netdev - Re: [PATCH net-next v5 3/3] samples/bpf: Add test_current_task_under

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Date:	Fri, 12 Aug 2016 09:10:08 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Sargun Dhillon <sargun@...gun.me>
Cc:	netdev@...r.kernel.org, daniel@...earbox.net, tj@...nel.org
Subject: Re: [PATCH net-next v5 3/3] samples/bpf: Add
 test_current_task_under_cgroup test

On Fri, Aug 12, 2016 at 08:57:04AM -0700, Sargun Dhillon wrote:
> This test has a BPF program which writes the last known pid to call the
> sync syscall within a given cgroup to a map.
> 
> The user mode program creates its own mount namespace, and mounts the
> cgroupsv2  hierarchy in there, as on all current test systems
> (Ubuntu 16.04, Debian), the cgroupsv2 vfs is unmounted by default.
> Once it does this, it proceeds to test.
> 
> The test checks for positive and negative condition. It ensures that
> when it's part of a given cgroup, its pid is captured in the map,
> and that when it leaves the cgroup, this doesn't happen.
> 
> It populate a cgroups arraymap prior to execution in userspace. This means
> that the program must be run in the same cgroups namespace as the programs
> that are being traced.
> 
> Signed-off-by: Sargun Dhillon <sargun@...gun.me>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Tejun Heo <tj@...nel.org>

I don't think there is much value explicitly adding 'cc:' to commit log.

> +	if (join_cgroup("/mnt/my-cgroup")) {
> +		log_err("Leaving target cgroup");
> +		goto cleanup_cgroup_err;
> +	}
> +
> +	/*
> +	 * The installed helper program catched the sync call, and should
> +	 * write it to the map.
> +	 */
> +
> +	sync();
> +	bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
> +
> +	if (local_pid != remote_pid) {
> +		fprintf(stderr,
> +			"BPF Helper didn't write correct PID to map, but: %d\n",
> +			remote_pid);
> +		goto leave_cgroup_err;
> +	}
> +
> +	/* Verify the negative scenario; leave the cgroup */
> +	if (join_cgroup(CGROUP_MOUNT_PATH))
> +		goto leave_cgroup_err;
> +
> +	remote_pid = 0;
> +	bpf_update_elem(map_fd[1], &idx, &remote_pid, BPF_ANY);
> +
> +	sync();
> +	bpf_lookup_elem(map_fd[1], &idx, &remote_pid);
> +
> +	if (local_pid == remote_pid) {
> +		fprintf(stderr, "BPF cgroup negative test did not work\n");
> +		goto cleanup_cgroup_err;
> +	}
> +
> +	rmdir(CGROUP_PATH);
> +	return 0;

Nice test. Thanks
Acked-by: Alexei Starovoitov <ast@...nel.org>