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Message-ID: <CAEf4Bza=qH6CLULLoVy1nKUicDG1zi4rW-sXU8fhgU6V+E8+kg@mail.gmail.com>
Date: Wed, 24 Sep 2025 16:51:24 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>
Cc: ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...ux.dev, pabeni@...hat.com, song@...nel.org, sdf@...gle.com,
haoluo@...gle.com, yhs@...com, edumazet@...gle.com, john.fastabend@...il.com,
kpsingh@...nel.org, jolsa@...nel.org, mjambigi@...ux.ibm.com,
wenjia@...ux.ibm.com, wintera@...ux.ibm.com, dust.li@...ux.alibaba.com,
tonylu@...ux.alibaba.com, guwen@...ux.alibaba.com, bpf@...r.kernel.org,
davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
sidraya@...ux.ibm.com, jaka@...ux.ibm.com
Subject: Re: [PATCH bpf-next v2 3/4] libbpf: fix error when st-prefix_ops and
ops from differ btf
On Wed, Sep 24, 2025 at 1:06 AM D. Wythe <alibuda@...ux.alibaba.com> wrote:
>
> On Fri, Sep 19, 2025 at 03:22:41PM -0700, Andrii Nakryiko wrote:
> > On Thu, Sep 18, 2025 at 1:03 AM D. Wythe <alibuda@...ux.alibaba.com> wrote:
> > >
> > >
> > > At present, cases 0, 1, and 3 can be correctly identified, because
> > > st_ops_xxx_ops is searched from the same btf with xxx_ops. In order to
> > > handle case 2 correctly without affecting other cases, we cannot simply
> > > change the search method for st_ops_xxx_ops from find_btf_by_prefix_kind()
> > > to find_ksym_btf_id(), because in this way, case 1 will not be
> > > recognized anymore.
> > >
> > > To address the issue, we always look for st_ops_xxx_ops first,
> > > figure out the btf, and then look for xxx_ops with the very btf to avoid
> >
> > What's "very btf"? Commit message would benefit from a little bit of
> > proof-reading, if you can. It's a bit hard to follow, even if it's
> > more or less clear at the end what problem you are trying to solve.
> >
> > Also, I'd suggest to send this fix as a separate patch and not block
> > it on the overall patch set, which probably will take longer. This fix
> > is independent, so we can land it much faster.
> >
>
> Thanks a lot for your suggestion. I'll improve the commit message.
>
> It's fine to send this patch separately, I'm concerned it won't be
> verifiable in isolation without the other patches. But if you feel
> it's okay to proceed, I'm happy to do so.
I think the issue is pretty clear, I don't mind fixing it outside of
the patch set introducing this mixed vmlinux vs module BTF. So yes,
please send a patch (unless you already did, as I'm catching up on
emails)
>
> > > such issue.
> > >
> > > Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
> > > Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> > > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > > ---
> > > tools/lib/bpf/libbpf.c | 37 ++++++++++++++++++-------------------
> > > 1 file changed, 18 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index fe4fc5438678..50ca13833511 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -1013,35 +1013,34 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw,
> > > const struct btf_member *kern_data_member;
> > > struct btf *btf = NULL;
> > > __s32 kern_vtype_id, kern_type_id;
> > > - char tname[256];
> > > + char tname[256], stname[256];
> > > __u32 i;
> > >
> > > snprintf(tname, sizeof(tname), "%.*s",
> > > (int)bpf_core_essential_name_len(tname_raw), tname_raw);
> > >
> > > - kern_type_id = find_ksym_btf_id(obj, tname, BTF_KIND_STRUCT,
> > > - &btf, mod_btf);
> > > - if (kern_type_id < 0) {
> > > - pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n",
> > > - tname);
> > > - return kern_type_id;
> > > - }
> > > - kern_type = btf__type_by_id(btf, kern_type_id);
> > > + snprintf(stname, sizeof(stname), "%s%.*s", STRUCT_OPS_VALUE_PREFIX,
> > > + (int)strlen(tname), tname);
> > >
> > > - /* Find the corresponding "map_value" type that will be used
> > > - * in map_update(BPF_MAP_TYPE_STRUCT_OPS). For example,
> > > - * find "struct bpf_struct_ops_tcp_congestion_ops" from the
> > > - * btf_vmlinux.
> > > + /* Look for the corresponding "map_value" type that will be used
> > > + * in map_update(BPF_MAP_TYPE_STRUCT_OPS) first, figure out the btf
> > > + * and the mod_btf.
> > > + * For example, find "struct bpf_struct_ops_tcp_congestion_ops".
> > > */
> > > - kern_vtype_id = find_btf_by_prefix_kind(btf, STRUCT_OPS_VALUE_PREFIX,
> > > - tname, BTF_KIND_STRUCT);
> > > + kern_vtype_id = find_ksym_btf_id(obj, stname, BTF_KIND_STRUCT, &btf, mod_btf);
> > > if (kern_vtype_id < 0) {
> > > - pr_warn("struct_ops init_kern: struct %s%s is not found in kernel BTF\n",
> > > - STRUCT_OPS_VALUE_PREFIX, tname);
> > > + pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", stname);
> > > return kern_vtype_id;
> > > }
> > > kern_vtype = btf__type_by_id(btf, kern_vtype_id);
> > >
> > > + kern_type_id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);
> > > + if (kern_type_id < 0) {
> > > + pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n", tname);
> > > + return kern_type_id;
> > > + }
> > > + kern_type = btf__type_by_id(btf, kern_type_id);
> > > +
> > > /* Find "struct tcp_congestion_ops" from
> > > * struct bpf_struct_ops_tcp_congestion_ops {
> > > * [ ... ]
> > > @@ -1054,8 +1053,8 @@ find_struct_ops_kern_types(struct bpf_object *obj, const char *tname_raw,
> > > break;
> > > }
> > > if (i == btf_vlen(kern_vtype)) {
> > > - pr_warn("struct_ops init_kern: struct %s data is not found in struct %s%s\n",
> > > - tname, STRUCT_OPS_VALUE_PREFIX, tname);
> > > + pr_warn("struct_ops init_kern: struct %s data is not found in struct %s\n",
> > > + tname, stname);
> > > return -EINVAL;
> > > }
> > >
> > > --
> > > 2.45.0
> > >
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