[RFC v2 02/12] kunit: test: add kunit_stream a std::stream like logger

[Daniel Latypov <dlatypov@google.com>]

From: Brendan Higgins <brendanhiggins@google.com>

A lot of the expectation and assertion infrastructure prints out fairly
complicated test failure messages, so add a C++ style log library for
for logging test results called `struct kunit_stream`.

kunit_stream allows us to construct a message before we know whether we
want to print it out; this can be extremely handy if there is
information you might need for a failure message that is easiest to
collect in the steps leading up to the actual check.

Note that kunit_stream is distinct from string_stream: whereas
string_stream is really just a string builder, kunit_stream is
specifically used for constructing expectation/assertion (introduced
later in this series) messages to a user of KUnit.

Patch was previously reviewed at
https://lore.kernel.org/linux-fsdevel/20190712081744.87097-5-brendanhiggins@google.com/
Primary differences are
* kunit/ => lib/kunit/
* re-expose string_stream_clear(), which was made static since then

Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
---
 include/kunit/kunit-stream.h  |  94 +++++++++++++++++++++++++++++
 include/kunit/string-stream.h |   2 +
 include/kunit/test.h          |   1 +
 lib/kunit/Makefile            |   1 +
 lib/kunit/kunit-stream.c      | 110 ++++++++++++++++++++++++++++++++++
 lib/kunit/string-stream.c     |   2 +-
 6 files changed, 209 insertions(+), 1 deletion(-)
 create mode 100644 include/kunit/kunit-stream.h
 create mode 100644 lib/kunit/kunit-stream.c

diff --git a/include/kunit/kunit-stream.h b/include/kunit/kunit-stream.h
new file mode 100644
index 000000000000..9a768732a04b
--- /dev/null
+++ b/include/kunit/kunit-stream.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * C++ stream style string formatter and printer used in KUnit for outputting
+ * KUnit messages.
+ *
+ * Copyright (C) 2020, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#ifndef _KUNIT_KUNIT_STREAM_H
+#define _KUNIT_KUNIT_STREAM_H
+
+#include <linux/types.h>
+#include <kunit/string-stream.h>
+
+struct kunit;
+
+/**
+ * struct kunit_stream - a std::stream style string builder.
+ *
+ * A std::stream style string builder. Allows messages to be built up and
+ * printed all at once. Note that the intention is to only use
+ * &struct kunit_stream to communicate with a user of KUnit, most often to
+ * communicate something about an expectation or an assertion to the user. If
+ * you want a similar interface, but aren't sure if this is the right class for
+ * you to use, you probably want to use the related string_stream class, which
+ * is allowed for generic string construction in a similar manner. This class is
+ * really only for the KUnit library to communicate certain kinds of information
+ * to KUnit users and should not be used by anyone else.
+ *
+ * A note on &struct kunit_stream's usage: a kunit_stream will generally
+ * accompany *one* expectation or assertion. Multiple expectations/assertions
+ * may be validated concurrently at any given time, even within a single test
+ * case, so sharing a kunit_stream between expectations/assertions may result in
+ * unintended consequences.
+ */
+struct kunit_stream {
+	/* private: internal use only. */
+	struct kunit *test;
+	struct string_stream *internal_stream;
+};
+
+/**
+ * alloc_kunit_stream() - constructs a new &struct kunit_stream.
+ * @test: The test context object.
+ * @gfp: The GFP flags to use for internal allocations.
+ *
+ * Constructs a new test managed &struct kunit_stream.
+ */
+struct kunit_stream *alloc_kunit_stream(struct kunit *test,
+					gfp_t gfp);
+
+/**
+ * kunit_stream_add(): adds the formatted input to the internal buffer.
+ * @kstream: the stream being operated on.
+ * @fmt: printf style format string to append to stream.
+ *
+ * Appends the formatted string, @fmt, to the internal buffer.
+ */
+void __printf(2, 3) kunit_stream_add(struct kunit_stream *kstream,
+				     const char *fmt, ...);
+
+/**
+ * kunit_stream_append(): appends the contents of @other to @kstream.
+ * @kstream: the stream to which @other is appended.
+ * @other: the stream whose contents are appended to @kstream.
+ *
+ * Appends the contents of @other to @kstream.
+ */
+void kunit_stream_append(struct kunit_stream *kstream,
+			 struct kunit_stream *other);
+
+/**
+ * kunit_stream_commit(): prints out the internal buffer to the user.
+ * @kstream: the stream being operated on.
+ *
+ * Outputs the contents of the internal buffer as a kunit_printk formatted
+ * output. KUNIT_STREAM ONLY OUTPUTS ITS BUFFER TO THE USER IF COMMIT IS
+ * CALLED!!! The reason for this is that it allows us to construct a message
+ * before we know whether we want to print it out; this can be extremely handy
+ * if there is information you might need for a failure message that is easiest
+ * to collect in the steps leading up to the actual check.
+ */
+void kunit_stream_commit(struct kunit_stream *kstream);
+
+/**
+ * kunit_stream_clear(): clears the internal buffer.
+ * @kstream: the stream being operated on.
+ *
+ * Clears the contents of the internal buffer.
+ */
+void kunit_stream_clear(struct kunit_stream *kstream);
+
+#endif /* _KUNIT_KUNIT_STREAM_H */
diff --git a/include/kunit/string-stream.h b/include/kunit/string-stream.h
index fe98a00b75a9..44677c386890 100644
--- a/include/kunit/string-stream.h
+++ b/include/kunit/string-stream.h
@@ -46,6 +46,8 @@ int string_stream_append(struct string_stream *stream,
 
 bool string_stream_is_empty(struct string_stream *stream);
 
