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Date: Sat, 29 Jun 2019 23:44:03 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc: Andrii Nakryiko <andriin@...com>, Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
Kernel Team <kernel-team@...com>,
Song Liu <songliubraving@...com>
Subject: Re: [PATCH v3 bpf-next 4/4] tools/bpftool: switch map event_pipe to
libbpf's perf_buffer
Re-sending as plain text, first time it somehow turned into HTML... :(
On Sat, Jun 29, 2019 at 11:24 AM Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
>
> On Fri, 28 Jun 2019 22:53:09 -0700, Andrii Nakryiko wrote:
> > map_info_len = sizeof(map_info);
> > map_fd = map_parse_fd_and_info(&argc, &argv, &map_info, &map_info_len);
> > - if (map_fd < 0)
> > + if (map_fd < 0) {
> > + p_err("failed to get map info");
>
> Can't do, map_parse_fd_and_info() prints an error already, we can't
> have multiple errors in JSON.
Oh.. I need to be more careful with printing error in bpftool due to
this JSON business... Thanks!
>
> > return -1;
> > + }
> >
> > if (map_info.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
> > p_err("map is not a perf event array");
> > @@ -205,7 +157,7 @@ int do_event_pipe(int argc, char **argv)
> > char *endptr;
> >
> > NEXT_ARG();
> > - cpu = strtoul(*argv, &endptr, 0);
> > + ctx.cpu = strtoul(*argv, &endptr, 0);
> > if (*endptr) {
> > p_err("can't parse %s as CPU ID", **argv);
> > goto err_close_map;
> > @@ -216,7 +168,7 @@ int do_event_pipe(int argc, char **argv)
> > char *endptr;
> >
> > NEXT_ARG();
> > - index = strtoul(*argv, &endptr, 0);
> > + ctx.idx = strtoul(*argv, &endptr, 0);
> > if (*endptr) {
> > p_err("can't parse %s as index", **argv);
> > goto err_close_map;
> > @@ -228,45 +180,32 @@ int do_event_pipe(int argc, char **argv)
> > goto err_close_map;
> > }
> >
> > - do_all = false;
> > + ctx.all_cpus = false;
> > }
> >
> > - if (!do_all) {
> > - if (index == -1 || cpu == -1) {
> > + if (!ctx.all_cpus) {
> > + if (ctx.idx == -1 || ctx.cpu == -1) {
> > p_err("cpu and index must be specified together");
> > goto err_close_map;
>
> Now that you look at err looks like we're missing an err = -1 assignment
> here? but...
No need, see below.
>
> > }
> > -
> > - nfds = 1;
> > } else {
> > - nfds = min(get_possible_cpus(), map_info.max_entries);
> > - cpu = 0;
> > - index = 0;
> > + ctx.cpu = 0;
> > + ctx.idx = 0;
> > }
> >
> > - rings = calloc(nfds, sizeof(rings[0]));
> > - if (!rings)
> > + opts.attr = &perf_attr;
> > + opts.event_cb = print_bpf_output;
> > + opts.ctx = &ctx;
> > + opts.cpu_cnt = ctx.all_cpus ? 0 : 1;
> > + opts.cpus = &ctx.cpu;
> > + opts.map_keys = &ctx.idx;
> > +
> > + pb = perf_buffer__new_raw(map_fd, MMAP_PAGE_CNT, &opts);
> > + err = libbpf_get_error(pb);
> > + if (err) {
> > + p_err("failed to create perf buffer: %s (%d)",
> > + strerror(err), err);
> > goto err_close_map;
> > -
> > - pfds = calloc(nfds, sizeof(pfds[0]));
> > - if (!pfds)
> > - goto err_free_rings;
> > -
> > - for (i = 0; i < nfds; i++) {
> > - rings[i].cpu = cpu + i;
> > - rings[i].key = index + i;
> > -
> > - rings[i].fd = bpf_perf_event_open(map_fd, rings[i].key,
> > - rings[i].cpu);
> > - if (rings[i].fd < 0)
> > - goto err_close_fds_prev;
> > -
> > - rings[i].mem = perf_event_mmap(rings[i].fd);
> > - if (!rings[i].mem)
> > - goto err_close_fds_current;
> > -
> > - pfds[i].fd = rings[i].fd;
> > - pfds[i].events = POLLIN;
> > }
> >
> > signal(SIGINT, int_exit);
> > @@ -277,35 +216,25 @@ int do_event_pipe(int argc, char **argv)
> > jsonw_start_array(json_wtr);
> >
> > while (!stop) {
> > - poll(pfds, nfds, 200);
> > - for (i = 0; i < nfds; i++)
> > - perf_event_read(&rings[i], &tmp_buf, &tmp_buf_sz);
> > + err = perf_buffer__poll(pb, 200);
> > + if (err < 0 && err != -EINTR) {
> > + p_err("perf buffer polling failed: %s (%d)",
> > + strerror(err), err);
> > + goto err_close_pb;
> > + }
> > }
> > - free(tmp_buf);
> >
> > if (json_output)
> > jsonw_end_array(json_wtr);
> >
> > - for (i = 0; i < nfds; i++) {
> > - perf_event_unmap(rings[i].mem);
> > - close(rings[i].fd);
> > - }
> > - free(pfds);
> > - free(rings);
> > + perf_buffer__free(pb);
> > close(map_fd);
> >
> > return 0;
> >
> > -err_close_fds_prev:
> > - while (i--) {
> > - perf_event_unmap(rings[i].mem);
> > -err_close_fds_current:
> > - close(rings[i].fd);
> > - }
> > - free(pfds);
> > -err_free_rings:
> > - free(rings);
> > +err_close_pb:
> > + perf_buffer__free(pb);
> > err_close_map:
> > close(map_fd);
> > - return -1;
> > + return err ? -1 : 0;
>
> ... how can we return 0 on the error path?
Good catch! I initially was going to merge success and error path, but
after seeing how many explicit `err = <something>` I had to do I
abandoned the effort, but forgot to undo this `return -1` change. I'll
return -1 unconditionally.
>
> > }
>
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