Re: [Xen-devel] [PATCH] Do not set page's count_info directly

[Gianluca Guida <gianluca.guida@xxxxxxxxxxxxx>]

Jiang, Yunhong wrote:
> Keir Fraser <mailto:keir.fraser@xxxxxxxxxxxxx> wrote:
> > On 05/03/2009 12:45, "Gianluca Guida" <glguida@xxxxxxxxx> wrote:
> >
> > > On Thu, Mar 5, 2009 at 1:38 PM, Tim Deegan
> > <Tim.Deegan@xxxxxxxxxx> wrote:
> > > > The check doesn't tell you it's a shadow page -- it just tells you it's
> > > > *not* allocated in another way.  Checking with the mask is OK here,
> > > > perhaps with a comment change.
> > > Yes, but this is what the code (in the shadow code) intends to check.
> > > My complete plan is to have this macro and restore the idea of having
> > > a flag for shadow pages because, as for now, the fact that we can't
> > > distinguish clearly a shadow page should be considered a sort of bug,
> > > given the code assumptions. Or at least a good basis for future bugs.
> > I'm happy for shadow code to have another bit in count_info
> > for its own use.
> > I don't think it's good to have other code (e.g., generic page offlining
> > code) peeking at it, is all. The particular case for a new
> > flag described
> > above sounds fine.
> The new code is not using that flag anymore, it is use the 
> page_get_owner_and_reference() to get the owner.
Yes, I was actually thinking about adding it. Turns out that I realized 
that it's not the best way to do stuff, but I think that I'll do the 
following:
- add a sh_page_is_a_shadow_page() in shadow code to make the code less 
confusing (with a small caveat comment about not being perfectly precise).
- exercise my English skills by writing a comment in page_info that 
summarizes this thread findings about current use if count_info and 
shadow pages.
Thanks,
Gianluca

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