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libbpf: Create a bpf_link in bpf_map__attach_struct_ops().

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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>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230323032405.3735486-5-kuifeng@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Kui-Feng Lee 2023-03-22 20:24:01 -07:00 committed by Martin KaFai Lau
parent 68b04864ca
commit 8d1608d709
1 changed files with 74 additions and 27 deletions
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101
tools/lib/bpf/libbpf.c
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@ -116,6 +116,7 @@ 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[] = {
@ -7686,6 +7687,37 @@ 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_prepare_struct_ops(struct bpf_object *obj)
{
int i;
for (i = 0; i < obj->nr_maps; i++)
if (bpf_map__is_struct_ops(&obj->maps[i]))
bpf_map_prepare_vdata(&obj->maps[i]);
return 0;
}
static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
{
int err, i;
@ -7711,6 +7743,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
err = err ? : bpf_object__load_progs(obj, extra_log_level);
err = err ? : bpf_object_init_prog_arrays(obj);
err = err ? : bpf_object_prepare_struct_ops(obj);
if (obj->gen_loader) {
/* reset FDs */
@ -11579,22 +11612,30 @@ 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))
return -errno;
st_link = container_of(link, struct bpf_link_struct_ops, link);
return 0;
if (st_link->map_fd < 0)
/* w/o a real link */
return bpf_map_delete_elem(link->fd, &zero);
return close(link->fd);
}
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);
@ -11603,31 +11644,37 @@ 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;
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;
}
err = bpf_map_update_elem(map->fd, &zero, st_ops->kern_vdata, 0);
if (err) {
err = -errno;
/* kern_vdata should be prepared during the loading phase. */
err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
/* It can be EBUSY if the map has been used to create or
* update a link before. We don't allow updating the value of
* a struct_ops once it is set. That ensures that the value
* never changed. So, it is safe to skip EBUSY.
*/
if (err && (!(map->def.map_flags & BPF_F_LINK) || err != -EBUSY)) {
free(link);
return libbpf_err_ptr(err);
}
link->detach = bpf_link__detach_struct_ops;
link->fd = map->fd;
link->link.detach = bpf_link__detach_struct_ops;
return link;
if (!(map->def.map_flags & BPF_F_LINK)) {
/* w/o a real link */
link->link.fd = map->fd;
link->map_fd = -1;
return &link->link;
}
fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);
if (fd < 0) {
free(link);
return libbpf_err_ptr(fd);
}
link->link.fd = fd;
link->map_fd = map->fd;
return &link->link;
}
typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,