Re: [PATCH bpf-next v2 0/2] libbpf: Add bpf_program__clone() for individual program loading

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

On 2/20/26 22:48, Alexei Starovoitov wrote:
> On Fri, Feb 20, 2026 at 11:18 AM Mykyta Yatsenko
> <mykyta.yatsenko5@gmail.com> wrote:
>> This series adds bpf_program__clone() to libbpf and converts veristat to
>> use it, replacing the costly per-program object re-opening pattern.
>>
>> veristat needs to load each BPF program in isolation to collect
>> per-program verification statistics. Previously it achieved this by
>> opening a fresh bpf_object for every program, disabling autoload on all
>> but the target, and loading the whole object. For object files with many
>> programs this meant repeating ELF parsing and BTF processing N times.
>>
>> Patch 1 introduces bpf_program__clone(), which loads a single program
>> from a prepared object into the kernel and returns an fd owned by the
>> caller. It resolves BTF attach targets, fills in func/line info,
>> fd_array, and other load parameters from the prepared object
>> automatically, while letting callers override any field via
>> bpf_prog_load_opts.
>>
>> Patch 2 converts veristat to prepare the object once and clone each
>> program individually, eliminating redundant work.
>>
>> Performance
>> Tested on selftests: 918 objects, ~4270 programs:
>>   - Wall time:   36.88s -> 23.18s (37% faster)
>>   - User time:   20.80s -> 16.07s (23% faster)
>>   - Kernel time: 12.07s ->  6.06s (50% faster)
>>
>> Per-program loading also improves coverage: 83 programs that previously
>> failed now succeed.
> Wait what? How is that possible?
Thanks for asking. Take for example verifier_unpriv.bpf.o object,
all progs fail to load on the system veristat, the errors are:
```
libbpf: map 'map_prog1_socket': failed to initialize slot [1]
to prog 'dummy_prog_loop1_socket' fd=-2: -EBADF
...
libbpf: map 'map_prog1_socket': failed to initialize slot
[0] to prog 'dummy_prog_42_socket' fd=-2: -EBADF
...
etc
```
I understand this is due to the libbpf trying to initialize
all PROG_ARRAY maps during object load, regardless if the corresponding
program is loading or not (currently only 1 program is
enabled at a time, so object that has those PROG_ARRAY has no
chance to succeed)
This root cause is the only reason for all 83
improvements.

This is not intentional, but it sounds like a nice side-effect,
so I mention it.

Is this something we would like to address in libbpf?