[PATCH] libbpf: add bpf object kern_version attribute setter

[PATCH] libbpf: add bpf object kern_version attribute setter

[Rafael David Tinoco]

Unfortunately some distros don't have their kernel version defined
accurately in <linux/version.h> due to different long term support
reasons.

It is important to have a way to override the bpf kern_version
attribute during runtime: some old kernels might still check for
kern_version attribute during bpf_prog_load().

Signed-off-by: Rafael David Tinoco <rafaeldtinoco@ubuntu.com>
---
 src/libbpf.c | 15 +++++++++++++++
 src/libbpf.h |  1 +
 2 files changed, 16 insertions(+)

diff --git a/src/libbpf.c b/src/libbpf.c
index 0c4a386..7b52cd6 100644
--- a/src/libbpf.c
+++ b/src/libbpf.c
@@ -8278,6 +8278,21 @@ int bpf_object__btf_fd(const struct bpf_object *obj)
 	return obj->btf ? btf__fd(obj->btf) : -1;
 }
 
+int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version)
+{
+	__u32 major, minor, patch;
+
+	if (!kern_version) {
+		obj->kern_version = 0;
+		return 0;
+	}
+	if (sscanf(kern_version, "%u.%u.%u", &major, &minor, &patch) != 3)
+		return -1;
+	obj->kern_version = KERNEL_VERSION(major, minor, patch);
+
+	return 0;
+}
+
 int bpf_object__set_priv(struct bpf_object *obj, void *priv,
 			 bpf_object_clear_priv_t clear_priv)
 {
diff --git a/src/libbpf.h b/src/libbpf.h
index 3c35eb4..3e14ae7 100644
--- a/src/libbpf.h
+++ b/src/libbpf.h
@@ -143,6 +143,7 @@ LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
 
 LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
 LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
+LIBBPF_API int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version);
 
 struct btf;
 LIBBPF_API struct btf *bpf_object__btf(const struct bpf_object *obj);
-- 
2.27.0

Re: [PATCH] libbpf: add bpf object kern_version attribute setter

[Andrii Nakryiko]

On Fri, Mar 19, 2021 at 9:16 PM Rafael David Tinoco
<rafaeldtinoco@ubuntu.com> wrote:
>
> Unfortunately some distros don't have their kernel version defined
> accurately in <linux/version.h> due to different long term support
> reasons.
>
> It is important to have a way to override the bpf kern_version
> attribute during runtime: some old kernels might still check for
> kern_version attribute during bpf_prog_load().
>
> Signed-off-by: Rafael David Tinoco <rafaeldtinoco@ubuntu.com>
> ---
>  src/libbpf.c | 15 +++++++++++++++
>  src/libbpf.h |  1 +
>  2 files changed, 16 insertions(+)
>
> diff --git a/src/libbpf.c b/src/libbpf.c
> index 0c4a386..7b52cd6 100644
> --- a/src/libbpf.c
> +++ b/src/libbpf.c
> @@ -8278,6 +8278,21 @@ int bpf_object__btf_fd(const struct bpf_object *obj)
>         return obj->btf ? btf__fd(obj->btf) : -1;
>  }
>
> +int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version)
> +{
> +       __u32 major, minor, patch;
> +
> +       if (!kern_version) {
> +               obj->kern_version = 0;
> +               return 0;
> +       }
> +       if (sscanf(kern_version, "%u.%u.%u", &major, &minor, &patch) != 3)

given SEC("version") expects `int` and bpf_object__kversion() returns
int, I think it's appropriate for bpf_object__set_kversion() to accept
just opaque int as well. Please also check that obj is not loaded and
return error if it is. Thanks!

