Re: [PATCH bpf-next v3 2/2] samples: bpf: refactor perf_event user program with libbpf bpf_link

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

On Fri, Mar 13, 2020 at 6:46 PM Daniel T. Lee <danieltimlee@gmail.com> wrote:
>
> On Sat, Mar 14, 2020 at 3:48 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Fri, Mar 13, 2020 at 4:52 AM Daniel T. Lee <danieltimlee@gmail.com> wrote:
> > >
> > > The bpf_program__attach of libbpf(using bpf_link) is much more intuitive
> > > than the previous method using ioctl.
> > >
> > > bpf_program__attach_perf_event manages the enable of perf_event and
> > > attach of BPF programs to it, so there's no neeed to do this
> > > directly with ioctl.
> > >
> > > In addition, bpf_link provides consistency in the use of API because it
> > > allows disable (detach, destroy) for multiple events to be treated as
> > > one bpf_link__destroy. Also, bpf_link__destroy manages the close() of
> > > perf_event fd.
> > >
> > > This commit refactors samples that attach the bpf program to perf_event
> > > by using libbbpf instead of ioctl. Also the bpf_load in the samples were
> > > removed and migrated to use libbbpf API.
> > >
> > > Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
> > > ---
> > > Changes in v2:
> > >  - check memory allocation is successful
> > >  - clean up allocated memory on error
> > >
> > > Changes in v3:
> > >  - Improve pointer error check (IS_ERR())
> > >  - change to calloc for easier destroy of bpf_link
> > >  - remove perf_event fd list since bpf_link handles fd
> > >  - use newer bpf_object__{open/load} API instead of bpf_prog_load
> > >  - perf_event for _SC_NPROCESSORS_ONLN instead of _SC_NPROCESSORS_CONF
> > >  - find program with name explicitly instead of bpf_program__next
> > >  - unconditional bpf_link__destroy() on cleanup
> > >  - return error code on int_exit
> > >
> > >  samples/bpf/Makefile           |   4 +-
> > >  samples/bpf/sampleip_user.c    | 100 ++++++++++++++++++++++-----------
> > >  samples/bpf/trace_event_user.c |  89 ++++++++++++++++++++---------
> > >  3 files changed, 131 insertions(+), 62 deletions(-)
> > >
> > > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > > index ff0061467dd3..424f6fe7ce38 100644
> > > --- a/samples/bpf/Makefile
> > > +++ b/samples/bpf/Makefile
> > > @@ -88,8 +88,8 @@ xdp2-objs := xdp1_user.o
> > >  xdp_router_ipv4-objs := xdp_router_ipv4_user.o
> > >  test_current_task_under_cgroup-objs := bpf_load.o $(CGROUP_HELPERS) \
> > >                                        test_current_task_under_cgroup_user.o
> > > -trace_event-objs := bpf_load.o trace_event_user.o $(TRACE_HELPERS)
> > > -sampleip-objs := bpf_load.o sampleip_user.o $(TRACE_HELPERS)
> > > +trace_event-objs := trace_event_user.o $(TRACE_HELPERS)
> > > +sampleip-objs := sampleip_user.o $(TRACE_HELPERS)
> > >  tc_l2_redirect-objs := bpf_load.o tc_l2_redirect_user.o
> > >  lwt_len_hist-objs := bpf_load.o lwt_len_hist_user.o
> > >  xdp_tx_iptunnel-objs := xdp_tx_iptunnel_user.o
> > > diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
> > > index b0f115f938bc..05eca7b00e22 100644
> > > --- a/samples/bpf/sampleip_user.c
> > > +++ b/samples/bpf/sampleip_user.c
> > > @@ -10,21 +10,23 @@
> > >  #include <errno.h>
> > >  #include <signal.h>
> > >  #include <string.h>
> > > -#include <assert.h>
> > >  #include <linux/perf_event.h>
> > >  #include <linux/ptrace.h>
> > >  #include <linux/bpf.h>
> > > -#include <sys/ioctl.h>
> > > +#include <bpf/bpf.h>
> > >  #include <bpf/libbpf.h>
> > > -#include "bpf_load.h"
> > >  #include "perf-sys.h"
> > >  #include "trace_helpers.h"
> > >
> > > +#define __must_check
> > > +#include <linux/err.h>
> > > +
> > >  #define DEFAULT_FREQ   99
> > >  #define DEFAULT_SECS   5
> > >  #define MAX_IPS                8192
> > >  #define PAGE_OFFSET    0xffff880000000000
> > >
> > > +static int map_fd;
> > >  static int nr_cpus;
> > >
> > >  static void usage(void)
> > > @@ -34,9 +36,10 @@ static void usage(void)
> > >         printf("       duration   # sampling duration (seconds), default 5\n");
> > >  }
> > >
> > > -static int sampling_start(int *pmu_fd, int freq)
> > > +static int sampling_start(int freq, struct bpf_program *prog,
> > > +                         struct bpf_link *links[])
