Re: [pbs-devel] [PATCH proxmox-backup v3] client: mount: wait for child to return before exiting

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Tue, Jun 18, 2024 at 03:35:56PM GMT, Gabriel Goller wrote:
> When using the `proxmox-backup-client mount` command, the parent sometimes
> exits before we can print any error message. Most notably this happens
> when no PBS_REPOSITORY is passed, as this is the first option checked.
> If the underlying file descriptor has been closed, wait for the client
> to complete and return the error message.
> 
> Reported-by: Friedrich Weber <f.weber@proxmox.com>
> Suggested-by: Christian Ebner <c.ebner@proxmox.com>
> Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
> ---
> 
> v3, thanks @Christian, @Friedrich:
>  - Removed stdout/stderr flush (which didn't solve the problem)
>  - Wait for child to finish
> 
> v2, thanks @Christian:
>  - Removed unneeded pw.try_clone()
> 
>  proxmox-backup-client/src/mount.rs | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/proxmox-backup-client/src/mount.rs b/proxmox-backup-client/src/mount.rs
> index b69e7e80..966ea1f9 100644
> --- a/proxmox-backup-client/src/mount.rs
> +++ b/proxmox-backup-client/src/mount.rs
> @@ -183,7 +183,17 @@ fn mount(
>          Ok(ForkResult::Parent { .. }) => {
>              drop(pw);
>              // Blocks the parent process until we are ready to go in the child
> -            let _res = nix::unistd::read(pr.as_raw_fd(), &mut [0]).unwrap();
> +            let mut buffer: Vec<u8> = vec![0];

No need to use a `Vec` here, just use `let mut buffer = [0u8];`

> +            nix::unistd::read(pr.as_raw_fd(), &mut buffer).unwrap();
> +
> +            // Read buffer didn't change, which indicates that nothing has been read and the file
> +            // descriptor has probably been closed. This means that there was an error in the child
> +            // process and it did not daemonize correctly.
> +            if buffer[0] == 0 {
> +                // Wait for the child process to finish, so it can return a nice error.
> +                nix::sys::wait::wait().unwrap();
> +            }
> +
>              Ok(Value::Null)
>          }
>          Ok(ForkResult::Child) => {
> @@ -264,7 +274,7 @@ async fn mount_do(param: Value, pipe: Option<OwnedFd>) -> Result<Value, Error> {
>              }
>              // Signal the parent process that we are done with the setup and it can
>              // terminate.
> -            nix::unistd::write(pipe.as_raw_fd(), &[0u8])?;
> +            nix::unistd::write(pipe.as_raw_fd(), &[1u8])?;
>              let _: OwnedFd = pipe;
>          }
>  
> -- 
> 2.43.0


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