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[PATCH v15 9/9] rust: page: add `from_raw()`

Andreas Hindborg posted 9 patches 1 month, 1 week ago
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[PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Andreas Hindborg 1 month, 1 week ago 
Add a method to `Page` that allows construction of an instance from `struct
page` pointer.

Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
---
 rust/kernel/page.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
index 4591b7b01c3d2..803f3e3d76b22 100644
--- a/rust/kernel/page.rs
+++ b/rust/kernel/page.rs
@@ -191,6 +191,17 @@ pub fn nid(&self) -> i32 {
         unsafe { bindings::page_to_nid(self.as_ptr()) }
     }
 
+    /// Create a `&Page` from a raw `struct page` pointer
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must be valid for use as a reference for the duration of `'a`.
+    pub unsafe fn from_raw<'a>(ptr: *const bindings::page) -> &'a Self {
+        // SAFETY: By function safety requirements, ptr is not null and is
+        // valid for use as a reference.
+        unsafe { &*Opaque::cast_from(ptr).cast::<Self>() }
+    }
+
     /// Runs a piece of code with this page mapped to an address.
     ///
     /// The page is unmapped when this call returns.

-- 
2.51.2
Re: [PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Miguel Ojeda 1 month, 1 week ago 
On Fri, Feb 20, 2026 at 10:52 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> +    /// Create a `&Page` from a raw `struct page` pointer

Please end sentences with a period.

> +        // SAFETY: By function safety requirements, ptr is not null and is

Please use Markdown in comments: `ptr`.

> +    /// `ptr` must be valid for use as a reference for the duration of `'a`.

Since we will likely try to starting introducing at least a subset of
the Safety Standard soon, we should try to use standard terms.

So I think this "valid for use as a reference" is not an established
one, no? Isn't "convertible to a shared reference" the official term?

  https://doc.rust-lang.org/std/ptr/index.html#pointer-to-reference-conversion

In fact, I see `as_ref_unchecked()` and `as_mut_unchecked()` just got
stabilized for 1.95.0, so we should probably starting using those were
applicable as we bump the minimum, but we should probably use already
a similar wording as the standard library for the safety section and
the comment:

  "`ptr` must be [convertible to a reference](...)."

where the term is a link to that section. Cc'ing Benno.

I have created a (future) issue for that:

  https://github.com/Rust-for-Linux/linux/issues/1225

Cc'ing Tamir since this is close to the cast work, so it may interest
him as well.

Cheers,
Miguel
Re: [PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Andreas Hindborg 1 month, 1 week ago 
Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> writes:

> On Fri, Feb 20, 2026 at 10:52 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>
>> +    /// Create a `&Page` from a raw `struct page` pointer
>
> Please end sentences with a period.

Ok.

>
>> +        // SAFETY: By function safety requirements, ptr is not null and is
>
> Please use Markdown in comments: `ptr`.

Ok.

>
>> +    /// `ptr` must be valid for use as a reference for the duration of `'a`.
>
> Since we will likely try to starting introducing at least a subset of
> the Safety Standard soon, we should try to use standard terms.
>
> So I think this "valid for use as a reference" is not an established
> one, no? Isn't "convertible to a shared reference" the official term?
>
>   https://doc.rust-lang.org/std/ptr/index.html#pointer-to-reference-conversion
>
> In fact, I see `as_ref_unchecked()` and `as_mut_unchecked()` just got
> stabilized for 1.95.0, so we should probably starting using those were
> applicable as we bump the minimum, but we should probably use already
> a similar wording as the standard library for the safety section and
> the comment:
>
>   "`ptr` must be [convertible to a reference](...)."

I'll change the wording to the "convertible" one.


