Re: [PATCH bpf-next v2 1/6] bpf: Create links for BPF struct_ops maps.

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On 02/22, Kui-Feng Lee wrote:
BPF struct_ops maps are employed directly to register TCP Congestion
Control algorithms. Unlike other BPF programs that terminate when
their links gone, the struct_ops program reduces its refcount solely
upon death of its FD. The link of a BPF struct_ops map provides a
uniform experience akin to other types of BPF programs.

bpf_links are responsible for registering their associated
struct_ops. You can only use a struct_ops that has the BPF_F_LINK flag
set to create a bpf_link, while a structs without this flag behaves in
the same manner as before and is registered upon updating its value.

Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxxxx>
---
  include/linux/bpf.h            |  11 +
  include/uapi/linux/bpf.h       |  12 +-
  kernel/bpf/bpf_struct_ops.c    | 376 ++++++++++++++++++++++++++++++---
  kernel/bpf/syscall.c           |  26 ++-
  tools/include/uapi/linux/bpf.h |  12 +-
  5 files changed, 402 insertions(+), 35 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8b5d0b4c4ada..9d6fd874e5ee 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1395,6 +1395,11 @@ struct bpf_link {
  	struct work_struct work;
  };

+struct bpf_struct_ops_link {
+	struct bpf_link link;
+	struct bpf_map __rcu *map;
+};
+
  struct bpf_link_ops {
  	void (*release)(struct bpf_link *link);
  	void (*dealloc)(struct bpf_link *link);
@@ -1961,6 +1966,7 @@ int bpf_link_new_fd(struct bpf_link *link);
  struct file *bpf_link_new_file(struct bpf_link *link, int *reserved_fd);
  struct bpf_link *bpf_link_get_from_fd(u32 ufd);
  struct bpf_link *bpf_link_get_curr_or_next(u32 *id);
+int bpf_struct_ops_link_create(union bpf_attr *attr);

  int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
  int bpf_obj_get_user(const char __user *pathname, int flags);
@@ -2305,6 +2311,11 @@ static inline void bpf_link_put(struct bpf_link *link)
  {
  }

+static inline int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	return -EOPNOTSUPP;
+}
+
static inline int bpf_obj_get_user(const char __user *pathname, int flags)
  {
  	return -EOPNOTSUPP;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 17afd2b35ee5..cd0ff39981e8 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1033,6 +1033,7 @@ enum bpf_attach_type {
  	BPF_PERF_EVENT,
  	BPF_TRACE_KPROBE_MULTI,
  	BPF_LSM_CGROUP,
+	BPF_STRUCT_OPS,
  	__MAX_BPF_ATTACH_TYPE
  };

@@ -1266,6 +1267,9 @@ enum {

/* Create a map that is suitable to be an inner map with dynamic max entries */
  	BPF_F_INNER_MAP		= (1U << 12),
+
+/* Create a map that will be registered/unregesitered by the backed bpf_link */
+	BPF_F_LINK		= (1U << 13),
  };

  /* Flags for BPF_PROG_QUERY. */
@@ -1507,7 +1511,10 @@ union bpf_attr {
  	} task_fd_query;

  	struct { /* struct used by BPF_LINK_CREATE command */
-		__u32		prog_fd;	/* eBPF program to attach */
+		union {
+			__u32		prog_fd;	/* eBPF program to attach */
+			__u32		map_fd;		/* eBPF struct_ops to attach */
+		};
  		union {
  			__u32		target_fd;	/* object to attach to */
  			__u32		target_ifindex; /* target ifindex */
@@ -6354,6 +6361,9 @@ struct bpf_link_info {
  		struct {
  			__u32 ifindex;
  		} xdp;
+		struct {
+			__u32 map_id;
+		} struct_ops;
  	};
  } __attribute__((aligned(8)));

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index ece9870cab68..cfc69033c1b8 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -14,8 +14,10 @@

  enum bpf_struct_ops_state {
  	BPF_STRUCT_OPS_STATE_INIT,
+	BPF_STRUCT_OPS_STATE_UNREG,
  	BPF_STRUCT_OPS_STATE_INUSE,
  	BPF_STRUCT_OPS_STATE_TOBEFREE,
+	BPF_STRUCT_OPS_STATE_TOBEUNREG,
  };

  #define BPF_STRUCT_OPS_COMMON_VALUE			\
@@ -58,6 +60,8 @@ struct bpf_struct_ops_map {
  	struct bpf_struct_ops_value kvalue;
  };

