Re: [PATCH bpf-next v1 2/2] veristat: memory accounting for bpf programs

[Eduard Zingerman <eddyz87@gmail.com>]

On Thu, 2025-06-05 at 16:06 -0700, Eduard Zingerman wrote:

[...]

> +/*
> + * Enters new cgroup namespace and mounts cgroupfs at /tmp/veristat-cgroup-mount-XXXXXX,
> + * enables "memory" controller for the root cgroup.
> + */
> +static int mount_cgroupfs(void)
> +{
> +	char buf[PATH_MAX + 1];
> +	int err;
> +
> +	env.memory_peak_fd = -1;
> +
> +	err = unshare(CLONE_NEWCGROUP);
> +	if (err < 0) {
> +		err = log_errno("unshare(CLONE_NEWCGROUP)");
> +		goto err_out;
> +	}

The `unshare` call is useless. I thought it would grant me a new
hierarchy with separate cgroup.subtree_control in the root.
But that's now how things work, hierarchy is shared across namespaces.
I'll drop this call and just complain if "memory" controller is not enabled.

The "mount" part can remain, I use it to avoid searching for cgroupfs
mount point. Alternatively I can inspect /proc/self/mountinfo and
complain if cgroupfs is not found. Please let me know which way is
preferred.

[...]