From: Brendan Higgins <brendanhiggins@google.com>
To: "Theodore Ts'o" <tytso@mit.edu>,
Greg KH <gregkh@linuxfoundation.org>,
Frank Rowand <frowand.list@gmail.com>,
Brendan Higgins <brendanhiggins@google.com>,
Kees Cook <keescook@google.com>,
Kieran Bingham <kieran.bingham@ideasonboard.com>,
Luis Chamberlain <mcgrof@kernel.org>,
Rob Herring <robh@kernel.org>, Stephen Boyd <sboyd@kernel.org>,
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Julia Lawall <julia.lawall@lip6.fr>,
Kevin Hilman <khilman@baylibre.com>,
Knut Omang <knut.omang@oracle.com>,
Logan Gunthorpe <logang@deltatee.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Petr Mladek <pmladek@suse.com>,
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David Rientjes <rientjes@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
wfg@linux.intel.com
Subject: Re: [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework
Date: Wed, 8 May 2019 12:17:59 -0700 [thread overview]
Message-ID: <CAFd5g47vQQeSHLX_cvWSVzva9YgsXz9DNqPv8Z=nw=-kAcmr3Q@mail.gmail.com> (raw)
In-Reply-To: <20190507172256.GB5900@mit.edu>
> On Tue, May 07, 2019 at 10:01:19AM +0200, Greg KH wrote:
> > > My understanding is that the intent of KUnit is to avoid booting a kernel on
> > > real hardware or in a virtual machine. That seems to be a matter of semantics
> > > to me because isn't invoking a UML Linux just running the Linux kernel in
> > > a different form of virtualization?
> > >
> > > So I do not understand why KUnit is an improvement over kselftest.
> > >
> > > It seems to me that KUnit is just another piece of infrastructure that I
> > > am going to have to be familiar with as a kernel developer. More overhead,
> > > more information to stuff into my tiny little brain.
> > >
> > > I would guess that some developers will focus on just one of the two test
> > > environments (and some will focus on both), splitting the development
> > > resources instead of pooling them on a common infrastructure.
> > >
> > > What am I missing?
> >
> > kselftest provides no in-kernel framework for testing kernel code
> > specifically. That should be what kunit provides, an "easy" way to
> > write in-kernel tests for things.
> >
> > Brendan, did I get it right?
>
> Yes, that's basically right. You don't *have* to use KUnit. It's
> supposed to be a simple way to run a large number of small tests that
> for specific small components in a system.
>
> For example, I currently use xfstests using KVM and GCE to test all of
> ext4. These tests require using multiple 5 GB and 20GB virtual disks,
> and it works by mounting ext4 file systems and exercising ext4 through
> the system call interfaces, using userspace tools such as fsstress,
> fsx, fio, etc. It requires time overhead to start the VM, create and
> allocate virtual disks, etc. For example, to run a single 3 seconds
> xfstest (generic/001), it requires full 10 seconds to run it via
> kvm-xfstests.
>
> KUnit is something else; it's specifically intended to allow you to
> create lightweight tests quickly and easily, and by reducing the
> effort needed to write and run unit tests, hopefully we'll have a lot
> more of them and thus improve kernel quality.
>
> As an example, I have a volunteer working on developing KUinit tests
> for ext4. We're going to start by testing the ext4 extent status
> tree. The source code is at fs/ext4/extent_status.c; it's
> approximately 1800 LOC. The Kunit tests for the extent status tree
> will exercise all of the corner cases for the various extent status
> tree functions --- e.g., ext4_es_insert_delayed_block(),
> ext4_es_remove_extent(), ext4_es_cache_extent(), etc. And it will do
> this in isolation without our needing to create a test file system or
> using a test block device.
>
> Next we'll test the ext4 block allocator, again in isolation. To test
> the block allocator we will have to write "mock functions" which
> simulate reading allocation bitmaps from disk. Again, this will allow
> the test writer to explicitly construct corner cases and validate that
> the block allocator works as expected without having to reverese
> engineer file system data structures which will force a particular
> code path to be executed.
>
> So this is why it's largely irrelevant to me that KUinit uses UML. In
> fact, it's a feature. We're not testing device drivers, or the
> scheduler, or anything else architecture-specific. UML is not about
> virtualization. What it's about in this context is allowing us to
> start running test code as quickly as possible. Booting KVM takes
> about 3-4 seconds, and this includes initializing virtio_scsi and
> other device drivers. If by using UML we can hold the amount of
> unnecessary kernel subsystem initialization down to the absolute
> minimum, and if it means that we can communicating to the test
> framework via a userspace "printf" from UML/KUnit code, as opposed to
> via a virtual serial port to KVM's virtual console, it all makes for
> lighter weight testing.
