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Date: Tue, 10 Mar 2020 21:55:14 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: "Daniel T. Lee" <danieltimlee@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 2/2] samples: bpf: refactor perf_event user
program with libbpf bpf_link
On Tue, Mar 10, 2020 at 4:27 PM Daniel T. Lee <danieltimlee@...il.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.
>
> 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@...il.com>
> ---
Daniel, thanks for this clean up! It's good to see samples be
modernized a bit :)
> Changes in v2:
> - check memory allocation is successful
> - clean up allocated memory on error
>
> samples/bpf/Makefile | 4 +-
> samples/bpf/sampleip_user.c | 76 ++++++++++++++++++++++------------
> samples/bpf/trace_event_user.c | 63 ++++++++++++++++++++--------
> 3 files changed, 97 insertions(+), 46 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..fd763a49c913 100644
> --- a/samples/bpf/sampleip_user.c
> +++ b/samples/bpf/sampleip_user.c
> @@ -10,13 +10,11 @@
> #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"
>
> @@ -25,6 +23,7 @@
> #define MAX_IPS 8192
> #define PAGE_OFFSET 0xffff880000000000
>
> +static int map_fd;
> static int nr_cpus;
>
> static void usage(void)
> @@ -34,7 +33,8 @@ 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 *pmu_fd, int freq, struct bpf_program *prog,
> + struct bpf_link **link)
It's not apparent from looking at struct bpf_link **link whether it's
an output parameter (so sampling_start is supposed to assign *single*
link to return it to calling function) or it's an array of pointers.
Seems like it's the latter, so I'd prefer this written as
struct bpf_link *links[] (notice also plural name).
Please consider this.
> {
> int i;
>
> @@ -53,20 +53,22 @@ static int sampling_start(int *pmu_fd, int freq)
> 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);
> + link[i] = bpf_program__attach_perf_event(prog, pmu_fd[i]);
> + if (link[i] < 0) {
link is a pointer, < 0 doesn't make sense and is always going to be
false on x86. Use IS_ERR(link[i]). It's also a good idea to set it to
NULL, if link creation failed to prevent accidental
bpf_link__destroy(link[i]) later on, trying to free bogus pointer.
> + fprintf(stderr, "ERROR: Attach perf event\n");
> + return 1;
> + }
> }
>
> return 0;
> }
>
> -static void sampling_end(int *pmu_fd)
> +static void sampling_end(struct bpf_link **link)
same as above, struct bpf_link *links[] would be much better here, IMO.
> {
> int i;
>
> for (i = 0; i < nr_cpus; i++)
> - close(pmu_fd[i]);
> + bpf_link__destroy(link[i]);
> }
>
> struct ipcount {
> @@ -128,14 +130,18 @@ 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 prog_fd, *pmu_fd, opt, freq = DEFAULT_FREQ, secs = DEFAULT_SECS;
> + struct bpf_program *prog;
> + struct bpf_object *obj;
> + struct bpf_link **link;
> char filename[256];
> - int *pmu_fd, opt, freq = DEFAULT_FREQ, secs = DEFAULT_SECS;
> + int error = 0;
>
> /* process arguments */
> while ((opt = getopt(argc, argv, "F:h")) != -1) {
> @@ -165,36 +171,54 @@ int main(int argc, char **argv)
> /* create perf FDs for each CPU */
> nr_cpus = sysconf(_SC_NPROCESSORS_CONF);
While neither approach is ideal, using number of online CPUs
(_SC_NPROCESSORS_ONLN) will probably work in slightly more cases
(there are machines configured with, say, 256 possible CPUs, but only
32 available, for instance).
> pmu_fd = malloc(nr_cpus * sizeof(int));
similar naming nit: pmu_fds?
> - if (pmu_fd == NULL) {
> - fprintf(stderr, "ERROR: malloc of pmu_fd\n");
> - return 1;
> + link = malloc(nr_cpus * sizeof(struct bpf_link *));
Use calloc() to have those links initialized to NULL automatically.
Makes clean up so much easier.
