Re: [pbs-devel] [PATCH proxmox-backup] tools/daemon: improve reload behaviour

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

On 16/12/2020 09:12, Dominik Csapak wrote:
> it seems that sometimes, the child process signal gets handled
> before the parent process signal. Systemd then ignores the
> childs signal (finished reloading) and only after going into
> reloading state because of the parent. this will never finish.
> 
> Instead, wait for the state to change to 'reloading' after sending
> that signal in the parent, an only fork afterwards. This way
> we ensure that systemd knows about the reloading before actually trying
> to do it.
> 
> Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
> ---
> this all goes away with systemds notify barrier hopefully....
> 
>  src/tools/daemon.rs | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/src/tools/daemon.rs b/src/tools/daemon.rs
> index 6bb4a41b..2aa52772 100644
> --- a/src/tools/daemon.rs
> +++ b/src/tools/daemon.rs
> @@ -291,6 +291,7 @@ where
>          if let Err(e) = systemd_notify(SystemdNotify::Reloading) {
>              log::error!("failed to notify systemd about the state change: {}", e);
>          }
> +        wait_service_is_active_or_reloading(service_name, true).await?;
>          if let Err(e) = reloader.take().unwrap().fork_restart() {
>              log::error!("error during reload: {}", e);
>              let _ = systemd_notify(SystemdNotify::Status("error during reload".to_string()));
> @@ -305,7 +306,7 @@ where
>  
>      // FIXME: this is a hack, replace with sd_notify_barrier when available
>      if server::is_reload_request() {
> -        wait_service_is_active(service_name).await?;
> +        wait_service_is_active_or_reloading(service_name, false).await?;
>      }
>  
>      log::info!("daemon shut down...");
> @@ -313,7 +314,7 @@ where
>  }
>  
>  // hack, do not use if unsure!
> -async fn wait_service_is_active(service: &str) -> Result<(), Error> {
> +async fn wait_service_is_active_or_reloading(service: &str, wait_for_reload: bool) -> Result<(), Error> {
>      tokio::time::delay_for(std::time::Duration::new(1, 0)).await;
>      loop {
>          let text = match tokio::process::Command::new("systemctl")
> @@ -328,7 +329,8 @@ async fn wait_service_is_active(service: &str) -> Result<(), Error> {
>              Err(err) => bail!("executing 'systemctl is-active' failed - {}", err),
>          };
>  
> -        if text.trim().trim_start() != "reloading" {
> +        let is_reload = text.trim().trim_start() == "reloading";
> +        if is_reload == wait_for_reload {

hmm, this feels and reads a bit weird, "wait_for_reload" false meaning
"wait for any status that is not reloading" seems subtle.

Combined with the name of the function this implies passing true means
that it will be waited until the service is active *or* reloading, and 
passing false implies its just waited until active.

Can you rethink the interface here, maybe split it (I'm a bit buried in
other work for more useful thoughts/proposal - sorry).

>              return Ok(());
>          }
>          tokio::time::delay_for(std::time::Duration::new(5, 0)).await;
>