Best regards,
Andreas Hindborg
Re: [PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Tamir Duberstein 1 month, 1 week ago 
On Fri, Feb 20, 2026 at 12:34 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Fri, Feb 20, 2026 at 10:52 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
> >
> > +    /// Create a `&Page` from a raw `struct page` pointer
>
> Please end sentences with a period.
>
> > +        // SAFETY: By function safety requirements, ptr is not null and is
>
> Please use Markdown in comments: `ptr`.
>
> > +    /// `ptr` must be valid for use as a reference for the duration of `'a`.
>
> Since we will likely try to starting introducing at least a subset of
> the Safety Standard soon, we should try to use standard terms.
>
> So I think this "valid for use as a reference" is not an established
> one, no? Isn't "convertible to a shared reference" the official term?
>
>   https://doc.rust-lang.org/std/ptr/index.html#pointer-to-reference-conversion
>
> In fact, I see `as_ref_unchecked()` and `as_mut_unchecked()` just got
> stabilized for 1.95.0, so we should probably starting using those were
> applicable as we bump the minimum, but we should probably use already
> a similar wording as the standard library for the safety section and
> the comment:
>
>   "`ptr` must be [convertible to a reference](...)."
>
> where the term is a link to that section. Cc'ing Benno.
>
> I have created a (future) issue for that:
>
>   https://github.com/Rust-for-Linux/linux/issues/1225
>
> Cc'ing Tamir since this is close to the cast work, so it may interest
> him as well.

Thanks Miguel -- FWIW there's no current cast work on my plate, I
believe everything was merged except for provenance which was a bit
too hard to work with given MSRV.
Re: [PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Alice Ryhl 1 month, 1 week ago 
On Fri, Feb 20, 2026 at 10:52 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>
> Add a method to `Page` that allows construction of an instance from `struct
> page` pointer.
>
> Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
> ---
>  rust/kernel/page.rs | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 4591b7b01c3d2..803f3e3d76b22 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs
> @@ -191,6 +191,17 @@ pub fn nid(&self) -> i32 {
>          unsafe { bindings::page_to_nid(self.as_ptr()) }
>      }
>
> +    /// Create a `&Page` from a raw `struct page` pointer
> +    ///
> +    /// # Safety
> +    ///
> +    /// `ptr` must be valid for use as a reference for the duration of `'a`.
> +    pub unsafe fn from_raw<'a>(ptr: *const bindings::page) -> &'a Self {
> +        // SAFETY: By function safety requirements, ptr is not null and is
> +        // valid for use as a reference.
> +        unsafe { &*Opaque::cast_from(ptr).cast::<Self>() }

If you're going to do a pointer cast, then keep it simple and just do
&*ptr.cast().

Alice
Re: [PATCH v15 9/9] rust: page: add `from_raw()`
Posted by Andreas Hindborg 1 month, 1 week ago 
Alice Ryhl <aliceryhl@google.com> writes:

> On Fri, Feb 20, 2026 at 10:52 AM Andreas Hindborg <a.hindborg@kernel.org> wrote:
>>
>> Add a method to `Page` that allows construction of an instance from `struct
>> page` pointer.
>>
>> Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
>> ---
>>  rust/kernel/page.rs | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
>> index 4591b7b01c3d2..803f3e3d76b22 100644
>> --- a/rust/kernel/page.rs
>> +++ b/rust/kernel/page.rs
>> @@ -191,6 +191,17 @@ pub fn nid(&self) -> i32 {
>>          unsafe { bindings::page_to_nid(self.as_ptr()) }
>>      }
>>
>> +    /// Create a `&Page` from a raw `struct page` pointer
>> +    ///
>> +    /// # Safety
>> +    ///
>> +    /// `ptr` must be valid for use as a reference for the duration of `'a`.
>> +    pub unsafe fn from_raw<'a>(ptr: *const bindings::page) -> &'a Self {
>> +        // SAFETY: By function safety requirements, ptr is not null and is
>> +        // valid for use as a reference.
>> +        unsafe { &*Opaque::cast_from(ptr).cast::<Self>() }
>
> If you're going to do a pointer cast, then keep it simple and just do
> &*ptr.cast().

Ok.


Best regards,
Andreas Hindborg

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