>
> Why did I go looking for a volunteer to write KUnit tests for ext4?
> Well, I have a plan to make some changes in restructing how ext4's
> write path works, in order to support things like copy-on-write, a
> more efficient delayed allocation system, etc. This will require
> making changes to the extent status tree, and by having unit tests for
> the extent status tree, we'll be able to detect any bugs that we might
> accidentally introduce in the es tree far more quickly than if we
> didn't have those tests available. Google has long found that having
> these sorts of unit tests is a real win for developer velocity for any
> non-trivial code module (or C++ class), even when you take into
> account the time it takes to create the unit tests.
>
> - Ted
>
> P.S. Many thanks to Brendan for finding such a volunteer for me; the
> person in question is a SRE from Switzerland who is interested in
> getting involved with kernel testing, and this is going to be their
> 20% project. :-)
Thanks Ted, I really appreciate it!
Since Ted provided such an awesome detailed response, I don't think I
really need to go into any detail; nevertheless, I think that Greg and
Shuah have the right idea; in particular, Shuah provides a good
summary.
Thanks everyone!
next prev parent reply other threads:[~2019-05-08 19:18 UTC|newest]
Thread overview: 131+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-01 23:01 [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 01/17] kunit: test: add KUnit test runner core Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 02/17] kunit: test: add test resource management API Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 03/17] kunit: test: add string_stream a std::stream like string builder Brendan Higgins
2019-05-03 1:26 ` shuah
2019-05-03 4:37 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 04/17] kunit: test: add kunit_stream a std::stream like logger Brendan Higgins
2019-05-02 11:00 ` Greg KH
2019-05-02 20:25 ` Brendan Higgins
2019-05-02 21:18 ` Frank Rowand
2019-05-03 1:50 ` shuah
2019-05-03 5:48 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 05/17] kunit: test: add the concept of expectations Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 06/17] kbuild: enable building KUnit Brendan Higgins
2019-05-10 3:03 ` Masahiro Yamada
2019-05-10 10:27 ` Brendan Higgins
2019-05-10 10:30 ` Masahiro Yamada
2019-05-10 10:33 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 07/17] kunit: test: add initial tests Brendan Higgins
2019-05-02 10:58 ` Greg KH
2019-05-02 20:30 ` Brendan Higgins
2019-05-03 1:27 ` shuah
2019-05-03 5:18 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 08/17] kunit: test: add support for test abort Brendan Higgins
2019-05-03 3:14 ` Logan Gunthorpe
2019-05-03 6:48 ` Brendan Higgins
2019-05-03 12:33 ` Logan Gunthorpe
2019-05-06 8:48 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 09/17] kunit: test: add tests for kunit " Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 10/17] kunit: test: add the concept of assertions Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 11/17] kunit: test: add test managed resource tests Brendan Higgins
2019-05-03 14:34 ` shuah
2019-05-06 9:03 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 12/17] kunit: tool: add Python wrappers for running KUnit tests Brendan Higgins
2019-05-02 11:02 ` Greg KH
2019-05-02 18:07 ` Brendan Higgins
2019-05-02 21:16 ` Frank Rowand
2019-05-02 23:45 ` Brendan Higgins
2019-05-03 1:45 ` Frank Rowand
