On Mon, Apr 05, 2021 at 04:15:54PM +0200, Toke Høiland-Jørgensen wrote:

Jiri Olsa [off-list ref] writes:

quoted

On Sat, Apr 03, 2021 at 11:21:55AM -0700, Alexei Starovoitov wrote:

quoted

On Sat, Apr 03, 2021 at 01:24:12PM +0200, Toke Høiland-Jørgensen wrote:

quoted

quoted

 	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? :)

The feature makes sense to me as well.
I don't quite see how it would get here with attach_btf == NULL.
Maybe WARN_ON then?

right, that should be always there

quoted

Also if we're allowing re-attach this way why exclude PROG_EXT and LSM?

I was enabling just what I needed for the test, which is so far
the only use case.. I'll see if I can enable that for all of them

How would that work? For PROG_EXT we clear the destination on the first
attach (to avoid keeping a ref on it), so re-attach can only be done
with an explicit target (which already works just fine)...

right, I'm just looking on it ;-) extensions already seem allow for that,
I'll check LSM

jirka