> + if (pmu_fd == NULL || link == NULL) {
> + fprintf(stderr, "ERROR: malloc of pmu_fd/link\n");
> + error = 1;
> + goto cleanup;
> }
>
> /* load BPF program */
> snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> - if (load_bpf_file(filename)) {
> + if (bpf_prog_load(filename, BPF_PROG_TYPE_PERF_EVENT, &obj, &prog_fd)) {
Using skeleton would be best, but it's probably more appropriate for
another patch to integrate skeleton generation with samples/bpf. So
the next one would be bpf_object__open_file(), instead of legacy
bpf_prog_load().
> 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;
> + error = 1;
> + goto cleanup;
> + }
> +
> + prog = bpf_program__next(NULL, obj);
I'm a bit lazy here, sorry, but isn't the name of the program known?
bpf_object__find_program_by_title() is preferable.
> + if (!prog) {
> + fprintf(stderr, "ERROR: finding a prog in obj 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(pmu_fd, freq, prog, link) != 0) {
> + error = 1;
> + goto cleanup;
> + }
> sleep(secs);
> - sampling_end(pmu_fd);
> - free(pmu_fd);
> + sampling_end(link);
>
> /* output sample counts */
> - print_ip_map(map_fd[0]);
> + print_ip_map(map_fd);
>
> - return 0;
> +cleanup:
> + free(pmu_fd);
> + free(link);
Uhm... you are freeing this only on clean up. Also, you need to
bpf_link__destroy() first. And close all pmu_fds. Surely process exit
will ensure all this is cleaned up, but it's a good tone to clean up
all resources explicitly.
> + return error;
> }
> diff --git a/samples/bpf/trace_event_user.c b/samples/bpf/trace_event_user.c
> index 356171bc392b..30c25ef99fc5 100644
> --- a/samples/bpf/trace_event_user.c
> +++ b/samples/bpf/trace_event_user.c
> @@ -6,22 +6,21 @@
> #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 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)
> @@ -137,9 +136,16 @@ 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);
> + struct bpf_link **link = malloc(nr_cpus * sizeof(struct bpf_link *));
same as above, calloc() is better choice here
> int *pmu_fd = malloc(nr_cpus * sizeof(int));
> int i, error = 0;
>
> + if (pmu_fd == NULL || link == NULL) {
> + printf("malloc of pmu_fd/link failed\n");
> + error = 1;
> + goto err;
> + }
> +
> /* system wide perf event, no need to inherit */
> attr->inherit = 0;
>
> @@ -151,8 +157,12 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
> 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);
> + link[i] = bpf_program__attach_perf_event(prog, pmu_fd[i]);
> + if (link[i] < 0) {
> + printf("bpf_program__attach_perf_event failed\n");
> + error = 1;
> + goto all_cpu_err;
> + }
> }
>
> if (generate_load() < 0) {
> @@ -161,11 +171,11 @@ 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]);
> - }
> + for (i--; i >= 0; i--)
> + bpf_link__destroy(link[i]);
still need close(pmu_fd[i]);
> +err:
> free(pmu_fd);
> + free(link);
> if (error)
> int_exit(0);
> }
> @@ -173,6 +183,7 @@ static void test_perf_event_all_cpu(struct perf_event_attr *attr)
> 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 +196,12 @@ 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 (link < 0) {
> + printf("bpf_program__attach_perf_event failed\n");
> + close(pmu_fd);
> + int_exit(0);
> + }
>
> if (generate_load() < 0) {
> error = 1;
> @@ -194,8 +209,7 @@ 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);
This will exit with 0 error code and won't notify about error... Pass
through err?
> }
> @@ -282,7 +296,9 @@ 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];
> + int prog_fd;
>
> snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> setrlimit(RLIMIT_MEMLOCK, &r);
> @@ -295,9 +311,20 @@ int main(int argc, char **argv)
> return 1;
> }
>
> - if (load_bpf_file(filename)) {
> - printf("%s", bpf_log_buf);
> - return 2;
> + if (bpf_prog_load(filename, BPF_PROG_TYPE_PERF_EVENT, &obj, &prog_fd))
> + return 1;
> +
> + prog = bpf_program__next(NULL, obj);
> + if (!prog) {
> + printf("finding a prog in obj 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
>
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