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Date: Mon, 28 Sep 2020 07:28:08 +0200 (CEST)
From: Dietmar Maurer <dietmar@proxmox.com>
To: Proxmox Backup Server development discussion <pbs-devel@lists.proxmox.com>, 
 Dominik Csapak <d.csapak@proxmox.com>
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Subject: Re: [pbs-devel] [PATCH proxmox-backup 02/10] server/worker_task:
 refactor locking of the task list
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> +fn lock_task_list_files(exclusive: bool) -> Result<std::fs::File, Error> {
> +    let backup_user = crate::backup::backup_user()?;
> +
> +    let lock = if exclusive {
> +        open_file_locked(PROXMOX_BACKUP_TASK_LOCK_FN, std::time::Duration::new(10, 0))?
> +    } else {
> +        open_file_locked_shared(PROXMOX_BACKUP_TASK_LOCK_FN, std::time::Duration::new(10, 0))?
> +    };
> +    nix::unistd::chown(PROXMOX_BACKUP_TASK_LOCK_FN, Some(backup_user.uid), Some(backup_user.gid))?;

You should use fchown here on the open file handle.

> +
> +    Ok(lock)
> +}

This starts to get clumsy. We have:

pub fn open_file_locked_shared<P: AsRef<Path>>(path: P, timeout: Duration) -> Result<File, Error>

and

pub fn open_file_locked<P: AsRef<Path>>(path: P, timeout: Duration) -> Result<File, Error>

and private:

fn open_file_locked_impl<P: AsRef<Path>>(path: P, timeout: Duration, exclusive: bool) -> Result<File, Error>

But we want:

pub fn open_file_locked<P: AsRef<Path>>(path: P, timeout: Duration, exclusive: bool) -> Result<File, Error>


...