Re: [RFC v2 3/3] tools/ufq_iosched: add BPF example scheduler and build scaffolding

[bot+bpf-ci]

> diff --git a/tools/ufq_iosched/ufq_simple.bpf.c b/tools/ufq_iosched/ufq_simple.bpf.c
> new file mode 100644
> index 000000000000..81954e73068a
> --- /dev/null
> +++ b/tools/ufq_iosched/ufq_simple.bpf.c

[ ... ]

> +int BPF_STRUCT_OPS(ufq_simple_insert_req, struct request_queue *q,
> +		   struct request *rq, blk_insert_t flags,
> +		   struct list_head *freeq)
                                              ^^^^^^^

Does this signature match the kernel's ufq_iosched_ops definition?

Looking at block/ufq-iosched.h, the insert_req member is defined with
three parameters:

    int (*insert_req)(struct request_queue *q, struct request *rq,
                     blk_insert_t flags);

The kernel-side callers in block/ufq-iosched.c also pass only three
arguments:

    ret = ops->insert_req(q, rq, flags);
    ops->insert_req(q, target, 0);

The BPF struct_ops verifier (check_struct_ops_btf_id) validates that each
BPF program matches the declared function-pointer signature in the kernel.
A program with four parameters registered against a three-parameter member
will be rejected at load time, so ufq_simple will fail to attach via
UFQ_OPS_LOAD / UFQ_OPS_ATTACH and the example cannot be used.

Even if the verifier accepted the mismatch, the trampoline would not
populate a fourth argument, leaving freeq uninitialized. Should the extra
'struct list_head *freeq' parameter be removed?

> +{
> +	struct ufq_simple_data *ufq_sd;
> +	struct queue_list_node *qnode;
> +	struct sort_tree_node *snode;

[ ... ]

> +UFQ_OPS_DEFINE(ufq_simple_ops,
> +	.init_sched		= (void *)ufq_simple_init_sched,
> +	.exit_sched		= (void *)ufq_simple_exit_sched,
> +	.insert_req		= (void *)ufq_simple_insert_req,
> +	.dispatch_req		= (void *)ufq_simple_dispatch_req,
> +	.has_req		= (void *)ufq_simple_has_req,
> +	.finish_req		= (void *)ufq_simple_finish_req,
> +	.merge_req		= (void *)ufq_simple_merge_req,
> +	.merge_bio		= (void *)ufq_simple_merge_bio,
> +	.name			= "ufq_simple");


---
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