aya-ebpf: add peek operation to stack and queue maps

Signed-off-by: Xiaobo Liu <cppcoffee@gmail.com>

ebpf/aya-ebpf/src/maps/queue.rs

@@ -2,7 +2,7 @@ use core::{cell::UnsafeCell, marker::PhantomData, mem};
 
 use crate::{
     bindings::{bpf_map_def, bpf_map_type::BPF_MAP_TYPE_QUEUE},
-    helpers::{bpf_map_pop_elem, bpf_map_push_elem},
+    helpers::{bpf_map_peek_elem, bpf_map_pop_elem, bpf_map_push_elem},
     maps::PinningType,
 };
 
@@ -63,4 +63,12 @@ impl<T> Queue<T> {
             (ret == 0).then_some(value.assume_init())
         }
     }
+
+    pub fn peek(&self) -> Option<T> {
+        unsafe {
+            let mut value = mem::MaybeUninit::uninit();
+            let ret = bpf_map_peek_elem(self.def.get() as *mut _, value.as_mut_ptr() as *mut _);
+            (ret == 0).then_some(value.assume_init())
+        }
+    }
 }

ebpf/aya-ebpf/src/maps/stack.rs

@@ -2,7 +2,7 @@ use core::{marker::PhantomData, mem};
 
 use crate::{
     bindings::{bpf_map_def, bpf_map_type::BPF_MAP_TYPE_STACK},
-    helpers::{bpf_map_pop_elem, bpf_map_push_elem},
+    helpers::{bpf_map_peek_elem, bpf_map_pop_elem, bpf_map_push_elem},
     maps::PinningType,
 };
 
@@ -64,4 +64,15 @@ impl<T> Stack<T> {
             (ret == 0).then_some(value.assume_init())
         }
     }
+
+    pub fn peek(&mut self) -> Option<T> {
+        unsafe {
+            let mut value = mem::MaybeUninit::uninit();
+            let ret = bpf_map_peek_elem(
+                &mut self.def as *mut _ as *mut _,
+                value.as_mut_ptr() as *mut _,
+            );
+            (ret == 0).then_some(value.assume_init())
+        }
+    }
 }