Date:   Fri, 17 May 2019 10:58:41 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Brendan Higgins <brendanhiggins@...gle.com>,
        frowand.list@...il.com, gregkh@...uxfoundation.org,
        jpoimboe@...hat.com, keescook@...gle.com,
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        peterz@...radead.org, robh@...nel.org, shuah@...nel.org,
        tytso@....edu, yamada.masahiro@...ionext.com
Cc:     devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        kunit-dev@...glegroups.com, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-um@...ts.infradead.org,
        Alexander.Levin@...rosoft.com, Tim.Bird@...y.com,
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        jdike@...toit.com, joel@....id.au, julia.lawall@...6.fr,
        khilman@...libre.com, knut.omang@...cle.com, logang@...tatee.com,
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        richard@....at, rientjes@...gle.com, rostedt@...dmis.org,
        wfg@...ux.intel.com, Brendan Higgins <brendanhiggins@...gle.com>
Subject: Re: [PATCH v4 04/18] kunit: test: add kunit_stream a std::stream like logger

Quoting Brendan Higgins (2019-05-14 15:16:57)
> diff --git a/kunit/kunit-stream.c b/kunit/kunit-stream.c
> new file mode 100644
> index 0000000000000..1884f1b550888
> --- /dev/null
> +++ b/kunit/kunit-stream.c
> @@ -0,0 +1,152 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * C++ stream style string formatter and printer used in KUnit for outputting
> + * KUnit messages.
> + *
> + * Copyright (C) 2019, Google LLC.
> + * Author: Brendan Higgins <brendanhiggins@...gle.com>
> + */
> +
> +#include <kunit/test.h>
> +#include <kunit/kunit-stream.h>
> +#include <kunit/string-stream.h>
> +
> +static const char *kunit_stream_get_level(struct kunit_stream *this)
> +{
> +       unsigned long flags;
> +       const char *level;
> +
> +       spin_lock_irqsave(&this->lock, flags);
> +       level = this->level;
> +       spin_unlock_irqrestore(&this->lock, flags);
> +
> +       return level;

Please remove this whole function and inline it to the one call-site.

> +}
> +
> +void kunit_stream_set_level(struct kunit_stream *this, const char *level)
> +{
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&this->lock, flags);
> +       this->level = level;
> +       spin_unlock_irqrestore(&this->lock, flags);

I don't get the locking here. What are we protecting against? Are tests
running in parallel using the same kunit_stream? If so, why is the level
changeable in one call and then adding strings is done in a different
function call? It would make sense to combine the level setting and
string adding so that it's one atomic operation if it's truly a parallel
operation, or remove the locking entirely.

> +}
> +
> +void kunit_stream_add(struct kunit_stream *this, const char *fmt, ...)
> +{
> +       va_list args;
> +       struct string_stream *stream = this->internal_stream;
> +
> +       va_start(args, fmt);
> +
> +       if (string_stream_vadd(stream, fmt, args) < 0)
> +               kunit_err(this->test, "Failed to allocate fragment: %s\n", fmt);
> +
> +       va_end(args);
> +}
> +
> +void kunit_stream_append(struct kunit_stream *this,
> +                               struct kunit_stream *other)
> +{
> +       struct string_stream *other_stream = other->internal_stream;
> +       const char *other_content;
> +
> +       other_content = string_stream_get_string(other_stream);
> +
> +       if (!other_content) {
> +               kunit_err(this->test,
> +                         "Failed to get string from second argument for appending.\n");
> +               return;
> +       }
> +
> +       kunit_stream_add(this, other_content);
> +}
> +
> +void kunit_stream_clear(struct kunit_stream *this)
> +{
> +       string_stream_clear(this->internal_stream);
> +}
> +
> +void kunit_stream_commit(struct kunit_stream *this)

Should this be rather called kunit_stream_flush()?

> +{
> +       struct string_stream *stream = this->internal_stream;
> +       struct string_stream_fragment *fragment;
> +       const char *level;
> +       char *buf;
> +
> +       level = kunit_stream_get_level(this);
> +       if (!level) {
> +               kunit_err(this->test,
> +                         "Stream was committed without a specified log level.\n");

Drop the full-stop?

> +               level = KERN_ERR;
> +               kunit_stream_set_level(this, level);
> +       }
> +
> +       buf = string_stream_get_string(stream);
> +       if (!buf) {
> +               kunit_err(this->test,

Can you grow a local variable for 'this->test'? It's used many times.

Also, 'this' is not very kernel idiomatic. We usually name variables by
their type instead of 'this' which is a keyword in other languages.
Perhaps it could be named 'kstream'?

> +                        "Could not allocate buffer, dumping stream:\n");
> +               list_for_each_entry(fragment, &stream->fragments, node) {
> +                       kunit_err(this->test, fragment->fragment);
> +               }
> +               kunit_err(this->test, "\n");
> +               goto cleanup;
> +       }
> +
> +       kunit_printk(level, this->test, buf);
> +       kfree(buf);
> +
> +cleanup:
> +       kunit_stream_clear(this);
> +}
> +
> +static int kunit_stream_init(struct kunit_resource *res, void *context)
> +{
> +       struct kunit *test = context;
> +       struct kunit_stream *stream;
> +
> +       stream = kzalloc(sizeof(*stream), GFP_KERNEL);

Of course, here it's called 'stream', so maybe it should be 'kstream'
here too.

> +       if (!stream)
> +               return -ENOMEM;
> +
> +       res->allocation = stream;
> +       stream->test = test;
> +       spin_lock_init(&stream->lock);
> +       stream->internal_stream = new_string_stream();

Can new_string_stream() be renamed to alloc_string_stream()? Sorry, I
just see so much C++ isms in here it's hard to read from the kernel
developer perspective.

> +
> +       if (!stream->internal_stream) {

Nitpick: Please join this to the "allocation" event above instead of
keeping it separated.

> +               kfree(stream);
> +               return -ENOMEM;
> +       }
> +
> +       return 0;
> +}
> +
> +static void kunit_stream_free(struct kunit_resource *res)
> +{
> +       struct kunit_stream *stream = res->allocation;
> +
> +       if (!string_stream_is_empty(stream->internal_stream)) {
> +               kunit_err(stream->test,
> +                        "End of test case reached with uncommitted stream entries.\n");
> +               kunit_stream_commit(stream);
> +       }
> +
> +       destroy_string_stream(stream->internal_stream);
> +       kfree(stream);
> +}
> +
> +struct kunit_stream *kunit_new_stream(struct kunit *test)
> +{
> +       struct kunit_resource *res;
> +
> +       res = kunit_alloc_resource(test,
> +                                  kunit_stream_init,
> +                                  kunit_stream_free,
> +                                  test);
> +
> +       if (res)
> +               return res->allocation;
> +       else
> +               return NULL;

Don't have if (...) return ...; else return ..., just return instead of
else.

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