daxctl: Opt-in to /sys/bus/dax ABI

In support of the kernel's conversion of the dax-subsystem from a
'class' to a 'bus', teach the libdaxctl subsystem-layout-specific code
to parse the new layout. The kernel changes do not effect the primary
ndctl use case of putting namespaces into 'dax' mode since that uses
libnvdimm namespace device relative paths, but it does break 'ndctl list
-X' and 'daxctl list'. For that reason the kernel provides a
dax_pmem_compat driver to support the old layout and give time for
userspace components to switch.

Installation of the latest libdaxctl package arranges for a daxctl
configuration file to be dropped in /etc/modprobe.d. The modprobe
configuration blacklists dax_pmem_compat modules and sets the proper
alias for the dax_pmem module. The modprobe configuration upgrades the
default kernel handling to the /sys/bus/dax scheme.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
6 files changed
tree: 85582605425eadbd993556a8a28da1ce4de7faa7
  1. .gitignore
  4. Documentation/
  5. Makefile.am
  6. Makefile.am.in
  7. README.md
  8. autogen.sh
  9. builtin.h
  10. ccan/
  11. configure.ac
  12. contrib/
  13. daxctl/
  14. git-version
  15. git-version-gen
  16. licenses/
  17. m4/
  18. make-git-snapshot.sh
  19. ndctl.spec.in
  20. ndctl/
  21. nfit.h
  22. rpmbuild.sh
  23. sles/
  24. test.h
  25. test/
  26. util/


Utility library for managing the libnvdimm (non-volatile memory device) sub-system in the Linux kernel


./configure CFLAGS='-g -O2' --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib64
make check
sudo make install

There are a number of packages required for the build steps that may not be installed by default. For information about the required packages, see the “BuildRequires:” lines in ndctl.spec.in.



See the latest documentation for the NVDIMM kernel sub-system here:


A getting started guide is also available on the kernel.org nvdimm wiki:


Unit Tests

The unit tests run by make check require the nfit_test.ko module to be loaded. To build and install nfit_test.ko:

  1. Obtain the kernel source. For example,
    git clone -b libnvdimm-for-next git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git

  2. Skip to step 3 if the kernel version is >= v4.8. Otherwise, for kernel versions < v4.8, configure the kernel to make some memory available to CMA (contiguous memory allocator). This will be used to emulate DAX.


    cma=200M on the kernel command line.

  3. Compile the libnvdimm sub-system as a module, make sure “zone device” memory is enabled, and enable the btt, pfn, and dax features of the sub-system:

  4. Build and install the unit test enabled libnvdimm modules in the following order. The unit test modules need to be in place prior to the depmod that runs during the final modules_install

    make M=tools/testing/nvdimm
    sudo make M=tools/testing/nvdimm modules_install
    sudo make modules_install
  5. Now run make check in the ndctl source directory, or ndctl test, if ndctl was built with --enable-test.


The unit tests will validate that the environment is set up correctly before they try to run. If the platform is misconfigured, i.e. the unit test modules are not available, or the test versions of the modules are superseded by the “in-tree/production” version of the modules make check will skip tests and report a message like the following in test/test-suite.log:

SKIP: libndctl
test/init: nfit_test_init: nfit.ko: appears to be production version: /lib/modules/4.8.8-200.fc24.x86_64/kernel/drivers/acpi/nfit/nfit.ko.xz
__ndctl_test_skip: explicit skip test_libndctl:2684
nfit_test unavailable skipping tests

If the unit test modules are indeed available in the modules ‘extra’ directory the default depmod policy can be overridden by adding a file to /etc/depmod.d with the following contents:

override nfit * extra
override device_dax * extra
override dax_pmem * extra
override libnvdimm * extra
override nd_blk * extra
override nd_btt * extra
override nd_e820 * extra
override nd_pmem * extra

The nfit_test module emulates pmem with memory allocated via vmalloc(). One of the side effects is that this breaks ‘physically contiguous’ assumptions in the driver. Use the '--align=4K option to ‘ndctl create-namespace’ to avoid these corner case scenarios.