[PATCH bpf-next v2 1/2] bpf: Add bpf_task_under_cgroup() kfunc

[Feng zhou]

From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>

Add a kfunc that's similar to the bpf_current_task_under_cgroup.
The difference is that it is a designated task.

When hook sched related functions, sometimes it is necessary to
specify a task instead of the current task.

Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
---
 kernel/bpf/helpers.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 00e5fb0682ac..88e3247b5c44 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2142,6 +2142,24 @@ __bpf_kfunc struct cgroup *bpf_cgroup_from_id(u64 cgid)
 		return NULL;
 	return cgrp;
 }
+
+/**
+ * bpf_task_under_cgroup - Check whether the task is a given subset of the
+ * cgroup2 hierarchy. The cgroup2 to test is assigned by cgrp.
+ * @cgrp: assigned cgrp.
+ * @task: assigned task.
+ */
+__bpf_kfunc int bpf_task_under_cgroup(struct cgroup *cgrp,
+				      struct task_struct *task)
+{
+	if (unlikely(!cgrp))
+		return -EAGAIN;
+
+	if (unlikely(!task))
+		return -ENOENT;
+
+	return task_under_cgroup_hierarchy(task, cgrp);
+}
 #endif /* CONFIG_CGROUPS */
 
 /**
@@ -2341,6 +2359,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_task_under_cgroup, KF_RCU)
 #endif
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_SET8_END(generic_btf_ids)
-- 
2.20.1