tools lib bpf: Extract and collect map names from BPF object file

This patch collects name of maps in BPF object files and saves them into
'maps' field in 'struct bpf_object'. 'bpf_object__get_map_by_name' is
introduced to retrive fd and definitions of a map through its name.

Signed-off-by: He Kuang <hekuang@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: He Kuang <hekuang@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1448614067-197576-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f509825..a298614 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -165,6 +165,7 @@ struct bpf_program {
 
 struct bpf_map {
        int fd;
+       char *name;
        struct bpf_map_def def;
        void *priv;
        bpf_map_clear_priv_t clear_priv;
@@ -526,12 +527,46 @@ bpf_object__init_maps(struct bpf_object *obj, void *data,
        return 0;
 }
 
+static void
+bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx)
+{
+       int i;
+       Elf_Data *symbols = obj->efile.symbols;
+
+       if (!symbols || maps_shndx < 0)
+               return;
+
+       for (i = 0; i < symbols->d_size / sizeof(GElf_Sym); i++) {
+               GElf_Sym sym;
+               size_t map_idx;
+               const char *map_name;
+
+               if (!gelf_getsym(symbols, i, &sym))
+                       continue;
+               if (sym.st_shndx != maps_shndx)
+                       continue;
+
+               map_name = elf_strptr(obj->efile.elf,
+                                     obj->efile.ehdr.e_shstrndx,
+                                     sym.st_name);
+               map_idx = sym.st_value / sizeof(struct bpf_map_def);
+               if (map_idx >= obj->nr_maps) {
+                       pr_warning("index of map \"%s\" is buggy: %zu > %zu\n",
+                                  map_name, map_idx, obj->nr_maps);
+                       continue;
+               }
+               obj->maps[map_idx].name = strdup(map_name);
+               pr_debug("map %zu is \"%s\"\n", map_idx,
+                        obj->maps[map_idx].name);
+       }
+}
+
 static int bpf_object__elf_collect(struct bpf_object *obj)
 {
        Elf *elf = obj->efile.elf;
        GElf_Ehdr *ep = &obj->efile.ehdr;
        Elf_Scn *scn = NULL;
-       int idx = 0, err = 0;
+       int idx = 0, err = 0, maps_shndx = -1;
 
        /* Elf is corrupted/truncated, avoid calling elf_strptr. */
        if (!elf_rawdata(elf_getscn(elf, ep->e_shstrndx), NULL)) {
@@ -581,10 +616,11 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                        err = bpf_object__init_kversion(obj,
                                                        data->d_buf,
                                                        data->d_size);
-               else if (strcmp(name, "maps") == 0)
+               else if (strcmp(name, "maps") == 0) {
                        err = bpf_object__init_maps(obj, data->d_buf,
                                                    data->d_size);
-               else if (sh.sh_type == SHT_SYMTAB) {
+                       maps_shndx = idx;
+               } else if (sh.sh_type == SHT_SYMTAB) {
                        if (obj->efile.symbols) {
                                pr_warning("bpf: multiple SYMTAB in %s\n",
                                           obj->path);
@@ -625,6 +661,9 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                if (err)
                        goto out;
        }
+
+       if (maps_shndx >= 0)
+               bpf_object__init_maps_name(obj, maps_shndx);
 out:
        return err;
 }
@@ -1086,6 +1125,7 @@ void bpf_object__close(struct bpf_object *obj)
        bpf_object__unload(obj);
 
        for (i = 0; i < obj->nr_maps; i++) {
+               zfree(&obj->maps[i].name);
                if (obj->maps[i].clear_priv)
                        obj->maps[i].clear_priv(&obj->maps[i],
                                                obj->maps[i].priv);
@@ -1266,6 +1306,13 @@ int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef)
        return 0;
 }
 
+const char *bpf_map__get_name(struct bpf_map *map)
+{
+       if (!map)
+               return NULL;
+       return map->name;
+}
+
 int bpf_map__set_private(struct bpf_map *map, void *priv,
                         bpf_map_clear_priv_t clear_priv)
 {
@@ -1318,3 +1365,15 @@ bpf_map__next(struct bpf_map *prev, struct bpf_object *obj)
                return NULL;
        return &obj->maps[idx];
 }
+
+struct bpf_map *
+bpf_object__get_map_by_name(struct bpf_object *obj, const char *name)
+{
+       struct bpf_map *pos;
+
+       bpf_map__for_each(pos, obj) {
+               if (strcmp(pos->name, name) == 0)
+                       return pos;
+       }
+       return NULL;
+}

diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index ef63125..a51594c 100644 (file)
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -170,6 +170,8 @@ struct bpf_map_def {
  * it is not a uapi header so no need to consider name clash.
  */
 struct bpf_map;
+struct bpf_map *
+bpf_object__get_map_by_name(struct bpf_object *obj, const char *name);
 
 struct bpf_map *
 bpf_map__next(struct bpf_map *map, struct bpf_object *obj);
@@ -180,6 +182,7 @@ bpf_map__next(struct bpf_map *map, struct bpf_object *obj);
 
 int bpf_map__get_fd(struct bpf_map *map);
 int bpf_map__get_def(struct bpf_map *map, struct bpf_map_def *pdef);
+const char *bpf_map__get_name(struct bpf_map *map);
 
 typedef void (*bpf_map_clear_priv_t)(struct bpf_map *, void *);
 int bpf_map__set_private(struct bpf_map *map, void *priv,