Re: [PATCH bpf-next v2 1/8] selftests/bpf: Add unshare_netns helper

[Martin KaFai Lau <martin.lau@linux.dev>]

On 5/15/24 6:13 PM, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> Many BPF selftests create new test network namespaces by using CLONE_NEWNET
> flag to unshare the network namespace, so that the calling process is moved
> into a new network namespace which is not shared with any previously
> existing process. So this patch adds a new helper in network_helpers.c
> named unshare_netns(), which create a new network namespace and set the
> net device lo up.
> 
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
>   tools/testing/selftests/bpf/network_helpers.c | 19 +++++++++++++++++++
>   tools/testing/selftests/bpf/network_helpers.h |  1 +
>   2 files changed, 20 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c
> index 35250e6cde7f..919bb2a0c6a6 100644
> --- a/tools/testing/selftests/bpf/network_helpers.c
> +++ b/tools/testing/selftests/bpf/network_helpers.c
> @@ -670,3 +670,22 @@ int send_recv_data(int lfd, int fd, uint32_t total_bytes)
>   
>   	return err;
>   }
> +
> +int unshare_netns(void)
> +{
> +	int err;
> +
> +	err = unshare(CLONE_NEWNET);
> +	if (err) {
> +		log_err("unshare netns failed");
> +		return err;
> +	}
> +
> +	err = SYS_NOFAIL("ip link set dev lo up");

Losing useful error output is not good. Please find a way to keep them available 
such that it is easier to debug. The same goes for similar cases in this patch 
set. I think the only exception could be the "ip netns del" during cleanup.

Also, bpf CI reports a crash (should be the test #18 bpf_ip_check_defrag). Not 
sure how this set indirectly triggered it more easily:

https://github.com/kernel-patches/bpf/actions/runs/9290828674/job/25569002645

pw-bot: cr

> +	if (err) {
> +		log_err("set dev lo up failed");
> +		return err;
> +	}
> +
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/bpf/network_helpers.h b/tools/testing/selftests/bpf/network_helpers.h
> index 883c7ea9d8d5..b087330f2861 100644
> --- a/tools/testing/selftests/bpf/network_helpers.h
> +++ b/tools/testing/selftests/bpf/network_helpers.h
> @@ -82,6 +82,7 @@ struct nstoken;
>   struct nstoken *open_netns(const char *name);
>   void close_netns(struct nstoken *token);
>   int send_recv_data(int lfd, int fd, uint32_t total_bytes);
> +int unshare_netns(void);
>   
>   static __u16 csum_fold(__u32 csum)
>   {