+static DEFINE_MUTEX(update_mutex);
+
  #define VALUE_PREFIX "bpf_struct_ops_"
  #define VALUE_PREFIX_LEN (sizeof(VALUE_PREFIX) - 1)

@@ -253,22 +257,23 @@ int bpf_struct_ops_map_sys_lookup_elem(struct bpf_map *map, void *key,
  	if (unlikely(*(u32 *)key != 0))
  		return -ENOENT;

+	mutex_lock(&st_map->lock);
+
  	kvalue = &st_map->kvalue;
-	/* Pair with smp_store_release() during map_update */
  	state = smp_load_acquire(&kvalue->state);
  	if (state == BPF_STRUCT_OPS_STATE_INIT) {
  		memset(value, 0, map->value_size);
+		mutex_unlock(&st_map->lock);
  		return 0;
  	}

-	/* No lock is needed.  state and refcnt do not need
-	 * to be updated together under atomic context.
-	 */
  	uvalue = value;
  	memcpy(uvalue, st_map->uvalue, map->value_size);
  	uvalue->state = state;
  	refcount_set(&uvalue->refcnt, refcount_read(&kvalue->refcnt));

+	mutex_unlock(&st_map->lock);
+
  	return 0;
  }

@@ -349,6 +354,150 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
  					   model, flags, tlinks, NULL);
  }

+/*
+ * Maintain the state of kvalue.
+ *
+ * For a struct_ops that has no link, its state diagram is
+ *
+ *   INIT ----> INUSE --> TOBEFREE
+ *     ^                     |
+ *     |     (refcnt == 0)   |
+ *     +---------------------+
+ *
+ * For a struct_ops that has a link (BPF_F_LINK), its state diagram is
+ *
+ *                   (refcnt == 0)
+ *              +-----------------------+
+ *              |                       |
+ *              V                       |
+ *   INIT ---> UNREG -+--> INUSE --> TOBEUNREG
+ *     ^              |
+ *     |              V
+ *     +---------- TOBEFREE
+ *     (refcnt == 0)
+ *
+ * After transiting to the INUSE state of a struct_ops, the refcnt of
+ * its kvalue is set to 1.
+ *
+ * After transiting from the INUSE state of a struct_ops, the caller
+ * should decrease the refcnt of its kvalue by 1 by calling
+ * bpf_struct_ops_put().
+ *
+ * TOBEFREE and TOBEUNREG are in a grace period, waiting for other
+ * tasks holding references of the struct_ops.  When the refcnt drops
+ * from 1 to 0, TOBEFREE and TOBEUNREG are transited to INIT and UNREG
+ * respectively.
+ *
+ * It is safe to assume that there will be no registration race
+ * conditions after a task transits the same struct_ops to INUSE,
+ * TOBEFREE and TOBEUNREG states.  The task is able to register or
+ * unregister the struct_ops without the need for any additional
+ * synchronization.
+ */
+static int bpf_struct_ops_transit_state(struct bpf_struct_ops_map *st_map,
+					enum bpf_struct_ops_state src,
+					enum bpf_struct_ops_state dst)
+{
+	int old_state;
+
+	switch (src) {
+	case BPF_STRUCT_OPS_STATE_INIT:
+		if (dst != BPF_STRUCT_OPS_STATE_INUSE &&
+		    dst != BPF_STRUCT_OPS_STATE_UNREG)
+			return -EINVAL;
+
+		old_state = cmpxchg(&st_map->kvalue.state, src, dst);
+		if (old_state != src)
+			break;
+
+		if (dst == BPF_STRUCT_OPS_STATE_INUSE)
+			refcount_set(&st_map->kvalue.refcnt, 1);
+		break;
+
+	case BPF_STRUCT_OPS_STATE_UNREG:
+		if (dst != BPF_STRUCT_OPS_STATE_INUSE &&
+		    dst != BPF_STRUCT_OPS_STATE_TOBEFREE)
+			return -EINVAL;
+
+		old_state = cmpxchg(&st_map->kvalue.state, src, dst);
+		if (old_state != src)
+			break;
+
+		if (dst == BPF_STRUCT_OPS_STATE_INUSE)
+			refcount_set(&st_map->kvalue.refcnt, 1);
+		else if (dst == BPF_STRUCT_OPS_STATE_TOBEFREE)
+			cmpxchg(&st_map->kvalue.state, dst, BPF_STRUCT_OPS_STATE_INIT);
+		break;
+
+	case BPF_STRUCT_OPS_STATE_INUSE:
+		if (dst != BPF_STRUCT_OPS_STATE_TOBEFREE &&
+		    dst != BPF_STRUCT_OPS_STATE_TOBEUNREG)
+			return -EINVAL;
+
+		old_state = cmpxchg(&st_map->kvalue.state, src, dst);
+		break;
+
+	case BPF_STRUCT_OPS_STATE_TOBEFREE:
+		/*
+		 * This transition should only be performed when the
+		 * refcnt drops to 0 from 1.
+		 */
+		if (dst != BPF_STRUCT_OPS_STATE_INIT)
+			return -EINVAL;
+		old_state = cmpxchg(&st_map->kvalue.state, src, dst);
+		if (old_state != src)
+			break;
+		break;
+
+	case BPF_STRUCT_OPS_STATE_TOBEUNREG:
+		/*
+		 * This transition should only be performed when the
+		 * refcnt drops to 0 from 1.
+		 */
+		if (dst != BPF_STRUCT_OPS_STATE_UNREG)
+			return -EINVAL;
+		old_state = cmpxchg(&st_map->kvalue.state, src, dst);
+		if (old_state != src)
+			return old_state;
+		break;
+
+	default:
+		return -EOPNOTSUPP;
+	}
+
+	return old_state;
+}
+
+static int bpf_struct_ops_transit_state_check(struct bpf_struct_ops_map *st_map,
+					      enum bpf_struct_ops_state src,
+					      enum bpf_struct_ops_state dst)
+{
+	int err;
+
+	err = bpf_struct_ops_transit_state(st_map, src, dst);
+	if (err < 0)
+		return err;
+	if (err != src)
+		return -EINVAL;
+	return 0;
+}
+
+/*
+ * Restore the state of a struct_ops to UNREG from INUSE.
+ *
+ * It handles the case which a struct_ops transited to INUSE from
+ * UNREG successfully; somehow, need to rollback the struct_ops state.
+ */
+static void bpf_struct_ops_restore_unreg(struct bpf_struct_ops_map *st_map)
+{
+	struct bpf_struct_ops_value *kvalue;
+
+	kvalue = &st_map->kvalue;
+	refcount_set(&kvalue->refcnt, 0);
+	/* Make sure the above change is seen before the state change. */
+	smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_UNREG);
+}
+
  static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
  					  void *value, u64 flags)
  {
@@ -390,7 +539,11 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,

