Nouveau - Mar 2025 - [PATCH v2 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

changes in v2:
 - updated safety comments
 - fixed rustdoc comment spacing
 - reworded commit messages to be imperative
 - Link to v1:
https://lore.kernel.org/rust-for-linux/20250315024235.5282-1-andrewjballance at
gmail.com/

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            | 62 ++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 10 deletions(-)

-- 
2.48.1

implement 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..18bcc59f0b38 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;
+        }
+
+        let drop_range = len..self.len();
+
+        // SAFETY: `drop_range` is a subrange of `[0, len)` by the bounds check
above.
+        let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
+
+        // SAFETY:
+        // - this will always shrink the vector because of the above bounds
check
+        // - [`new_len`, `self.len`) will be dropped through the call to
`drop_in_place` below
+        unsafe { self.set_len(len) };
+
+        // SAFETY:
+        // - the dropped values are valid `T`s by the type invariant
+        // - we are allowed to invalidate [`new_len`, `old_len`) because we
just changed the
+        //   len, therefore we have exclusive access to [`new_len`, `old_len`)
+        unsafe { ptr::drop_in_place(ptr) };
+    }
 }
 
 impl<T: Clone, A: Allocator> Vec<T, A> {
-- 
2.48.1

implement 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 | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 18bcc59f0b38..eb6d40a1bf8b 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -554,6 +554,32 @@ 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`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// 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 Sun, Mar 16, 2025 at 06:16:42AM -0500, Andrew Ballance
wrote:
> implement 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..18bcc59f0b38 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;
> +        }
> +
> +        let drop_range = len..self.len();
> +
> +        // SAFETY: `drop_range` is a subrange of `[0, len)` by the bounds
check above.
> +        let ptr: *mut [T] = unsafe { self.get_unchecked_mut(drop_range) };
> +
> +        // SAFETY:
> +        // - this will always shrink the vector because of the above
bounds check
> +        // - [`new_len`, `self.len`) will be dropped through the call to
`drop_in_place` below
We've just figured out that this part is not needed after all, sorry for the
inconvenience. No need to resend for this though, I can remove this line when
applying the patch.
> +        unsafe { self.set_len(len) };
> +
> +        // SAFETY:
> +        // - the dropped values are valid `T`s by the type invariant
> +        // - we are allowed to invalidate [`new_len`, `old_len`) because
we just changed the
> +        //   len, therefore we have exclusive access to [`new_len`,
`old_len`)
> +        unsafe { ptr::drop_in_place(ptr) };
> +    }
>  }
>  
>  impl<T: Clone, A: Allocator> Vec<T, A> {
> -- 
> 2.48.1
>

On Sun, Mar 16, 2025 at 7:17?AM Andrew Ballance
<andrewjballance at gmail.com> wrote:
>
> implement 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 | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>
> diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
> index 18bcc59f0b38..eb6d40a1bf8b 100644
> --- a/rust/kernel/alloc/kvec.rs
> +++ b/rust/kernel/alloc/kvec.rs
> @@ -554,6 +554,32 @@ 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`.
> +    ///
> +    /// # Examples
> +    ///
> +    /// ```
> +    /// 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(())
> +        }
> +    }
You can avoid underflow checking in debug builds by using `checked_sub`:

        match new_len.checked_sub(self.len()) {
            Some(n) => self.extend_with(n, value, flags),
            None => {
                self.truncate(new_len);
                Ok(())
            }
        }
>  }
>
>  impl<T, A> Drop for Vec<T, A>
> --
> 2.48.1
>
>
Either way:

Reviewed-by: Tamir Duberstein <tamird at gmail.com>

On 3/16/25 12:16 PM, 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
> 
> changes in v2:
>   - updated safety comments
>   - fixed rustdoc comment spacing
>   - reworded commit messages to be imperative
>   - Link to v1:
https://lore.kernel.org/rust-for-linux/20250315024235.5282-1-andrewjballance at
gmail.com/
> 
> Andrew Ballance (3):
>    rust: alloc: add Vec::truncate method
>    rust: alloc: add Vec::resize method
With the following changes, applied to rust/alloc-next, thanks!

   - Rewrote safety comment of set_len().
   - Use checked_sub(), as suggested by Tamir.
>    gpu: nova-core: remove completed Vec extentions from task list
Applied to nova-next, thanks!
>   Documentation/gpu/nova/core/todo.rst | 10 -----
>   rust/kernel/alloc/kvec.rs            | 62 ++++++++++++++++++++++++++++
>   2 files changed, 62 insertions(+), 10 deletions(-)
>