Subsystems that want to implement a struct bpf_struct_ops structure to
enable struct_ops maps must currently reverse engineer how the structure
works. Given that this is meant to be a way for subsystem maintainers to
extend their subsystems using BPF, let's document it to make it a bit
easier on them.
Signed-off-by: David Vernet <void@xxxxxxxxxxxxx>
---
include/linux/bpf.h | 47 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 47 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cfabbcf47bdb..eced6400f778 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1550,6 +1550,53 @@ struct bpf_struct_ops_value;
struct btf_member;
#define BPF_STRUCT_OPS_MAX_NR_MEMBERS 64
+/**
+ * struct bpf_struct_ops - A structure of callbacks allowing a subsystem to
+ * define a BPF_MAP_TYPE_STRUCT_OPS map type composed
+ * of BPF_PROG_TYPE_STRUCT_OPS progs.
+ * @verifier_ops: A structure of callbacks that are invoked by the verifier
+ * when determining whether the struct_ops progs in the
+ * struct_ops map are valid.
+ * @init: A callback that is invoked a single time, and before any other
+ * callback, to initialize the structure. A nonzero return value means
+ * the subsystem could not be initialized.
+ * @check_member: When defined, a callback invoked by the verifier to allow
+ * the subsystem to determine if an entry in the struct_ops map
+ * is valid. A nonzero return value means that the map is
+ * invalid and should be rejected by the verifier.
+ * @init_member: A callback that is invoked for each member of the struct_ops
+ * map to allow the subsystem to initialize the member. A nonzero
+ * value means the member could not be initialized. This callback
+ * is exclusive with the @type, @type_id, @value_type, and
+ * @value_id fields.
+ * @reg: A callback that is invoked when the struct_ops map has been
+ * initialized and is being attached to. Zero means the struct_ops map
+ * has been successfully registered and is live. A nonzero return value
+ * means the struct_ops map could not be registered.
+ * @unreg: A callback that is invoked when the struct_ops map should be
+ * unregistered.
+ * @update: A callback that is invoked when the live struct_ops map is being
+ * updated to contain new values. This callback is only invoked when
+ * the struct_ops map is loaded with BPF_F_LINK. If not defined, the
+ * it is assumed that the struct_ops map cannot be updated.
+ * @validate: A callback that is invoked after all of the members have been
+ * initialized. This callback should perform static checks on the
+ * map, meaning that it should either fail or succeed
+ * deterministically. A struct_ops map that has been validated may
+ * not necessarily succeed in being registered if the call to @reg
+ * fails. For example, a valid struct_ops map may be loaded, but
+ * then fail to be registered due to there being another active
+ * struct_ops map on the system in the subsystem already. For this
+ * reason, if this callback is not defined, the check is skipped as
+ * the struct_ops map will have final verification performed in
+ * @reg.
+ * @type: BTF type.
+ * @value_type: Value type.
+ * @name: The name of the struct bpf_struct_ops object.
+ * @func_models: Func models
+ * @type_id: BTF type id.
+ * @value_id: BTF value id.
+ */
struct bpf_struct_ops {
const struct bpf_verifier_ops *verifier_ops;
int (*init)(struct btf *btf);
--
2.41.0
