[PATCH v2 4/4] generic: test to run fsx eof pollution

[Brian Foster <bfoster@redhat.com>]

Filesystem regressions related to partial page zeroing can go
unnoticed for a decent amount of time. A recent example is the issue
of iomap zero range not handling dirty pagecache over unwritten
extents, which leads to wrong behavior on certain file extending
operations (i.e. truncate, write extension, etc.).

fsx does occasionally uncover these sorts of problems, but failures
can be rare and/or require longer running tests outside what is
typically run via full fstests regression runs. fsx now supports a
mode that injects post-eof data in order to explicitly test partial
eof zeroing behavior. This uncovers certain problems more quickly
and applies coverage more broadly across size changing operations.

Add a new test that runs an fsx instance (modeled after generic/127)
with eof pollution mode enabled. While the test is generic, it is
currently limited to XFS as that is currently the only known major
fs that does enough zeroing to satisfy the strict semantics expected
by fsx. The long term goal is to uncover and fix issues so more
filesystems can enable this test.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 tests/generic/363     | 23 +++++++++++++++++++++++
 tests/generic/363.out |  2 ++
 2 files changed, 25 insertions(+)
 create mode 100755 tests/generic/363
 create mode 100644 tests/generic/363.out

diff --git a/tests/generic/363 b/tests/generic/363
new file mode 100755
index 00000000..477c111c
--- /dev/null
+++ b/tests/generic/363
@@ -0,0 +1,23 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Red Hat, Inc.  All Rights Reserved.
+#
+# FSQA Test No. 363
+#
+# Run fsx with EOF pollution enabled. This provides test coverage for partial
+# EOF page/block zeroing for operations that change file size.
+#
+
+. ./common/preamble
+_begin_fstest rw auto
+
+_require_test
+
+# currently only xfs performs enough zeroing to satisfy fsx
+_supported_fs xfs
+
+# on failure, replace -q with -d to see post-eof writes in the dump output
+run_fsx "-q -S 0 -e 1 -N 100000"
+
+status=0
+exit
diff --git a/tests/generic/363.out b/tests/generic/363.out
new file mode 100644
index 00000000..3d219cd0
--- /dev/null
+++ b/tests/generic/363.out
@@ -0,0 +1,2 @@
+QA output created by 363
+fsx -q -S 0 -e 1 -N 100000
-- 
2.45.0