[pbs-devel] [PATCH proxmox-backup v8 3/4] fix #3935: datastore: move manifest locking to new locking method

[Christian Ebner]

On 3/24/25 13:51, Shannon Sterz wrote:
> adds double stat'ing and removes directory hierarchy to bring manifest
> locking in-line with other locks used by the BackupDir trait.
> 
> if the old locking mechanism is still supposed to be used, this still
> falls back to the previous lock file. however, we already add double
> stat'ing since it is trivial to do here and should only provide better
> safety when it comes to removing locks.
> 
> Signed-off-by: Shannon Sterz <s.sterz at proxmox.com>
> ---
>   pbs-datastore/src/backup_info.rs | 45 ++++++++++++++++++++------------
>   1 file changed, 29 insertions(+), 16 deletions(-)
> 
> diff --git a/pbs-datastore/src/backup_info.rs b/pbs-datastore/src/backup_info.rs
> index b79e8196..0602867a 100644
> --- a/pbs-datastore/src/backup_info.rs
> +++ b/pbs-datastore/src/backup_info.rs
> @@ -469,25 +469,41 @@ impl BackupDir {
>       /// Returns the filename to lock a manifest
>       ///
>       /// Also creates the basedir. The lockfile is located in
> -    /// '/run/proxmox-backup/locks/{datastore}/[ns/{ns}/]+{type}/{id}/{timestamp}.index.json.lck'
> -    fn manifest_lock_path(&self) -> Result<PathBuf, Error> {
> -        let mut path = PathBuf::from(&format!("/run/proxmox-backup/locks/{}", self.store.name()));
> -        path.push(self.relative_path());
> +    /// `${DATASTORE_LOCKS_DIR}/${datastore name}/${lock_file_path_helper(rpath)}.index.json.lck`
> +    /// where rpath is the relative path of the snapshot.
> +    fn manifest_lock_path(&self) -> PathBuf {
> +        let path = Path::new(DATASTORE_LOCKS_DIR).join(self.store.name());
>   
> -        std::fs::create_dir_all(&path)?;
> -        let ts = self.backup_time_string();
> -        path.push(format!("{ts}{MANIFEST_LOCK_NAME}"));
> +        let rpath = Path::new(self.dir.group.ty.as_str())
> +            .join(&self.dir.group.id)
> +            .join(&self.backup_time_string)
> +            .join(MANIFEST_LOCK_NAME);
>   
> -        Ok(path)
> +        path.join(lock_file_path_helper(&self.ns, rpath))
>       }
>   
>       /// Locks the manifest of a snapshot, for example, to update or delete it.
>       pub(crate) fn lock_manifest(&self) -> Result<BackupLockGuard, Error> {
> -        let path = self.manifest_lock_path()?;
> +        let path = if *OLD_LOCKING {
> +            // old manifest lock path
> +            let path = Path::new(DATASTORE_LOCKS_DIR)
> +                .join(self.store.name())
> +                .join(self.relative_path());
>   
> -        // actions locking the manifest should be relatively short, only wait a few seconds
> -        open_backup_lockfile(&path, Some(std::time::Duration::from_secs(5)), true)
> -            .map_err(|err| format_err!("unable to acquire manifest lock {:?} - {}", &path, err))
> +            std::fs::create_dir_all(&path)?;
> +
> +            path.join(format!("{}{MANIFEST_LOCK_NAME}", self.backup_time_string()))
> +        } else {
> +            self.manifest_lock_path()
> +        };
> +
> +        lock_helper(self.store.name(), &path, |p| {
> +            // update_manifest should never take a long time, so if
> +            // someone else has the lock we can simply block a bit
> +            // and should get it soon
> +            open_backup_lockfile(p, Some(Duration::from_secs(5)), true)
> +                .map_err(|err| format_err!("unable to acquire manifest lock {p:?} - {err}"))

nit: same as other patch. Should this use anyhow error context instead 
of map_err?

> +        })
>       }
>   
>       /// Returns a file name for locking a snapshot.
> @@ -563,10 +579,7 @@ impl BackupDir {
>           })?;
>   
>           // remove no longer needed lock files
> -        if let Ok(path) = self.manifest_lock_path() {
> -            let _ = std::fs::remove_file(path); // ignore errors
> -        }
> -
> +        let _ = std::fs::remove_file(self.manifest_lock_path()); // ignore errors
>           let _ = std::fs::remove_file(self.lock_path()); // ignore errors
>   
>           Ok(())