  	mutex_lock(&st_map->lock);

-	if (kvalue->state != BPF_STRUCT_OPS_STATE_INIT) {

[..]


+	/* Make sure that all following changes are seen after the
+	 * state value here.
+	 */
+	if (smp_load_acquire(&kvalue->state) >= BPF_STRUCT_OPS_STATE_INUSE ||
+	    refcount_read(&kvalue->refcnt)) {
  		err = -EBUSY;
  		goto unlock;
  	}

I've been starting at this for too long, might as well just ask.
Why are we caring about the ordering here? I understand why we used
to when bpf_struct_ops_map_sys_lookup_elem was lockless, but since
you're grabbing the lock in bpf_struct_ops_map_sys_lookup_elem now,
I don't see why we need acquire/store semantics.

I'm also in general a bit confused about
lock+kvalue_refcnt+uvalue_refcnt. I'll try to dig more, but I'm assuming
Martin will probably beat me to it and explain :-)


@@ -491,17 +644,21 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,
  		*(unsigned long *)(udata + moff) = prog->aux->id;
  	}

-	refcount_set(&kvalue->refcnt, 1);
+	if (st_map->map.map_flags & BPF_F_LINK) {
+		/* Let bpf_link handle registration & unregistration. */
+ err = bpf_struct_ops_transit_state_check(st_map, BPF_STRUCT_OPS_STATE_INIT,
+							 BPF_STRUCT_OPS_STATE_UNREG);
+		goto unlock;
+	}
+
  	bpf_map_inc(map);

  	set_memory_rox((long)st_map->image, 1);
  	err = st_ops->reg(kdata);
  	if (likely(!err)) {
-		/* Pair with smp_load_acquire() during lookup_elem().
-		 * It ensures the above udata updates (e.g. prog->aux->id)
-		 * can be seen once BPF_STRUCT_OPS_STATE_INUSE is set.
-		 */
-		smp_store_release(&kvalue->state, BPF_STRUCT_OPS_STATE_INUSE);
+		/* Infallible */
+		bpf_struct_ops_transit_state(st_map, BPF_STRUCT_OPS_STATE_INIT,
+					     BPF_STRUCT_OPS_STATE_INUSE);
  		goto unlock;
  	}

