Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > On Mon, Dec 16, 2019 at 07:17:59PM +0100, Björn Töpel wrote: >> On Mon, 16 Dec 2019 at 16:28, Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: >> > >> > This adds a new tracepoint, xdp_prog_return, which is triggered at every >> > XDP program return. This was first discussed back in August[0] as a way to >> > hook XDP into the kernel drop_monitor framework, to have a one-stop place >> > to find all packet drops in the system. >> > >> > Because trace/events/xdp.h includes filter.h, some ifdef guarding is needed >> > to be able to use the tracepoint from bpf_prog_run_xdp(). If anyone has any >> > ideas for how to improve on this, please to speak up. Sending this RFC >> > because of this issue, and to get some feedback from Ido on whether this >> > tracepoint has enough data for drop_monitor usage. >> > >> >> I get that it would be useful, but can it be solved with BPF tracing >> (i.e. tracing BPF with BPF)? It would be neat not adding another >> tracepoint in the fast-path... > > That was my question as well. > Here is an example from Eelco: > https://lore.kernel.org/bpf/78D7857B-82E4-42BC-85E1-E3D7C97BF840@xxxxxxxxxx/ > BPF_TRACE_2("fexit/xdp_prog_simple", trace_on_exit, > struct xdp_buff*, xdp, int, ret) > { > bpf_debug("fexit: [ifindex = %u, queue = %u, ret = %d]\n", > xdp->rxq->dev->ifindex, xdp->rxq->queue_index, ret); > > return 0; > } > 'ret' is return code from xdp program. > Such approach is per xdp program, but cheaper when not enabled > and faster when it's triggering comparing to static tracepoint. > Anything missing there that you'd like to see? For userspace, sure, the fentry/fexit stuff is fine. The main use case for this new tracepoint is to hook into the (in-kernel) drop monitor. Dunno if that can be convinced to hook into the BPF tracing infrastructure instead of tracepoints. Ido, WDYT? -Toke
