Re: [Qemu-devel] [qemu PATCH v4 3/4] nvdimm, acpi: support NFIT platform capabilities

[Ross Zwisler]

On Tue, Jun 05, 2018 at 09:37:25PM +0300, Michael S. Tsirkin wrote:
> On Tue, Jun 05, 2018 at 11:15:00AM -0700, Dan Williams wrote:
> > On Tue, Jun 5, 2018 at 9:42 AM, Ross Zwisler
> > <address@hidden> wrote:
> > > On Tue, Jun 05, 2018 at 06:25:27PM +0300, Michael S. Tsirkin wrote:
> > >> On Mon, May 21, 2018 at 10:32:02AM -0600, Ross Zwisler wrote:
> > >> > Add a machine command line option to allow the user to control the 
> > >> > Platform
> > >> > Capabilities Structure in the virtualized NFIT.  This Platform 
> > >> > Capabilities
> > >> > Structure was added in ACPI 6.2 Errata A.
> > >> >
> > >> > Signed-off-by: Ross Zwisler <address@hidden>
> > >>
> > >> I tried playing with it and encoding the capabilities is
> > >> quite awkward.
> > >>
> > >> Can we add bits for specific capabilities instead of nvdimm-cap?
> > >>
> > >> How about:
> > >>
> > >> "cpu-flush-on-power-loss-cap"
> > >> "memory-flush-on-power-loss-cap"
> > >> "byte-addressable-mirroring-cap"
> > >
> > > Hmmm...I don't like that as much because:
> > >
> > > a) It's very verbose.  Looking at my current qemu command line few other
> > >    options require that many characters, and you'd commonly be defining 
> > > more
> > >    than one of these for a given VM.
> > >
> > > b) It means that the QEMU will need to be updated if/when new flags are 
> > > added,
> > >    because we'll have to have new options for each flag.  The current
> > >    implementation is more future-proof because you can specify any flags
> > >    value you want.
> > >
> > > However, if you feel strongly about this, I'll make the change.
> > 
> > Straw-man: Could we do something similar with what we are doing in ndctl?
> > 
> > enum ndctl_persistence_domain {
> >         PERSISTENCE_NONE = 0,
> >         PERSISTENCE_MEM_CTRL = 10,
> >         PERSISTENCE_CPU_CACHE = 20,
> >         PERSISTENCE_UNKNOWN = INT_MAX,
> > };
> > 
> > ...and have the command line take a number where "10" and "20" are
> > supported today, but allows us to adapt to new persistence domains in
> > the future.
> 
> I'm fine with that except can we have symbolic names instead of numbers
> on command line?
> 
> -- 
> MST

Okay, we can move to the symbolic names.  Do you want them to be that long, or
would:

nvdimm-cap-cpu
nvdimm-cap-mem-ctrl
nvdimm-cap-mirroring

or something be better?