@@ -526,28 +683,49 @@ static int bpf_struct_ops_map_update_elem(struct bpf_map *map, void *key,

  static int bpf_struct_ops_map_delete_elem(struct bpf_map *map, void *key)
  {
-	enum bpf_struct_ops_state prev_state;
  	struct bpf_struct_ops_map *st_map;
+	int old_state;
+	int err = 0;

  	st_map = (struct bpf_struct_ops_map *)map;
-	prev_state = cmpxchg(&st_map->kvalue.state,
-			     BPF_STRUCT_OPS_STATE_INUSE,
-			     BPF_STRUCT_OPS_STATE_TOBEFREE);
-	switch (prev_state) {
+
+	old_state = bpf_struct_ops_transit_state(st_map,
+						 (st_map->map.map_flags & BPF_F_LINK ?
+						  BPF_STRUCT_OPS_STATE_UNREG :
+						  BPF_STRUCT_OPS_STATE_INUSE),
+						 BPF_STRUCT_OPS_STATE_TOBEFREE);
+
+	if (old_state < 0)
+		return old_state;
+
+	switch (old_state) {
+	case BPF_STRUCT_OPS_STATE_UNREG:
+		break;
  	case BPF_STRUCT_OPS_STATE_INUSE:
-		st_map->st_ops->unreg(&st_map->kvalue.data);
-		if (refcount_dec_and_test(&st_map->kvalue.refcnt))
-			bpf_map_put(map);
-		return 0;
+		if (st_map->map.map_flags & BPF_F_LINK)
+			err = -EBUSY;
+		else {
+			st_map->st_ops->unreg(&st_map->kvalue.data);
+			bpf_struct_ops_put(&st_map->kvalue.data);
+		}
+		break;
  	case BPF_STRUCT_OPS_STATE_TOBEFREE:
-		return -EINPROGRESS;
+		err = -EINPROGRESS;
+		break;
+	case BPF_STRUCT_OPS_STATE_TOBEUNREG:
+		err = -EBUSY;
+		break;
  	case BPF_STRUCT_OPS_STATE_INIT:
-		return -ENOENT;
+		err = -ENOENT;
+		break;
  	default:
  		WARN_ON_ONCE(1);
  		/* Should never happen.  Treat it as not found. */
-		return -ENOENT;
+		err = -ENOENT;
+		break;
  	}
+
+	return err;
  }

static void bpf_struct_ops_map_seq_show_elem(struct bpf_map *map, void *key, @@ -585,7 +763,7 @@ static void bpf_struct_ops_map_free(struct bpf_map *map)
  static int bpf_struct_ops_map_alloc_check(union bpf_attr *attr)
  {
  	if (attr->key_size != sizeof(unsigned int) || attr->max_entries != 1 ||
-	    attr->map_flags || !attr->btf_vmlinux_value_type_id)
+	    (attr->map_flags & ~BPF_F_LINK) || !attr->btf_vmlinux_value_type_id)
  		return -EINVAL;
  	return 0;
  }
@@ -671,6 +849,15 @@ static void bpf_struct_ops_put_rcu(struct rcu_head *head)
  	struct bpf_struct_ops_map *st_map;

  	st_map = container_of(head, struct bpf_struct_ops_map, rcu);
+
+	/* The struct_ops can be reused after a rcu grace period. */
+	if (st_map->kvalue.state == BPF_STRUCT_OPS_STATE_TOBEFREE)
+		bpf_struct_ops_transit_state(st_map, BPF_STRUCT_OPS_STATE_TOBEFREE,
+					     BPF_STRUCT_OPS_STATE_INIT);
+	else if (st_map->kvalue.state == BPF_STRUCT_OPS_STATE_TOBEUNREG)
+		bpf_struct_ops_transit_state(st_map, BPF_STRUCT_OPS_STATE_TOBEUNREG,
+					     BPF_STRUCT_OPS_STATE_UNREG);
+
  	bpf_map_put(&st_map->map);
  }

