Nouveau - Mar 2025 - [PATCH 0/3] rust: alloc: add Vec::resize and Vec::truncate

This patch series implements the Vec::truncate and Vec::resize methods
that were needed by the nova driver and removes the corresponding item
from their task list

Andrew Ballance (3):
  rust: alloc: add Vec::truncate method
  rust: alloc: add Vec::resize method
  gpu: nova-core: remove completed Vec extentions from task list

 Documentation/gpu/nova/core/todo.rst | 10 -----
 rust/kernel/alloc/kvec.rs            | 61 ++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 10 deletions(-)

-- 
2.48.1

implements the equivalent to the std's Vec::truncate
on the kernel's Vec type.

Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
---
 rust/kernel/alloc/kvec.rs | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index ae9d072741ce..75e9feebb81f 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -452,6 +452,42 @@ pub fn reserve(&mut self, additional: usize, flags:
Flags) -> Result<(), AllocEr
 
         Ok(())
     }
+
+    /// Shortens the vector, setting the length to `len` and drops the removed
values.
+    /// If `len` is greater than or equal to the current length, this does
nothing.
+    ///
+    /// This has no effect on the capacity and will not allocate.
+    /// # Examples
+    /// ```
+    /// let mut v = kernel::kvec![1, 2, 3]?;
+    /// v.truncate(1);
+    /// assert_eq!(v.len(), 1);
+    /// assert_eq!(&v, &[1]);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn truncate(&mut self, len: usize) {
+        if len >= self.len() {
+            return;
+        }
+
+        // [new_len, len) is guaranteed to be valid because [0, len) is
guaranteed to be valid
+        let drop_range = len..self.len();
+
+        // SAFETY:
+        // we can safely ignore the bounds check because we already did our own
check
+        let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
+
+        // SAFETY:
+        // it is safe to shrink the length because the new length is
+        // guaranteed to be less than the old length
+        unsafe { self.set_len(len) };
+
+        // SAFETY:
+        // - the dropped values are valid `T`s
+        // - we are allowed to invalidate [new_len, old_len) because we just
changed the len
+        unsafe { ptr::drop_in_place(ptr) };
+    }
 }
 
 impl<T: Clone, A: Allocator> Vec<T, A> {
-- 
2.48.1

implemnts the equivalent of the rust std's Vec::resize
on the kernel's Vec type.

Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
---
 rust/kernel/alloc/kvec.rs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 75e9feebb81f..cbfef2e56f9c 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -554,6 +554,31 @@ pub fn from_elem(value: T, n: usize, flags: Flags) ->
Result<Self, AllocError> {
 
         Ok(v)
     }
+
+    /// Resizes the [`Vec`] so that `len` is equal to `new_len`.
+    ///
+    /// If `new_len` is smaller than `len`, the `Vec` is [`Vec::truncate`]d.
+    /// If `new_len` is larger, each new slot is filled with clones of `value`.
+    ///
+    /// # Example
+    /// ```
+    /// let mut v = kernel::kvec![1, 2, 3]?;
+    /// v.resize(1, 42, GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1]);
+    ///
+    /// v.resize(3, 42, GFP_KERNEL)?;
+    /// assert_eq!(&v, &[1, 42, 42]);
+    ///
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn resize(&mut self, new_len: usize, value: T, flags: Flags) ->
Result<(), AllocError> {
+        if new_len > self.len() {
+            self.extend_with(new_len - self.len(), value, flags)
+        } else {
+            self.truncate(new_len);
+            Ok(())
+        }
+    }
 }
 
 impl<T, A> Drop for Vec<T, A>
-- 
2.48.1

The requested Vec methods have been implemented thus, removes
the completed item from the nova task list

Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
---
 Documentation/gpu/nova/core/todo.rst | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/Documentation/gpu/nova/core/todo.rst
b/Documentation/gpu/nova/core/todo.rst
index ca08377d3b73..234d753d3eac 100644
--- a/Documentation/gpu/nova/core/todo.rst
+++ b/Documentation/gpu/nova/core/todo.rst
@@ -190,16 +190,6 @@ Rust abstraction for debugfs APIs.
 | Reference: Export GSP log buffers
 | Complexity: Intermediate
 
-Vec extensions
---------------
-
-Implement ``Vec::truncate`` and ``Vec::resize``.
-
-Currently this is used for some experimental code to parse the vBIOS.
-
-| Reference vBIOS support
-| Complexity: Beginner
-
 GPU (general)
 ============ 
-- 
2.48.1

On Sat Mar 15, 2025 at 3:42 AM CET, Andrew Ballance
wrote:
> implements the equivalent to the std's Vec::truncate
> on the kernel's Vec type.
>
> Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
> ---
>  rust/kernel/alloc/kvec.rs | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index ae9d072741ce..75e9feebb81f 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -452,6 +452,42 @@ pub fn reserve(&mut self, additional: usize,
flags: Flags) -> Result<(), AllocEr
>  
>          Ok(())
>      }
> +
> +    /// Shortens the vector, setting the length to `len` and drops the
removed values.
> +    /// If `len` is greater than or equal to the current length, this does
nothing.
> +    ///
> +    /// This has no effect on the capacity and will not allocate.
> +    /// # Examples
> +    /// ```
> +    /// let mut v = kernel::kvec![1, 2, 3]?;
> +    /// v.truncate(1);
> +    /// assert_eq!(v.len(), 1);
> +    /// assert_eq!(&v, &[1]);
> +    ///
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn truncate(&mut self, len: usize) {
> +        if len >= self.len() {
> +            return;
> +        }
> +
> +        // [new_len, len) is guaranteed to be valid because [0, len) is
guaranteed to be valid
> +        let drop_range = len..self.len();
> +
> +        // SAFETY:
> +        // we can safely ignore the bounds check because we already did
our own check
> +        let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
What's this `get_unchecked_mut` method, I don't see it in `rust-next` or
`alloc-next`.
> +
> +        // SAFETY:
> +        // it is safe to shrink the length because the new length is
> +        // guaranteed to be less than the old length
Please take a look at the documentation of `set_len`, in the safety
section you'll find what you need to justify here.
> +        unsafe { self.set_len(len) };
> +
> +        // SAFETY:
A couple points missing:
- why is the pointer valid?
> +        // - the dropped values are valid `T`s
> +        // - we are allowed to invalidate [new_len, old_len) because we
just changed the len
This should justify why the value will never be accessed again.

