Re: [ndctl PATCH 0/7] Policy based reconfiguration for daxctl

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

On Tue, Aug 31, 2021 at 2:05 AM Vishal Verma <vishal.l.verma@intel.com> wrote:
>
> These patches add policy (config file) support to daxctl. The
> introductory user is daxctl-reconfigure-device. Sysadmins may wish to
> use daxctl devices as system-ram, but it may be cumbersome to automate
> the reconfiguration step for every device upon boot.
>
> Introduce a new option for daxctl-reconfigure-device, --check-config.
> This is at the heart of policy based reconfiguration, as it allows
> daxctl to look up reconfiguration parameters for a given device from the
> config system instead of the command line.
>
> Some systemd and udev glue then automates this for every new dax device
> that shows up, providing a way for the administrator to simply list all
> the 'system-ram' UUIDs in a config file, and not have to worry about
> anything else.
>
> An example config file can be:
>
>   # cat /etc/ndctl/daxctl.conf

Take these comments as provisional until I read through the rest, but
this is just a reaction to the proposed ini format.

>
>   [auto-online unique_identifier_foo]

I am thinking this section name should be "reconfigure-device
unique_identifier_foo" if only because resize might also be something
someone wants to do, and if other commands get config automation it
makes it clearer which config snippets apply to which command.

>   uuid = 48d8e42c-a2f0-4312-9e70-a837faafe862

I think this should be called:

"nvdimm.uuid"

...or something like that to make it clear this depends on dax devices
emitted by libnvdimm, and not those that come from "soft-reserved"
memory. It also helps distinguish if we ever get UUIDs in the HMAT
which is something I have been meaning to propose.

>   mode = system-ram

I can see this being "mode = devdax" if feature was being used to
change size or alignment.

>   online = true
>   movable = false

I wonder if these keys should be prefixed by the mode name:

system-ram.online = true
system-ram.movable = false

...so it's a bit more self documenting about which parameters are
sub-options, and delineates them from generic options like size.

> Any file under '/etc/ndctl/' can be used - all files with a '.conf' suffix
> will be considered when looking for matches.

any concern about name collisions between ndctl, daxctl, and cxl-cli
section names?