Re: [PATCH bpf-next v7 2/6] bpf: Support associating BPF program with struct_ops

[Martin KaFai Lau <martin.lau@linux.dev>]

On 11/21/25 3:13 PM, Amery Hung wrote:
> Add a new BPF command BPF_PROG_ASSOC_STRUCT_OPS to allow associating
> a BPF program with a struct_ops map. This command takes a file
> descriptor of a struct_ops map and a BPF program and set
> prog->aux->st_ops_assoc to the kdata of the struct_ops map.
> 
> The command does not accept a struct_ops program nor a non-struct_ops
> map. Programs of a struct_ops map is automatically associated with the
> map during map update. If a program is shared between two struct_ops
> maps, prog->aux->st_ops_assoc will be poisoned to indicate that the
> associated struct_ops is ambiguous. The pointer, once poisoned, cannot
> be reset since we have lost track of associated struct_ops. For other
> program types, the associated struct_ops map, once set, cannot be
> changed later. This restriction may be lifted in the future if there is
> a use case.
> 
> A kernel helper bpf_prog_get_assoc_struct_ops() can be used to retrieve
> the associated struct_ops pointer. The returned pointer, if not NULL, is
> guaranteed to be valid and point to a fully updated struct_ops struct.
> For struct_ops program reused in multiple struct_ops map, the return
> will be NULL.
> 
> prog->aux->st_ops_assoc is protected by bumping the refcount for
> non-struct_ops programs and RCU for struct_ops programs. Since it would
> be inefficient to track programs associated with a struct_ops map, every
> non-struct_ops program will bump the refcount of the map to make sure
> st_ops_assoc stays valid. For a struct_ops program, it is protected by
> RCU as map_free will wait for an RCU grace period before disassociating
> the program with the map. The helper must be called in BPF program
> context or RCU read-side critical section.
> 
> struct_ops implementers should note that the struct_ops returned may not
> be initialized nor attached yet. The struct_ops implementer will be
> responsible for tracking and checking the state of the associated
> struct_ops map if the use case expects an initialized or attached
> struct_ops.

Acked-by: Martin KaFai Lau <martin.lau@kernel.org>