---
Cheers,
Benno
> +        unsafe { ptr::drop_in_place(ptr) };
> +    }
>  }
>  
>  impl<T: Clone, A: Allocator> Vec<T, A> {

On Sat Mar 15, 2025 at 3:42 AM CET, Andrew Ballance
wrote:
> implemnts the equivalent of the rust std's Vec::resize
> on the kernel's Vec type.
>
> Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
Reviewed-by: Benno Lossin <benno.lossin at proton.me>

---
Cheers,
Benno
> ---
>  rust/kernel/alloc/kvec.rs | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)

Hi Andrew,

On Fri, Mar 14, 2025 at 09:42:32PM -0500, Andrew Ballance
wrote:
> This patch series implements the Vec::truncate and Vec::resize methods
> that were needed by the nova driver and removes the corresponding item
> from their task list
> 
> Andrew Ballance (3):
>   rust: alloc: add Vec::truncate method
>   rust: alloc: add Vec::resize method
>   gpu: nova-core: remove completed Vec extentions from task list
Thanks for picking this up!

Once ready, I will pick up the first two patches for alloc-next and take the
third one through the nova tree.

But you can keep them in the same series for subsequent submissions.

- Danilo

On Fri, Mar 14, 2025 at 09:42:34PM -0500, Andrew Ballance
wrote:
> implemnts the equivalent of the rust std's Vec::resize
> on the kernel's Vec type.
Nit: It is preferred to use the imperative form, i.e. "Implement the
equivalent
[...]".
> 
> Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
> ---
>  rust/kernel/alloc/kvec.rs | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index 75e9feebb81f..cbfef2e56f9c 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -554,6 +554,31 @@ pub fn from_elem(value: T, n: usize, flags: Flags)
-> Result<Self, AllocError> {
>  
>          Ok(v)
>      }
> +
> +    /// Resizes the [`Vec`] so that `len` is equal to `new_len`.
> +    ///
> +    /// If `new_len` is smaller than `len`, the `Vec` is
[`Vec::truncate`]d.
> +    /// If `new_len` is larger, each new slot is filled with clones of
`value`.
> +    ///
> +    /// # Example
Nit: Please add an empty line after the heading.
> +    /// ```
> +    /// let mut v = kernel::kvec![1, 2, 3]?;
> +    /// v.resize(1, 42, GFP_KERNEL)?;
> +    /// assert_eq!(&v, &[1]);
> +    ///
> +    /// v.resize(3, 42, GFP_KERNEL)?;
> +    /// assert_eq!(&v, &[1, 42, 42]);
> +    ///
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn resize(&mut self, new_len: usize, value: T, flags: Flags)
-> Result<(), AllocError> {
> +        if new_len > self.len() {
> +            self.extend_with(new_len - self.len(), value, flags)
> +        } else {
> +            self.truncate(new_len);
> +            Ok(())
> +        }
> +    }
>  }
>  
>  impl<T, A> Drop for Vec<T, A>
> -- 
> 2.48.1
>

On Fri, Mar 14, 2025 at 09:42:33PM -0500, Andrew Ballance
wrote:
> implements the equivalent to the std's Vec::truncate
> on the kernel's Vec type.
> 
> Signed-off-by: Andrew Ballance <andrewjballance at gmail.com>
> ---
>  rust/kernel/alloc/kvec.rs | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index ae9d072741ce..75e9feebb81f 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -452,6 +452,42 @@ pub fn reserve(&mut self, additional: usize,
flags: Flags) -> Result<(), AllocEr
>  
>          Ok(())
>      }
> +
> +    /// Shortens the vector, setting the length to `len` and drops the
removed values.
> +    /// If `len` is greater than or equal to the current length, this does
nothing.
> +    ///
> +    /// This has no effect on the capacity and will not allocate.
Nit: Please also add an empty line here.
> +    /// # Examples
> +    /// ```
> +    /// let mut v = kernel::kvec![1, 2, 3]?;
> +    /// v.truncate(1);
> +    /// assert_eq!(v.len(), 1);
> +    /// assert_eq!(&v, &[1]);
> +    ///
> +    /// # Ok::<(), Error>(())
> +    /// ```
> +    pub fn truncate(&mut self, len: usize) {
> +        if len >= self.len() {
> +            return;
> +        }
> +
> +        // [new_len, len) is guaranteed to be valid because [0, len) is
guaranteed to be valid
We typically use markdown for comments.
> +        let drop_range = len..self.len();
> +
> +        // SAFETY:
> +        // we can safely ignore the bounds check because we already did
our own check
> +        let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
> +
> +        // SAFETY:
> +        // it is safe to shrink the length because the new length is
> +        // guaranteed to be less than the old length
> +        unsafe { self.set_len(len) };
I just sent out a fix [1] for the safety requirements of set_len() in [1], which
I think would be good to consider.

[1] https://lore.kernel.org/rust-for-linux/20250315154436.65065-1-dakr at
kernel.org/