[pbs-devel] [PATCH proxmox-backup v4 4/5] fix #3935: datastore: move manifest locking to new locking method

[Stefan Sterz]

adds double stat'ing and removes directory hierarchy to bring manifest
locking in-line with other locks used by the BackupDir trait.

Signed-off-by: Stefan Sterz <s.sterz at proxmox.com>
---
 pbs-datastore/src/backup_info.rs | 35 ++++++++++++++++----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/pbs-datastore/src/backup_info.rs b/pbs-datastore/src/backup_info.rs
index 046ed6e9..43712700 100644
--- a/pbs-datastore/src/backup_info.rs
+++ b/pbs-datastore/src/backup_info.rs
@@ -443,25 +443,29 @@ 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_name_helper(rpath)}.index.json.lck`
+    /// where rpath is the relative path of the snapshot.
+    ///
+    /// If the snapshot's relative path contains non-Unicode sequences they will be replaced via
+    /// [std::ffi::OsStr::to_string_lossy()].
+    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 = self.relative_path().join(&format!("{MANIFEST_LOCK_NAME}"));
+        let rpath = rpath.as_os_str().to_string_lossy();
 
-        Ok(path)
+        path.join(lock_file_name_helper(&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()?;
-
-        // 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))
+        lock_helper(self.store.name(), &self.manifest_lock_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}"))
+        })
     }
 
     /// Returns a file name for locking a snapshot.
@@ -518,10 +522,7 @@ 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(())
-- 
2.30.2