[PATCH v4 bpf-next 3/9] libbpf: add ability to attach/detach BPF program to perf event

[Andrii Nakryiko <andriin@fb.com>]

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@fb.com>
---
 tools/lib/bpf/libbpf.c   | 61 ++++++++++++++++++++++++++++++++++++++++
 tools/lib/bpf/libbpf.h   |  3 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 65 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 455795e6f8af..98c155ec3bfa 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 +3959,66 @@ 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 */
+};
+
+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);
+	if (err)
+		err = -errno;
+
+	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 prog_fd, err;
+
+	prog_fd = bpf_program__fd(prog);
+	if (prog_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, prog_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