On 2023/12/16 1:36, Stephen Hemminger wrote:
On Fri, 15 Dec 2023 14:49:56 +0900
Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
It is exactly what BPF_PROG_TYPE_SOCKET_FILTER does, but it lacks a
mechanism to report hash values so I need to extend it or invent a new
method. Extending BPF_PROG_TYPE_SOCKET_FILTER is not a way forward since
CO-RE is superior to the context rewrite it relies on. But apparently
adopting kfuncs and CO-RE also means to lose the "we don't break user
space" contract although I have no intention to expose kernel internals
to the eBPF program.
An example is how one part of DPDK recomputes RSS over TAP.
https://git.dpdk.org/dpdk/tree/drivers/net/tap/bpf/tap_bpf_program.c
This feature is likely to be removed, because it is not actively used
and the changes in BPF program loading broke it on current kernel
releases. Which brings up the point that since the kernel does
not have stable API/ABI for BPF program infrastructure, I would
avoid it for projects that don't want to deal with that.
It's unfortunate to hear that, but thanks for the information.
I'll consider more about the option not using BPF (plain ioctl and
in-kernel implementation).
With libbpf, things are much better. It is just that projects like
DPDK have to support wide range of kernels including older versions of RHEL.
I have checked DPDK documentation. It says it supports the oldest LTS
kernel:
https://doc.dpdk.org/guides/linux_gsg/sys_reqs.html#system-software
My use case is QEMU, which has much more relaxed compatibility
requirement that refers to recent distribution versions instead of LTS
kernels:
https://qemu.readthedocs.io/en/v8.1.0/about/build-platforms.html
That said, I'm not really concerned about the case running QEMU on older
kernels. QEMU developers can just pay extra efforts to support those old
kernels if necessary.
The more concerning scenario is that a newer kernel breaks compatibility
with older QEMU versions; such a scenario has not been considered before
AFAIK.
QEMU already uses libbpf to load a BPF_PROG_TYPE_SOCKET_FILTER program.
