Commit c016b68e authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: Add bpf_link pinning/unpinning 



With bpf_link abstraction supported by kernel explicitly, add
pinning/unpinning API for links. Also allow to create (open) bpf_link from BPF
FS file.

This API allows to have an "ephemeral" FD-based BPF links (like raw tracepoint
or fexit/freplace attachments) surviving user process exit, by pinning them in
a BPF FS, which is an important use case for long-running BPF programs.

As part of this, expose underlying FD for bpf_link. While legacy bpf_link's
might not have a FD associated with them (which will be expressed as
a bpf_link with fd=-1), kernel's abstraction is based around FD-based usage,
so match it closely. This, subsequently, allows to have a generic
pinning/unpinning API for generalized bpf_link. For some types of bpf_links
kernel might not support pinning, in which case bpf_link__pin() will return
error.

With FD being part of generic bpf_link, also get rid of bpf_link_fd in favor
of using vanialla bpf_link.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200303043159.323675-3-andriin@fb.com
parent 70ed506c

tools/lib/bpf/libbpf.c

+104 −27
Original line number Diff line number Diff line
@@ -6931,6 +6931,8 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr, 
struct bpf_link {

	int (*detach)(struct bpf_link *link);

	int (*destroy)(struct bpf_link *link);

	char *pin_path;		/* NULL, if not pinned */

	int fd;			/* hook FD, -1 if not applicable */

	bool disconnected;

};
@@ -6960,26 +6962,109 @@ int bpf_link__destroy(struct bpf_link *link) 
		err = link->detach(link);

	if (link->destroy)

		link->destroy(link);

	if (link->pin_path)

		free(link->pin_path);

	free(link);



	return err;

}



struct bpf_link_fd {

	struct bpf_link link; /* has to be at the top of struct */

	int fd; /* hook FD */

};

int bpf_link__fd(const struct bpf_link *link)

{

	return link->fd;

}



const char *bpf_link__pin_path(const struct bpf_link *link)

{

	return link->pin_path;

}



static int bpf_link__detach_fd(struct bpf_link *link)

{

	return close(link->fd);

}



struct bpf_link *bpf_link__open(const char *path)

{

	struct bpf_link *link;

	int fd;



	fd = bpf_obj_get(path);

	if (fd < 0) {

		fd = -errno;

		pr_warn("failed to open link at %s: %d\n", path, fd);

		return ERR_PTR(fd);

	}



	link = calloc(1, sizeof(*link));

	if (!link) {

		close(fd);

		return ERR_PTR(-ENOMEM);

	}

	link->detach = &bpf_link__detach_fd;

	link->fd = fd;



	link->pin_path = strdup(path);

	if (!link->pin_path) {

		bpf_link__destroy(link);

		return ERR_PTR(-ENOMEM);

	}



	return link;

}



int bpf_link__pin(struct bpf_link *link, const char *path)

{

	int err;



	if (link->pin_path)

		return -EBUSY;

	err = make_parent_dir(path);

	if (err)

		return err;

	err = check_path(path);

	if (err)

		return err;



	link->pin_path = strdup(path);

	if (!link->pin_path)

		return -ENOMEM;



	if (bpf_obj_pin(link->fd, link->pin_path)) {

		err = -errno;

		zfree(&link->pin_path);

		return err;

	}



	pr_debug("link fd=%d: pinned at %s\n", link->fd, link->pin_path);

	return 0;

}



int bpf_link__unpin(struct bpf_link *link)

{

	int err;



	if (!link->pin_path)

		return -EINVAL;



	err = unlink(link->pin_path);

	if (err != 0)

		return -errno;



	pr_debug("link fd=%d: unpinned from %s\n", link->fd, link->pin_path);

	zfree(&link->pin_path);

	return 0;

}



static int bpf_link__detach_perf_event(struct bpf_link *link)

{

	struct bpf_link_fd *l = (void *)link;

	int err;



	err = ioctl(l->fd, PERF_EVENT_IOC_DISABLE, 0);

	err = ioctl(link->fd, PERF_EVENT_IOC_DISABLE, 0);

	if (err)

		err = -errno;



	close(l->fd);

	close(link->fd);

	return err;

}
@@ -6987,7 +7072,7 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, 
						int pfd)

{

	char errmsg[STRERR_BUFSIZE];

	struct bpf_link_fd *link;

	struct bpf_link *link;

	int prog_fd, err;



	if (pfd < 0) {
@@ -7005,7 +7090,7 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, 
	link = calloc(1, sizeof(*link));

	if (!link)

		return ERR_PTR(-ENOMEM);

	link->link.detach = &bpf_link__detach_perf_event;

	link->detach = &bpf_link__detach_perf_event;

	link->fd = pfd;



	if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) {
@@ -7024,7 +7109,7 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog, 
			   libbpf_strerror_r(err, errmsg, sizeof(errmsg)));

		return ERR_PTR(err);