@@ -684,6 +871,7 @@ void bpf_struct_ops_put(const void *kdata)

  		st_map = container_of(kvalue, struct bpf_struct_ops_map,
  				      kvalue);
+
  		/* The struct_ops's function may switch to another struct_ops.
  		 *
  		 * For example, bpf_tcp_cc_x->init() may switch to
@@ -698,3 +886,143 @@ void bpf_struct_ops_put(const void *kdata)
  		call_rcu(&st_map->rcu, bpf_struct_ops_put_rcu);
  	}
  }
+
+static void bpf_struct_ops_map_link_dealloc(struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_struct_ops_map *st_map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	if (st_link->map) {
+		st_map = (struct bpf_struct_ops_map *)st_link->map;
+		bpf_struct_ops_transit_state(st_map, BPF_STRUCT_OPS_STATE_INUSE,
+					     (st_map->map.map_flags & BPF_F_LINK ?
+					      BPF_STRUCT_OPS_STATE_TOBEUNREG :
+					      BPF_STRUCT_OPS_STATE_TOBEFREE));
+		st_map->st_ops->unreg(&st_map->kvalue.data);
+		bpf_struct_ops_put(&st_map->kvalue.data);
+	}
+	kfree(st_link);
+}
+
+static int bpf_struct_ops_map_link_detach(struct bpf_link *link)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_struct_ops_map *st_map;
+
+	mutex_lock(&update_mutex);
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	st_map = container_of(st_link->map, struct bpf_struct_ops_map, map);
+	if (st_map) {
+		/*
+		 * All chaning on st_link->map are protected by
+		 * update_mutex.  This ensures that the struct_ops is
+		 * INUSE, and the state transition always success.
+		 */
+		rcu_assign_pointer(st_link->map, NULL);
+		bpf_struct_ops_transit_state(st_map, BPF_STRUCT_OPS_STATE_INUSE,
+					     (st_map->map.map_flags & BPF_F_LINK ?
+					      BPF_STRUCT_OPS_STATE_TOBEUNREG :
+					      BPF_STRUCT_OPS_STATE_TOBEFREE));
+		st_map->st_ops->unreg(&st_map->kvalue.data);
+		bpf_struct_ops_put(&st_map->kvalue.data);
+	}
+	mutex_unlock(&update_mutex);
+
+	return 0;
+}
+
+static void bpf_struct_ops_map_link_show_fdinfo(const struct bpf_link *link,
+					    struct seq_file *seq)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	rcu_read_lock_trace();
+	map = rcu_dereference(st_link->map);
+	if (map)
+		seq_printf(seq, "map_id:\t%d\n", map->id);
+	rcu_read_unlock_trace();
+}
+
+static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link,
+					       struct bpf_link_info *info)
+{
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *map;
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+	rcu_read_lock_trace();
+	map = rcu_dereference(st_link->map);
+	if (map)
+		info->struct_ops.map_id = map->id;
+	rcu_read_unlock_trace();
+	return 0;
+}
+
+static const struct bpf_link_ops bpf_struct_ops_map_lops = {
+	.dealloc = bpf_struct_ops_map_link_dealloc,
+	.detach = bpf_struct_ops_map_link_detach,
+	.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
+	.fill_link_info = bpf_struct_ops_map_link_fill_link_info,
+};
+
+int bpf_struct_ops_link_create(union bpf_attr *attr)
+{
+	struct bpf_struct_ops_link *link = NULL;
+	struct bpf_link_primer link_primer;
+	struct bpf_struct_ops_map *st_map;
+	struct bpf_map *map;
+	int err;
+
+	map = bpf_map_get(attr->link_create.map_fd);
+	if (!map)
+		return -EINVAL;
+
+ if (map->map_type != BPF_MAP_TYPE_STRUCT_OPS || !(map->map_flags & BPF_F_LINK)) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	link = kzalloc(sizeof(*link), GFP_USER);
+	if (!link) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+ bpf_link_init(&link->link, BPF_LINK_TYPE_STRUCT_OPS, &bpf_struct_ops_map_lops, NULL);
+	link->map = map;
+
+	st_map = (struct bpf_struct_ops_map *)map;
+
+ err = bpf_struct_ops_transit_state_check(st_map, BPF_STRUCT_OPS_STATE_UNREG,
+						 BPF_STRUCT_OPS_STATE_INUSE);
+	if (err)
+		goto err_out;
+
+	err = bpf_link_prime(&link->link, &link_primer);
+	if (err) {
+		bpf_struct_ops_restore_unreg(st_map);
+		goto err_out;
+	}
+
+	set_memory_rox((long)st_map->image, 1);
+	err = st_map->st_ops->reg(st_map->kvalue.data);
+	if (err) {
+		bpf_struct_ops_restore_unreg(st_map);
+		bpf_link_cleanup(&link_primer);
+
+		set_memory_nx((long)st_map->image, 1);
+		set_memory_rw((long)st_map->image, 1);
+		goto err_out;
+	}
+
+
+	return bpf_link_settle(&link_primer);
+
+err_out:
+	bpf_map_put(map);
+	kfree(link);
+	return err;
+}
+
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cda8d00f3762..2670de8dd0d4 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2735,10 +2735,11 @@ void bpf_link_inc(struct bpf_link *link)
  static void bpf_link_free(struct bpf_link *link)
  {
  	bpf_link_free_id(link->id);
+	/* detach BPF program, clean up used resources */
  	if (link->prog) {
-		/* detach BPF program, clean up used resources */
  		link->ops->release(link);
  		bpf_prog_put(link->prog);
+		/* The struct_ops links clean up map by them-selves. */
  	}
  	/* free bpf_link and its containing memory */
  	link->ops->dealloc(link);
@@ -2794,16 +2795,19 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
  	const struct bpf_prog *prog = link->prog;
  	char prog_tag[sizeof(prog->tag) * 2 + 1] = { };

