On Fri, Nov 1, 2019 at 12:36 PM Toke Høiland-Jørgensen [off-list ref] wrote:

Alexei Starovoitov [off-list ref] writes:

quoted

On Fri, Nov 1, 2019 at 12:27 AM Jiri Olsa [off-list ref] wrote:

quoted

On Thu, Oct 31, 2019 at 01:39:12PM -0700, Alexei Starovoitov wrote:

quoted

On Thu, Oct 31, 2019 at 12:18 PM Jiri Olsa [off-list ref] wrote:

quoted

quoted

yes. older vmlinux and newer installed libbpf.so
or any version of libbpf.a that is statically linked into apps
is something that libbpf code has to support.
The server can be rebooted into older than libbpf kernel and
into newer than libbpf kernel. libbpf has to recognize all these
combinations and work appropriately.
That's what backward and forward compatibility is.
That's what makes libbpf so difficult to test, develop and code review.
What that particular server has in /usr/include is irrelevant.

sure, anyway we can't compile following:

        tredaell@aldebaran ~ $ echo "#include <bpf/xsk.h>" | gcc -x c -
        In file included from <stdin>:1:
        /usr/include/bpf/xsk.h: In function ‘xsk_ring_prod__needs_wakeup’:
        /usr/include/bpf/xsk.h:82:21: error: ‘XDP_RING_NEED_WAKEUP’ undeclared (first use in this function)
           82 |  return *r->flags & XDP_RING_NEED_WAKEUP;
        ...

        XDP_RING_NEED_WAKEUP is defined in kernel v5.4-rc1 (77cd0d7b3f257fd0e3096b4fdcff1a7d38e99e10).
        XSK_UNALIGNED_BUF_ADDR_MASK and XSK_UNALIGNED_BUF_OFFSET_SHIFT are defined in kernel v5.4-rc1 (c05cd3645814724bdeb32a2b4d953b12bdea5f8c).

with:
  kernel-headers-5.3.6-300.fc31.x86_64
  libbpf-0.0.5-1.fc31.x86_64

if you're saying this is not supported, I guess we could be postponing
libbpf rpm releases until we have the related fedora kernel released

why? github/libbpf is the source of truth for building packages
and afaik it builds fine.

because we will get issues like above if there's no kernel
avilable that we could compile libbpf against

what is the issue again?
bpf-next builds fine. github/libbpf builds fine.
If distro is doing something else it's distro's mistake.

With that you're saying that distros should always keep their kernel
headers and libbpf version in sync. Which is fine in itself; they can
certainly do that.

No. I'm not suggesting that.
distro is free to package whatever /usr/include headers.
kernel version is often != /usr/include headers

The only concern with this is that without a flow of bugfixes into the
'bpf' tree (and stable), users may end up with buggy versions of libbpf.
Which is in no one's interest. So how do we avoid that?

As I explained earlier. There is no 'bpf' tree for libbpf. It always
moves forward.