> +               return -1;
> +       obj->kern_version = KERNEL_VERSION(major, minor, patch);
> +
> +       return 0;
> +}
> +
>  int bpf_object__set_priv(struct bpf_object *obj, void *priv,
>                          bpf_object_clear_priv_t clear_priv)
>  {
> diff --git a/src/libbpf.h b/src/libbpf.h
> index 3c35eb4..3e14ae7 100644
> --- a/src/libbpf.h
> +++ b/src/libbpf.h
> @@ -143,6 +143,7 @@ LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
>
>  LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
>  LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
> +LIBBPF_API int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version);
>
>  struct btf;
>  LIBBPF_API struct btf *bpf_object__btf(const struct bpf_object *obj);
> --
> 2.27.0
>

Re: [PATCH] libbpf: add bpf object kern_version attribute setter

[Andrii Nakryiko]

On Sat, Mar 20, 2021 at 10:23 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Mar 19, 2021 at 9:16 PM Rafael David Tinoco
> <rafaeldtinoco@ubuntu.com> wrote:
> >
> > Unfortunately some distros don't have their kernel version defined
> > accurately in <linux/version.h> due to different long term support
> > reasons.
> >
> > It is important to have a way to override the bpf kern_version
> > attribute during runtime: some old kernels might still check for
> > kern_version attribute during bpf_prog_load().
> >
> > Signed-off-by: Rafael David Tinoco <rafaeldtinoco@ubuntu.com>
> > ---
> >  src/libbpf.c | 15 +++++++++++++++
> >  src/libbpf.h |  1 +
> >  2 files changed, 16 insertions(+)
> >
> > diff --git a/src/libbpf.c b/src/libbpf.c
> > index 0c4a386..7b52cd6 100644
> > --- a/src/libbpf.c
> > +++ b/src/libbpf.c
> > @@ -8278,6 +8278,21 @@ int bpf_object__btf_fd(const struct bpf_object *obj)
> >         return obj->btf ? btf__fd(obj->btf) : -1;
> >  }
> >
> > +int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version)
> > +{
> > +       __u32 major, minor, patch;
> > +
> > +       if (!kern_version) {
> > +               obj->kern_version = 0;
> > +               return 0;
> > +       }
> > +       if (sscanf(kern_version, "%u.%u.%u", &major, &minor, &patch) != 3)
>
> given SEC("version") expects `int` and bpf_object__kversion() returns
> int, I think it's appropriate for bpf_object__set_kversion() to accept
> just opaque int as well. Please also check that obj is not loaded and
> return error if it is. Thanks!
>

Oh, and please use [PATCH bpf-next] subject prefix to specify that
this is destined to the bpf-next tree. You'll also add v2 in between
PATCH and bpf-next for the next version, of course.


> > +               return -1;
> > +       obj->kern_version = KERNEL_VERSION(major, minor, patch);
> > +
> > +       return 0;
> > +}
> > +
> >  int bpf_object__set_priv(struct bpf_object *obj, void *priv,
> >                          bpf_object_clear_priv_t clear_priv)
> >  {
> > diff --git a/src/libbpf.h b/src/libbpf.h
> > index 3c35eb4..3e14ae7 100644
> > --- a/src/libbpf.h
> > +++ b/src/libbpf.h
> > @@ -143,6 +143,7 @@ LIBBPF_API int bpf_object__unload(struct bpf_object *obj);
> >
> >  LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
> >  LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
> > +LIBBPF_API int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version);
> >
> >  struct btf;
> >  LIBBPF_API struct btf *bpf_object__btf(const struct bpf_object *obj);
> > --
> > 2.27.0
> >

Re: [PATCH] libbpf: add bpf object kern_version attribute setter

[Rafael David Tinoco]

>>> +int bpf_object__set_kversion(struct bpf_object *obj, char *kern_version)
>>> +{
>>> +       __u32 major, minor, patch;
>>> +
>>> +       if (!kern_version) {
>>> +               obj->kern_version = 0;
>>> +               return 0;
>>> +       }
>>> +       if (sscanf(kern_version, "%u.%u.%u", &major, &minor, &patch) !=  
>>> 3)
>>
>> given SEC("version") expects `int` and bpf_object__kversion() returns
>> int, I think it's appropriate for bpf_object__set_kversion() to accept
>> just opaque int as well. Please also check that obj is not loaded and
>> return error if it is. Thanks!
>
> Oh, and please use [PATCH bpf-next] subject prefix to specify that
> this is destined to the bpf-next tree. You'll also add v2 in between
> PATCH and bpf-next for the next version, of course.

will do, and sorry for the initial burden, getting used to libbpf devel.