On Fri, 25 Mar 2022, Andrii Nakryiko wrote: > Last part of architecture-agnostic user-space USDT handling logic is to > set up BPF spec and, optionally, IP-to-ID maps from user-space. > usdt_manager performs a compact spec ID allocation to utilize > fixed-sized BPF maps as efficiently as possible. We also use hashmap to > deduplicate USDT arg spec strings and map identical strings to single > USDT spec, minimizing the necessary BPF map size. usdt_manager supports > arbitrary sequences of attachment and detachment, both of the same USDT > and multiple different USDTs and internally maintains a free list of > unused spec IDs. bpf_link_usdt's logic is extended with proper setup and > teardown of this spec ID free list and supporting BPF maps. > It might be good to describe the relationship between a USDT specification (spec) and the site specific targets that can be associated with it. So the spec is the description of the provider + name + args, and the the target represents the potentially multiple sites associated with that spec. Specs are stored in the spec array map, indexed by spec_id; targets are stored in the ip_map, and these reference a spec id. So from the BPF side we can use the bpf_cookie to look up the spec directly, or if cookies are not supported on the BPF side, we can look up ip -> spec_id mapping in ip_map, and from there can look up the spec_id -> spec in the spec map. Dumb question here: the spec id recycling is a lot of work; instead of maintaining this for the array map, couldn't we use a hashmap for spec ids with a monotonically-increasing next_spec_id value or something similar? > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> one suggestion below, but Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx> > --- > tools/lib/bpf/usdt.c | 167 ++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 166 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c > index 86d5d8390eb1..22f5f56992f8 100644 > --- a/tools/lib/bpf/usdt.c > +++ b/tools/lib/bpf/usdt.c <snip> > opts.ref_ctr_offset = target->sema_off; > + opts.bpf_cookie = man->has_bpf_cookie ? spec_id : 0; > uprobe_link = bpf_program__attach_uprobe_opts(prog, pid, path, > target->rel_ip, &opts); > err = libbpf_get_error(link); should be uprobe_link I think.
