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From: Brendan Higgins <brendanhiggins@google.com>
To: Stephen Boyd <sboyd@kernel.org>
Cc: Iurii Zaikin <yzaikin@google.com>,
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Subject: Re: [PATCH v4 17/18] kernel/sysctl-test: Add null pointer test for sysctl.c:proc_dointvec()
Date: Tue, 11 Jun 2019 13:29:01 -0700
Message-ID: <CAFd5g47dmcHOCX41cr2v9Kaj3xa_5-PoqUPX_1=AoQLUG90NkQ@mail.gmail.com> (raw)
In-Reply-To: <20190611185018.2E1C021744@mail.kernel.org>

On Tue, Jun 11, 2019 at 11:50 AM Stephen Boyd <sboyd@kernel.org> wrote:
>
> Quoting Brendan Higgins (2019-06-11 10:58:30)
> > On Fri, Jun 07, 2019 at 12:00:47PM -0700, Stephen Boyd wrote:
> > > Quoting Iurii Zaikin (2019-06-05 18:29:42)
> > > > On Fri, May 17, 2019 at 11:22 AM Stephen Boyd <sboyd@kernel.org> wrote:
> > > > >
> > > > > Quoting Brendan Higgins (2019-05-14 15:17:10)
> > > > > > diff --git a/kernel/sysctl-test.c b/kernel/sysctl-test.c
> > > > > > new file mode 100644
> > > > > > index 0000000000000..fe0f2bae66085
> > > > > > --- /dev/null
> > > > > > +++ b/kernel/sysctl-test.c
> > > > > > +
> > > > > > +
> > > > > > +static void sysctl_test_dointvec_happy_single_negative(struct kunit *test)
> > > > > > +{
> > > > > > +       struct ctl_table table = {
> > > > > > +               .procname = "foo",
> > > > > > +               .data           = &test_data.int_0001,
> > > > > > +               .maxlen         = sizeof(int),
> > > > > > +               .mode           = 0644,
> > > > > > +               .proc_handler   = proc_dointvec,
> > > > > > +               .extra1         = &i_zero,
> > > > > > +               .extra2         = &i_one_hundred,
> > > > > > +       };
> > > > > > +       char input[] = "-9";
> > > > > > +       size_t len = sizeof(input) - 1;
> > > > > > +       loff_t pos = 0;
> > > > > > +
> > > > > > +       table.data = kunit_kzalloc(test, sizeof(int), GFP_USER);
> > > > > > +       KUNIT_EXPECT_EQ(test, 0, proc_dointvec(&table, 1, input, &len, &pos));
> > > > > > +       KUNIT_EXPECT_EQ(test, sizeof(input) - 1, len);
> > > > > > +       KUNIT_EXPECT_EQ(test, sizeof(input) - 1, pos);
> > > > > > +       KUNIT_EXPECT_EQ(test, -9, *(int *)table.data);
> > > > >
> > > > > Is the casting necessary? Or can the macro do a type coercion of the
> > > > > second parameter based on the first type?
> > > >  Data field is defined as void* so I believe casting is necessary to
> > > > dereference it as a pointer to an array of ints. I don't think the
> > > > macro should do any type coercion that == operator wouldn't do.
> > > >  I did change the cast to make it more clear that it's a pointer to an
> > > > array of ints being dereferenced.
> > >
> > > Ok, I still wonder if we should make KUNIT_EXPECT_EQ check the types on
> > > both sides and cause a build warning/error if the types aren't the same.
> > > This would be similar to our min/max macros that complain about
> > > mismatched types in the comparisons. Then if a test developer needs to
> > > convert one type or the other they could do so with a
> > > KUNIT_EXPECT_EQ_T() macro that lists the types to coerce both sides to
> > > explicitly.
> >
> > Do you think it would be better to do a phony compare similar to how
> > min/max used to work prior to 4.17, or to use the new __typecheck(...)
> > macro? This might seem like a dumb question (and maybe it is), but Iurii
> > and I thought the former created an error message that was a bit easier
> > to understand, whereas __typecheck is obviously superior in terms of
> > code reuse.
> >
> > This is what we are thinking right now; if you don't have any complaints
> > I will squash it into the relevant commits on the next revision:
>
> Can you provide the difference in error messages and describe that in
> the commit text? The commit message is where you "sell" the patch, so
> being able to compare the tradeoff of having another macro to do type
> comparisons vs. reusing the one that's there in kernel.h would be useful
> to allay concerns that we're duplicating logic for better error
> messages.

