Re: [Xen-devel] [PATCH v2 2/5] iommu: introduce dom0-iommu option

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Aug 02, 2018 at 02:23:23AM -0600, Jan Beulich wrote:
> >>> On 02.08.18 at 09:46, <kevin.tian@xxxxxxxxx> wrote:
> >>  From: Roger Pau Monne [mailto:roger.pau@xxxxxxxxxx]
> >> Sent: Wednesday, August 1, 2018 7:04 PM
> >> --- a/docs/misc/xen-command-line.markdown
> >> +++ b/docs/misc/xen-command-line.markdown
> >> @@ -1150,12 +1150,18 @@ detection of systems known to misbehave
> >> upon accesses to that port.
> >> 
> >>  > `dom0-passthrough`
> >> 
> >> +> **WARNING: This command line option is deprecated, and superseded
> >> by
> >> +> _dom0-iommu=none_ - using both options in combination is
> >> undefined.**
> >> +
> > 
> > in patch description you said 'supersede'... is it better to say that
> > new dom0_iommu is favored if both options are specified than
> > saying 'undefined'?
> 
> That would complicate handling (perhaps just slightly, but anyway),
> since we'd have to maintain a second boolean. Without that the
> order on the command line determines behavior. (And I see that in
> the end you've figured that out.)
> 
> >> @@ -1198,6 +1204,32 @@ detection of systems known to misbehave upon
> >> accesses to that port.
> >> 
> >>  >> Enable IOMMU debugging code (implies `verbose`).
> >> 
> >> +### dom0-iommu
> >> +> `= List of [ none | strict | relaxed ]`
> >> +
> >> +> Sub-options are of boolean kind and can be prefixed with `no-` to effect
> >> the
> >> +> inverse meaning.
> > 
> > not important comment, but doesn't "no-none" sound weird? :-)
> 
> Only positive (true) values should be permitted for I think all of
> these. I didn't look at the patch yes, so perhaps that's already
> the case.

For the current set of options introduced in this patch none, strict
or relaxed it doesn't make much sense to allow the no- prefix.

For options added in later patches (inclusive and reserved) it makes
sense to allow the no- prefix, so that a user can do
'dom0-iommu=no-inclusive' in order to change the default value.

I will make it clear which options allow the no- prefix, and add the
code to parse such prefix when it's needed.

Roger.

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