cgroup ID is an userspace-visible 64bit value uniquely identifying a given
cgroup. As the IDs are used widely, it's useful to be able to look up the
matching cgroups. Add bpf_cgroup_from_id().
v2: Separate out selftest into its own patch as suggested by Alexei.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
Documentation/bpf/kfuncs.rst | 10 +++++++---
kernel/bpf/helpers.c | 18 ++++++++++++++++++
2 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index ca96ef3f6896..226313747be5 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -583,13 +583,17 @@ You may also acquire a reference to a ``struct cgroup`` kptr that's already
----
-Another kfunc available for interacting with ``struct cgroup *`` objects is
-bpf_cgroup_ancestor(). This allows callers to access the ancestor of a cgroup,
-and return it as a cgroup kptr.
+Other kfuncs available for interacting with ``struct cgroup *`` objects are
+bpf_cgroup_ancestor() and bpf_cgroup_from_id(), allowing callers to access
+the ancestor of a cgroup and find a cgroup by its ID, respectively. Both
+return a cgroup kptr.
.. kernel-doc:: kernel/bpf/helpers.c
:identifiers: bpf_cgroup_ancestor
+.. kernel-doc:: kernel/bpf/helpers.c
+ :identifiers: bpf_cgroup_from_id
+
Eventually, BPF should be updated to allow this to happen with a normal memory
load in the program itself. This is currently not possible without more work in
the verifier. bpf_cgroup_ancestor() can be used as follows:
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5b278a38ae58..a784be6f8bac 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2101,6 +2101,23 @@ __bpf_kfunc struct cgroup *bpf_cgroup_ancestor(struct cgroup *cgrp, int level)
cgroup_get(ancestor);
return ancestor;
}
+
+/**
+ * bpf_cgroup_from_id - Find a cgroup from its ID. A cgroup returned by this
+ * kfunc which is not subsequently stored in a map, must be released by calling
+ * bpf_cgroup_release().
+ * @cgrp: The cgroup for which we're performing a lookup.
+ * @level: The level of ancestor to look up.
+ */
+__bpf_kfunc struct cgroup *bpf_cgroup_from_id(u64 cgid)
+{
+ struct cgroup *cgrp;
+
+ cgrp = cgroup_get_from_id(cgid);
+ if (IS_ERR(cgrp))
+ return NULL;
+ return cgrp;
+}
#endif /* CONFIG_CGROUPS */
/**
@@ -2167,6 +2184,7 @@ BTF_ID_FLAGS(func, bpf_cgroup_acquire, KF_ACQUIRE | KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_cgroup_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_cgroup_release, KF_RELEASE)
BTF_ID_FLAGS(func, bpf_cgroup_ancestor, KF_ACQUIRE | KF_TRUSTED_ARGS | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_cgroup_from_id, KF_ACQUIRE | KF_RET_NULL)
#endif
BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
BTF_SET8_END(generic_btf_ids)
--
2.39.2
