Re: [PATCH bpf-next v2 1/2] libbpf: Introduce bpf_program__clone()

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 2/24/26 19:28, Eduard Zingerman wrote:
> On Fri, 2026-02-20 at 11:18 -0800, Mykyta Yatsenko wrote:
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Add bpf_program__clone() API that loads a single BPF program from a
>> prepared BPF object into the kernel, returning a file descriptor owned
>> by the caller.
>>
>> After bpf_object__prepare(), callers can use bpf_program__clone() to
>> load individual programs with custom bpf_prog_load_opts, instead of
>> loading all programs at once via bpf_object__load(). Non-zero fields in
>> opts override the defaults derived from the program and object
>> internals; passing NULL opts populates everything automatically.
>>
>> Internally, bpf_program__clone() resolves BTF-based attach targets
>> (attach_btf_id, attach_btf_obj_fd) and the sleepable flag, fills
>> func/line info, fd_array, license, and kern_version from the
>> prepared object before calling bpf_prog_load().
>>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
>>   tools/lib/bpf/libbpf.c   | 64 ++++++++++++++++++++++++++++++++++++++++++++++++
>>   tools/lib/bpf/libbpf.h   | 17 +++++++++++++
>>   tools/lib/bpf/libbpf.map |  1 +
>>   3 files changed, 82 insertions(+)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 0c8bf0b5cce4..4b084bda3f47 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -9793,6 +9793,70 @@ __u32 bpf_program__line_info_cnt(const struct bpf_program *prog)
>>   	return prog->line_info_cnt;
>>   }
>>   
>> +int bpf_program__clone(struct bpf_program *prog, const struct bpf_prog_load_opts *opts)
>> +{
>> +	LIBBPF_OPTS(bpf_prog_load_opts, attr);
>> +	struct bpf_prog_load_opts *pattr = &attr;
>> +	struct bpf_object *obj;
>> +	int err, fd;
>> +
>> +	if (!prog)
>> +		return libbpf_err(-EINVAL);
>> +
>> +	if (!OPTS_VALID(opts, bpf_prog_load_opts))
>> +		return libbpf_err(-EINVAL);
>> +
>> +	obj = prog->obj;
>> +	if (obj->state < OBJ_PREPARED)
>> +		return libbpf_err(-EINVAL);
>> +
>> +	/* Copy caller opts, fall back to prog/object defaults */
>> +	OPTS_SET(pattr, expected_attach_type,
>> +		 OPTS_GET(opts, expected_attach_type, 0) ?: prog->expected_attach_type);
>> +	OPTS_SET(pattr, attach_btf_id, OPTS_GET(opts, attach_btf_id, 0) ?: prog->attach_btf_id);
>> +	OPTS_SET(pattr, attach_btf_obj_fd,
>> +		 OPTS_GET(opts, attach_btf_obj_fd, 0) ?: prog->attach_btf_obj_fd);
>> +	OPTS_SET(pattr, attach_prog_fd, OPTS_GET(opts, attach_prog_fd, 0) ?: prog->attach_prog_fd);
>> +	OPTS_SET(pattr, prog_flags, OPTS_GET(opts, prog_flags, 0) ?: prog->prog_flags);
>> +	OPTS_SET(pattr, prog_ifindex, OPTS_GET(opts, prog_ifindex, 0) ?: prog->prog_ifindex);
>> +	OPTS_SET(pattr, kern_version, OPTS_GET(opts, kern_version, 0) ?: obj->kern_version);
>> +	OPTS_SET(pattr, fd_array, OPTS_GET(opts, fd_array, NULL) ?: obj->fd_array);
> It seems 'fd_array_cnt' is not copied, should it be?
>
>> +	OPTS_SET(pattr, token_fd, OPTS_GET(opts, token_fd, 0) ?: obj->token_fd);
>> +	if (attr.token_fd)
>> +		attr.prog_flags |= BPF_F_TOKEN_FD;
> Nit: should this be 'if (OPTS_GET(opts, token_fd, 0) && attr.token_fd)' ?
>
>> +
>> +	/* BTF func/line info */
>> +	if (obj->btf && btf__fd(obj->btf) >= 0) {
>> +		OPTS_SET(pattr, prog_btf_fd, OPTS_GET(opts, prog_btf_fd, 0) ?: btf__fd(obj->btf));
>> +		OPTS_SET(pattr, func_info, OPTS_GET(opts, func_info, NULL) ?: prog->func_info);
>> +		OPTS_SET(pattr, func_info_cnt,
>> +			 OPTS_GET(opts, func_info_cnt, 0) ?: prog->func_info_cnt);
>> +		OPTS_SET(pattr, func_info_rec_size,
>> +			 OPTS_GET(opts, func_info_rec_size, 0) ?: prog->func_info_rec_size);
>> +		OPTS_SET(pattr, line_info, OPTS_GET(opts, line_info, NULL) ?: prog->line_info);
>> +		OPTS_SET(pattr, line_info_cnt,
>> +			 OPTS_GET(opts, line_info_cnt, 0) ?: prog->line_info_cnt);
>> +		OPTS_SET(pattr, line_info_rec_size,
>> +			 OPTS_GET(opts, line_info_rec_size, 0) ?: prog->line_info_rec_size);
>> +	}
>> +
>> +	OPTS_SET(pattr, log_buf, OPTS_GET(opts, log_buf, NULL));
>> +	OPTS_SET(pattr, log_size, OPTS_GET(opts, log_size, 0));
>> +	OPTS_SET(pattr, log_level, OPTS_GET(opts, log_level, 0));
> Just curious why did you decide not to inherit logging properties from
> the original program?
> Unless overridden, the original program would point to the buffer
> specified for the object in bpf_object_open_opts->kernel_log_buf, right?
Inheriting the object's log_buf here would mean writing
into a shared mutable buffer, which sounds not very good,
I don't see where this scenario is useful.
>
>> +
>> +	/* Resolve BTF attach targets, set sleepable/XDP flags, etc. */
>> +	if (prog->sec_def && prog->sec_def->prog_prepare_load_fn) {
>> +		err = prog->sec_def->prog_prepare_load_fn(prog, pattr, prog->sec_def->cookie);
>> +		if (err)
>> +			return libbpf_err(err);
>> +	}
>> +
>> +	fd = bpf_prog_load(prog->type, prog->name, obj->license, prog->insns, prog->insns_cnt,
>> +			   pattr);
>> +
>> +	return libbpf_err(fd);
>> +}
>> +
>>   #define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {			    \
>>   	.sec = (char *)sec_pfx,						    \
>>   	.prog_type = BPF_PROG_TYPE_##ptype,				    \