Re: [PATCH bpf-next 5/9] samples: bpf: refactor ibumad program with libbpf

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Nov 17, 2020 at 7:05 PM Daniel T. Lee <danieltimlee@gmail.com> wrote:
>
> On Wed, Nov 18, 2020 at 11:52 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Tue, Nov 17, 2020 at 6:57 AM Daniel T. Lee <danieltimlee@gmail.com> wrote:
> > >
> > > This commit refactors the existing ibumad program with libbpf bpf
> > > loader. Attach/detach of Tracepoint bpf programs has been managed
> > > with the generic bpf_program__attach() and bpf_link__destroy() from
> > > the libbpf.
> > >
> > > Also, instead of using the previous BPF MAP definition, this commit
> > > refactors ibumad MAP definition with the new BTF-defined MAP format.
> > >
> > > To verify that this bpf program works without an infiniband device,
> > > try loading ib_umad kernel module and test the program as follows:
> > >
> > >     # modprobe ib_umad
> > >     # ./ibumad
> > >
> > > Moreover, TRACE_HELPERS has been removed from the Makefile since it is
> > > not used on this program.
> > >
> > > Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> > > ---
> > >  samples/bpf/Makefile      |  2 +-
> > >  samples/bpf/ibumad_kern.c | 26 +++++++--------
> > >  samples/bpf/ibumad_user.c | 66 ++++++++++++++++++++++++++++++---------
> > >  3 files changed, 65 insertions(+), 29 deletions(-)
> > >
> > > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > > index 36b261c7afc7..bfa595379493 100644
> > > --- a/samples/bpf/Makefile
> > > +++ b/samples/bpf/Makefile
> > > @@ -109,7 +109,7 @@ xsk_fwd-objs := xsk_fwd.o
> > >  xdp_fwd-objs := xdp_fwd_user.o
> > >  task_fd_query-objs := task_fd_query_user.o $(TRACE_HELPERS)
> > >  xdp_sample_pkts-objs := xdp_sample_pkts_user.o $(TRACE_HELPERS)
> > > -ibumad-objs := bpf_load.o ibumad_user.o $(TRACE_HELPERS)
> > > +ibumad-objs := ibumad_user.o
> > >  hbm-objs := hbm.o $(CGROUP_HELPERS) $(TRACE_HELPERS)
> > >
> > >  # Tell kbuild to always build the programs
> > > diff --git a/samples/bpf/ibumad_kern.c b/samples/bpf/ibumad_kern.c
> > > index 3a91b4c1989a..26dcd4dde946 100644
> > > --- a/samples/bpf/ibumad_kern.c
> > > +++ b/samples/bpf/ibumad_kern.c
> > > @@ -16,19 +16,19 @@
> > >  #include <bpf/bpf_helpers.h>
> > >
> > >
> > > -struct bpf_map_def SEC("maps") read_count = {
> > > -       .type        = BPF_MAP_TYPE_ARRAY,
> > > -       .key_size    = sizeof(u32), /* class; u32 required */
> > > -       .value_size  = sizeof(u64), /* count of mads read */
> > > -       .max_entries = 256, /* Room for all Classes */
> > > -};
> > > -
> > > -struct bpf_map_def SEC("maps") write_count = {
> > > -       .type        = BPF_MAP_TYPE_ARRAY,
> > > -       .key_size    = sizeof(u32), /* class; u32 required */
> > > -       .value_size  = sizeof(u64), /* count of mads written */
> > > -       .max_entries = 256, /* Room for all Classes */
> > > -};
> > > +struct {
> > > +       __uint(type, BPF_MAP_TYPE_ARRAY);
> > > +       __type(key, u32); /* class; u32 required */
> > > +       __type(value, u64); /* count of mads read */
> > > +       __uint(max_entries, 256); /* Room for all Classes */
> > > +} read_count SEC(".maps");
> > > +
> > > +struct {
> > > +       __uint(type, BPF_MAP_TYPE_ARRAY);
> > > +       __type(key, u32); /* class; u32 required */
> > > +       __type(value, u64); /* count of mads written */
> > > +       __uint(max_entries, 256); /* Room for all Classes */
> > > +} write_count SEC(".maps");
> > >
> > >  #undef DEBUG
> > >  #ifndef DEBUG
> > > diff --git a/samples/bpf/ibumad_user.c b/samples/bpf/ibumad_user.c
> > > index fa06eef31a84..66a06272f242 100644
> > > --- a/samples/bpf/ibumad_user.c
> > > +++ b/samples/bpf/ibumad_user.c
> > > @@ -23,10 +23,15 @@
> > >  #include <getopt.h>
> > >  #include <net/if.h>
> > >
> > > -#include "bpf_load.h"
> > > +#include <bpf/bpf.h>
> > >  #include "bpf_util.h"
> > >  #include <bpf/libbpf.h>
> > >
> > > +struct bpf_link *tp_links[3] = {};
> > > +struct bpf_object *obj;
> >
> > statics and you can drop = {} part.
> >
> > > +static int map_fd[2];
> > > +static int tp_cnt;
> > > +
