[Cc Kairui in case he's interested]
On Thu, Nov 21, 2024 at 11:30:13AM +0200, Abdiel Janulgue wrote:
> Hi Boqun, Matthew:
>
> On 21/11/2024 02:24, Boqun Feng wrote:
> > > > So if I understand correctly, what Abdiel needs here is a way to convert
> > > > a virtual address to the corresponding page, would it make sense to just
> > > > use folio in this case? Abdiel, what's the operation you are going to
> > > > call on the page you get?
> > >
> > > Yes that's basically it. The goal here is represent those existing struct
> > > page within this rust Page abstraction but at the same time to avoid taking
> > > over its ownership.
> > >
> > > Boqun, Alice, should we reconsider Ownable and Owned trait again? :)
> > >
> >
> > Could you use folio in your case? If so, we can provide a simple binding
> > for folio which should be `AlwaysRefcounted`, and re-investigate how
> > page should be wrapped.
> >
>
> I'm not sure. Is there a way to get the struct folio from a vmalloc'd
> address, e.g vmalloc_to_folio()?
>
I think you can use page_folio(vmalloc_to_page(..)) to get the folio,
but one thing to notice is that folio is guaranteed to be a non-tail
page, so if you want to do something later for the particular page (if
it's a tail page), you will need to know the offset of the that page in
folio. You can do something like below:
pub fn page_slice_to_folio<'a>(page: &PageSlice) -> Result<(&'a Folio, usize)> {
...
let page = vmalloc_to_page(ptr);
let folio = page_folio(page);
let offset = folio_page_idx(folio, page);
Ok((folio, offset))
}
And you have a folio -> page function like:
pub struct Folio(Opaque<bindings::folio>);
impl Folio {
pub fn nth_page(&self, n: usize) -> &Page {
&*(nth_page(self.0.get(), n))
}
}
Of course, this is me acting as I know MM ;-) but I feel this is the way
to go. And if binder can use folio as well (I don't see a reason why
not, but it's extra work, so defer to Alice), then we would only need
the `pub struct Page { inner: Opaque<bindings::page> }` part in your
patch #1, and can avoid doing `Ownable` or `AlwaysRefcounted` for
`Page`.
Thoughts?
Regards,
Boqun
> Regards,
> Abdiel
