[PATCH bpf-next v2 3/6] libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

Kui-Feng Lee
2023-02-23T01:12:54Z

bpf_map__attach_struct_ops() was creating a dummy bpf_link as a
placeholder, but now it is constructing an authentic one by calling
bpf_link_create() if the map has the BPF_F_LINK flag.

You can flag a struct_ops map with BPF_F_LINK by calling
bpf_map__set_map_flags().

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
tools/lib/bpf/bpf.c | 2 +
tools/lib/bpf/libbpf.c | 84 ++++++++++++++++++++++++++++++++----------
2 files changed, 66 insertions(+), 20 deletions(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 9aff98f42a3d..6e270bb95ab7 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -731,6 +731,8 @@ int bpf_link_create(int prog_fd, int target_fd,
if (!OPTS_ZEROED(opts, tracing))
return libbpf_err(-EINVAL);
break;
+ case BPF_STRUCT_OPS:
+ break;
default:
if (!OPTS_ZEROED(opts, flags))
return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 35a698eb825d..40f239cd1150 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -115,6 +115,7 @@ static const char * const attach_type_name[] = {
[BPF_SK_REUSEPORT_SELECT_OR_MIGRATE] = "sk_reuseport_select_or_migrate",
[BPF_PERF_EVENT] = "perf_event",
[BPF_TRACE_KPROBE_MULTI] = "trace_kprobe_multi",
+ [BPF_STRUCT_OPS] = "struct_ops",
};

static const char * const link_type_name[] = {
@@ -7677,6 +7678,26 @@ static int bpf_object__resolve_externs(struct bpf_object *obj,
return 0;
}

+static void bpf_map_prepare_vdata(const struct bpf_map *map)
+{
+ struct bpf_struct_ops *st_ops;
+ __u32 i;
+
+ st_ops = map->st_ops;
+ for (i = 0; i < btf_vlen(st_ops->type); i++) {
+ struct bpf_program *prog = st_ops->progs[i];
+ void *kern_data;
+ int prog_fd;
+
+ if (!prog)
+ continue;
+
+ prog_fd = bpf_program__fd(prog);
+ kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
+ *(unsigned long *)kern_data = prog_fd;
+ }
+}
+
static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
{
int err, i;
@@ -7728,6 +7749,10 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
btf__free(obj->btf_vmlinux);
obj->btf_vmlinux = NULL;

+ for (i = 0; i < obj->nr_maps; i++)
+ if (bpf_map__is_struct_ops(&obj->maps[i]))
+ bpf_map_prepare_vdata(&obj->maps[i]);
+
obj->loaded = true; /* doesn't matter if successfully or not */

if (err)
@@ -11429,11 +11454,29 @@ struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
return link;
}

+struct bpf_link_struct_ops {
+ struct bpf_link link;
+ int map_fd;
+};
+
static int bpf_link__detach_struct_ops(struct bpf_link *link)
{
+ struct bpf_link_struct_ops *st_link;
__u32 zero = 0;

- if (bpf_map_delete_elem(link->fd, &zero))
+ st_link = container_of(link, struct bpf_link_struct_ops, link);
+
+ if (st_link->map_fd < 0) {
+ /* Fake bpf_link */
+ if (bpf_map_delete_elem(link->fd, &zero))
+ return -errno;
+ return 0;
+ }
+
+ if (bpf_map_delete_elem(st_link->map_fd, &zero))
+ return -errno;
+
+ if (close(link->fd))
return -errno;

return 0;
@@ -11441,10 +11484,9 @@ static int bpf_link__detach_struct_ops(struct bpf_link *link)

struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
{
- struct bpf_struct_ops *st_ops;
- struct bpf_link *link;
- __u32 i, zero = 0;
- int err;
+ struct bpf_link_struct_ops *link;
+ __u32 zero = 0;
+ int err, fd;

if (!bpf_map__is_struct_ops(map) || map->fd == -1)
return libbpf_err_ptr(-EINVAL);
@@ -11453,31 +11495,33 @@ struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
if (!link)
return libbpf_err_ptr(-EINVAL);

- st_ops = map->st_ops;
- for (i = 0; i < btf_vlen(st_ops->type); i++) {
- struct bpf_program *prog = st_ops->progs[i];
- void *kern_data;
- int prog_fd;
+ err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
+ if (err) {
+ err = -errno;
+ free(link);
+ return libbpf_err_ptr(err);
+ }

- if (!prog)
- continue;
+ link->link.detach = bpf_link__detach_struct_ops;

- prog_fd = bpf_program__fd(prog);
- kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
- *(unsigned long *)kern_data = prog_fd;
+ if (!(map->def.map_flags & BPF_F_LINK)) {
+ /* Fake bpf_link */
+ link->link.fd = map->fd;
+ link->map_fd = -1;
+ return &link->link;
}

- err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
- if (err) {
+ fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
+ if (fd < 0) {
err = -errno;
free(link);
return libbpf_err_ptr(err);
}

- link->detach = bpf_link__detach_struct_ops;
- link->fd = map->fd;
+ link->link.fd = fd;
+ link->map_fd = map->fd;

- return link;
+ return &link->link;
}

typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
--
2.30.2