[PATCH RFC bpf-next 3/7] libbpf: Support BPF_MAP_TYPE_STRUCT_OPS in bpf_gen__map_create()

[Siddharth Nayyar]

Handle BPF_MAP_TYPE_STRUCT_OPS in bpf_gen__map_create() when generating
a light skeleton:
- Extend map_create_attr size to include value_type_btf_obj_fd.
- Populate attr.btf_fd from the loader stack when
  btf_vmlinux_value_type_id is set.
- Populate attr.value_size and attr.btf_vmlinux_value_type_id from the
  runtime-resolved values in the loader data blob.
- If the struct_ops type resides in a kernel module (btf_obj_fd > 0),
  populate attr.value_type_btf_obj_fd, set BPF_F_VTYPE_BTF_OBJ_FD in
  attr.map_flags, and close value_type_btf_obj_fd after BPF_MAP_CREATE.

Signed-off-by: Siddharth Nayyar <sidnayyar@xxxxxxxxxx>
---
 tools/lib/bpf/gen_loader.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index 09713c39f71e..6027a2762c35 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -508,7 +508,7 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 			 __u32 key_size, __u32 value_size, __u32 max_entries,
 			 struct bpf_map_create_opts *map_attr, int map_idx)
 {
-	int attr_size = offsetofend(union bpf_attr, map_extra);
+	int attr_size = offsetofend(union bpf_attr, value_type_btf_obj_fd);
 	bool close_inner_map_fd = false;
 	int map_create_attr, idx;
 	union bpf_attr attr;
@@ -532,7 +532,7 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 		 map_name, map_idx, map_type, map_attr->btf_value_type_id,
 		 map_create_attr, attr_size);
 
-	if (map_attr->btf_value_type_id)
+	if (map_attr->btf_value_type_id || map_attr->btf_vmlinux_value_type_id)
 		/* populate union bpf_attr with btf_fd saved in the stack earlier */
 		move_stack2blob(gen, attr_field(map_create_attr, btf_fd), 4,
 				stack_off(btf_fd));
@@ -543,6 +543,27 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 				stack_off(inner_map_fd));
 		close_inner_map_fd = true;
 		break;
+	case BPF_MAP_TYPE_STRUCT_OPS:
+		move_blob2blob(gen, attr_field(map_create_attr, value_size), 4,
+			       value_size);
+		emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
+						 0, 0, 0, map_attr->btf_vmlinux_value_type_id));
+		emit(gen, BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0));
+		emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
+						 0, 0, 0, map_create_attr));
+		emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				      offsetof(union bpf_attr, btf_vmlinux_value_type_id)));
+		emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_0, 32));
+		emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 4));
+		emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				      offsetof(union bpf_attr, value_type_btf_obj_fd)));
+		emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				      offsetof(union bpf_attr, map_flags)));
+		emit(gen, BPF_ALU32_IMM(BPF_OR, BPF_REG_0,
+					tgt_endian(BPF_F_VTYPE_BTF_OBJ_FD)));
+		emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				      offsetof(union bpf_attr, map_flags)));
+		break;
 	default:
 		break;
 	}
@@ -568,6 +589,9 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 	debug_ret(gen, "map_create %s idx %d type %d value_size %d value_btf_id %d",
 		  map_name, map_idx, map_type, value_size,
 		  map_attr->btf_value_type_id);
+	if (map_type == BPF_MAP_TYPE_STRUCT_OPS)
+		emit_sys_close_blob(gen,
+				    attr_field(map_create_attr, value_type_btf_obj_fd));
 	emit_check_err(gen);
 	/* remember map_fd in the stack, if successful */
 	if (map_idx < 0) {

-- 
2.56.0.455.g6c5a503b38-goog