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

[Michael S. Tsirkin]

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