Re: [PATCH ndctl v1 0/8] daxctl: Add device align and range mapping allocation

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Dec 16, 2020 at 3:41 AM Joao Martins <joao.m.martins@oracle.com> wrote:
>
> On 7/16/20 7:46 PM, Joao Martins wrote:
> > Hey,
> >
> > This series builds on top of this one[0] and does the following improvements
> > to the Soft-Reserved subdivision:
> >
> >  1) Support for {create,reconfigure}-device for selecting @align (hugepage size).
> >  Here we add a '-a|--align 4K|2M|1G' option to the existing commands;
> >
> >  2) Listing improvements for device alignment and mappings;
> >  Note: Perhaps it is better to hide the mappings by default, and only
> >        print with -v|--verbose. This would align with ndctl, as the mappings
> >        info can be quite large.
> >
> >  3) Allow creating devices from selecting ranges. This allows to keep the
> >    same GPA->HPA mapping as before we kexec the hypervisor with running guests:
> >
> >    daxctl list -d dax0.1 > /var/log/dax0.1.json
> >    kexec -d -l bzImage
> >    systemctl kexec
> >    daxctl create -u --restore /var/log/dax0.1.json
> >
> >    The JSON was what I though it would be easier for an user, given that it is
> >    the data format daxctl outputs. Alternatives could be adding multiple:
> >       --mapping <pgoff>:<start>-<end>
> >
> >    But that could end up in a gigantic line and a little more
> >    unmanageable I think.
> >
> > This series requires this series[0] on top of Dan's patches[1]:
> >
> >  [0] https://lore.kernel.org/linux-nvdimm/20200716172913.19658-1-joao.m.martins@oracle.com/
> >  [1] https://lore.kernel.org/linux-nvdimm/159457116473.754248.7879464730875147365.stgit@dwillia2-desk3.amr.corp.intel.com/
> >
> > The only TODO here is docs and improving tests to validate mappings, and test
> > the restore path.
> >
> > Suggestions/comments are welcome.
> >
> There's a couple of issues in this series regarding daxctl-reconfigure options and
> breakage of ndctl with kernels (<5.10) that do not supply a device @align upon testing
> with NVDIMMs. Plus it is missing daxctl-create.sh unit test for @align.

What's the breakage with older kernels, is it the kernel regressing
old daxctl, or is it new daxctl being incompatible with old kernels?
If it's the latter, it needs a fixup, if it's the former it needs a
kernel compat change.
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