Andrii Nakryiko <andriin@xxxxxx> writes:
> With bpf_link abstraction supported by kernel explicitly, add
> pinning/unpinning API for links. Also allow to create (open) bpf_link from BPF
> FS file.
>
> This API allows to have an "ephemeral" FD-based BPF links (like raw tracepoint
> or fexit/freplace attachments) surviving user process exit, by pinning them in
> a BPF FS, which is an important use case for long-running BPF programs.
>
> As part of this, expose underlying FD for bpf_link. While legacy bpf_link's
> might not have a FD associated with them (which will be expressed as
> a bpf_link with fd=-1), kernel's abstraction is based around FD-based usage,
> so match it closely. This, subsequently, allows to have a generic
> pinning/unpinning API for generalized bpf_link. For some types of bpf_links
> kernel might not support pinning, in which case bpf_link__pin() will return
> error.
>
> With FD being part of generic bpf_link, also get rid of bpf_link_fd in favor
> of using vanialla bpf_link.
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 131 +++++++++++++++++++++++++++++++--------
> tools/lib/bpf/libbpf.h | 5 ++
> tools/lib/bpf/libbpf.map | 5 ++
> 3 files changed, 114 insertions(+), 27 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 996162801f7a..f8c4042e5855 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -6931,6 +6931,8 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
> struct bpf_link {
> int (*detach)(struct bpf_link *link);
> int (*destroy)(struct bpf_link *link);
> + char *pin_path; /* NULL, if not pinned */
> + int fd; /* hook FD, -1 if not applicable */
> bool disconnected;
> };
>
> @@ -6960,26 +6962,109 @@ int bpf_link__destroy(struct bpf_link *link)
> err = link->detach(link);
> if (link->destroy)
> link->destroy(link);
> + if (link->pin_path)
> + free(link->pin_path);
This will still detach the link even if it's pinned, won't it? What's
the expectation, that the calling application just won't call
bpf_link__destroy() if it pins the link? But then it will leak memory?
Or is it just that __destroy() will close the fd, but if it's pinned the
kernel won't actually detach anything? In that case, it seems like the
function name becomes somewhat misleading?
-Toke
