Jiri Olsa <jolsa@xxxxxxxxxx> writes:
> Currently we don't allow re-attaching of trampolines. Once
> it's detached, it can't be re-attach even when the program
> is still loaded.
>
> Adding the possibility to re-attach the loaded tracing
> kernel program.
Hmm, yeah, didn't really consider this case when I added the original
disallow. But don't see why not, so (with one nit below):
Acked-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> kernel/bpf/syscall.c | 25 +++++++++++++++++++------
> kernel/bpf/trampoline.c | 2 +-
> 2 files changed, 20 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 9603de81811a..e14926b2e95a 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2645,14 +2645,27 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
> * target_btf_id using the link_create API.
> *
> * - if tgt_prog == NULL when this function was called using the old
> - * raw_tracepoint_open API, and we need a target from prog->aux
> - *
> - * The combination of no saved target in prog->aux, and no target
> - * specified on load is illegal, and we reject that here.
> + * raw_tracepoint_open API, and we need a target from prog->aux
> + *
> + * The combination of no saved target in prog->aux, and no target
> + * specified on is legal only for tracing programs re-attach, rest
> + * is illegal, and we reject that here.
> */
> if (!prog->aux->dst_trampoline && !tgt_prog) {
> - err = -ENOENT;
> - goto out_unlock;
> + /*
> + * Allow re-attach for tracing programs, if it's currently
> + * linked, bpf_trampoline_link_prog will fail.
> + */
> + if (prog->type != BPF_PROG_TYPE_TRACING) {
> + err = -ENOENT;
> + goto out_unlock;
> + }
> + if (!prog->aux->attach_btf) {
> + err = -EINVAL;
> + goto out_unlock;
> + }
I'm wondering about the two different return codes here. Under what
circumstances will aux->attach_btf be NULL, and why is that not an
ENOENT error? :)
-Toke
