libbpf: Auto-attach struct_ops BPF maps in BPF skeleton

Similarly to `bpf_program`, support `bpf_map` automatic attachment in
`bpf_object__attach_skeleton`. Currently only struct_ops maps could be
attached.

On bpftool side, code-generate links in skeleton struct for struct_ops maps.
Similarly to `bpf_program_skeleton`, set links in `bpf_map_skeleton`.

On libbpf side, extend `bpf_map` with new `autoattach` field to support
enabling or disabling autoattach functionality, introducing
getter/setter for this field.

`bpf_object__(attach|detach)_skeleton` is extended with
attaching/detaching struct_ops maps logic.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240605175135.117127-1-yatsenko@meta.com

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index d244a7de387e7f318e6a22128d381da2da83fdcb..4a4eedfcd47920b313067d42d4b31db5deb0aadd 100644 (file)
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -848,7 +848,7 @@ out:
 }
 
 static void
-codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
+codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped, bool populate_links)
 {
        struct bpf_map *map;
        char ident[256];
@@ -888,6 +888,14 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped)
                        printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n",
                                i, ident);
                }
+
+               if (populate_links && bpf_map__type(map) == BPF_MAP_TYPE_STRUCT_OPS) {
+                       codegen("\
+                               \n\
+                                       s->maps[%zu].link = &obj->links.%s;\n\
+                               ",
+                               i, ident);
+               }
                i++;
        }
 }
@@ -1141,7 +1149,7 @@ static void gen_st_ops_shadow_init(struct btf *btf, struct bpf_object *obj)
 static int do_skeleton(int argc, char **argv)
 {
        char header_guard[MAX_OBJ_NAME_LEN + sizeof("__SKEL_H__")];
-       size_t map_cnt = 0, prog_cnt = 0, file_sz, mmap_sz;
+       size_t map_cnt = 0, prog_cnt = 0, attach_map_cnt = 0, file_sz, mmap_sz;
        DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts);
        char obj_name[MAX_OBJ_NAME_LEN] = "", *obj_data;
        struct bpf_object *obj = NULL;
@@ -1225,6 +1233,10 @@ static int do_skeleton(int argc, char **argv)
                              bpf_map__name(map));
                        continue;
                }
+
+               if (bpf_map__type(map) == BPF_MAP_TYPE_STRUCT_OPS)
+                       attach_map_cnt++;
+
                map_cnt++;
        }
        bpf_object__for_each_program(prog, obj) {
@@ -1297,6 +1309,9 @@ static int do_skeleton(int argc, char **argv)
                                       bpf_program__name(prog));
                }
                printf("\t} progs;\n");
+       }
+
+       if (prog_cnt + attach_map_cnt) {
                printf("\tstruct {\n");
                bpf_object__for_each_program(prog, obj) {
                        if (use_loader)
@@ -1306,6 +1321,19 @@ static int do_skeleton(int argc, char **argv)
                                printf("\t\tstruct bpf_link *%s;\n",
                                       bpf_program__name(prog));
                }
+
+               bpf_object__for_each_map(map, obj) {
+                       if (!get_map_ident(map, ident, sizeof(ident)))
+                               continue;
+                       if (bpf_map__type(map) != BPF_MAP_TYPE_STRUCT_OPS)
+                               continue;
+
+                       if (use_loader)
+                               printf("t\tint %s_fd;\n", ident);
+                       else
+                               printf("\t\tstruct bpf_link *%s;\n", ident);
+               }
+
                printf("\t} links;\n");
        }
 
@@ -1448,7 +1476,7 @@ static int do_skeleton(int argc, char **argv)
                obj_name
        );
 
-       codegen_maps_skeleton(obj, map_cnt, true /*mmaped*/);
+       codegen_maps_skeleton(obj, map_cnt, true /*mmaped*/, true /*links*/);
        codegen_progs_skeleton(obj, prog_cnt, true /*populate_links*/);
 
        codegen("\
@@ -1786,7 +1814,7 @@ static int do_subskeleton(int argc, char **argv)
                }
        }
 
-       codegen_maps_skeleton(obj, map_cnt, false /*mmaped*/);
+       codegen_maps_skeleton(obj, map_cnt, false /*mmaped*/, false /*links*/);
        codegen_progs_skeleton(obj, prog_cnt, false /*links*/);
 
        codegen("\

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index d1627a2ca30bb817213c126265de2df2dff837f6..4a28fac4908a6e119d1e69be2e3a873cc8d20ad4 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -572,6 +572,7 @@ struct bpf_map {
        bool pinned;
        bool reused;
        bool autocreate;
+       bool autoattach;
        __u64 map_extra;
 };
 
@@ -1400,6 +1401,7 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
                map->def.value_size = type->size;
                map->def.max_entries = 1;
                map->def.map_flags = strcmp(sec_name, STRUCT_OPS_LINK_SEC) == 0 ? BPF_F_LINK : 0;
+               map->autoattach = true;
 
                map->st_ops = calloc(1, sizeof(*map->st_ops));
                if (!map->st_ops)
@@ -4819,6 +4821,20 @@ int bpf_map__set_autocreate(struct bpf_map *map, bool autocreate)
        return 0;
 }
 
