Re: Startup fd to avoid busywaits

[Paul Holzinger <pholzing@redhat.com>]

Hi,

On 27/05/2026 19:08, Lisanna Dettwyler wrote:
> Hello! I would like to propose a patch that allows the invoker to pass 
> a "ready fd" on startup that gets written to once the setup has been 
> completed, similar to slirp4netns's `--ready-fd` flag. Currently we 
> have to poll the interface in a loop to wait for setup to be 
> completed, and it would be much better if we could instead block on fd 
> activity.
>
> Just wanted to check if such a contribution would be welcome before 
> putting in the work of authoring it, or if there's already a better 
> way to wait for the interface to come up. This is our current 
> implementation: 
> https://github.com/NixOS/nix/pull/15919/changes#diff-2a9176262efad1ef345d882b0779646e7a5aaf9ca8db33e9da7fc408594b5377R94-R125
>
I am not a pasta maintainer but this is rather simple as we do it in 
podman. By default pasta forks into the background, when the parent 
exists the child is ready for connections. So all you need to do is 
fork/exec and then wait for the exit, that way you also get easily the 
exit code to know if the setup failed and can read the stderr for errors.

 From your linked code I see the use of --foreground so the question 
would be why are you using this over the default?

-- 
Paul Holzinger