	}

	return (struct bpf_link *)link;

	return link;

}



/*
@@ -7312,18 +7397,11 @@ out: 
	return link;

}



static int bpf_link__detach_fd(struct bpf_link *link)

{

	struct bpf_link_fd *l = (void *)link;



	return close(l->fd);

}



struct bpf_link *bpf_program__attach_raw_tracepoint(struct bpf_program *prog,

						    const char *tp_name)

{

	char errmsg[STRERR_BUFSIZE];

	struct bpf_link_fd *link;

	struct bpf_link *link;

	int prog_fd, pfd;



	prog_fd = bpf_program__fd(prog);
@@ -7336,7 +7414,7 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(struct bpf_program *prog, 
	link = calloc(1, sizeof(*link));

	if (!link)

		return ERR_PTR(-ENOMEM);

	link->link.detach = &bpf_link__detach_fd;

	link->detach = &bpf_link__detach_fd;



	pfd = bpf_raw_tracepoint_open(tp_name, prog_fd);

	if (pfd < 0) {
@@ -7348,7 +7426,7 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(struct bpf_program *prog, 
		return ERR_PTR(pfd);

	}

	link->fd = pfd;

	return (struct bpf_link *)link;

	return link;

}



static struct bpf_link *attach_raw_tp(const struct bpf_sec_def *sec,
@@ -7362,7 +7440,7 @@ static struct bpf_link *attach_raw_tp(const struct bpf_sec_def *sec, 
struct bpf_link *bpf_program__attach_trace(struct bpf_program *prog)

{

	char errmsg[STRERR_BUFSIZE];

	struct bpf_link_fd *link;

	struct bpf_link *link;

	int prog_fd, pfd;



	prog_fd = bpf_program__fd(prog);
@@ -7375,7 +7453,7 @@ struct bpf_link *bpf_program__attach_trace(struct bpf_program *prog) 
	link = calloc(1, sizeof(*link));

	if (!link)

		return ERR_PTR(-ENOMEM);

	link->link.detach = &bpf_link__detach_fd;

	link->detach = &bpf_link__detach_fd;



	pfd = bpf_raw_tracepoint_open(NULL, prog_fd);

	if (pfd < 0) {
@@ -7409,10 +7487,9 @@ struct bpf_link *bpf_program__attach(struct bpf_program *prog) 


static int bpf_link__detach_struct_ops(struct bpf_link *link)

{

	struct bpf_link_fd *l = (void *)link;

	__u32 zero = 0;



	if (bpf_map_delete_elem(l->fd, &zero))

	if (bpf_map_delete_elem(link->fd, &zero))

		return -errno;



	return 0;
@@ -7421,7 +7498,7 @@ static int bpf_link__detach_struct_ops(struct bpf_link *link) 
struct bpf_link *bpf_map__attach_struct_ops(struct bpf_map *map)

{

	struct bpf_struct_ops *st_ops;

	struct bpf_link_fd *link;

	struct bpf_link *link;

	__u32 i, zero = 0;

	int err;
@@ -7453,10 +7530,10 @@ struct bpf_link *bpf_map__attach_struct_ops(struct bpf_map *map) 
		return ERR_PTR(err);

	}



	link->link.detach = bpf_link__detach_struct_ops;

	link->detach = bpf_link__detach_struct_ops;

	link->fd = map->fd;



	return (struct bpf_link *)link;

	return link;

}



enum bpf_perf_event_ret

tools/lib/bpf/libbpf.h

+5 −0
Original line number Diff line number Diff line
@@ -219,6 +219,11 @@ LIBBPF_API void bpf_program__unload(struct bpf_program *prog); 


struct bpf_link;



LIBBPF_API struct bpf_link *bpf_link__open(const char *path);

LIBBPF_API int bpf_link__fd(const struct bpf_link *link);

LIBBPF_API const char *bpf_link__pin_path(const struct bpf_link *link);

LIBBPF_API int bpf_link__pin(struct bpf_link *link, const char *path);

LIBBPF_API int bpf_link__unpin(struct bpf_link *link);

LIBBPF_API void bpf_link__disconnect(struct bpf_link *link);

LIBBPF_API int bpf_link__destroy(struct bpf_link *link);

tools/lib/bpf/libbpf.map

+5 −0
Original line number Diff line number Diff line
@@ -238,5 +238,10 @@ LIBBPF_0.0.7 { 


LIBBPF_0.0.8 {

	global:

		bpf_link__fd;

		bpf_link__open;

		bpf_link__pin;

		bpf_link__pin_path;

		bpf_link__unpin;

		bpf_program__set_attach_target;

} LIBBPF_0.0.7;

CRA Git | Maintained and supported by SUSTech CRA and CCSE