Re: [PATCH v2 1/5] rust: types: add `Owned` type and `Ownable` trait

[Abdiel Janulgue]

Hi Alice, Boqun:

On 24/10/2024 10:33, Alice Ryhl wrote:
> > > > > > > Please rename this function to from_raw to match the name used by
> > > > > > > other similar functions.
> > > > > > >
> > > > > > > Also, I don't love this wording. We don't really want to guarantee
> > > > > > > that it is unique. For example, pages have one primary owner, but
> > > > > > > there can be others who also have refcounts to the page, so it's not
> > > > > > > really unique. I think you just want to say that `ptr` must point at a
> > > > >
> > > > > But then when `Owned<Page>` dropped, it will call __free_pages() which
> > > > > invalidate any other existing users. Do you assume that the users will
> > > > > use pointers anyway, so it's their unsafe responsiblity to guarantee
> > > > > that they don't use an invalid pointer?
> > > > >
> > > > > Also I assume you mean the others have refcounts to the page *before* an
> > > > > `Owned<Page>` is created, right? Because if we really have a use case
> > > > > where we want to have multiple users of a page after `Owned<Page>`
> > > > > created, we should better provide a `Owned<Page>` to `ARef<Page>`
> > > > > function.
> > > >
> > > > The __free_pages function just decrements a refcount. If there are
> > > > other references to it, it's not actually freed.
> > >
> > > Then why don't we use page_put() there? ;-) And instead of
> > > `Owned<Page>`, we can wrap the kernel::page as `ARef<Page>`, no?
> >
> > I don't think there's a function called page_put?
>
> Sorry I confused myself. It's because it's called put_page.

How do I proceed with this? Should we use the page's reference count to 
decide when to free the allocation and use put_page() instead of 
__free_pages() in Page::Drop?.

In that case, there would be no need for `Ownable`, right? As we could 
just return ARef<Page> in both vmalloc_to_page() case and in 
Page::alloc_page(), letting the kernel handle ownership internally.

Regards,
Abdiel