On 3/17/23 15:23, Andrii Nakryiko wrote:
On Wed, Mar 15, 2023 at 7:37 PM Kui-Feng Lee <kuifeng@xxxxxxxx> wrote:
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@xxxxxxxx>
---
tools/lib/bpf/libbpf.c | 90 +++++++++++++++++++++++++++++++-----------
1 file changed, 66 insertions(+), 24 deletions(-)
[...]
- 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)) {
+ /* w/o a real 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) {
- err = -errno;
+ fd = bpf_link_create(map->fd, -1, BPF_STRUCT_OPS, NULL);
pass 0, not -1. BPF APIs have a convention that fd=0 means "no fd was
provided". And actually kernel should have rejected this -1, so please
check why that didn't happen in your testing, we might be missing some
kernel validation.
Oh! probe_perf_link() also pass -1 as well.
I will fix it.
+ if (fd < 0) {
free(link);
- return libbpf_err_ptr(err);
+ return libbpf_err_ptr(fd);
}
- 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,
--
2.34.1
