linux-kernel - Re: [PATCH v2 bpf-next 3/4] selftests/bpf: enable all available cgroup v2 controllers

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Date:   Thu, 23 May 2019 05:45:05 +0000
From:   Yonghong Song <yhs@...com>
To:     Roman Gushchin <guro@...com>, Alexei Starovoitov <ast@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Kernel Team <Kernel-team@...com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Stanislav Fomichev <sdf@...ichev.me>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 3/4] selftests/bpf: enable all available
 cgroup v2 controllers



On 5/22/19 4:20 PM, Roman Gushchin wrote:
> Enable all available cgroup v2 controllers when setting up
> the environment for the bpf kselftests. It's required to properly test
> the bpf prog auto-detach feature. Also it will generally increase
> the code coverage.
> 
> Signed-off-by: Roman Gushchin <guro@...com>
Looks good to me. Ack with one nit below.
Acked-by: Yonghong Song <yhs@...com>

> ---
>   tools/testing/selftests/bpf/cgroup_helpers.c | 57 ++++++++++++++++++++
>   1 file changed, 57 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/cgroup_helpers.c b/tools/testing/selftests/bpf/cgroup_helpers.c
> index 6692a40a6979..4efe57c171cd 100644
> --- a/tools/testing/selftests/bpf/cgroup_helpers.c
> +++ b/tools/testing/selftests/bpf/cgroup_helpers.c
> @@ -33,6 +33,60 @@
>   	snprintf(buf, sizeof(buf), "%s%s%s", CGROUP_MOUNT_PATH, \
>   		 CGROUP_WORK_DIR, path)
>   
> +/**
> + * enable_all_controllers() - Enable all available cgroup v2 controllers
> + *
> + * Enable all available cgroup v2 controllers in order to increase
> + * the code coverage.
> + *
> + * If successful, 0 is returned.
> + */
> +int enable_all_controllers(char *cgroup_path)
> +{
> +	char path[PATH_MAX + 1];
> +	char buf[PATH_MAX];
> +	char *c, *c2;
> +	int fd, cfd;
> +	size_t len;
> +
> +	snprintf(path, sizeof(path), "%s/cgroup.controllers", cgroup_path);
> +	fd = open(path, O_RDONLY);
> +	if (fd < 0) {
> +		log_err("Opening cgroup.controllers: %s", path);
> +		return -1;
It looks like either -1 or 1 could be returned to indicate an error
in this file. Maybe, at least for the consistency of this file,
always returning 1 is preferred as setup_cgroup_environment()
has the following comments:
  * This function will print an error to stderr and return 1 if it is unable
  * to setup the cgroup environment. If setup is successful, 0 is returned.

> +	}
> +
> +	len = read(fd, buf, sizeof(buf) - 1);
> +	if (len < 0) {
> +		close(fd);
> +		log_err("Reading cgroup.controllers: %s", path);
> +		return -1;
> +	}
> +	buf[len] = 0;
> +	close(fd);
> +
> +	/* No controllers available? We're probably on cgroup v1. */
> +	if (len == 0)
> +		return 0;
> +
> +	snprintf(path, sizeof(path), "%s/cgroup.subtree_control", cgroup_path);
> +	cfd = open(path, O_RDWR);
> +	if (cfd < 0) {
> +		log_err("Opening cgroup.subtree_control: %s", path);
> +		return -1;
> +	}
> +
> +	for (c = strtok_r(buf, " ", &c2); c; c = strtok_r(NULL, " ", &c2)) {
> +		if (dprintf(cfd, "+%s\n", c) <= 0) {
> +			log_err("Enabling controller %s: %s", c, path);
> +			close(cfd);
> +			return -1;
> +		}
> +	}
> +	close(cfd);
> +	return 0;
> +}
> +
>   /**
>    * setup_cgroup_environment() - Setup the cgroup environment
>    *
> @@ -71,6 +125,9 @@ int setup_cgroup_environment(void)
>   		return 1;
>   	}
>   
> +	if (enable_all_controllers(cgroup_workdir))
> +		return 1;
> +
>   	return 0;
>   }
>   
>