bpf: refactor special field-type detection

Reduce code duplication in detection of the known special field types in
map values. This refactoring helps to avoid copying a chunk of code in
the next patch of the series.

Signed-off-by: Mykyta Yatsenko <[email protected]>
Acked-by: Eduard Zingerman <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mykyta5

kernel/bpf/btf.c

@@ -3478,60 +3478,44 @@ btf_find_graph_root(const struct btf *btf, const struct btf_type *pt,
 	return BTF_FIELD_FOUND;
 }
 
-#define field_mask_test_name(field_type, field_type_str) \
-	if (field_mask & field_type && !strcmp(name, field_type_str)) { \
-		type = field_type;					\
-		goto end;						\
-	}
-
 static int btf_get_field_type(const struct btf *btf, const struct btf_type *var_type,
-			      u32 field_mask, u32 *seen_mask,
-			      int *align, int *sz)
-{
-	int type = 0;
+			      u32 field_mask, u32 *seen_mask, int *align, int *sz)
+{
+	const struct {
+		enum btf_field_type type;
+		const char *const name;
+		const bool is_unique;
+	} field_types[] = {
+		{ BPF_SPIN_LOCK, "bpf_spin_lock", true },
+		{ BPF_RES_SPIN_LOCK, "bpf_res_spin_lock", true },
+		{ BPF_TIMER, "bpf_timer", true },
+		{ BPF_WORKQUEUE, "bpf_wq", true },
+		{ BPF_LIST_HEAD, "bpf_list_head", false },
+		{ BPF_LIST_NODE, "bpf_list_node", false },
+		{ BPF_RB_ROOT, "bpf_rb_root", false },
+		{ BPF_RB_NODE, "bpf_rb_node", false },
+		{ BPF_REFCOUNT, "bpf_refcount", false },
+	};
+	int type = 0, i;
 	const char *name = __btf_name_by_offset(btf, var_type->name_off);
-
-	if (field_mask & BPF_SPIN_LOCK) {
-		if (!strcmp(name, "bpf_spin_lock")) {
-			if (*seen_mask & BPF_SPIN_LOCK)
-				return -E2BIG;
-			*seen_mask |= BPF_SPIN_LOCK;
-			type = BPF_SPIN_LOCK;
-			goto end;
-		}
-	}
-	if (field_mask & BPF_RES_SPIN_LOCK) {
-		if (!strcmp(name, "bpf_res_spin_lock")) {
-			if (*seen_mask & BPF_RES_SPIN_LOCK)
-				return -E2BIG;
-			*seen_mask |= BPF_RES_SPIN_LOCK;
-			type = BPF_RES_SPIN_LOCK;
-			goto end;
-		}
-	}
-	if (field_mask & BPF_TIMER) {
-		if (!strcmp(name, "bpf_timer")) {
-			if (*seen_mask & BPF_TIMER)
-				return -E2BIG;
-			*seen_mask |= BPF_TIMER;
-			type = BPF_TIMER;
-			goto end;
-		}
-	}
-	if (field_mask & BPF_WORKQUEUE) {
-		if (!strcmp(name, "bpf_wq")) {
-			if (*seen_mask & BPF_WORKQUEUE)
+	const char *field_type_name;
+	enum btf_field_type field_type;
+	bool is_unique;
+
+	for (i = 0; i < ARRAY_SIZE(field_types); ++i) {
+		field_type = field_types[i].type;
+		field_type_name = field_types[i].name;
+		is_unique = field_types[i].is_unique;
+		if (!(field_mask & field_type) || strcmp(name, field_type_name))
+			continue;
+		if (is_unique) {
+			if (*seen_mask & field_type)
 				return -E2BIG;
-			*seen_mask |= BPF_WORKQUEUE;
-			type = BPF_WORKQUEUE;
-			goto end;
+			*seen_mask |= field_type;
 		}
+		type = field_type;
+		goto end;
 	}
-	field_mask_test_name(BPF_LIST_HEAD, "bpf_list_head");
-	field_mask_test_name(BPF_LIST_NODE, "bpf_list_node");
-	field_mask_test_name(BPF_RB_ROOT,   "bpf_rb_root");
-	field_mask_test_name(BPF_RB_NODE,   "bpf_rb_node");
-	field_mask_test_name(BPF_REFCOUNT,  "bpf_refcount");
 
 	/* Only return BPF_KPTR when all other types with matchable names fail */
 	if (field_mask & (BPF_KPTR | BPF_UPTR) && !__btf_type_is_struct(var_type)) {
@@ -3545,8 +3529,6 @@ static int btf_get_field_type(const struct btf *btf, const struct btf_type *var_
 	return type;
 }
 
-#undef field_mask_test_name
-
 /* Repeat a number of fields for a specified number of times.
  *
  * Copy the fields starting from the first field and repeat them for