Commit aef56f2e authored by Kui-Feng Lee's avatar Kui-Feng Lee Committed by Martin KaFai Lau
Browse files

bpf: Update the struct_ops of a bpf_link. 



By improving the BPF_LINK_UPDATE command of bpf(), it should allow you
to conveniently switch between different struct_ops on a single
bpf_link. This would enable smoother transitions from one struct_ops
to another.

The struct_ops maps passing along with BPF_LINK_UPDATE should have the
BPF_F_LINK flag.

Signed-off-by: default avatarKui-Feng Lee <kuifeng@meta.com>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230323032405.3735486-6-kuifeng@meta.com


Signed-off-by: default avatarMartin KaFai Lau <martin.lau@kernel.org>
parent 8d1608d7

include/linux/bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -1476,6 +1476,8 @@ struct bpf_link_ops { 
	void (*show_fdinfo)(const struct bpf_link *link, struct seq_file *seq);

	int (*fill_link_info)(const struct bpf_link *link,

			      struct bpf_link_info *info);

	int (*update_map)(struct bpf_link *link, struct bpf_map *new_map,

			  struct bpf_map *old_map);

};



struct bpf_tramp_link {
@@ -1518,6 +1520,7 @@ struct bpf_struct_ops { 
			   void *kdata, const void *udata);

	int (*reg)(void *kdata);

	void (*unreg)(void *kdata);

	int (*update)(void *kdata, void *old_kdata);

	int (*validate)(void *kdata);

	const struct btf_type *type;

	const struct btf_type *value_type;

include/uapi/linux/bpf.h

+16 −5
Original line number Diff line number Diff line
@@ -1555,12 +1555,23 @@ union bpf_attr { 


	struct { /* struct used by BPF_LINK_UPDATE command */

		__u32		link_fd;	/* link fd */

		union {

			/* new program fd to update link with */

			__u32		new_prog_fd;

			/* new struct_ops map fd to update link with */

			__u32           new_map_fd;

		};

		__u32		flags;		/* extra flags */

		union {

			/* expected link's program fd; is specified only if

		 * BPF_F_REPLACE flag is set in flags */

			 * BPF_F_REPLACE flag is set in flags.

			 */

			__u32		old_prog_fd;

			/* expected link's map fd; is specified only

			 * if BPF_F_REPLACE flag is set.

			 */

			__u32           old_map_fd;

		};

	} link_update;



	struct {

kernel/bpf/bpf_struct_ops.c

+47 −1
Original line number Diff line number Diff line
@@ -65,6 +65,8 @@ struct bpf_struct_ops_link { 
	struct bpf_map __rcu *map;

};



static DEFINE_MUTEX(update_mutex);



#define VALUE_PREFIX "bpf_struct_ops_"

#define VALUE_PREFIX_LEN (sizeof(VALUE_PREFIX) - 1)
@@ -664,7 +666,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) 
	if (attr->value_size != vt->size)

		return ERR_PTR(-EINVAL);



	if (attr->map_flags & BPF_F_LINK && !st_ops->validate)

	if (attr->map_flags & BPF_F_LINK && (!st_ops->validate || !st_ops->update))

		return ERR_PTR(-EOPNOTSUPP);



	t = st_ops->type;
@@ -810,10 +812,54 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, 
	return 0;

}



static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map *new_map,

					  struct bpf_map *expected_old_map)

{

	struct bpf_struct_ops_map *st_map, *old_st_map;

	struct bpf_map *old_map;

	struct bpf_struct_ops_link *st_link;

	int err = 0;



	st_link = container_of(link, struct bpf_struct_ops_link, link);

	st_map = container_of(new_map, struct bpf_struct_ops_map, map);



	if (!bpf_struct_ops_valid_to_reg(new_map))

		return -EINVAL;



	mutex_lock(&update_mutex);



	old_map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex));

	if (expected_old_map && old_map != expected_old_map) {

		err = -EPERM;

		goto err_out;

	}



	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);

	/* The new and old struct_ops must be the same type. */

	if (st_map->st_ops != old_st_map->st_ops) {

		err = -EINVAL;

		goto err_out;

	}



	err = st_map->st_ops->update(st_map->kvalue.data, old_st_map->kvalue.data);

	if (err)

		goto err_out;



	bpf_map_inc(new_map);

	rcu_assign_pointer(st_link->map, new_map);

	bpf_map_put(old_map);



err_out:

	mutex_unlock(&update_mutex);



	return err;

}



static const struct bpf_link_ops bpf_struct_ops_map_lops = {

	.dealloc = bpf_struct_ops_map_link_dealloc,

	.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,

	.fill_link_info = bpf_struct_ops_map_link_fill_link_info,

	.update_map = bpf_struct_ops_map_link_update,

};



int bpf_struct_ops_link_create(union bpf_attr *attr)

kernel/bpf/syscall.c

+34 −0
Original line number Diff line number Diff line
@@ -4682,6 +4682,35 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) 
	return ret;

}



static int link_update_map(struct bpf_link *link, union bpf_attr *attr)

{

	struct bpf_map *new_map, *old_map = NULL;

	int ret;



	new_map = bpf_map_get(attr->link_update.new_map_fd);

	if (IS_ERR(new_map))

		return -EINVAL;



	if (attr->link_update.flags & BPF_F_REPLACE) {

		old_map = bpf_map_get(attr->link_update.old_map_fd);

		if (IS_ERR(old_map)) {

			ret = -EINVAL;

			goto out_put;

		}

	} else if (attr->link_update.old_map_fd) {

		ret = -EINVAL;

		goto out_put;

	}



	ret = link->ops->update_map(link, new_map, old_map);



	if (old_map)

		bpf_map_put(old_map);

out_put:

	bpf_map_put(new_map);

	return ret;

}



#define BPF_LINK_UPDATE_LAST_FIELD link_update.old_prog_fd



static int link_update(union bpf_attr *attr)
@@ -4702,6 +4731,11 @@ static int link_update(union bpf_attr *attr) 
	if (IS_ERR(link))

		return PTR_ERR(link);



	if (link->ops->update_map) {

		ret = link_update_map(link, attr);

		goto out_put_link;

	}



	new_prog = bpf_prog_get(attr->link_update.new_prog_fd);

	if (IS_ERR(new_prog)) {

		ret = PTR_ERR(new_prog);

net/ipv4/bpf_tcp_ca.c

+6 −0
Original line number Diff line number Diff line
@@ -264,6 +264,11 @@ static void bpf_tcp_ca_unreg(void *kdata) 
	tcp_unregister_congestion_control(kdata);

}



static int bpf_tcp_ca_update(void *kdata, void *old_kdata)

{

	return tcp_update_congestion_control(kdata, old_kdata);

}



static int bpf_tcp_ca_validate(void *kdata)

{

	return tcp_validate_congestion_control(kdata);
@@ -273,6 +278,7 @@ struct bpf_struct_ops bpf_tcp_congestion_ops = { 
	.verifier_ops = &bpf_tcp_ca_verifier_ops,

	.reg = bpf_tcp_ca_reg,

	.unreg = bpf_tcp_ca_unreg,

	.update = bpf_tcp_ca_update,

	.check_member = bpf_tcp_ca_check_member,

	.init_member = bpf_tcp_ca_init_member,

	.init = bpf_tcp_ca_init,