On Fri, Jun 28, 2019 at 10:54 AM Stanislav Fomichev <sdf@xxxxxxxxxxx> wrote: > > On 06/28, Andrii Nakryiko wrote: > > On Fri, Jun 28, 2019 at 9:04 AM Stanislav Fomichev <sdf@xxxxxxxxxxx> wrote: > > > > > > On 06/27, Andrii Nakryiko wrote: > > > > bpf_program__attach_perf_event allows to attach BPF program to existing > > > > perf event hook, providing most generic and most low-level way to attach BPF > > > > programs. It returns struct bpf_link, which should be passed to > > > > bpf_link__destroy to detach and free resources, associated with a link. > > > > > > > > Signed-off-by: Andrii Nakryiko <andriin@xxxxxx> > > > > --- > > > > tools/lib/bpf/libbpf.c | 58 ++++++++++++++++++++++++++++++++++++++++ > > > > tools/lib/bpf/libbpf.h | 3 +++ > > > > tools/lib/bpf/libbpf.map | 1 + > > > > 3 files changed, 62 insertions(+) > > > > > > > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > > > > index 455795e6f8af..606705f878ba 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> > > > > @@ -3958,6 +3959,63 @@ int bpf_link__destroy(struct bpf_link *link) > > > > return err; > > > > } > > > > > > > > +struct bpf_link_fd { > > > > + struct bpf_link link; /* has to be at the top of struct */ > > > [..] > > > > + int fd; /* hook FD */ > > > > +}; > > > Any cons to storing everything in bpf_link, instead of creating a > > > "subclass"? Less things to worry about. > > > > Yes, it's not always enough to just have single FD to detach BPF > > program. Check bpf_prog_detach and bpf_prog_detach2 in > > tools/lib/bpf/bpf.c. For some types of attachment you have to provide > > target_fd+attach_type, for some target_fd+attach_type+attach_bpf_fd. > > So those two will use their own bpf_link extensions. > > > > I haven't implemented those attachment APIs yet, but we should. > > > > What should go into bpf_link itself is any information that's common > > to any kind of attachment (e.g, "kind of attachment" itself). It's > > conceivable that we might allow "casting" bpf_link into specific > > variation and having extra "methods" on those. I haven't done that, as > > I didn't have a need yet. > You're optimizing for a memory footprint, I guess. I was trying to > point out that maybe it's easier just to put everything in the bpf_link > and don't do any castings. Some events would use attach_type, some > won't. But, OTOH, maybe having a specific bpf_link variation per > attachment is more readable, idk :-) Ah, I see, you want to have superset of all possible things that constitute bpf_link. I generally don't like that, because it becomes harder to understand what's really used and what's there just in case :) Good thing is that all this is libbpf-internal, so we can change any of that easily without any breakage of users. > > > > > +static int bpf_link__destroy_perf_event(struct bpf_link *link) > > > > +{ > > > > + struct bpf_link_fd *l = (void *)link; > > > > + int err; > > > > + > > > > + if (l->fd < 0) > > > > + return 0; > > > > + > > > > + err = ioctl(l->fd, PERF_EVENT_IOC_DISABLE, 0); > > > > + close(l->fd); > > > > + return err; > > > > +} > > > > + > > > > +struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, > > > > + int pfd) > > > > +{ > > > > + char errmsg[STRERR_BUFSIZE]; > > > > + struct bpf_link_fd *link; > > > > + 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 ERR_PTR(-EINVAL); > > > > + } > > > > + > > > > + link = malloc(sizeof(*link)); > > > > + if (!link) > > > > + return ERR_PTR(-ENOMEM); > > > > + link->link.destroy = &bpf_link__destroy_perf_event; > > > > + link->fd = pfd; > > > > + > > > > + if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, bpf_fd) < 0) { > > > > + err = -errno; > > > > + free(link); > > > > + 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_PTR(err); > > > > + } > > > > + if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) { > > > > + err = -errno; > > > > + free(link); > > > > + 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_PTR(err); > > > > + } > > > > + return (struct bpf_link *)link; > > > > +} > > > > + > > > > 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 5082a5ebb0c2..1bf66c4a9330 100644 > > > > --- a/tools/lib/bpf/libbpf.h > > > > +++ b/tools/lib/bpf/libbpf.h > > > > @@ -169,6 +169,9 @@ struct bpf_link; > > > > > > > > LIBBPF_API int bpf_link__destroy(struct bpf_link *link); > > > > > > > > +LIBBPF_API struct bpf_link * > > > > +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 3cde850fc8da..756f5aa802e9 100644 > > > > --- a/tools/lib/bpf/libbpf.map > > > > +++ b/tools/lib/bpf/libbpf.map > > > > @@ -169,6 +169,7 @@ LIBBPF_0.0.4 { > > > > global: > > > > bpf_link__destroy; > > > > bpf_object__load_xattr; > > > > + bpf_program__attach_perf_event; > > > > btf_dump__dump_type; > > > > btf_dump__free; > > > > btf_dump__new; > > > > -- > > > > 2.17.1 > > > >