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tools: libbpf: allow map reuse

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More advanced applications may want to only replace programs without
destroying associated maps.  Allow libbpf users to achieve that.
Instead of always creating all of the maps at load time, expose to
users an API to reconstruct the map object from already existing
map.

The map parameters are read from the kernel and replace the parameters
of the ELF map.  libbpf does not restrict the map replacement, i.e.
the reused map does not have to be compatible with the ELF map
definition.  We relay on the verifier for checking the compatibility
between maps and programs.  The ELF map definition is completely
overwritten by the information read from the kernel, to make sure
libbpf's view of map object corresponds to the actual map.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Jakub Kicinski
2018-07-10 14:43:06 -07:00
committed by Daniel Borkmann
parent 531b014e7a
commit 26736eb9a4
2 changed files with 54 additions and 0 deletions
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53
tools/lib/bpf/libbpf.c
View File

@@ -1035,6 +1035,53 @@ static int bpf_map_find_btf_info(struct bpf_map *map, const struct btf *btf)
return 0;
}
int bpf_map__reuse_fd(struct bpf_map *map, int fd)
{
struct bpf_map_info info = {};
__u32 len = sizeof(info);
int new_fd, err;
char *new_name;
err = bpf_obj_get_info_by_fd(fd, &info, &len);
if (err)
return err;
new_name = strdup(info.name);
if (!new_name)
return -errno;
new_fd = open("/", O_RDONLY | O_CLOEXEC);
if (new_fd < 0)
goto err_free_new_name;
new_fd = dup3(fd, new_fd, O_CLOEXEC);
if (new_fd < 0)
goto err_close_new_fd;
err = zclose(map->fd);
if (err)
goto err_close_new_fd;
free(map->name);
map->fd = new_fd;
map->name = new_name;
map->def.type = info.type;
map->def.key_size = info.key_size;
map->def.value_size = info.value_size;
map->def.max_entries = info.max_entries;
map->def.map_flags = info.map_flags;
map->btf_key_type_id = info.btf_key_type_id;
map->btf_value_type_id = info.btf_value_type_id;
return 0;
err_close_new_fd:
close(new_fd);
err_free_new_name:
free(new_name);
return -errno;
}
static int
bpf_object__create_maps(struct bpf_object *obj)
{
@@ -1047,6 +1094,12 @@ bpf_object__create_maps(struct bpf_object *obj)
struct bpf_map_def *def = &map->def;
int *pfd = &map->fd;
if (map->fd >= 0) {
pr_debug("skip map create (preset) %s: fd=%d\n",
map->name, map->fd);
continue;
}
create_attr.name = map->name;
create_attr.map_ifindex = map->map_ifindex;
create_attr.map_type = def->type;