> > >  static void dump_counts(int fd)
> > >  {
> > >         __u32 key;
> > > @@ -53,6 +58,11 @@ static void dump_all_counts(void)
> > >  static void dump_exit(int sig)
> > >  {
> > >         dump_all_counts();
> > > +       /* Detach tracepoints */
> > > +       while (tp_cnt)
> > > +               bpf_link__destroy(tp_links[--tp_cnt]);
> > > +
> > > +       bpf_object__close(obj);
> > >         exit(0);
> > >  }
> > >
> > > @@ -73,19 +83,11 @@ static void usage(char *cmd)
> > >
> > >  int main(int argc, char **argv)
> > >  {
> > > +       struct bpf_program *prog;
> > >         unsigned long delay = 5;
> > > +       char filename[256];
> > >         int longindex = 0;
> > >         int opt;
> > > -       char bpf_file[256];
> > > -
> > > -       /* Create the eBPF kernel code path name.
> > > -        * This follows the pattern of all of the other bpf samples
> > > -        */
> > > -       snprintf(bpf_file, sizeof(bpf_file), "%s_kern.o", argv[0]);
> > > -
> > > -       /* Do one final dump when exiting */
> > > -       signal(SIGINT, dump_exit);
> > > -       signal(SIGTERM, dump_exit);
> > >
> > >         while ((opt = getopt_long(argc, argv, "hd:rSw",
> > >                                   long_options, &longindex)) != -1) {
> > > @@ -107,10 +109,38 @@ int main(int argc, char **argv)
> > >                 }
> > >         }
> > >
> > > -       if (load_bpf_file(bpf_file)) {
> > > -               fprintf(stderr, "ERROR: failed to load eBPF from file : %s\n",
> > > -                       bpf_file);
> > > -               return 1;
> > > +       /* Do one final dump when exiting */
> > > +       signal(SIGINT, dump_exit);
> > > +       signal(SIGTERM, dump_exit);
> > > +
> > > +       snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> > > +       obj = bpf_object__open_file(filename, NULL);
> > > +       if (libbpf_get_error(obj)) {
> > > +               fprintf(stderr, "ERROR: opening BPF object file failed\n");
> > > +               return 0;
> >
> > not really a success, no?
> >
> > > +       }
> > > +
> > > +       /* load BPF program */
> > > +       if (bpf_object__load(obj)) {
> > > +               fprintf(stderr, "ERROR: loading BPF object file failed\n");
> > > +               goto cleanup;
> > > +       }
> > > +
> > > +       map_fd[0] = bpf_object__find_map_fd_by_name(obj, "read_count");
> > > +       map_fd[1] = bpf_object__find_map_fd_by_name(obj, "write_count");
> > > +       if (map_fd[0] < 0 || map_fd[1] < 0) {
> > > +               fprintf(stderr, "ERROR: finding a map in obj file failed\n");
> > > +               goto cleanup;
> > > +       }
> > > +
> > > +       bpf_object__for_each_program(prog, obj) {
> > > +               tp_links[tp_cnt] = bpf_program__attach(prog);
> > > +               if (libbpf_get_error(tp_links[tp_cnt])) {
> > > +                       fprintf(stderr, "ERROR: bpf_program__attach failed\n");
> > > +                       tp_links[tp_cnt] = NULL;
> > > +                       goto cleanup;
> > > +               }
> > > +               tp_cnt++;
> > >         }
> >
> > This cries for the BPF skeleton... But one step at a time :)
> >
>
> I will make sure it'll be updated by using skeleton next time. :D
>
> > >
> > >         while (1) {
> > > @@ -118,5 +148,11 @@ int main(int argc, char **argv)
> > >                 dump_all_counts();
> > >         }
> > >
> > > +cleanup:
> > > +       /* Detach tracepoints */
> > > +       while (tp_cnt)
> > > +               bpf_link__destroy(tp_links[--tp_cnt]);
> > > +
> > > +       bpf_object__close(obj);
> > >         return 0;
> >
> > same, in a lot of cases it's not a success, probably need int err
> > variable somewhere.
> >
>
> I will correct the return code and send the next version of patch.
>
> Thanks for your time and effort for the review.

You don't have to write that every time :) It's an implicit contract:
you contribute your time to prepare, test, and submit a patch.
Maintainers and reviewers contribute theirs to review, maybe improve,
and eventually apply it. Together as a community we move the needle.

>
> --
> Best,
> Daniel T. Lee