Remove unnecessary Index impls (#22)

Author: Jake-Shadle

src/rings.rs

@@ -163,6 +163,9 @@ struct XskRing<T: 'static> {
     cached_consumed: u32,
     /// Total number of entries in the ring
     count: u32,
+    /// Mask for indexing ops, since rings are required to be power of 2 this
+    /// lets us get away with a simple `&` instead of `%`
+    mask: usize,
 }
 
 /// Creates a memory map for a ring
@@ -196,6 +199,7 @@ fn map_ring<T>(
             producer,
             consumer,
             count,
+            mask: count as usize - 1,
             ring,
             cached_produced: 0,
             cached_consumed: 0,
@@ -210,8 +214,11 @@ struct XskProducer<T: 'static>(XskRing<T>);
 
 impl<T> XskProducer<T> {
     #[inline]
-    fn mask(&self) -> usize {
-        self.0.count as usize - 1
+    fn set(&mut self, i: usize, item: T) {
+        // SAFETY: The mask ensures the index is always within range
+        unsafe {
+            *self.0.ring.get_unchecked_mut(i & self.0.mask) = item;
+        }
     }
 
     /// The equivalent of [`xsk_ring_prod__reserve`](https://docs.ebpf.io/ebpf-library/libxdp/functions/xsk_ring_prod__reserve/)
@@ -255,31 +262,14 @@ impl<T> XskProducer<T> {
     }
 }
 
-impl<T> std::ops::Index<usize> for XskProducer<T> {
-    type Output = T;
-
-    #[inline]
-    fn index(&self, index: usize) -> &Self::Output {
-        // SAFETY: each ring impl ensures the index is valid
-        unsafe { self.0.ring.get_unchecked(index) }
-    }
-}
-
-impl<T> std::ops::IndexMut<usize> for XskProducer<T> {
-    #[inline]
-    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
-        // SAFETY: each ring impl ensures the index is valid
-        unsafe { self.0.ring.get_unchecked_mut(index) }
-    }
-}
-
 /// Used for rx and completion rings where userspace is the consumer
 struct XskConsumer<T: 'static>(XskRing<T>);
 
-impl<T> XskConsumer<T> {
+impl<T: Copy> XskConsumer<T> {
     #[inline]
-    fn mask(&self) -> usize {
-        self.0.count as usize - 1
+    fn get(&self, i: usize) -> T {
+        // SAFETY: The mask ensures the index is always within range
+        unsafe { *self.0.ring.get_unchecked(i & self.0.mask) }
     }
 
     /// The equivalent of [`xsk_ring_cons__peek`](https://docs.ebpf.io/ebpf-library/libxdp/functions/xsk_ring_cons__peek/)
@@ -316,14 +306,3 @@ impl<T> XskConsumer<T> {
         self.0.consumer.fetch_add(nb, Ordering::Release);
     }
 }
-
-impl<T> std::ops::Index<usize> for XskConsumer<T> {
-    type Output = T;
-
-    #[inline]
-    fn index(&self, index: usize) -> &Self::Output {
-        // SAFETY: Since we force power of 2 the same as libxdp, we know
-        // it will always be within bounds
-        unsafe { self.0.ring.get_unchecked(index) }
-    }
-}

src/rings/completion.rs

@@ -49,9 +49,9 @@ impl CompletionRing {
         let (actual, idx) = self.ring.peek(requested as _);
 
         if actual > 0 {
-            let mask = self.ring.mask();
             for i in idx..idx + actual {
-                let addr = self.ring[i & mask];
+                // SAFETY: The mask ensures the index is always within range
+                let addr = self.ring.get(i);
                 umem.free_addr(addr);
             }
 
@@ -74,9 +74,8 @@ impl CompletionRing {
         let (actual, idx) = self.ring.peek(requested as _);
 
         if actual > 0 {
-            let mask = self.ring.mask();
             for (ts, i) in timestamps.iter_mut().zip(idx..idx + actual) {
-                let addr = self.ring[i & mask];
+                let addr = self.ring.get(i);
                 *ts = umem.free_get_timestamp(addr);
             }
 

src/rings/fill.rs

@@ -60,9 +60,8 @@ impl FillRing {
         let (actual, idx) = self.ring.reserve(requested as _);
 
         if actual > 0 {
-            let mask = self.ring.mask();
             for i in idx..idx + actual {
-                self.ring[i & mask] = available.pop_front().unwrap();
+                self.ring.set(i, available.pop_front().unwrap());
             }
 
             self.ring.submit(actual as _);

src/rings/rx.rs

@@ -57,9 +57,8 @@ impl RxRing {
         let (actual, idx) = self.ring.peek(nb as _);
 
         if actual > 0 {
-            let mask = self.ring.mask();
             for i in idx..idx + actual {
-                let desc = self.ring[i & mask];
+                let desc = self.ring.get(i);
                 packets.push_front(
                     // SAFETY: The user is responsible for the lifetime of the
                     // packets we are returning

src/rings/tx.rs

@@ -65,13 +65,12 @@ impl TxRing {
         let (actual, idx) = self.ring.reserve(requested as _);
 
         if actual > 0 {
-            let mask = self.ring.mask();
             for i in idx..idx + actual {
                 let Some(packet) = packets.pop_back() else {
                     unreachable!()
                 };
 
-                self.ring[i & mask] = packet.into();
+                self.ring.set(i, packet.into());
             }
 
             self.ring.submit(actual as _);