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Subject: Re: [RFC bpf-next v2 2/9] bpf: add register and unregister functions
 for struct_ops.
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To: thinker.li@gmail.com
Cc: sinquersw@gmail.com, kuifeng@meta.com, bpf@vger.kernel.org,
 ast@kernel.org, song@kernel.org, kernel-team@meta.com, andrii@kernel.org
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 <20230913061449.1918219-3-thinker.li@gmail.com>
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	lindbergh.monkeyblade.net

On 9/12/23 11:14 PM, thinker.li@gmail.com wrote:
> +int register_bpf_struct_ops(struct bpf_struct_ops_mod *mod)
> +{
> +	struct bpf_struct_ops *st_ops = mod->st_ops;
> +	struct bpf_verifier_log *log;
> +	struct btf *btf;
> +	int err;
> +
> +	if (mod->st_ops == NULL ||
> +	    mod->owner == NULL)
> +		return -EINVAL;
> +
> +	log = kzalloc(sizeof(*log), GFP_KERNEL | __GFP_NOWARN);
> +	if (!log) {
> +		err = -ENOMEM;
> +		goto errout;
> +	}
> +
> +	log->level = BPF_LOG_KERNEL;
> +
> +	btf = btf_get_module_btf(mod->owner);

Where is btf_put called?

It is not stored anywhere in patch 2, so a bit confusing. I quickly looked at 
the following patches but also don't see the bpf_put.

> +	if (!btf) {
> +		err = -EINVAL;
> +		goto errout;
> +	}
> +
> +	bpf_struct_ops_init_one(st_ops, btf, log);
> +	err = add_struct_ops(st_ops);
> +
> +errout:
> +	kfree(log);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL(register_bpf_struct_ops);
> +
> +int unregister_bpf_struct_ops(struct bpf_struct_ops_mod *mod)

It is not clear to me why the subsystem needs to explicitly call 
unregister_bpf_struct_ops(). Can it be done similar to the module kfunc support 
(the kfunc_set_tab goes away with the btf)?

Related to this, does it need to maintain a global struct_ops array for all 
kernel module? Can the struct_ops be maintained under its corresponding module 
btf itself?

> +{
> +	struct bpf_struct_ops *st_ops = mod->st_ops;
> +	int err;
> +
> +	err = remove_struct_ops(st_ops);
> +	if (!err && st_ops->uninit)
> +		err = st_ops->uninit();
> +
> +	return err;
> +}
> +EXPORT_SYMBOL(unregister_bpf_struct_ops);