* [PATCH bpf-next] libbpf: fix error when st-prefix_ops and ops from differ btf
@ 2025-09-26 7:17 D. Wythe
2025-09-26 16:53 ` Martin KaFai Lau
0 siblings, 1 reply; 3+ messages in thread
From: D. Wythe @ 2025-09-26 7:17 UTC (permalink / raw)
To: ast, daniel, andrii, martin.lau, pabeni, song, sdf, haoluo, yhs,
edumazet, john.fastabend, kpsingh, jolsa, mjambigi, wenjia,
wintera, dust.li, tonylu, guwen
Cc: bpf, davem, kuba, netdev, sidraya, jaka
When a module registers a struct_ops, the struct_ops type and its
corresponding map_value type ("bpf_struct_ops_") may reside in different
btf objects, here are four possible case:
+--------+---------------+-------------+---------------------------------+
| |bpf_struct_ops_| xxx_ops | |
+--------+---------------+-------------+---------------------------------+
| case 0 | btf_vmlinux | bft_vmlinux | be used and reg only in vmlinux |
+--------+---------------+-------------+---------------------------------+
| case 1 | btf_vmlinux | mod_btf | INVALID |
+--------+---------------+-------------+---------------------------------+
| case 2 | mod_btf | btf_vmlinux | reg in mod but be used both in |
| | | | vmlinux and mod. |
+--------+---------------+-------------+---------------------------------+
| case 3 | mod_btf | mod_btf | be used and reg only in mod |
+--------+---------------+-------------+---------------------------------+
Currently we figure out the mod_btf by searching with the struct_ops type,
which makes it impossible to figure out the mod_btf when the struct_ops
type is in btf_vmlinux while it's corresponding map_value type is in
mod_btf (case 2).
The fix is to use the corresponding map_value type ("bpf_struct_ops_")
as the lookup anchor instead of the struct_ops type to figure out the
`btf` and `mod_btf` via find_ksym_btf_id(), and then we can locate
the kern_type_id via btf__find_by_name_kind() with the `btf` we just
obtained from find_ksym_btf_id().
With this change the lookup obtains the correct btf and mod_btf for case 2,
preserves correct behavior for other valid cases, and still fails as
expected for the invalid scenario (case 1).
Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Acked-by: Andrii Nakryiko <andrii@kernel.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 5161c2b39875..a93eed660404 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1018,35 +1018,34 @@ 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 {
* [ ... ]
@@ -1059,8 +1058,8 @@ 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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: fix error when st-prefix_ops and ops from differ btf
2025-09-26 7:17 [PATCH bpf-next] libbpf: fix error when st-prefix_ops and ops from differ btf D. Wythe
@ 2025-09-26 16:53 ` Martin KaFai Lau
2025-09-26 20:12 ` Andrii Nakryiko
0 siblings, 1 reply; 3+ messages in thread
From: Martin KaFai Lau @ 2025-09-26 16:53 UTC (permalink / raw)
To: D. Wythe
Cc: ast, daniel, andrii, pabeni, song, sdf, haoluo, yhs, edumazet,
john.fastabend, kpsingh, jolsa, mjambigi, wenjia, wintera,
dust.li, tonylu, guwen, bpf, davem, kuba, netdev, sidraya, jaka
On 9/26/25 12:17 AM, D. Wythe wrote:
> When a module registers a struct_ops, the struct_ops type and its
> corresponding map_value type ("bpf_struct_ops_") may reside in different
> btf objects, here are four possible case:
>
> +--------+---------------+-------------+---------------------------------+
> | |bpf_struct_ops_| xxx_ops | |
> +--------+---------------+-------------+---------------------------------+
> | case 0 | btf_vmlinux | bft_vmlinux | be used and reg only in vmlinux |
s/bft/btf/
> +--------+---------------+-------------+---------------------------------+
> | case 1 | btf_vmlinux | mod_btf | INVALID |
> +--------+---------------+-------------+---------------------------------+
> | case 2 | mod_btf | btf_vmlinux | reg in mod but be used both in |
> | | | | vmlinux and mod. |
> +--------+---------------+-------------+---------------------------------+
> | case 3 | mod_btf | mod_btf | be used and reg only in mod |
> +--------+---------------+-------------+---------------------------------+
>
> Currently we figure out the mod_btf by searching with the struct_ops type,
> which makes it impossible to figure out the mod_btf when the struct_ops
> type is in btf_vmlinux while it's corresponding map_value type is in
> mod_btf (case 2).
