[PATCH v2 bpf-next 2/7] libbpf: add ability to attach/detach BPF to perf event

[Andrii Nakryiko <andriin@xxxxxx>]

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)
+{
+	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