[PATCH RFC bpf-next 07/10] libbpf: Support init of inner maps in light skeleton.

[Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>]

From: Alexei Starovoitov <ast@xxxxxxxxxx>

Add ability to initialize inner maps in light skeleton.

Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
 tools/lib/bpf/bpf_gen_internal.h |  1 +
 tools/lib/bpf/gen_loader.c       | 31 +++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.c           |  6 +++---
 3 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
index 1b27faf71080..e7f6ad53aed6 100644
--- a/tools/lib/bpf/bpf_gen_internal.h
+++ b/tools/lib/bpf/bpf_gen_internal.h
@@ -49,5 +49,6 @@ void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, int kind, int
 struct bpf_core_relo;
 void bpf_gen__record_relo_core(struct bpf_gen *gen, const struct bpf_core_relo *core_relo,
 			       int insn_idx);
+void bpf_gen__populate_outer_map(struct bpf_gen *gen, int outer_map_idx, int key, int inner_map_idx);
 
 #endif
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index 28ecd932713b..35f51d837320 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -763,6 +763,37 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
 	emit_check_err(gen);
 }
 
+void bpf_gen__populate_outer_map(struct bpf_gen *gen, int outer_map_idx, int slot,
+				 int inner_map_idx)
+{
+	int attr_size = offsetofend(union bpf_attr, flags);
+	int map_update_attr, key;
+	union bpf_attr attr;
+
+	memset(&attr, 0, attr_size);
+	pr_debug("gen: populate_outer_map: outer %d key %d inner %d\n",
+		 outer_map_idx, slot, inner_map_idx);
+
+	key = add_data(gen, &slot, sizeof(slot));
+
+	map_update_attr = add_data(gen, &attr, attr_size);
+	move_stack2blob(gen, attr_field(map_update_attr, map_fd), 4,
+			stack_off(map_fd[outer_map_idx]));
+	emit_rel_store(gen, attr_field(map_update_attr, key), key);
+
+	emit(gen, BPF_MOV64_REG(BPF_REG_1, BPF_REG_10));
+	emit(gen, BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, stack_off(map_fd[inner_map_idx])));
+	emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_2, BPF_PSEUDO_MAP_IDX_VALUE,
+					 0, 0, 0, attr_field(map_update_attr, value)));
+	emit(gen, BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1, 0));
+
+	/* emit MAP_UPDATE_ELEM command */
+	emit_sys_bpf(gen, BPF_MAP_UPDATE_ELEM, map_update_attr, attr_size);
+	debug_ret(gen, "populate_outer_map outer %d key %d inner %d",
+		  outer_map_idx, slot, inner_map_idx);
+	emit_check_err(gen);
+}
+
 void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx)
 {
 	int attr_size = offsetofend(union bpf_attr, map_fd);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ed2c4f6661fe..b4ebe19c4f6c 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4693,9 +4693,9 @@ static int init_map_slots(struct bpf_object *obj, struct bpf_map *map)
 		targ_map = map->init_slots[i];
 		fd = bpf_map__fd(targ_map);
 		if (obj->gen_loader) {
-			pr_warn("// TODO map_update_elem: idx %td key %d value==map_idx %td\n",
-				map - obj->maps, i, targ_map - obj->maps);
-			return -ENOTSUP;
+			bpf_gen__populate_outer_map(obj->gen_loader,
+						    map - obj->maps, i,
+						    targ_map - obj->maps);
 		} else {
 			err = bpf_map_update_elem(map->fd, &i, &fd, 0);
 		}
-- 
2.30.2