On 06/12/2018 15:37, Matthew Wilcox wrote:
On Thu, Dec 06, 2018 at 12:32:47PM +0000, Kieran Bingham wrote:
> On 04/12/2018 20:47, Luis Chamberlain wrote:
>> On Mon, Dec 03, 2018 at 03:48:15PM -0800, Brendan Higgins wrote:
>>> On Thu, Nov 29, 2018 at 5:54 AM Kieran Bingham
>>> <kieran.bingham(a)ideasonboard.com> wrote:
>>>> Hi Brendan,
>>>> Thanks again for this series!
>>>> On 28/11/2018 19:36, Brendan Higgins wrote:
>>>>> The ultimate goal is to create minimal isolated test binaries; in
>>>>> meantime we are using UML to provide the infrastructure to run tests,
>>>>> define an abstract way to configure and run tests that allow us to
>>>>> change the context in which tests are built without affecting the
>>>>> This also makes pretty and dynamic error reporting, and a lot of
>>>>> nice features easier.
>>>> I wonder if we could somehow generate a shared library object
>>>> 'libkernel' or 'libumlinux' from a UM configured set of
>>>> objects so that we could create binary targets directly ?
>>> That's an interesting idea. I think it would be difficult to figure
>>> out exactly where to draw the line of what goes in there and what
>>> needs to be built specific to a test a priori. Of course, that leads
>>> into the biggest problem in general, needed to know what I need to
>>> build to test the thing that I want to test.
>>> Nevertheless, I could definitely imagine that being useful in a lot of
>> Whether or not we can abstract away the kernel into such a mechanism
>> with uml libraries is a good question worth exploring.
>> Developers working upstream do modify their kernels a lot, so we'd have
>> to update such libraries quite a bit, but I think that's fine too. The
>> *real* value I think from the above suggestion would be enterprise /
>> mobile distros or stable kernel maintainers which have a static kernel
>> they need to support for a relatively *long time*, consider a 10 year
>> time frame. Running unit tests without qemu with uml and libraries for
>> respective kernels seems real worthy.
> I think any such library might be something generated by the kernel
> build system, so if someone makes substantial changes to a core
> component provided by the library - it can be up to them to build a
> corresponding userspace library as well.
> We could also consider to only provide *static* libraries rather than
> dynamic. So any one building some userspace tool / test with this would
> be required to compile against (the version of) the kernel they expect
> perhaps... - much like we expect modules to be compiled currently.
> And then the userspace binary would be sufficiently able to live it's
> life on it's own :)
>> The overhead for testing a unit test for said targets, *ideally*, would
>> just be to to reboot into the system with such libraries available, a
>> unit test would just look for the respective uname -r library and mimic
>> that kernel, much the same way enterprise distributions today rely on
>> having debugging symbols available to run against crash / gdb. Having
>> debug modules / kernel for crash requires such effort already, so this
>> would just be an extra layer of other prospect tests.
> Oh - although, yes - there are some good concepts there - but I'm a bit
> weary of how easy it would be to 'run' the said test against multiple
> kernel version libraries... there would be a lot of possible ABI
> conflicts perhaps.
> My main initial idea for a libumlinux is to provide infrastructure such
> as our linked-lists and other kernel formatting so that we can take
> kernel code directly to userspace for test and debug (assuming that
> there are no hardware dependencies or things that we can't mock out)
> I think all of this could complement kunit of course - this isn't
> suggesting an alternative implementation :-)
I suspect the reason Luis cc'd me on this is that we already have some
artisinally-crafted userspace kernel-mocking interfaces under tools/.
Aha - excellent - I had hoped to grab you at Plumbers to talk about
this, after hearing you mention something at your Xarray talk - but
didn't seem to find a suitable time.
The tools/testing/radix-tree directory is the source of some of
but I've been moving pieces out into tools/ more generally where it
makes sense to.
Sounds like we already have a starting point then.
We have liburcu already, which is good. The main sticking points
- No emulation of kernel thread interfaces
Scheduling finesse aside, This shouldn't be too hard to emulate/wrap
- The kernel does not provide the ability to aggressively fail
allocations (which is useful when trying to exercise the memory failure
Fault injection throughout would certainly be a valuable addition to any
Wrapping tests into a single userspace binary could facilitate further
memory leak checking or other valgrind facilities too.
- printk has started adding a lot of %pX enhancements which printf
obviously doesn't know about.
Wrapping through User-mode linux essentially provides this already
though. In fact I guess that goes for the thread interfaces topic above too.
- No global pseudo-random number generator in the kernel. Probably
we should steal the i915 one.
I know Dan Williams has also done a lot of working mocking kernel
interfaces for libnvdimm.
Thanks for the references - more to investigate.