Oh sorry, I didn't think too hard about the commit message since I
figured it would get split up and squashed into the existing commits.
I just wanted to get it out sooner to discuss this before I post the
next revision (probably later this week).

> Honestly, I'd prefer we just use the macros that we've developed in
> kernel.h to do comparisons here so that we can get code reuse, but more
> importantly so that we don't trip over problems that caused those macros
> to be created in the first place. If the error message is bad, perhaps
> that can be fixed with some sort of compiler directive to make the error
> message a little more useful, i.e. compiletime_warning() thrown into
> __typecheck() or something.

That's a good point. I have no qualms sticking with __typecheck(...)
for now; if we later feel that it is causing problems, we can always
fix it later by supplying our own warning in the manner you suggest.

Iurii, do you have any additional thoughts on this?

>
> > ---
> > From: Iurii Zaikin <yzaikin@google.com>
> >
> > Adds a warning message when comparing values of different types similar
> > to what min() / max() macros do.
> >
> > Signed-off-by: Iurii Zaikin <yzaikin@google.com>

  reply index

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-14 22:16 [PATCH v4 00/18] kunit: introduce KUnit, the Linux kernel unit testing framework Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 01/18] kunit: test: add KUnit test runner core Brendan Higgins
2019-05-17  0:35   ` Stephen Boyd
2019-05-17 18:53   ` Stephen Boyd
2019-06-14 23:22     ` Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 02/18] kunit: test: add test resource management API Brendan Higgins
2019-05-17  0:38   ` Stephen Boyd
2019-06-04 23:34     ` Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 03/18] kunit: test: add string_stream a std::stream like string builder Brendan Higgins
2019-05-17 17:42   ` Stephen Boyd
2019-06-05  0:19     ` Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 04/18] kunit: test: add kunit_stream a std::stream like logger Brendan Higgins
2019-05-17 17:58   ` Stephen Boyd
2019-06-05  0:47     ` Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 05/18] kunit: test: add the concept of expectations Brendan Higgins
2019-05-14 22:16 ` [PATCH v4 06/18] kbuild: enable building KUnit Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 07/18] kunit: test: add initial tests Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 08/18] objtool: add kunit_try_catch_throw to the noreturn list Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 09/18] kunit: test: add support for test abort Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 10/18] kunit: test: add tests for kunit " Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 11/18] kunit: test: add the concept of assertions Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 12/18] kunit: test: add tests for KUnit managed resources Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 13/18] kunit: tool: add Python wrappers for running KUnit tests Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 14/18] kunit: defconfig: add defconfigs for building " Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 15/18] Documentation: kunit: add documentation for KUnit Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 16/18] MAINTAINERS: add entry for KUnit the unit testing framework Brendan Higgins
2019-05-14 23:25   ` Brendan Higgins
2019-05-14 22:17 ` [PATCH v4 17/18] kernel/sysctl-test: Add null pointer test for sysctl.c:proc_dointvec() Brendan Higgins
2019-05-17 18:22   ` Stephen Boyd
2019-06-06  1:29     ` Iurii Zaikin
2019-06-07 19:00       ` Stephen Boyd
2019-06-07 22:22         ` Brendan Higgins
2019-06-11 17:58         ` Brendan Higgins
2019-06-11 18:50           ` Stephen Boyd
2019-06-11 20:29             ` Brendan Higgins [this message]
2019-05-14 22:17 ` [PATCH v4 18/18] MAINTAINERS: add proc sysctl KUnit test to PROC SYSCTL section Brendan Higgins

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