> > >  {
> > > -       int i;
> > > +       int i, pmu_fd;
> > >
> > >         struct perf_event_attr pe_sample_attr = {
> > >                 .type = PERF_TYPE_SOFTWARE,
> > > @@ -47,26 +50,29 @@ static int sampling_start(int *pmu_fd, int freq)
> > >         };
> > >
> > >         for (i = 0; i < nr_cpus; i++) {
> > > -               pmu_fd[i] = sys_perf_event_open(&pe_sample_attr, -1 /* pid */, i,
> > > +               pmu_fd = sys_perf_event_open(&pe_sample_attr, -1 /* pid */, i,
> > >                                             -1 /* group_fd */, 0 /* flags */);
> > > -               if (pmu_fd[i] < 0) {
> > > +               if (pmu_fd < 0) {
> > >                         fprintf(stderr, "ERROR: Initializing perf sampling\n");
> > >                         return 1;
> > >                 }
> > > -               assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_SET_BPF,
> > > -                            prog_fd[0]) == 0);
> > > -               assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_ENABLE, 0) == 0);
> > > +               links[i] = bpf_program__attach_perf_event(prog, pmu_fd);
> > > +               if (IS_ERR(links[i])) {
> >
> > links[i] = NULL;
> >
>
> Since bpf_program__attach_perf_event will return err code such
> as ERR_PTR(-EINVAL), so it is natural to reset the pointer to NULL!
> Thank you for the heads up!
>
> > > +                       fprintf(stderr, "ERROR: Attach perf event\n");
> > > +                       close(pmu_fd);
> > > +                       return 1;
> > > +               }
> > >         }
> > >
> > >         return 0;
> > >  }
> > >
> > > -static void sampling_end(int *pmu_fd)
> > > +static void sampling_end(struct bpf_link *links[])
> > >  {
> > >         int i;
> > >
> > >         for (i = 0; i < nr_cpus; i++)
> > > -               close(pmu_fd[i]);
> > > +               bpf_link__destroy(links[i]);
> > >  }
> > >
> > >  struct ipcount {
> > > @@ -128,14 +134,17 @@ static void print_ip_map(int fd)
> > >  static void int_exit(int sig)
> > >  {
> > >         printf("\n");
> > > -       print_ip_map(map_fd[0]);
> > > +       print_ip_map(map_fd);
> > >         exit(0);
> > >  }
> > >
> > >  int main(int argc, char **argv)
> > >  {
> > > +       int opt, freq = DEFAULT_FREQ, secs = DEFAULT_SECS, error = 0;
> > > +       struct bpf_program *prog;
> > > +       struct bpf_object *obj;
> >
> > initialize to NULL here
> >
>
> I'll apply this at next version patch.
>
> > > +       struct bpf_link **links;
> > >         char filename[256];
> > > -       int *pmu_fd, opt, freq = DEFAULT_FREQ, secs = DEFAULT_SECS;
> > >
> > >         /* process arguments */
> > >         while ((opt = getopt(argc, argv, "F:h")) != -1) {
> > > @@ -163,38 +172,61 @@ int main(int argc, char **argv)
> > >         }
> > >
> > >         /* create perf FDs for each CPU */
> > > -       nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
> > > -       pmu_fd = malloc(nr_cpus * sizeof(int));
> > > -       if (pmu_fd == NULL) {
> > > -               fprintf(stderr, "ERROR: malloc of pmu_fd\n");
> > > -               return 1;
> > > +       nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> > > +       links = calloc(nr_cpus, sizeof(struct bpf_link *));
> > > +       if (!links) {
> > > +               fprintf(stderr, "ERROR: malloc of links\n");
> > > +               error = 1;
> > > +               goto cleanup;
> > >         }
> > >
> > > -       /* load BPF program */
> > >         snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> > > -       if (load_bpf_file(filename)) {
> > > -               fprintf(stderr, "ERROR: loading BPF program (errno %d):\n",
> > > -                       errno);
> > > -               if (strcmp(bpf_log_buf, "") == 0)
> > > -                       fprintf(stderr, "Try: ulimit -l unlimited\n");
> > > -               else
> > > -                       fprintf(stderr, "%s", bpf_log_buf);
> > > -               return 1;
> > > +       obj = bpf_object__open_file(filename, NULL);
> > > +       if (IS_ERR(obj)) {
> >
> > obj = NULL;
> >
>
> Also again, bpf_object__open_file will return err code of pointer,
> and the pointer needs to be set to NULL for bpf_object__close.
