This commit adds tests for some of the core functionalities
of cgroups v2.

The commit adds tests for some core principles of croup V2 API:

- test_cgcore_internal_process_constraint

  Tests internal process constraint.
  You can't add a pid to a domain parent if a controller is enabled.

- test_cgcore_top_down_constraint_enable

   Tests that you can't enable a controller on a child if it's not enabled
   on the parent.

- test_cgcore_top_down_constraint_disable

  Tests that you can't disable a controller on a parent if it's
  enabled in a child.

- test_cgcore_no_internal_process_constraint_on_threads

  Tests that there's no internal process constrain on threaded cgroups.
  You can add threads/processes on a parent with a controller enabled.

- test_cgcore_parent_becomes_threaded

  Tests that when a child becomes threaded the parent type becomes
  domain threaded.

- test_cgcore_invalid_domain

  In a situation like:

  A (domain threaded) - B (threaded) - C (domain)

  it tests that C can't be used until it is turned into a threaded cgroup.
  The "cgroup.type" file will report "domain (invalid)" in these cases.
  Operations which fail due to invalid topology use EOPNOTSUPP as the errno.

- test_cgcore_populated

  In a situation like:

  A(0) - B(0) - C(1)
         \ D(0)

  It tests that A, B and C's "populated" fields would be 1 while D's 0.
  It tests that after the one process in C is moved to root, A,B and C's
  "populated" fields would flip to "0" and file modified events will
  be generated on the "cgroup.events" files of both cgroups.
Signed-off-by: NClaudio Zumbo <claudioz@fb.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: kernel-team@fb.com
Acked-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NShuah Khan (Samsung OSG) <shuah@kernel.org>

"len" needs to be signed for the error handling to work.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NShuah Khan (Samsung OSG) <shuah@kernel.org>

cg_name(const char *root, const char *name) is always called with
non-empty root and name arguments, so there is no sense in checking
it in the function body (after using in strlen()).
Signed-off-by: NRoman Gushchin <guro@fb.com>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NShuah Khan (Samsung OSG) <shuah@kernel.org>

The new test verifies that memory.swap.max and memory.swap.current behave
as expected for simple allocation scenarios
Signed-off-by: NMike Rapoport <rppt@linux.vnet.ibm.com>
Acked-by: NTejun Heo <tj@kernel.org>
Acked-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NShuah Khan (Samsung OSG) <shuah@kernel.org>

Cgroups are used for controlling the physical resource distribution
(memory, CPU, io, etc) and often are used as basic building blocks
for large distributed computing systems. Even small differences
in the actual behavior may lead to significant incidents.

The codebase is under the active development, which will unlikely
stop at any time soon. Also it's scattered over different kernel
subsystems, which makes regressions more probable.

Given that, the lack of any tests is crying.

This patch implements some basic tests for the memory controller,
as well as a minimal required framework. It doesn't pretend for a
very good coverage, but pretends to be a starting point.

Hopefully, any following significant changes will include corresponding
tests.

Tests for CPU and io controllers, as well as cgroup core
are next in the todo list.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: kernel-team@fb.com
Cc: linux-kselftest@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NShuah Khan (Samsung OSG) <shuah@kernel.org>