+void string_stream_clear(struct string_stream *stream);
+
 int string_stream_destroy(struct string_stream *stream);
 
 #endif /* _KUNIT_STRING_STREAM_H */
diff --git a/include/kunit/test.h b/include/kunit/test.h
index 59f3144f009a..687782fa44d9 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -10,6 +10,7 @@
 #define _KUNIT_TEST_H
 
 #include <kunit/assert.h>
+#include <kunit/kunit-stream.h>
 #include <kunit/try-catch.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 724b94311ca3..523a7b0f9783 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -3,6 +3,7 @@ obj-$(CONFIG_KUNIT) +=			kunit.o
 kunit-objs +=				test.o \
 					string-stream.o \
 					assert.o \
+					kunit-stream.o \
 					try-catch.o
 
 ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
diff --git a/lib/kunit/kunit-stream.c b/lib/kunit/kunit-stream.c
new file mode 100644
index 000000000000..744798693f39
--- /dev/null
+++ b/lib/kunit/kunit-stream.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * C++ stream style string formatter and printer used in KUnit for outputting
+ * KUnit messages.
+ *
+ * Copyright (C) 2020, Google LLC.
+ * Author: Brendan Higgins <brendanhiggins@google.com>
+ */
+
+#include <kunit/test.h>
+#include <kunit/kunit-stream.h>
+#include <kunit/string-stream.h>
+
+void kunit_stream_add(struct kunit_stream *kstream, const char *fmt, ...)
+{
+	va_list args;
+	struct string_stream *stream = kstream->internal_stream;
+
+	va_start(args, fmt);
+
+	if (string_stream_vadd(stream, fmt, args))
+		kunit_err(kstream->test,
+			  "Failed to allocate fragment: %s\n",
+			  fmt);
+
+	va_end(args);
+}
+
+void kunit_stream_append(struct kunit_stream *kstream,
+			 struct kunit_stream *other)
+{
+	int ret;
+
+	ret = string_stream_append(kstream->internal_stream,
+				   other->internal_stream);
+
+	if (ret)
+		kunit_err(kstream->test,
+			  "Failed to append other stream: %d\n", ret);
+}
+
+void kunit_stream_clear(struct kunit_stream *kstream)
+{
+	string_stream_clear(kstream->internal_stream);
+}
+
+void kunit_stream_commit(struct kunit_stream *kstream)
+{
+	struct string_stream *stream = kstream->internal_stream;
+	struct string_stream_fragment *fragment;
+	struct kunit *test = kstream->test;
+	char *buf;
+
+	buf = string_stream_get_string(stream);
+	if (!buf) {
+		kunit_err(test,
+			  "Could not allocate buffer, dumping stream:\n");
+		list_for_each_entry(fragment, &stream->fragments, node) {
+			kunit_err(test, "%s", fragment->fragment);
+		}
+		kunit_err(test, "\n");
+	} else {
+		kunit_err(test, "%s", buf);
+	}
+
+	kunit_stream_clear(kstream);
+}
+
+struct kunit_stream_alloc_context {
+	struct kunit *test;
+	gfp_t gfp;
+};
+
+static int kunit_stream_init(struct kunit_resource *res, void *context)
+{
+	struct kunit_stream_alloc_context *ctx = context;
+	struct kunit_stream *stream;
+
+	stream = kunit_kzalloc(ctx->test, sizeof(*stream), ctx->gfp);
+	if (!stream)
+		return -ENOMEM;
+
+	stream->test = ctx->test;
+	stream->internal_stream = alloc_string_stream(ctx->test, ctx->gfp);
+	if (!stream->internal_stream)
+		return -ENOMEM;
+
+	res->data = stream;
+	return 0;
+}
+
+static void kunit_stream_free(struct kunit_resource *res)
+{
+	/* Do nothing because cleanup is handled by KUnit managed resources */
+}
+
+struct kunit_stream *alloc_kunit_stream(struct kunit *test,
+					gfp_t gfp)
+{
+	struct kunit_stream_alloc_context ctx = {
+		.test = test,
+		.gfp = gfp
+	};
+
+	return kunit_alloc_resource(test,
+				    kunit_stream_init,
+				    kunit_stream_free,
+				    gfp,
+				    &ctx);
+}
diff --git a/lib/kunit/string-stream.c b/lib/kunit/string-stream.c
index 151a0e7ac349..a94004134928 100644
--- a/lib/kunit/string-stream.c
+++ b/lib/kunit/string-stream.c
@@ -112,7 +112,7 @@ int string_stream_add(struct string_stream *stream, const char *fmt, ...)
 	return result;
 }
 
-static void string_stream_clear(struct string_stream *stream)
+void string_stream_clear(struct string_stream *stream)
 {
 	struct string_stream_fragment *frag_container, *frag_container_safe;
 
-- 
2.28.0.1011.ga647a8990f-goog