>
> > > +               fprintf(stderr, "ERROR: opening BPF object file failed\n");
> > > +               error = 1;
> > > +               goto cleanup;
> > > +       }
> > > +
> > > +       prog = bpf_object__find_program_by_name(obj, "do_sample");
> > > +       if (!prog) {
> > > +               fprintf(stderr, "ERROR: finding a prog in obj file failed\n");
> > > +               error = 1;
> > > +               goto cleanup;
> > >         }
> > > +
> > > +       /* load BPF program */
> > > +       if (bpf_object__load(obj)) {
> > > +               fprintf(stderr, "ERROR: loading BPF object file failed\n");
> > > +               error = 1;
> > > +               goto cleanup;
> > > +       }
> > > +
> > > +       map_fd = bpf_object__find_map_fd_by_name(obj, "ip_map");
> > > +       if (map_fd < 0) {
> > > +               fprintf(stderr, "ERROR: finding a map in obj file failed\n");
> > > +               error = 1;
> > > +               goto cleanup;
> > > +       }
> > > +
> > >         signal(SIGINT, int_exit);
> > >         signal(SIGTERM, int_exit);
> > >
> > >         /* do sampling */
> > >         printf("Sampling at %d Hertz for %d seconds. Ctrl-C also ends.\n",
> > >                freq, secs);
> > > -       if (sampling_start(pmu_fd, freq) != 0)
> > > -               return 1;
> > > +       if (sampling_start(freq, prog, links) != 0) {
> > > +               error = 1;
> > > +               goto cleanup;
> > > +       }
> > >         sleep(secs);
> > > -       sampling_end(pmu_fd);
> > > -       free(pmu_fd);
> > >
> > > +cleanup:
> > > +       sampling_end(links);
> >
> > bpf_object__destroy(obj)
> >
>
> Sorry, but I might not following you, but is there bpf_object__destroy
> exist in libbpf? I guess you're talking about bpf_object__close, right?

Yeah, I meant bpf_object__close, sorry.

>
> > >         /* output sample counts */
> > > -       print_ip_map(map_fd[0]);
> > > +       if (!error)
> > > +               print_ip_map(map_fd);
> > >
> > > -       return 0;
> > > +       free(links);
> > > +       return error;
> > >  }
> > > diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
> > > index 356171bc392b..5f64ff524cc3 100644
> > > --- a/samples/bpf/trace_event_user.c
> > > +++ b/samples/bpf/trace_event_user.c
> > > @@ -6,22 +6,24 @@
> > >  #include <stdlib.h>
> > >  #include <stdbool.h>
> > >  #include <string.h>
> > > -#include <fcntl.h>
> > > -#include <poll.h>
> > > -#include <sys/ioctl.h>
> > >  #include <linux/perf_event.h>
> > >  #include <linux/bpf.h>
> > >  #include <signal.h>
> > > -#include <assert.h>
> > >  #include <errno.h>
> > >  #include <sys/resource.h>
> > > +#include <bpf/bpf.h>
> > >  #include <bpf/libbpf.h>
> > > -#include "bpf_load.h"
> > >  #include "perf-sys.h"
> > >  #include "trace_helpers.h"
> > >
> > > +#define __must_check
> > > +#include <linux/err.h>
> > > +
> > >  #define SAMPLE_FREQ 50
> > >
> > > +/* counts, stackmap */
> > > +static int map_fd[2];
> > > +struct bpf_program *prog;
> > >  static bool sys_read_seen, sys_write_seen;
> > >
> > >  static void print_ksym(__u64 addr)
> > > @@ -136,23 +138,34 @@ static inline int generate_load(void)
> > >
> > >  static void test_perf_event_all_cpu(struct perf_event_attr *attr)
> > >  {
> > > -       int nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
> > > -       int *pmu_fd = malloc(nr_cpus * sizeof(int));
> > > -       int i, error = 0;
> > > +       int nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> > > +       struct bpf_link **links = calloc(nr_cpus, sizeof(struct bpf_link *));
> > > +       int i, pmu_fd, error = 0;
> > > +
> > > +       if (!links) {
> > > +               printf("malloc of links failed\n");
> > > +               error = 1;
> > > +               goto err;
> > > +       }
> > >
> > >         /* system wide perf event, no need to inherit */
> > >         attr->inherit = 0;
> > >
> > >         /* open perf_event on all cpus */
> > >         for (i = 0; i < nr_cpus; i++) {
> > > -               pmu_fd[i] = sys_perf_event_open(attr, -1, i, -1, 0);
> > > -               if (pmu_fd[i] < 0) {
> > > +               pmu_fd = sys_perf_event_open(attr, -1, i, -1, 0);
> > > +               if (pmu_fd < 0) {
> > >                         printf("sys_perf_event_open failed\n");
> > >                         error = 1;
> > >                         goto all_cpu_err;
> > >                 }
> > > -               assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
