[RFC PATCH v4 2/4] mm: thp: add a new kfunc bpf_mm_get_mem_cgroup()

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

We will utilize this new kfunc bpf_mm_get_mem_cgroup() to retrieve the
associated mem_cgroup from the given @mm. The obtained mem_cgroup must
be released by calling bpf_put_mem_cgroup() as a paired operation.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 mm/bpf_thp.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/mm/bpf_thp.c b/mm/bpf_thp.c
index 10b486dd8bc4..040f988dbdbd 100644
--- a/mm/bpf_thp.c
+++ b/mm/bpf_thp.c
@@ -161,10 +161,59 @@ static struct bpf_struct_ops bpf_bpf_thp_ops = {
 	.name = "bpf_thp_ops",
 };
 
+__bpf_kfunc_start_defs();
+
+/**
+ * bpf_mm_get_mem_cgroup - Get the memory cgroup associated with a mm_struct.
+ * @mm: The mm_struct to query
+ *
+ * The obtained mem_cgroup must be released by calling bpf_put_mem_cgroup().
+ *
+ * Return: The associated mem_cgroup on success, or NULL on failure. Note that
+ * this function depends on CONFIG_MEMCG being enabled - it will always return
+ * NULL if CONFIG_MEMCG is not configured.
+ */
+__bpf_kfunc struct mem_cgroup *bpf_mm_get_mem_cgroup(struct mm_struct *mm)
+{
+	return get_mem_cgroup_from_mm(mm);
+}
+
+/**
+ * bpf_put_mem_cgroup - Release a memory cgroup obtained from bpf_mm_get_mem_cgroup()
+ * @memcg: The memory cgroup to release
+ */
+__bpf_kfunc void bpf_put_mem_cgroup(struct mem_cgroup *memcg)
+{
+#ifdef CONFIG_MEMCG
+	if (!memcg)
+		return;
+	css_put(&memcg->css);
+#endif
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(bpf_thp_ids)
+BTF_ID_FLAGS(func, bpf_mm_get_mem_cgroup, KF_TRUSTED_ARGS | KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_put_mem_cgroup, KF_RELEASE)
+BTF_KFUNCS_END(bpf_thp_ids)
+
+static const struct btf_kfunc_id_set bpf_thp_set = {
+	.owner = THIS_MODULE,
+	.set = &bpf_thp_ids,
+};
+
 static int __init bpf_thp_ops_init(void)
 {
-	int err = register_bpf_struct_ops(&bpf_bpf_thp_ops, bpf_thp_ops);
+	int err;
+
+	err = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_thp_set);
+	if (err) {
+		pr_err("bpf_thp: Failed to register kfunc sets (%d)\n", err);
+		return err;
+	}
 
+	err = register_bpf_struct_ops(&bpf_bpf_thp_ops, bpf_thp_ops);
 	if (err)
 		pr_err("bpf_thp: Failed to register struct_ops (%d)\n", err);
 	return err;
-- 
2.43.5