+int bpf_map__set_autoattach(struct bpf_map *map, bool autoattach)
+{
+       if (!bpf_map__is_struct_ops(map))
+               return libbpf_err(-EINVAL);
+
+       map->autoattach = autoattach;
+       return 0;
+}
+
+bool bpf_map__autoattach(const struct bpf_map *map)
+{
+       return map->autoattach;
+}
+
 int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 {
        struct bpf_map_info info;
@@ -12900,8 +12916,10 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
        __u32 zero = 0;
        int err, fd;
 
-       if (!bpf_map__is_struct_ops(map))
+       if (!bpf_map__is_struct_ops(map)) {
+               pr_warn("map '%s': can't attach non-struct_ops map\n", map->name);
                return libbpf_err_ptr(-EINVAL);
+       }
 
        if (map->fd < 0) {
                pr_warn("map '%s': can't attach BPF map without FD (was it created?)\n", map->name);
@@ -13945,6 +13963,35 @@ int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
                 */
        }
 
+       /* Skeleton is created with earlier version of bpftool
+        * which does not support auto-attachment
+        */
+       if (s->map_skel_sz < sizeof(struct bpf_map_skeleton))
+               return 0;
+
+       for (i = 0; i < s->map_cnt; i++) {
+               struct bpf_map *map = *s->maps[i].map;
+               struct bpf_link **link = s->maps[i].link;
+
+               if (!map->autocreate || !map->autoattach)
+                       continue;
+
+               if (*link)
+                       continue;
+
+               /* only struct_ops maps can be attached */
+               if (!bpf_map__is_struct_ops(map))
+                       continue;
+               *link = bpf_map__attach_struct_ops(map);
+
+               if (!*link) {
+                       err = -errno;
+                       pr_warn("map '%s': failed to auto-attach: %d\n",
+                               bpf_map__name(map), err);
+                       return libbpf_err(err);
+               }
+       }
+
        return 0;
 }
 
@@ -13958,6 +14005,18 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)
                bpf_link__destroy(*link);
                *link = NULL;
        }
+
+       if (s->map_skel_sz < sizeof(struct bpf_map_skeleton))
+               return;
+
+       for (i = 0; i < s->map_cnt; i++) {
+               struct bpf_link **link = s->maps[i].link;
+
+               if (link) {
+                       bpf_link__destroy(*link);
+                       *link = NULL;
+               }
+       }
 }
 
 void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
@@ -13965,8 +14024,7 @@ void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
        if (!s)
                return;
 
-       if (s->progs)
-               bpf_object__detach_skeleton(s);
+       bpf_object__detach_skeleton(s);
        if (s->obj)
                bpf_object__close(*s->obj);
        free(s->maps);

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 26e4e35528c5335101d6cdf19e1eff5503fce9dd..64a6a3d323e378c3ee9c6152db01d7891a6b98c0 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -978,6 +978,23 @@ bpf_object__prev_map(const struct bpf_object *obj, const struct bpf_map *map);
 LIBBPF_API int bpf_map__set_autocreate(struct bpf_map *map, bool autocreate);
 LIBBPF_API bool bpf_map__autocreate(const struct bpf_map *map);
 
+/**
+ * @brief **bpf_map__set_autoattach()** sets whether libbpf has to auto-attach
+ * map during BPF skeleton attach phase.
+ * @param map the BPF map instance
+ * @param autoattach whether to attach map during BPF skeleton attach phase
+ * @return 0 on success; negative error code, otherwise
+ */
+LIBBPF_API int bpf_map__set_autoattach(struct bpf_map *map, bool autoattach);
+
+/**
+ * @brief **bpf_map__autoattach()** returns whether BPF map is configured to
+ * auto-attach during BPF skeleton attach phase.
+ * @param map the BPF map instance
+ * @return true if map is set to auto-attach during skeleton attach phase; false, otherwise
+ */
+LIBBPF_API bool bpf_map__autoattach(const struct bpf_map *map);
+
 /**
  * @brief **bpf_map__fd()** gets the file descriptor of the passed
  * BPF map
@@ -1672,6 +1689,7 @@ struct bpf_map_skeleton {
        const char *name;
        struct bpf_map **map;
        void **mmaped;
+       struct bpf_link **link;
 };
 
 struct bpf_prog_skeleton {

diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index c1ce8aa3520bf4a833fad43de1db5b1caef62c07..40595233dc7fb2ba1536f10ad083b989a433495e 100644 (file)
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -419,6 +419,8 @@ LIBBPF_1.4.0 {
 
 LIBBPF_1.5.0 {
        global:
+               bpf_map__autoattach;
+               bpf_map__set_autoattach;
                bpf_program__attach_sockmap;
                ring__consume_n;
                ring_buffer__consume_n;