> > > -               assert(ioctl(pmu_fd[i], PERF_EVENT_IOC_ENABLE) == 0);
> > > +               links[i] = bpf_program__attach_perf_event(prog, pmu_fd);
> > > +               if (IS_ERR(links[i])) {
> > > +                       printf("bpf_program__attach_perf_event failed\n");
> > > +                       close(pmu_fd);
> > > +                       error = 1;
> > > +                       goto all_cpu_err;
> > > +               }
> > >         }
> > >
> > >         if (generate_load() < 0) {
> > > @@ -161,18 +174,18 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
> > >         }
> > >         print_stacks();
> > >  all_cpu_err:
> > > -       for (i--; i >= 0; i--) {
> > > -               ioctl(pmu_fd[i], PERF_EVENT_IOC_DISABLE);
> > > -               close(pmu_fd[i]);
> > > -       }
> > > -       free(pmu_fd);
> > > +       for (i--; i >= 0; i--)
> > > +               bpf_link__destroy(links[i]);
> > > +err:
> > > +       free(links);
> > >         if (error)
> > > -               int_exit(0);
> > > +               int_exit(error);
> > >  }
> > >
> > >  static void test_perf_event_task(struct perf_event_attr *attr)
> > >  {
> > >         int pmu_fd, error = 0;
> > > +       struct bpf_link *link;
> > >
> > >         /* per task perf event, enable inherit so the "dd ..." command can be traced properly.
> > >          * Enabling inherit will cause bpf_perf_prog_read_time helper failure.
> > > @@ -185,8 +198,12 @@ static void test_perf_event_task(struct perf_event_attr *attr)
> > >                 printf("sys_perf_event_open failed\n");
> > >                 int_exit(0);
> > >         }
> > > -       assert(ioctl(pmu_fd, PERF_EVENT_IOC_SET_BPF, prog_fd[0]) == 0);
> > > -       assert(ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE) == 0);
> > > +       link = bpf_program__attach_perf_event(prog, pmu_fd);
> > > +       if (IS_ERR(link)) {
> > > +               printf("bpf_program__attach_perf_event failed\n");
> > > +               close(pmu_fd);
> > > +               int_exit(0);
> > > +       }
> > >
> > >         if (generate_load() < 0) {
> > >                 error = 1;
> > > @@ -194,10 +211,9 @@ static void test_perf_event_task(struct perf_event_attr *attr)
> > >         }
> > >         print_stacks();
> > >  err:
> > > -       ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
> > > -       close(pmu_fd);
> > > +       bpf_link__destroy(link);
> > >         if (error)
> > > -               int_exit(0);
> > > +               int_exit(error);
> > >  }
> > >
> > >  static void test_bpf_perf_event(void)
> > > @@ -282,6 +298,7 @@ static void test_bpf_perf_event(void)
> > >  int main(int argc, char **argv)
> > >  {
> > >         struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
> > > +       struct bpf_object *obj;
> > >         char filename[256];
> > >
> > >         snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> > > @@ -295,9 +312,29 @@ int main(int argc, char **argv)
> > >                 return 1;
> > >         }
> > >
> > > -       if (load_bpf_file(filename)) {
> > > -               printf("%s", bpf_log_buf);
> > > -               return 2;
> > > +       obj = bpf_object__open_file(filename, NULL);
> > > +       if (IS_ERR(obj)) {
> > > +               printf("opening BPF object file failed\n");
> > > +               return 1;
> > > +       }
> > > +
> > > +       prog = bpf_object__find_program_by_name(obj, "bpf_prog1");
> > > +       if (!prog) {
> > > +               printf("finding a prog in obj file failed\n");
> >
> >
> > bpf_object__close(obj);
> >
>
> Also, I'll apply this at next version patch.
>
> > > +               return 1;
> > > +       }
> > > +
> > > +       /* load BPF program */
> > > +       if (bpf_object__load(obj)) {
> >
> > close bpf_object (better do goto clean approach, of course)
> >
>
> I will modify this with goto cleanup approach.
>
> > > +               printf("loading BPF object file failed\n");
> > > +               return 1;
> > > +       }
> > > +
> > > +       map_fd[0] = bpf_object__find_map_fd_by_name(obj, "counts");
> > > +       map_fd[1] = bpf_object__find_map_fd_by_name(obj, "stackmap");
> > > +       if (map_fd[0] < 0 || map_fd[1] < 0) {
> > > +               printf("finding a counts/stackmap map in obj file failed\n");
> > > +               return 1;
> > >         }
> > >
> > >         if (fork() == 0) {
> > > --
> > > 2.25.1
> > >
>
> Thank you for your time and effort for the review :)
>
> Best,
> Daniel