>
> The fix is to use the corresponding map_value type ("bpf_struct_ops_")
> as the lookup anchor instead of the struct_ops type to figure out the
> `btf` and `mod_btf` via find_ksym_btf_id(), and then we can locate
> the kern_type_id via btf__find_by_name_kind() with the `btf` we just
> obtained from find_ksym_btf_id().
>
> With this change the lookup obtains the correct btf and mod_btf for case 2,
> preserves correct behavior for other valid cases, and still fails as
> expected for the invalid scenario (case 1).
>
> Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
> Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
> Acked-by: Andrii Nakryiko <andrii@kernel.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 5161c2b39875..a93eed660404 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -1018,35 +1018,34 @@ 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);
nit. strlen(tname) should not be needed. Others lgtm.
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: fix error when st-prefix_ops and ops from differ btf
2025-09-26 16:53 ` Martin KaFai Lau
@ 2025-09-26 20:12 ` Andrii Nakryiko
0 siblings, 0 replies; 3+ messages in thread
From: Andrii Nakryiko @ 2025-09-26 20:12 UTC (permalink / raw)
To: Martin KaFai Lau
Cc: D. Wythe, ast, daniel, andrii, pabeni, song, sdf, haoluo, yhs,
edumazet, john.fastabend, kpsingh, jolsa, mjambigi, wenjia,
wintera, dust.li, tonylu, guwen, bpf, davem, kuba, netdev,
sidraya, jaka
On Fri, Sep 26, 2025 at 9:53 AM Martin KaFai Lau <martin.lau@linux.dev> wrote:
>
> On 9/26/25 12:17 AM, D. Wythe wrote:
> > When a module registers a struct_ops, the struct_ops type and its
> > corresponding map_value type ("bpf_struct_ops_") may reside in different
> > btf objects, here are four possible case:
> >
> > +--------+---------------+-------------+---------------------------------+
> > | |bpf_struct_ops_| xxx_ops | |
> > +--------+---------------+-------------+---------------------------------+
> > | case 0 | btf_vmlinux | bft_vmlinux | be used and reg only in vmlinux |
>
> s/bft/btf/
>
> > +--------+---------------+-------------+---------------------------------+
> > | case 1 | btf_vmlinux | mod_btf | INVALID |
> > +--------+---------------+-------------+---------------------------------+
> > | case 2 | mod_btf | btf_vmlinux | reg in mod but be used both in |
> > | | | | vmlinux and mod. |
> > +--------+---------------+-------------+---------------------------------+
> > | case 3 | mod_btf | mod_btf | be used and reg only in mod |
> > +--------+---------------+-------------+---------------------------------+
> >
> > Currently we figure out the mod_btf by searching with the struct_ops type,
> > which makes it impossible to figure out the mod_btf when the struct_ops
> > type is in btf_vmlinux while it's corresponding map_value type is in
> > mod_btf (case 2).
> >
> > The fix is to use the corresponding map_value type ("bpf_struct_ops_")
> > as the lookup anchor instead of the struct_ops type to figure out the
> > `btf` and `mod_btf` via find_ksym_btf_id(), and then we can locate
> > the kern_type_id via btf__find_by_name_kind() with the `btf` we just
> > obtained from find_ksym_btf_id().
> >
> > With this change the lookup obtains the correct btf and mod_btf for case 2,
> > preserves correct behavior for other valid cases, and still fails as
> > expected for the invalid scenario (case 1).
> >
> > Fixes: 590a00888250 ("bpf: libbpf: Add STRUCT_OPS support")
> > Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
> > Acked-by: Andrii Nakryiko <andrii@kernel.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 5161c2b39875..a93eed660404 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -1018,35 +1018,34 @@ 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];
I adjusted tname size down to 192 to avoid compiler complains that
snprintf below can truncate output (useless warning, but oh well)
> > __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);
>
> nit. strlen(tname) should not be needed. Others lgtm.
yeah, dropped that while applying, thanks. this was a copy/paste from
tname's snprint, but there we do actually need a prefix of a type, not
here, so strlen() makes no sense
applied to bpf-next
>
> Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
>
>
>
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2025-09-26 7:17 [PATCH bpf-next] libbpf: fix error when st-prefix_ops and ops from differ btf D. Wythe
2025-09-26 16:53 ` Martin KaFai Lau
2025-09-26 20:12 ` Andrii Nakryiko
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