[bpf-next,v3,5/8] bpf: Update the struct_ops of a bpf_link.

Commit Message

Kui-Feng Lee March 3, 2023, 1:21 a.m. UTC

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: Kui-Feng Lee <[e-mail]>
---
 include/linux/bpf.h         |  1 +
 include/uapi/linux/bpf.h    |  8 +++++--
 kernel/bpf/bpf_struct_ops.c | 46 +++++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c        | 43 ++++++++++++++++++++++++++++++----
 4 files changed, 92 insertions(+), 6 deletions(-)

Patch

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index acb18aa64b77..643f94432b65 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1410,6 +1410,7 @@  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_tramp_link {
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index cd0ff39981e8..0702e88f7c08 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1555,8 +1555,12 @@  union bpf_attr {
 
 	struct { /* struct used by BPF_LINK_UPDATE command */
 		__u32		link_fd;	/* link fd */
-		/* new program fd to update link with */
-		__u32		new_prog_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 */
 		/* expected link's program fd; is specified only if
 		 * BPF_F_REPLACE flag is set in flags */
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index 9ec675576d97..ce856811359f 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -771,10 +771,56 @@  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_struct_ops_value *kvalue;
+	struct bpf_struct_ops_map *st_map, *old_st_map;
+	struct bpf_struct_ops_link *st_link;
+	struct bpf_map *old_map;
+	int err = 0;
+
+	if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS ||
+	    !(new_map->map_flags & BPF_F_LINK))
+		return -EINVAL;
+
+	mutex_lock(&update_mutex);
+
+	st_link = container_of(link, struct bpf_struct_ops_link, link);
+
+	/* The new and old struct_ops must be the same type. */
+	st_map = container_of(new_map, struct bpf_struct_ops_map, map);
+
+	old_map = st_link->map;
+	old_st_map = container_of(old_map, struct bpf_struct_ops_map, map);
+	if (st_map->st_ops != old_st_map->st_ops ||
+	    /* Pair with smp_store_release() during map_update */
+	    smp_load_acquire(&st_map->kvalue.state) != BPF_STRUCT_OPS_STATE_READY) {
+		err = -EINVAL;
+		goto err_out;
+	}
+
+	kvalue = &st_map->kvalue;
+
+	err = st_map->st_ops->update(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)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 3db4938212d6..a640a280bff9 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4655,6 +4655,30 @@  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;
+	int ret = 0;
+
+	new_map = bpf_map_get(attr->link_update.new_map_fd);
+	if (IS_ERR(new_map))
+		return -EINVAL;
+
+	if (new_map->map_type != BPF_MAP_TYPE_STRUCT_OPS) {
+		ret = -EINVAL;
+		goto out_put_map;
+	}
+
+	if (link->ops->update_map)
+		ret = link->ops->update_map(link, new_map);
+	else
+		ret = -EINVAL;
+
+out_put_map:
+	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)
@@ -4667,14 +4691,25 @@  static int link_update(union bpf_attr *attr)
 	if (CHECK_ATTR(BPF_LINK_UPDATE))
 		return -EINVAL;
 
-	flags = attr->link_update.flags;
-	if (flags & ~BPF_F_REPLACE)
-		return -EINVAL;
-
 	link = bpf_link_get_from_fd(attr->link_update.link_fd);
 	if (IS_ERR(link))
 		return PTR_ERR(link);
 
+	flags = attr->link_update.flags;
+
+	if (link->ops->update_map) {
+		if (flags)	/* always replace the existing one */
+			ret = -EINVAL;
+		else
+			ret = link_update_map(link, attr);
+		goto out_put_link;
+	}
+
+	if (flags & ~BPF_F_REPLACE) {
+		ret = -EINVAL;
+		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);