On Thu, Jun 20, 2019 at 5:01 PM Stanislav Fomichev <sdf@xxxxxxxxxxx> wrote:
>
> On 06/20, Andrii Nakryiko wrote:
> > bpf_program__attach_perf_event allows to attach BPF program to existing
> > perf event, providing most generic and most low-level way to attach BPF
> > programs.
> >
> > libbpf_perf_event_disable_and_close API is added to disable and close
> > existing perf event by its FD.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> > ---
> > tools/lib/bpf/libbpf.c | 41 ++++++++++++++++++++++++++++++++++++++++
> > tools/lib/bpf/libbpf.h | 4 ++++
> > tools/lib/bpf/libbpf.map | 2 ++
> > 3 files changed, 47 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 8ce3beba8551..2bb1fa008be3 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -32,6 +32,7 @@
> > #include <linux/limits.h>
> > #include <linux/perf_event.h>
> > #include <linux/ring_buffer.h>
> > +#include <sys/ioctl.h>
> > #include <sys/stat.h>
> > #include <sys/types.h>
> > #include <sys/vfs.h>
> > @@ -3928,6 +3929,46 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
> > return 0;
> > }
> >
> [..]
> > +int libbpf_perf_event_disable_and_close(int pfd)
> nit: why not call it libbpf_perf_event_detach[_and_close]?
> It's usually attach/detach.
I think detach is actually confusing for perf event. Here's what you
do for tracing:
1. open perf event
2. enable perf event
3. attach BPF program to perf event
...
4. <is there a way to detach BPF program?>
5. disable perf event
6. close perf event
So open/close event, enable/disable event, attach / (auto-detach on
close right now) BPF program.
It seems like there should be explicit "detach this BPF program from
perf event without killing event itself", but I haven't found it.
But my point is that for event open/close and enable/disable seems
very complementary.
>
> > +{
> > + int err;
> > +
> > + if (pfd < 0)
> > + return 0;
> > +
> > + err = ioctl(pfd, PERF_EVENT_IOC_DISABLE, 0);
> > + close(pfd);
> > + return err;
> > +}
> > +
> > +int bpf_program__attach_perf_event(struct bpf_program *prog, int pfd)
> > +{
> > + char errmsg[STRERR_BUFSIZE];
> > + int bpf_fd, err;
> > +
> > + bpf_fd = bpf_program__fd(prog);
> > + if (bpf_fd < 0) {
> > + pr_warning("program '%s': can't attach before loaded\n",
> > + bpf_program__title(prog, false));
> > + return -EINVAL;
> > + }
> > + if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, bpf_fd) < 0) {
> > + err = -errno;
> > + pr_warning("program '%s': failed to attach to pfd %d: %s\n",
> > + bpf_program__title(prog, false), pfd,
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + return err;
> > + }
> > + if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
> > + err = -errno;
> > + pr_warning("program '%s': failed to enable pfd %d: %s\n",
> > + bpf_program__title(prog, false), pfd,
> > + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> > + return err;
> > + }
> > + return 0;
> > +}
> > +
> > enum bpf_perf_event_ret
> > bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
> > void **copy_mem, size_t *copy_size,
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index d639f47e3110..76db1bbc0dac 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -165,6 +165,10 @@ LIBBPF_API int bpf_program__pin(struct bpf_program *prog, const char *path);
> > LIBBPF_API int bpf_program__unpin(struct bpf_program *prog, const char *path);
> > LIBBPF_API void bpf_program__unload(struct bpf_program *prog);
> >
> > +LIBBPF_API int libbpf_perf_event_disable_and_close(int pfd);
> > +LIBBPF_API int bpf_program__attach_perf_event(struct bpf_program *prog,
> > + int pfd);
> > +
> > struct bpf_insn;
> >
> > /*
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 2c6d835620d2..d27406982b5a 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -172,5 +172,7 @@ LIBBPF_0.0.4 {
> > btf_dump__new;
> > btf__parse_elf;
> > bpf_object__load_xattr;
> > + bpf_program__attach_perf_event;
> > libbpf_num_possible_cpus;
> > + libbpf_perf_event_disable_and_close;
> > } LIBBPF_0.0.3;
> > --
> > 2.17.1
> >
