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Date: Thu, 12 Mar 2020 15:15:48 +0900
From: "Daniel T. Lee" <danieltimlee@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...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 Wed, Mar 11, 2020 at 1:55 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> 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 :)
>
Thank you for your time and effort for the review :)
> > 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.
>
This approach looks more apparent!
I'll update code using this way.
> > {
> > 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.
>
Failure on link creation is exactly what I was concerned about.
Thank you for giving me a clear solution!
> > + 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.
>
Also, I'll apply this at next version patch.
> > {
> > 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).
>
Thank you for pointing me out!
I've never thought about situation when processors may be offline.
>
> > pmu_fd = malloc(nr_cpus * sizeof(int));
>
> similar naming nit: pmu_fds?
>
Same again, apply this at next version patch.
> > - 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.
>
About NULL set, like you mentioned, calloc approach looks more neat.
> > + 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().
>
I'll try skeleton with other sample cleanup. For now, I'll stick with
bpf_object__{open/load}() instead of 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.
>
I also think it is good to specify the program title clearly.
> > + 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.
>
Well, cleanup: could cover link destroy (sampling_end), but I think
it is strange to clean up the link even though the bpf program is not
attached to the event. I think it is better to specify the link destroy
after the sampling starts.
And, I've missed the link destroy when sampling got error.
Since sampling_end will destroy the links, so I'll add this on error.
if (sampling_start(pmu_fd, freq, prog, link) != 0) {
error = 1;
+ sampling_end(links);
goto cleanup;
}
> > + 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
>
Will apply this at next version patch.
> > 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]);
>
AFAIK, bpf_link__detach_perf_event() closes the pmu_fd.
Am I missed something?
static int bpf_link__detach_perf_event(struct bpf_link *link)
// TRUNCATED
close(link->fd);
return err;
}
> > +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?
>
You're right. Missed the return code.
Will apply this at next version patch.
> > }
> > @@ -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
> >
Thank you for your detailed review!
Best,
Daniel
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