rust: alloc: add Vec::zeroed method

Add a constructor for kernel Vec that allocates a vector of a given length
with all elements zero-initialized. Memory is allocated with the __GFP_ZERO
flag, matching the existing KBox::zeroed() pattern.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260731201017.2580713-2-ttabi@nvidia.com
Co-developed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/alloc/kvec.rs

@@ -9,6 +9,7 @@
         Vmalloc,
         VmallocPageIter, //
     },
+    flags::__GFP_ZERO,
     layout::ArrayLayout,
     AllocError,
     Allocator,
@@ -51,6 +52,8 @@
     }, //
 };
 
+use pin_init::Zeroable;
+
 mod errors;
 pub use self::errors::{InsertError, PushError, RemoveError};
 
@@ -532,6 +535,30 @@ pub fn with_capacity(capacity: usize, flags: Flags) -> Result<Self, AllocError>
         Ok(v)
     }
 
+    /// Creates a new [`Vec`] with `n` zero-initialized elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = KVec::<u32>::zeroed(20, GFP_KERNEL)?;
+    ///
+    /// assert!(v.iter().all(|&x| x == 0));
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn zeroed(n: usize, flags: Flags) -> Result<Self, AllocError>
+    where
+        T: Zeroable,
+    {
+        let mut v = Self::with_capacity(n, flags | __GFP_ZERO)?;
+
+        // SAFETY:
+        // - `n <= capacity - len`: `with_capacity(n)` guarantees capacity >= n, len is 0.
+        // - All elements in `[0, n)` are initialized: `__GFP_ZERO` zeroes the allocation,
+        //   and `T: Zeroable` guarantees all-zeroes is a valid bit pattern.
+        unsafe { v.inc_len(n) };
+        Ok(v)
+    }
+
     /// Creates a `Vec<T, A>` from a pointer, a length and a capacity using the allocator `A`.
     ///
     /// # Examples