sched: basic infrastructure for scheduler bpf

maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8OIT1

Reference: https://lore.kernel.org/all/20210916162451.709260-1-guro@fb.com/



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This commit introduces basic definitions and infrastructure for
scheduler bpf programs. It defines the BPF_PROG_TYPE_SCHED program
type and the BPF_SCHED attachment type.

The implementation is inspired by lsm bpf programs and is based on
kretprobes. This will allow to add new hooks with a minimal changes to
the kernel code and without any changes to libbpf/bpftool.
It's very convenient as I anticipate a large number of private patches
being used for a long time before (or if at all) reaching upstream.

Sched programs are expected to return an int, which meaning will be
context defined.

This patch doesn't add any real scheduler hooks (only a stub), it will
be done by following patches in the series.

Scheduler bpf programs as now are very restricted in what they can do:
only the bpf_printk() helper is available. The scheduler context can
impose significant restrictions on what's safe and what's not. So
let's extend their abilities on case by case basis when a need arise.

Signed-off-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Chen Hui <judy.chenhui@huawei.com>
Signed-off-by: Ren Zhijie <renzhijie2@huawei.com>
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Signed-off-by: Guan Jing <guanjing6@huawei.com>