-	bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
  	seq_printf(m,
  		   "link_type:\t%s\n"
-		   "link_id:\t%u\n"
-		   "prog_tag:\t%s\n"
-		   "prog_id:\t%u\n",
+		   "link_id:\t%u\n",
  		   bpf_link_type_strs[link->type],
-		   link->id,
-		   prog_tag,
-		   prog->aux->id);
+		   link->id);
+	if (prog) {
+		bin2hex(prog_tag, prog->tag, sizeof(prog->tag));
+		seq_printf(m,
+			   "prog_tag:\t%s\n"
+			   "prog_id:\t%u\n",
+			   prog_tag,
+			   prog->aux->id);
+	}
  	if (link->ops->show_fdinfo)
  		link->ops->show_fdinfo(link, m);
  }
@@ -4278,7 +4282,8 @@ static int bpf_link_get_info_by_fd(struct file *file,

  	info.type = link->type;
  	info.id = link->id;
-	info.prog_id = link->prog->aux->id;
+	if (link->prog)
+		info.prog_id = link->prog->aux->id;

  	if (link->ops->fill_link_info) {
  		err = link->ops->fill_link_info(link, &info);
@@ -4541,6 +4546,9 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
  	if (CHECK_ATTR(BPF_LINK_CREATE))
  		return -EINVAL;

+	if (attr->link_create.attach_type == BPF_STRUCT_OPS)
+		return bpf_struct_ops_link_create(attr);
+
  	prog = bpf_prog_get(attr->link_create.prog_fd);
  	if (IS_ERR(prog))
  		return PTR_ERR(prog);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 17afd2b35ee5..cd0ff39981e8 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1033,6 +1033,7 @@ enum bpf_attach_type {
  	BPF_PERF_EVENT,
  	BPF_TRACE_KPROBE_MULTI,
  	BPF_LSM_CGROUP,
+	BPF_STRUCT_OPS,
  	__MAX_BPF_ATTACH_TYPE
  };

@@ -1266,6 +1267,9 @@ enum {

/* Create a map that is suitable to be an inner map with dynamic max entries */
  	BPF_F_INNER_MAP		= (1U << 12),
+
+/* Create a map that will be registered/unregesitered by the backed bpf_link */
+	BPF_F_LINK		= (1U << 13),
  };

  /* Flags for BPF_PROG_QUERY. */
@@ -1507,7 +1511,10 @@ union bpf_attr {
  	} task_fd_query;

  	struct { /* struct used by BPF_LINK_CREATE command */
-		__u32		prog_fd;	/* eBPF program to attach */
+		union {
+			__u32		prog_fd;	/* eBPF program to attach */
+			__u32		map_fd;		/* eBPF struct_ops to attach */
+		};
  		union {
  			__u32		target_fd;	/* object to attach to */
  			__u32		target_ifindex; /* target ifindex */
@@ -6354,6 +6361,9 @@ struct bpf_link_info {
  		struct {
  			__u32 ifindex;
  		} xdp;
+		struct {
+			__u32 map_id;
+		} struct_ops;
  	};
  } __attribute__((aligned(8)));

--
2.30.2




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