]; then
+		rm -f "$test_file"
+		_fail "_require_inplace_writes failed to write to test file"
+	fi
+
+	# Grab fiemap output before overwriting.
+	fiemap_before=$($XFS_IO_PROG -c "fiemap" "$test_file")
+	if [ $? -ne 0 ]; then
+		rm -f "$test_file"
+		_fail "_require_inplace_writes first fiemap call failed"
+	fi
+
+	$XFS_IO_PROG -c "pwrite 0 128K" -c "fsync" "$test_file" &> /dev/null
+	if [ $? -ne 0 ]; then
+		rm -f "$test_file"
+		_fail "_require_inplace_writes failed to overwrite test file"
+	fi
+
+	fiemap_after=$($XFS_IO_PROG -c "fiemap" "$test_file")
+	if [ $? -ne 0 ]; then
+		rm -f "$test_file"
+		_fail "_require_inplace_writes second fiemap call failed"
+	fi
+
+	rm -f "$test_file"
+
+	# If the filesystem supports inplace writes, then the extent mapping is
+	# the same before and after overwriting.
+	if [ "${fiemap_after}" != "${fiemap_before}" ]; then
+		_notrun "in-place writes not supported"
+	fi
+}
+
 ################################################################################
 # make sure this script returns success
 /bin/true
diff --git a/tests/generic/211 b/tests/generic/211
index e87d1e01..6eda1608 100755
--- a/tests/generic/211
+++ b/tests/generic/211
@@ -27,15 +27,10 @@ fs_size=$(_small_fs_size_mb 512)
 _try_scratch_mkfs_sized $((fs_size * 1024 * 1024)) >>$seqres.full 2>&1 || \
 	_fail "mkfs failed"
 _scratch_mount
+_require_inplace_writes $SCRATCH_MNT
 
 touch $SCRATCH_MNT/foobar
-
-# Set the file to NOCOW mode on btrfs, which must be done while the file is
-# empty, otherwise it fails.
-if [ $FSTYP == "btrfs" ]; then
-	_require_chattr C
-	$CHATTR_PROG +C $SCRATCH_MNT/foobar
-fi
+_force_inplace_writes $SCRATCH_MNT/foobar
 
 # Add initial data to the file we will later overwrite with mmap.
 $XFS_IO_PROG -c "pwrite -S 0xab 0 1M" $SCRATCH_MNT/foobar | _filter_xfs_io
-- 
2.39.5