[PATCH netfs v1 2/2] netfs: add KUnit coverage for reissue prepare_write errno

["Iván Ezequiel Rodriguez" <ivanrwcm25@gmail.com>]

Stub netfs_write_subrequest_terminated() and call netfs_reissue_write()
with FAILED + -EIO.  Unpatched trees terminate with 0; patched keep -EIO.

  ./tools/testing/kunit/kunit.py run --kunitconfig=fs/netfs/.kunitconfig \
	netfs_reissue_write*

Signed-off-by: Iván Ezequiel Rodriguez <ivanrwcm25@gmail.com>
---
 fs/netfs/.kunitconfig          |  3 ++
 fs/netfs/Kconfig               |  9 +++++
 fs/netfs/Makefile              |  2 +
 fs/netfs/write_collect.c       |  4 ++
 fs/netfs/write_reissue_kunit.c | 73 ++++++++++++++++++++++++++++++++++
 5 files changed, 91 insertions(+)
 create mode 100644 fs/netfs/.kunitconfig
 create mode 100644 fs/netfs/write_reissue_kunit.c

diff --git a/fs/netfs/.kunitconfig b/fs/netfs/.kunitconfig
new file mode 100644
index 000000000000..c783d180ab8f
--- /dev/null
+++ b/fs/netfs/.kunitconfig
@@ -0,0 +1,3 @@
+CONFIG_KUNIT=y
+CONFIG_NETFS_SUPPORT=y
+CONFIG_NETFS_KUNIT_TESTS=y
diff --git a/fs/netfs/Kconfig b/fs/netfs/Kconfig
index d0e7b0971fa3..d796dbe4bd7c 100644
--- a/fs/netfs/Kconfig
+++ b/fs/netfs/Kconfig
@@ -33,6 +33,15 @@ config NETFS_DEBUG
 	  management module.  If this is set, the debugging output may be
 	  enabled by setting bits in /sys/module/netfs/parameters/debug.
 
+config NETFS_KUNIT_TESTS
+	tristate "KUnit tests for netfs" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	select NETFS_SUPPORT
+	help
+	  This builds netfs KUnit tests (e.g. write reissue errno).
+	  Say N unless developing netfs.
+
 config FSCACHE
 	bool "General filesystem local caching manager"
 	depends on NETFS_SUPPORT
diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index 54834cde7e56..fa1544b9a199 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -33,4 +33,6 @@ netfs-$(CONFIG_FSCACHE) += fscache_proc.o
 endif
 netfs-$(CONFIG_FSCACHE_STATS) += fscache_stats.o
 
+netfs-$(CONFIG_NETFS_KUNIT_TESTS) += write_reissue_kunit.o
+
 obj-$(CONFIG_NETFS_SUPPORT) += netfs.o
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 6e8ea534230d..f3236fe494bf 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -11,6 +11,7 @@
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/slab.h>
+#include <kunit/static_stub.h>
 #include "internal.h"
 
 /* Notes made in the collector */
@@ -529,6 +530,9 @@ void netfs_write_subrequest_terminated(void *_op, ssize_t transferred_or_error)
 	struct netfs_io_subrequest *subreq = _op;
 	struct netfs_io_request *wreq = subreq->rreq;
 
+	KUNIT_STATIC_STUB_REDIRECT(netfs_write_subrequest_terminated,
+				   _op, transferred_or_error);
+
 	_enter("%x[%x] %zd", wreq->debug_id, subreq->debug_index, transferred_or_error);
 
 	switch (subreq->source) {
diff --git a/fs/netfs/write_reissue_kunit.c b/fs/netfs/write_reissue_kunit.c
new file mode 100644
index 000000000000..fca5f7dd9265
--- /dev/null
+++ b/fs/netfs/write_reissue_kunit.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * netfs_reissue_write must not clear prepare_write() errno.
+ */
+#include <kunit/test.h>
+#include <kunit/static_stub.h>
+#include <linux/uio.h>
+#include "internal.h"
+
+struct term_capture {
+	ssize_t transferred_or_error;
+	bool called;
+};
+
+static void capture_terminated(void *_op, ssize_t transferred_or_error)
+{
+	struct netfs_io_subrequest *subreq = _op;
+	struct term_capture *cap = kunit_get_current_test()->priv;
+
+	cap->called = true;
+	cap->transferred_or_error = transferred_or_error;
+	/* Mirror production: leave subreq->error as prepare_write set it. */
+	(void)subreq;
+}
+
+/*
+ * prepare_write_failed() sets FAILED + errno, then write_retry still calls
+ * reissue_write().  Before the fix, reissue wiped error to 0 so terminated
+ * reported success and mapping_set_error(0) was a no-op.
+ */
+static void reissue_preserves_prep_error(struct kunit *test)
+{
+	struct term_capture cap = {};
+	struct netfs_io_request wreq = {};
+	struct netfs_io_stream stream = {
+		.source = NETFS_UPLOAD_TO_SERVER,
+	};
+	struct netfs_io_subrequest subreq = {
+		.rreq = &wreq,
+		.len = 1,
+		.transferred = 0,
+		.error = -EIO,
+		.source = NETFS_UPLOAD_TO_SERVER,
+	};
+	char buf[1] = { 0 };
+	struct kvec kvec = { .iov_base = buf, .iov_len = 1 };
+	struct iov_iter source;
+
+	__set_bit(NETFS_SREQ_FAILED, &subreq.flags);
+	iov_iter_kvec(&source, ITER_SOURCE, &kvec, 1, 1);
+
+	test->priv = &cap;
+	kunit_activate_static_stub(test, netfs_write_subrequest_terminated,
+				   capture_terminated);
+
+	netfs_reissue_write(&stream, &subreq, &source);
+
+	KUNIT_EXPECT_TRUE(test, cap.called);
+	KUNIT_EXPECT_EQ(test, cap.transferred_or_error, -EIO);
+	KUNIT_EXPECT_EQ(test, subreq.error, -EIO);
+}
+
+static struct kunit_case netfs_reissue_test_cases[] = {
+	KUNIT_CASE(reissue_preserves_prep_error),
+	{}
+};
+
+static struct kunit_suite netfs_reissue_test_suite = {
+	.name = "netfs_reissue_write",
+	.test_cases = netfs_reissue_test_cases,
+};
+
+kunit_test_suite(netfs_reissue_test_suite);
-- 
2.43.0