Re: [PATCH v4 4/4] docs: add document to introduce CDP command

[Ian Campbell <ian.campbell@citrix.com>]

On Fri, 2015-09-25 at 18:16 +0800, He Chen wrote:
> 
[...]
> > And if cdp is not enabled:
> > 
[...]
> Right above.
> 
> > xl psr-cat-cbm-set -c -d <domid> 0xd00dfeed
> > 
> > *ERRROR*
> > [now: cbm=<default>]
> > 
> 
> In current code, it is valid since -c & -d have the same behaviour as
> neither of them.
> So, it will not show error, and cbm=0xd00dfeed

I think with cdp disabled this seems like surprising behaviour, but you
might want to argue that when CDP is disabled the single CBM acts like  a
unified code and data CBM and it therefore makes sense to act this way.

If you agree this behaviour is surprising then the simplest answer would be
to disallow -c and -d together in both cdp enabled and disabled
configurations (since otherwise you would have to ask Xen if it was on to
validate the options, which is too much faff).

If you think it makes sense then you could leave it as is.

> What do you think of this? Is it proper to do so?

Like I say I found it surprising, but I'm not an expert in CDP/CBM or what
their semantics should be, so my surprise might be misplaced. Please do
feel free to disagree if you think the correct behaviour is as the current
behaviour (or indeed something else).

Ultimately if you have considered these corner cases and have an opinion on
what the right behaviour is then I'm happy to go with what you choose.

Ian.