[PATCH RFC 7/9] bpf: add BPF_MAP_RECHARGE syscall

[Yafang Shao <laoar.shao@gmail.com>]

This patch adds a new bpf syscall BPF_MAP_RECHARGE, which means to
recharge the allocated memory of a bpf map from an offline memcg to
the current memcg.

The recharge methord for each map will be implemented in the follow-up
patches.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/linux/bpf.h      |  2 ++
 include/uapi/linux/bpf.h |  9 +++++++++
 kernel/bpf/syscall.c     | 19 ++++++++++++++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 88449fb..fca274e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -147,6 +147,8 @@ struct bpf_map_ops {
 				     bpf_callback_t callback_fn,
 				     void *callback_ctx, u64 flags);
 
+	bool (*map_recharge_memcg)(struct bpf_map *map);
+
 	/* BTF name and id of struct allocated by map_alloc */
 	const char * const map_btf_name;
 	int *map_btf_id;
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a448b06..290ea67 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -821,6 +821,14 @@ struct bpf_cgroup_storage_key {
  *		Returns zero on success. On error, -1 is returned and *errno*
  *		is set appropriately.
  *
+ * BPF_MAP_RECHARGE
+ *  Description
+ *		Recharge bpf memory from an offline memcg
+ *
+ *	Return
+ *		Returns zero on success. On error, -1 is returned and *errno*
+ *		is set appropriately.
+ *
  * NOTES
  *	eBPF objects (maps and programs) can be shared between processes.
  *
@@ -875,6 +883,7 @@ enum bpf_cmd {
 	BPF_ITER_CREATE,
 	BPF_LINK_DETACH,
 	BPF_PROG_BIND_MAP,
+	BPF_MAP_RECHARGE,
 };
 
 enum bpf_map_type {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 68fea3b..85456f1 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1128,7 +1128,6 @@ static int map_lookup_elem(union bpf_attr *attr)
 	return err;
 }
 
-
 #define BPF_MAP_UPDATE_ELEM_LAST_FIELD flags
 
 static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr)
@@ -4621,6 +4620,21 @@ static int bpf_prog_bind_map(union bpf_attr *attr)
 	return ret;
 }
 
+static int map_recharge_elem(union bpf_attr *attr)
+{
+	int id = attr->map_id;
+	struct bpf_map *map;
+
+	map = bpf_map_idr_find(id);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+
+	if (map->ops->map_recharge_memcg)
+		map->ops->map_recharge_memcg(map);
+
+	return 0;
+}
+
 static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size)
 {
 	union bpf_attr attr;
@@ -4757,6 +4771,9 @@ static int __sys_bpf(int cmd, bpfptr_t uattr, unsigned int size)
 	case BPF_PROG_BIND_MAP:
 		err = bpf_prog_bind_map(&attr);
 		break;
+	case BPF_MAP_RECHARGE:
+		err = map_recharge_elem(&attr);
+		break;
 	default:
 		err = -EINVAL;
 		break;
-- 
1.8.3.1