Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

[Alexei Starovoitov]

On Thu, Mar 28, 2024 at 10:22 AM Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> Hello, Djalal.
>
> On Wed, Mar 27, 2024 at 11:53:22PM +0100, Djalal Harouni wrote:
> > This patch series adds support to freeze the task cgroup hierarchy
> > that is on a default cgroup v2 without going through kernfs interface.
> >
> > For some cases we want to freeze the cgroup of a task based on some
> > signals, doing so from bpf is better than user space which could be
> > too late.
> >
> > Planned users of this feature are: tetragon and systemd when freezing
> > a cgroup hierarchy that could be a K8s pod, container, system service
> > or a user session.
> >
> > Patch 1: cgroup: add cgroup_freeze_no_kn() to freeze a cgroup from bpf
> > Patch 2: bpf: add bpf_task_freeze_cgroup() to freeze the cgroup of a task
> > Patch 3: selftests/bpf: add selftest for bpf_task_freeze_cgroup
>
> It bothers me a bit that it's adding a dedicated interface for something
> which already has a defined userspace interface. Would it be better to have
> kfunc wrappers for kernel_read() and kernel_write()?

How would that look ?
prog cannot and shouldn't open a file.
The seq_file would be passed/pinned by user space?