On Wed, Nov 22, 2023 at 11:22 AM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote: > > Currently, it's not allowed to attach an fentry/fexit prog to another > one of the same type. At the same time it's not uncommon to see a > tracing program with lots of logic in use, and the attachment limitation > prevents usage of fentry/fexit for performance analysis (e.g. with > "bpftool prog profile" command) in this case. An example could be > falcosecurity libs project that uses tp_btf tracing programs. > > Following the corresponding discussion [1], the reason for that is to > avoid tracing progs call cycles without introducing more complex > solutions. Relax "no same type" requirement to "no progs that are > already an attach target themselves" for the tracing type. In this way > only a standalone tracing program (without any other progs attached to > it) could be attached to another one, and no cycle could be formed. Actually, is it really possible to have tracing programs form a cycle? AFAICT, attach_prog_fd is specified at BPF_PROG_LOAD. So a program can never attach to another program loaded after it. Did I miss something? Only BPF_PROG_TYPE_EXT program can change target_fd at BPF_LINK_CREATE time. Thanks, Song
