Commit 332ea1f6 authored by Tejun Heo's avatar Tejun Heo Committed by Alexei Starovoitov
Browse files

bpf: Add bpf_cgroup_from_id() kfunc 



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: default avatarTejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/Y/bBaG96t0/gQl9/@slm.duckdns.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 746ce767

Documentation/bpf/kfuncs.rst

+7 −3
Original line number Diff line number Diff line
@@ -583,13 +583,17 @@ Here's an example of how it can be used: 


----



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:

kernel/bpf/helpers.c

+18 −0
Original line number Diff line number Diff line
@@ -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)