2021-07-23 08:54 UTC-0700 ~ Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > On Fri, Jul 23, 2021 at 2:31 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: >> >> 2021-07-22 17:39 UTC-0700 ~ Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> >>> On Wed, Jul 21, 2021 at 8:38 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: >>>> >>>> Rename function btf__get_from_id() as btf__load_from_kernel_by_id() to >>>> better indicate what the function does. Change the new function so that, >>>> instead of requiring a pointer to the pointer to update and returning >>>> with an error code, it takes a single argument (the id of the BTF >>>> object) and returns the corresponding pointer. This is more in line with >>>> the existing constructors. >>>> >>>> The other tools calling the deprecated btf__get_from_id() function will >>>> be updated in a future commit. >>>> >>>> References: >>>> >>>> - https://github.com/libbpf/libbpf/issues/278 >>>> - https://github.com/libbpf/libbpf/wiki/Libbpf:-the-road-to-v1.0#btfh-apis >>>> >>>> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c >>>> index 7e0de560490e..6654bdee7ad7 100644 >>>> --- a/tools/lib/bpf/btf.c >>>> +++ b/tools/lib/bpf/btf.c >>>> @@ -1383,21 +1383,30 @@ struct btf *btf_get_from_fd(int btf_fd, struct btf *base_btf) >>>> return btf; >>>> } >>>> >>>> +struct btf *btf__load_from_kernel_by_id(__u32 id) >>>> +{ >>>> + struct btf *btf; >>>> + int btf_fd; >>>> + >>>> + btf_fd = bpf_btf_get_fd_by_id(id); >>>> + if (btf_fd < 0) >>>> + return ERR_PTR(-errno); >>> >>> please use libbpf_err_ptr() for consistency, see >>> bpf_object__open_mem() for an example >> >> I can do that, but I'll need to uncouple btf__get_from_id() from the new >> function. If it calls btf__load_from_kernel_by_id() and >> LIBBPF_STRICT_CLEAN_PTRS is set, it would change its return value. > > No it won't, if libbpf_get_error() is used right after the API call. But we cannot be sure that users currently call libbpf_get_error() after btf__get_from_id()? I'm fine if we assume they do (users currently selecting the CLEAN_PTRS are probably savvy enough to call it I guess), I'll update as you suggest. > With CLEAN_PTRS the result pointer is NULL but actual error is passed > through errno. libbpf_get_error() knows about this and extracts error > from errno if passed NULL pointer. With returning ERR_PTR(-errno) from > btf__load_from_kernel_by_id() you are breaking CLEAN_PTRS guarantees. OK right, this makes sense to me for btf__load_from_kernel_by_id().
