rust: page: remove unnecessary helper function from doctest

Doctests in `page.rs` contained a helper function `dox` which acted
as a wrapper for using the `?` operator. However, this is not needed
b

rust: page: remove unnecessary helper function from doctest

Doctests in `page.rs` contained a helper function `dox` which acted
as a wrapper for using the `?` operator. However, this is not needed
because doctests are implicitly wrapped in function see [1].

Link: https://doc.rust-lang.org/rustdoc/write-documentation/documentation-tests.html#using--in-doc-tests [1]
Suggested-by: Dirk Behme <[email protected]>
Suggested-by: Miguel Ojeda <[email protected]>
Link: https://lore.kernel.org/rust-for-linux/[email protected]/
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Tamir Duberstein <[email protected]>
Signed-off-by: Daniel Sedlak <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Fixed typo in SoB. Slightly reworded commit. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

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rust: page: add Rust version of PAGE_ALIGN

This is a useful for helper for working with indices into buffers that
consist of several pages. I forgot to include it when I added PAGE_SIZE
and PAGE_MAS

rust: page: add Rust version of PAGE_ALIGN

This is a useful for helper for working with indices into buffers that
consist of several pages. I forgot to include it when I added PAGE_SIZE
and PAGE_MASK for the same purpose in commit fc6e66f4696b ("rust: add
abstraction for `struct page`").

Reviewed-by: Boqun Feng <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Added intra-doc links, formatted comment and replaced "Brackets" with
"Parentheses" as discussed in the list. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

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rust: add abstraction for `struct page`

Adds a new struct called `Page` that wraps a pointer to `struct page`.
This struct is assumed to hold ownership over the page, so that Rust
code can allocate

rust: add abstraction for `struct page`

Adds a new struct called `Page` that wraps a pointer to `struct page`.
This struct is assumed to hold ownership over the page, so that Rust
code can allocate and manage pages directly.

The page type has various methods for reading and writing into the page.
These methods will temporarily map the page to allow the operation. All
of these methods use a helper that takes an offset and length, performs
bounds checks, and returns a pointer to the given offset in the page.

This patch only adds support for pages of order zero, as that is all
Rust Binder needs. However, it is written to make it easy to add support
for higher-order pages in the future. To do that, you would add a const
generic parameter to `Page` that specifies the order. Most of the
methods do not need to be adjusted, as the logic for dealing with
mapping multiple pages at once can be isolated to just the
`with_pointer_into_page` method.

Rust Binder needs to manage pages directly as that is how transactions
are delivered: Each process has an mmap'd region for incoming
transactions. When an incoming transaction arrives, the Binder driver
will choose a region in the mmap, allocate and map the relevant pages
manually, and copy the incoming transaction directly into the page. This
architecture allows the driver to copy transactions directly from the
address space of one process to another, without an intermediate copy
to a kernel buffer.

This code is based on Wedson's page abstractions from the old rust
branch, but it has been modified by Alice by removing the incomplete
support for higher-order pages, by introducing the `with_*` helpers
to consolidate the bounds checking logic into a single place, and
various other changes.

Co-developed-by: Wedson Almeida Filho <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Trevor Gross <[email protected]>
Reviewed-by: Benno Lossin <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Fixed typos and added a few intra-doc links. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>

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