batch: Fix DeleteKeyBatch (#198)

when dealing with partial deletion, more context on #162

Signed-off-by: Francisco Javier Honduvilla Coto <javierhonduco@gmail.com>

libbpfgo.go

@@ -877,7 +877,8 @@ func (b *BPFMap) UpdateBatch(keys, values unsafe.Pointer, count uint32) error {
 // DeleteKeyBatch allows for batch deletion of multiple elements in the map.
 //
 // `count` number of keys will be deleted from the map. Passing an argument that greater than the number of keys
-// in the map will cause the function to return a syscall.EPERM as an error.
+// in the map will cause the function to delete fewer keys than requested. See the inline comment in
+// `GetValueAndDeleteBatch` for more context.
 func (b *BPFMap) DeleteKeyBatch(keys unsafe.Pointer, count uint32) error {
 	countC := C.uint(count)
 
@@ -887,17 +888,13 @@ func (b *BPFMap) DeleteKeyBatch(keys unsafe.Pointer, count uint32) error {
 		Flags:     C.BPF_ANY,
 	}
 
-	errC := C.bpf_map_delete_batch(b.fd, keys, &countC, bpfMapBatchOptsToC(opts))
-	if errC != 0 {
-		sc := syscall.Errno(-errC)
-		if sc != syscall.EFAULT {
-			if uint32(countC) != count {
-				return fmt.Errorf("failed to batch delete ALL keys from map %s, deleted (%d/%d): %w", b.name, uint32(countC), count, sc)
-			}
-		}
-		return fmt.Errorf("failed to batch delete keys from map %s: %w", b.name, syscall.Errno(-errC))
+	ret, errC := C.bpf_map_delete_batch(b.fd, keys, &countC, bpfMapBatchOptsToC(opts))
+
+	if ret != 0 && errC != syscall.ENOENT {
+		return fmt.Errorf("failed to batch delete keys %v in map %s: ret %d (err: %s)", keys, b.name, ret, errC)
 	}
 
+	// ret = -1 && errno == syscall.ENOENT indicates a partial deletion.
 	return nil
 }
 

selftest/map-batch/main.go

@@ -110,7 +110,12 @@ func main() {
 	}
 
 	// Test batch delete.
-	testerMap.DeleteKeyBatch(unsafe.Pointer(&keys[0]), uint32(len(keys)-1))
+	// Trying to delete more keys than we have.
+	err = testerMap.DeleteKeyBatch(unsafe.Pointer(&keys[0]), uint32(len(keys)+100))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "testerMap.DeleteKeyBatch was expected to not fail")
+		os.Exit(-1)
+	}
 
 	// Ensure value is no longer there.
 	_, err = testerMap.GetValue(unsafe.Pointer(&keys[0]))
@@ -119,6 +124,20 @@ func main() {
 		os.Exit(-1)
 	}
 
+	// Re-add deleted entries.
+	if err := testerMap.UpdateBatch(unsafe.Pointer(&keys[0]), unsafe.Pointer(&values[0]), uint32(len(keys))); err != nil {
+		fmt.Fprintf(os.Stderr, "testerMap.UpdateBatch failed: %v", err)
+		os.Exit(-1)
+	}
+
+	// Test batch delete.
+	// Trying to delete fewer or equal keys than we have.
+	err = testerMap.DeleteKeyBatch(unsafe.Pointer(&keys[0]), uint32(len(keys)-1))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "testerMap.DeleteKeyBatch was expected to not fail")
+		os.Exit(-1)
+	}
+
 	// Test batch lookup and delete when requesting more elements than are in the map.
 	deleteKeys = make([]uint32, 3)
 	nextKey = uint32(0)