> On Wed, Dec 20, 2023 at 08:55:43AM +0100, Dmitry Dolgov wrote: > > On Mon, Dec 18, 2023 at 09:10:19PM +0100, Dmitry Dolgov wrote: > > > > > I guess it's corner case that does not make much sense, but still it > > > > > feels more natural to me to set it in attach time > > > > > > > > If we set attach_tracing_prog at attach time, the following will > > > > succeed: > > > > > > > > load (fentry1 -> kernel function) > > > > load (fentry2 -> fentry1) > > > > load (fentry3 -> fentry2) > > > > attach (fentry1) > > > > attach (fentry2) > > > > attach (fentry3) > > > > > > > > We can even make attach chain longer, as long as we load > > > > the chain first. This is really confusing to me. So I think we should > > > > set the flag at load() time. > > > > > > > > Does this make sense? > > > > > > yes, I did not consider this option.. makes sense > > > > Thanks for pointing out this case folks, haven't thought about this > > either. > > > > Just for me to clarify explicitly, the reason why the case (loading a > > chain and only then attaching every program) would work is that there is > > no additional bpf_check_attach_target in bpf_tracing_prog_attach when > > the trampoline is getting reused. I've tried to change this a little, it > > seems to possible to prevent such situation, and still keep > > attach_tracing_prog flag at attach time if there will be one more > > bpf_check_attach_target. > > > > At the same time setting attach_tracing_prog flag at load time would be > > probably less invasive, making it more preferable I guess. Will post the > > new patch series with this change soon. > > Thinking about this more, it seems setting attach_tracing_prog flag at > load time should be done not as a replacement (what I've assumed > originally), but in addition to setting it at attach time. Otherwise, > reattaching the same prog will lead to an inconsistency. On the second thought, at the moment it's not allowed to change an attachment target for a tracing prog. Which means the attach_tracing_prog flag could be set for the whole lifetime of a tracing prog, from load until release -- this way there is even no need to change bpf_tracing_link_release, and the fist patch will become smaller.
