Fix return values from bpf_map_delete_elem etc helpers (#362)

Per https://github.com/iovisor/bpf-docs/blob/master/bpf_helpers.rst
negative numbers indicate failure.

Signed-off-by: Dave Thaler <dthaler@microsoft.com>

include/ebpf_helpers.h

@@ -38,7 +38,7 @@ EBPF_HELPER(void*, bpf_map_lookup_elem, (struct bpf_map * map, void* key));
  * @param[in] value Value to insert into the map.
  * @param[in] flags Map flags.
  * @retval EBPF_SUCCESS The operation was successful.
- * @retval EBPF_NO_MEMORY Unable to allocate resources for this
+ * @retval -EBPF_NO_MEMORY Unable to allocate resources for this
  *  entry.
  */
 EBPF_HELPER(int64_t, bpf_map_update_elem, (struct bpf_map * map, void* key, void* value, uint64_t flags));
@@ -52,7 +52,7 @@ EBPF_HELPER(int64_t, bpf_map_update_elem, (struct bpf_map * map, void* key, void
  * @param[in] map Map to update.
  * @param[in] key Key to use when searching and updating the map.
  * @retval EBPF_SUCCESS The operation was successful.
- * @retval EBPF_INVALID_ARGUMENT One or more parameters are invalid.
+ * @retval -EBPF_INVALID_ARGUMENT One or more parameters are invalid.
  */
 EBPF_HELPER(int64_t, bpf_map_delete_elem, (struct bpf_map * map, void* key));
 #ifndef __doxygen
@@ -66,9 +66,9 @@ EBPF_HELPER(int64_t, bpf_map_delete_elem, (struct bpf_map * map, void* key));
  * @param[in] prog_array_map Map of program fds.
  * @param[in] index Index in map of program to call.
  * @retval EBPF_SUCCESS The operation was successful.
- * @retval EBPF_INVALID_ARGUMENT One or more parameters are invalid.
+ * @retval -EBPF_INVALID_ARGUMENT One or more parameters are invalid.
  */
-EBPF_HELPER(int, bpf_tail_call, (void* ctx, struct bpf_map* prog_array_map, uint32_t index));
+EBPF_HELPER(int64_t, bpf_tail_call, (void* ctx, struct bpf_map* prog_array_map, uint32_t index));
 #ifndef __doxygen
 #define bpf_tail_call ((bpf_tail_call_t)4)
 #endif

libs/execution_context/ebpf_core.c

@@ -26,9 +26,9 @@ static void*
 _ebpf_core_map_find_element(ebpf_map_t* map, const uint8_t* key);
 static int64_t
 _ebpf_core_map_update_element(ebpf_map_t* map, const uint8_t* key, const uint8_t* data, uint64_t flags);
-static void
+static int64_t
 _ebpf_core_map_delete_element(ebpf_map_t* map, const uint8_t* key);
-static long
+static int64_t
 _ebpf_core_tail_call(void* ctx, ebpf_map_t* map, uint32_t index);
 
 #define EBPF_CORE_GLOBAL_HELPER_EXTENSION_VERSION 0
@@ -937,22 +937,22 @@ static int64_t
 _ebpf_core_map_update_element(ebpf_map_t* map, const uint8_t* key, const uint8_t* value, uint64_t flags)
 {
     UNREFERENCED_PARAMETER(flags);
-    return ebpf_map_update_entry(map, key, value) == EBPF_SUCCESS ? 0 : -1;
+    return -ebpf_map_update_entry(map, key, value);
 }
 
-static void
+static int64_t
 _ebpf_core_map_delete_element(ebpf_map_t* map, const uint8_t* key)
 {
-    ebpf_map_delete_entry(map, key);
+    return -ebpf_map_delete_entry(map, key);
 }
 
-static long
+static int64_t
 _ebpf_core_tail_call(void* context, ebpf_map_t* map, uint32_t index)
 {
     // Get program from map[index].
     ebpf_program_t* callee = ebpf_map_get_program_from_entry(map, (uint8_t*)&index, sizeof(index));
     if (callee == NULL) {
-        return -1;
+        return -EBPF_INVALID_ARGUMENT;
     }
 
     // TODO(issue #344): Jump to (not call) the callee.

tests/unit/libbpf_test.cpp

@@ -314,4 +314,4 @@ TEST_CASE("good tail_call", "[libbpf]")
     _ebpf_test_tail_call("tail_call.o", 6);
 }
 
-TEST_CASE("bad tail_call", "[libbpf]") { _ebpf_test_tail_call("tail_call_bad.o", -1); }
+TEST_CASE("bad tail_call", "[libbpf]") { _ebpf_test_tail_call("tail_call_bad.o", -EBPF_INVALID_ARGUMENT); }