rust: alloc: add KUnit tests for KVVec shrink_to

Add comprehensive KUnit tests for the shrink_to method for KVVec.
The tests verify:
- Basic shrinking from multiple pages to fewer pages with data integrity
  preservation
- Empty vector shrinking to zero capacity
- No-op behavior when shrinking to a larger capacity than current
- Respect for min_capacity parameter when larger than vector length
These tests ensure that the shrinking logic correctly identifies when
memory can be reclaimed (by freeing at least one page) and that data
integrity is maintained throughout shrink operations.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
Link: https://patch.msgid.link/20260216-binder-shrink-vec-v3-v6-2-ece8e8593e53@zohomail.in
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index e7bc439538e499d47b12b2ef4c279987f4bdc287..6438385e4322e56e99e55639777182cc09052efc 100644 (file)
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -1510,4 +1510,106 @@ mod tests {
             func.push_within_capacity(false).unwrap();
         }
     }
+
+    #[test]
+    fn test_kvvec_shrink_to() {
+        use crate::page::PAGE_SIZE;
+
+        // Create a vector with capacity spanning multiple pages.
+        let mut v = KVVec::<u8>::with_capacity(PAGE_SIZE * 4, GFP_KERNEL).unwrap();
+
+        // Add a few elements.
+        v.push(1, GFP_KERNEL).unwrap();
+        v.push(2, GFP_KERNEL).unwrap();
+        v.push(3, GFP_KERNEL).unwrap();
+
+        let initial_capacity = v.capacity();
+        assert!(initial_capacity >= PAGE_SIZE * 4);
+
+        // Shrink to a capacity that would free at least one page.
+        v.shrink_to(PAGE_SIZE, GFP_KERNEL).unwrap();
+
+        // Capacity should have been reduced.
+        assert!(v.capacity() < initial_capacity);
+        assert!(v.capacity() >= PAGE_SIZE);
+
+        // Elements should be preserved.
+        assert_eq!(v.len(), 3);
+        assert_eq!(v[0], 1);
+        assert_eq!(v[1], 2);
+        assert_eq!(v[2], 3);
+
+        // Shrink to zero (should shrink to len).
+        v.shrink_to(0, GFP_KERNEL).unwrap();
+
+        // Capacity should be at least the length.
+        assert!(v.capacity() >= v.len());
+
+        // Elements should still be preserved.
+        assert_eq!(v.len(), 3);
+        assert_eq!(v[0], 1);
+        assert_eq!(v[1], 2);
+        assert_eq!(v[2], 3);
+    }
+
+    #[test]
+    fn test_kvvec_shrink_to_empty() {
+        use crate::page::PAGE_SIZE;
+
+        // Create a vector with large capacity but no elements.
+        let mut v = KVVec::<u8>::with_capacity(PAGE_SIZE * 4, GFP_KERNEL).unwrap();
+
+        assert!(v.is_empty());
+
+        // Shrink empty vector to zero.
+        v.shrink_to(0, GFP_KERNEL).unwrap();
+
+        // Should have freed the allocation.
+        assert_eq!(v.capacity(), 0);
+        assert!(v.is_empty());
+    }
+
+    #[test]
+    fn test_kvvec_shrink_to_no_op() {
+        use crate::page::PAGE_SIZE;
+
+        // Create a small vector.
+        let mut v = KVVec::<u8>::with_capacity(PAGE_SIZE, GFP_KERNEL).unwrap();
+        v.push(1, GFP_KERNEL).unwrap();
+
+        let capacity_before = v.capacity();
+
+        // Try to shrink to a capacity larger than current - should be no-op.
+        v.shrink_to(capacity_before + 100, GFP_KERNEL).unwrap();
+
+        assert_eq!(v.capacity(), capacity_before);
+        assert_eq!(v.len(), 1);
+        assert_eq!(v[0], 1);
+    }
+
+    #[test]
+    fn test_kvvec_shrink_to_respects_min_capacity() {
+        use crate::page::PAGE_SIZE;
+
+        // Create a vector with large capacity.
+        let mut v = KVVec::<u8>::with_capacity(PAGE_SIZE * 4, GFP_KERNEL).unwrap();
+
+        // Add some elements.
+        for i in 0..10u8 {
+            v.push(i, GFP_KERNEL).unwrap();
+        }
+
+        // Shrink to a min_capacity larger than length.
+        let min_cap = PAGE_SIZE * 2;
+        v.shrink_to(min_cap, GFP_KERNEL).unwrap();
+
+        // Capacity should be at least min_capacity.
+        assert!(v.capacity() >= min_cap);
+
+        // All elements preserved.
+        assert_eq!(v.len(), 10);
+        for i in 0..10u8 {
+            assert_eq!(v[i as usize], i);
+        }
+    }
 }