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@xxxxxxxxxxxxxxxx> 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 the > >>>> meantime we are using UML to provide the infrastructure to run tests, so > >>>> define an abstract way to configure and run tests that allow us to > >>>> change the context in which tests are built without affecting the user. > >>>> This also makes pretty and dynamic error reporting, and a lot of other > >>>> nice features easier. > >>> > >>> > >>> I wonder if we could somehow generate a shared library object > >>> 'libkernel' or 'libumlinux' from a UM configured set of headers and > >>> 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 cases. > > > > 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/. The tools/testing/radix-tree directory is the source of some of this, but I've been moving pieces out into tools/ more generally where it makes sense to. We have liburcu already, which is good. The main sticking points are: - No emulation of kernel thread interfaces - The kernel does not provide the ability to aggressively fail memory allocations (which is useful when trying to exercise the memory failure paths). - printk has started adding a lot of %pX enhancements which printf obviously doesn't know about. - 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.
