[PATCH] generic: test lseek with seek data mode on a one byte file

[fdmanana@xxxxxxxxxx]

From: Filipe Manana <fdmanana@xxxxxxxx>

Test that seeking for data on a 1 byte file works correctly, the returned
offset should be 0 if the start offset is 0.

This is a regression test motivated by a btrfs bug introduced in kernel
6.1, which got recently fixed by the following kernel commit:

  2f2e84ca6066 ("btrfs: fix off-by-one in delalloc search during lseek")

Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
---
 src/seek_sanity_test.c | 36 ++++++++++++++++++++++++++++++++++++
 tests/generic/706      | 36 ++++++++++++++++++++++++++++++++++++
 tests/generic/706.out  |  2 ++
 3 files changed, 74 insertions(+)
 create mode 100755 tests/generic/706
 create mode 100644 tests/generic/706.out

diff --git a/src/seek_sanity_test.c b/src/seek_sanity_test.c
index 8a586f74..48b3ccc0 100644
--- a/src/seek_sanity_test.c
+++ b/src/seek_sanity_test.c
@@ -292,6 +292,41 @@ out:
 	return ret;
 }
 
+/*
+ * Test seeking for data on a 1 byte file, both when there's delalloc and also
+ * after delalloc is flushed.
+ */
+static int test22(int fd, int testnum)
+{
+	const char buf = 'X';
+	int ret;
+
+	ret = do_pwrite(fd, &buf, 1, 0);
+	if (ret)
+		return ret;
+
+	/*
+	 * Our file as a size of 1 byte and that byte is in delalloc. Seeking
+	 * for data, with a start offset of 0, should return file offset 0.
+	 */
+	ret = do_lseek(testnum, 1, fd, 1, SEEK_DATA, 0, 0);
+	if (ret)
+		return ret;
+
+	/* Flush all delalloc. */
+	ret = fsync(fd);
+	if (ret) {
+		fprintf(stderr, "fsync failed: %s (%d)\n", strerror(errno), errno);
+		return ret;
+	}
+
+	/*
+	 * We should get the same result we got when we had delalloc, 0 is the
+	 * offset with data.
+	 */
+	return do_lseek(testnum, 2, fd, 1, SEEK_DATA, 0, 0);
+}
+
 /*
  * Make sure hole size is properly reported when punched in the middle of a file
  */
@@ -1131,6 +1166,7 @@ struct testrec seek_tests[] = {
        { 19, test19, "Test file SEEK_DATA from middle of a large hole" },
        { 20, test20, "Test file SEEK_DATA from middle of a huge hole" },
        { 21, test21, "Test file SEEK_HOLE that was created by PUNCH_HOLE" },
+       { 22, test22, "Test a 1 byte file" },
 };
 
 static int run_test(struct testrec *tr)
diff --git a/tests/generic/706 b/tests/generic/706
new file mode 100755
index 00000000..b3e7aa7c
--- /dev/null
+++ b/tests/generic/706
@@ -0,0 +1,36 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2023 SUSE Linux Products GmbH. All Rights Reserved.
+#
+# FS QA Test 706
+#
+# Test that seeking for data on a 1 byte file works correctly, the returned
+# offset should be 0 if the start offset is 0.
+#
+. ./common/preamble
+_begin_fstest auto quick seek
+
+[ $FSTYP == "btrfs" ] &&
+	_fixed_by_kernel_commit 2f2e84ca6066 \
+	"btrfs: fix off-by-one in delalloc search during lseek"
+
+_supported_fs generic
+_require_test
+_require_seek_data_hole
+_require_test_program "seek_sanity_test"
+
+test_file=$TEST_DIR/seek_sanity_testfile.$seq
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	rm -f $test_file
+}
+
+_run_seek_sanity_test -s 22 -e 22 $test_file > $seqres.full 2>&1 ||
+	_fail "seek sanity check failed!"
+
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/generic/706.out b/tests/generic/706.out
new file mode 100644
index 00000000..577697c6
--- /dev/null
+++ b/tests/generic/706.out
@@ -0,0 +1,2 @@
+QA output created by 706
+Silence is golden
-- 
2.35.1