Subject: Re: [PATCH net-next 2/4] selftests: drv-net: add a way to wait for a local process

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 18 Feb 2025 13:10:14 -0800

On 02/18, Jakub Kicinski wrote:
> We use wait_port_listen() extensively to wait for a process
> we spawned to be ready. Not all processes will open listening
> sockets. Add a method of explicitly waiting for a child to
> be ready. Pass a FD to the spawned process and wait for it
> to write a message to us. FD number is passed via KSFT_READY_FD
> env variable.
> 
> Make use of this method in the queues test to make it less flaky.
> 
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
>  .../selftests/drivers/net/xdp_helper.c        | 22 ++++++-
>  tools/testing/selftests/drivers/net/queues.py | 46 ++++++---------
>  tools/testing/selftests/net/lib/py/utils.py   | 58 +++++++++++++++++--
>  3 files changed, 93 insertions(+), 33 deletions(-)
> 
> diff --git a/tools/testing/selftests/drivers/net/xdp_helper.c b/tools/testing/selftests/drivers/net/xdp_helper.c
> index cf06a88b830b..8f77da4f798f 100644
> --- a/tools/testing/selftests/drivers/net/xdp_helper.c
> +++ b/tools/testing/selftests/drivers/net/xdp_helper.c
> @@ -14,6 +14,25 @@
>  #define UMEM_SZ (1U << 16)
>  #define NUM_DESC (UMEM_SZ / 2048)
>  
> +/* Move this to a common header when reused! */
> +static void ksft_ready(void)
> +{
> +	const char msg[7] = "ready\n";
> +	char *env_str;
> +	int fd;

[..]

> +	env_str = getenv("KSFT_READY_FD");
> +	if (!env_str)
> +		return;
> +
> +	fd = atoi(env_str);
> +	if (!fd)
> +		return;

optional nit: should these fail with error() instead of silent return?
Should guarantee that the caller is doing everything correctly.
(passing wait_init vs waiting for a port)