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bpf: Document struct bpf_struct_ops fields 

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@manifault.com>
Link: https://lore.kernel.org/r/20230814185908.700553-3-void@manifault.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
David Vernet 2023-08-14 13:59:08 -05:00 committed by Martin KaFai Lau
parent 8ba651ed7f
commit bb48cf1679
1 changed files with 47 additions and 0 deletions
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47
include/linux/bpf.h
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@ -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);