2019-05-03 5:36 ` Brendan Higgins
2019-05-03 18:59 ` Frank Rowand
2019-05-03 23:14 ` Brendan Higgins
2019-05-04 10:42 ` Greg KH
2019-05-06 0:19 ` Frank Rowand
2019-05-06 17:43 ` Kees Cook
2019-05-06 21:42 ` Brendan Higgins
2019-05-06 21:39 ` Brendan Higgins
2019-05-07 19:13 ` Tim.Bird
2019-05-03 6:41 ` Greg KH
2019-05-01 23:01 ` [PATCH v2 13/17] kunit: defconfig: add defconfigs for building " Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 14/17] Documentation: kunit: add documentation for KUnit Brendan Higgins
2019-05-09 5:08 ` Randy Dunlap
2019-05-09 17:38 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 15/17] MAINTAINERS: add entry for KUnit the unit testing framework Brendan Higgins
2019-05-03 14:38 ` shuah
2019-05-06 9:18 ` Brendan Higgins
2019-05-01 23:01 ` [PATCH v2 16/17] kernel/sysctl-test: Add null pointer test for sysctl.c:proc_dointvec() Brendan Higgins
2019-05-02 11:03 ` Greg KH
2019-05-02 18:14 ` Tim.Bird
2019-05-02 18:45 ` Brendan Higgins
2019-05-03 6:42 ` Greg KH
2019-05-03 23:41 ` Brendan Higgins
2019-05-04 10:40 ` Greg KH
2019-05-01 23:01 ` [PATCH v2 17/17] MAINTAINERS: add proc sysctl KUnit test to PROC SYSCTL section Brendan Higgins
2019-05-02 10:50 ` [PATCH v2 00/17] kunit: introduce KUnit, the Linux kernel unit testing framework Greg KH
2019-05-02 11:05 ` Greg KH
2019-05-03 0:41 ` Brendan Higgins
2019-05-02 14:04 ` shuah
2019-05-03 0:44 ` Brendan Higgins
2019-05-03 3:18 ` Logan Gunthorpe
2019-05-07 3:14 ` Frank Rowand
2019-05-07 8:01 ` Greg KH
2019-05-07 15:23 ` shuah
2019-05-09 1:01 ` Frank Rowand
2019-05-07 17:22 ` Theodore Ts'o
2019-05-08 19:17 ` Brendan Higgins [this message]
2019-05-09 0:58 ` Frank Rowand
2019-05-09 1:44 ` Theodore Ts'o
2019-05-09 2:18 ` Frank Rowand
2019-05-14 8:22 ` Brendan Higgins
2019-05-09 0:43 ` Frank Rowand
2019-05-09 1:58 ` Theodore Ts'o
2019-05-09 2:13 ` Frank Rowand
2019-05-09 3:20 ` Theodore Ts'o
2019-05-09 11:52 ` Knut Omang
2019-05-09 13:35 ` Theodore Ts'o
2019-05-09 14:48 ` Knut Omang
2019-05-09 17:00 ` Tim.Bird
2019-05-09 17:42 ` Daniel Vetter
2019-05-09 18:12 ` Frank Rowand
2019-05-09 21:42 ` Theodore Ts'o
2019-05-09 22:20 ` Logan Gunthorpe
2019-05-09 23:30 ` Theodore Ts'o
2019-05-09 23:40 ` Logan Gunthorpe
2019-05-10 4:47 ` Theodore Ts'o
2019-05-10 5:18 ` Frank Rowand
2019-05-10 5:48 ` Knut Omang
2019-05-10 8:12 ` Daniel Vetter
2019-05-10 10:23 ` Brendan Higgins
2019-05-10 12:12 ` Knut Omang
2019-05-10 20:54 ` Brendan Higgins
2019-05-10 22:18 ` Frank Rowand
2019-05-11 6:17 ` Knut Omang
2019-05-14 6:39 ` Brendan Higgins
2019-05-10 21:59 ` Frank Rowand
2019-05-11 6:43 ` Knut Omang
2019-05-14 8:00 ` Brendan Higgins
2019-05-10 11:36 ` Knut Omang
2019-05-10 16:17 ` Logan Gunthorpe
2019-05-10 22:13 ` Frank Rowand
2019-05-14 8:38 ` Brendan Higgins
2019-05-15 0:14 ` Frank Rowand
2019-05-15 0:26 ` Logan Gunthorpe
2019-05-10 21:52 ` Frank Rowand
2019-05-14 20:54 ` Brendan Higgins
2019-05-10 21:12 ` Frank Rowand
2019-05-11 17:33 ` Theodore Ts'o
2019-05-13 14:44 ` Daniel Vetter
2019-05-14 6:04 ` Brendan Higgins
2019-05-14 12:05 ` Daniel Vetter
2019-05-14 18:36 ` Brendan Higgins
2019-05-15 7:41 ` Daniel Vetter
2019-05-22 21:38 ` Brendan Higgins
2019-05-23 8:40 ` Daniel Vetter
2019-05-15 0:26 ` Frank Rowand
2019-05-15 4:28 ` Theodore Ts'o
2019-05-10 5:11 ` Frank Rowand
2019-05-10 10:43 ` Theodore Ts'o
2019-05-10 21:05 ` Frank Rowand
2019-05-09 15:19 ` Masahiro Yamada
2019-05-10 10:25 ` Brendan Higgins
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