server/worker_task: simplify task log writing

instead of prerotating 1000 tasks
(which resulted in 2 writes each time an active worker was finished)
simply append finished tasks to the archive (which will be rotated)

page cache should be good enough so that we can get the task logs fast

since existing installations might have an 'index' file, we
still have to read tasks from there, but only if it exists

this simplifies the TaskListInfoIterator a good amount

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/server/worker_task.rs

@@ -35,8 +35,6 @@ pub const PROXMOX_BACKUP_ACTIVE_TASK_FN: &str = concat!(PROXMOX_BACKUP_TASK_DIR_
 pub const PROXMOX_BACKUP_INDEX_TASK_FN: &str = concat!(PROXMOX_BACKUP_TASK_DIR_M!(), "/index");
 pub const PROXMOX_BACKUP_ARCHIVE_TASK_FN: &str = concat!(PROXMOX_BACKUP_TASK_DIR_M!(), "/archive");
 
-const MAX_INDEX_TASKS: usize = 1000;
-
 lazy_static! {
     static ref WORKER_TASK_LIST: Mutex<HashMap<usize, Arc<WorkerTask>>> = Mutex::new(HashMap::new());
 
@@ -363,7 +361,10 @@ fn update_active_workers(new_upid: Option<&UPID>) -> Result<(), Error> {
 
     let lock = lock_task_list_files(true)?;
 
+    // TODO remove with 1.x
     let mut finish_list: Vec<TaskListInfo> = read_task_file_from_path(PROXMOX_BACKUP_INDEX_TASK_FN)?;
+    let had_index_file = !finish_list.is_empty();
+
     let mut active_list: Vec<TaskListInfo> = read_task_file_from_path(PROXMOX_BACKUP_ACTIVE_TASK_FN)?
         .into_iter()
         .filter_map(|info| {
@@ -412,33 +413,10 @@ fn update_active_workers(new_upid: Option<&UPID>) -> Result<(), Error> {
         }
     });
 
-
+    if !finish_list.is_empty() {
-    let start = if finish_list.len() > MAX_INDEX_TASKS {
-        finish_list.len() - MAX_INDEX_TASKS
-    } else {
-        0
-    };
-
-    let end = (start+MAX_INDEX_TASKS).min(finish_list.len());
-
-    let index_raw = if end > start {
-        render_task_list(&finish_list[start..end])
-    } else {
-        "".to_string()
-    };
-
-    replace_file(
-        PROXMOX_BACKUP_INDEX_TASK_FN,
-        index_raw.as_bytes(),
-        CreateOptions::new()
-            .owner(backup_user.uid)
-            .group(backup_user.gid),
-    )?;
-
-    if !finish_list.is_empty() && start > 0 {
         match std::fs::OpenOptions::new().append(true).create(true).open(PROXMOX_BACKUP_ARCHIVE_TASK_FN) {
             Ok(mut writer) => {
-                for info in &finish_list[0..start] {
+                for info in &finish_list {
                     writer.write_all(render_task_line(&info).as_bytes())?;
                 }
             },
@@ -448,6 +426,12 @@ fn update_active_workers(new_upid: Option<&UPID>) -> Result<(), Error> {
         nix::unistd::chown(PROXMOX_BACKUP_ARCHIVE_TASK_FN, Some(backup_user.uid), Some(backup_user.gid))?;
     }
 
+    // TODO Remove with 1.x
+    // for compatibility, if we had an INDEX file, we do not need it anymore
+    if had_index_file {
+        let _ = nix::unistd::unlink(PROXMOX_BACKUP_INDEX_TASK_FN);
+    }
+
     drop(lock);
 
     Ok(())
@@ -511,16 +495,9 @@ where
     read_task_file(file)
 }
 
-enum TaskFile {
-    Active,
-    Index,
-    Archive,
-    End,
-}
-
 pub struct TaskListInfoIterator {
     list: VecDeque<TaskListInfo>,
-    file: TaskFile,
+    end: bool,
     archive: Option<LogRotateFiles>,
     lock: Option<File>,
 }
@@ -535,7 +512,10 @@ impl TaskListInfoIterator {
                 .iter()
                 .any(|info| info.state.is_some() || !worker_is_active_local(&info.upid));
 
-            if needs_update {
+            // TODO remove with 1.x
+            let index_exists = std::path::Path::new(PROXMOX_BACKUP_INDEX_TASK_FN).is_file();
+
+            if needs_update || index_exists {
                 drop(lock);
                 update_active_workers(None)?;
                 let lock = lock_task_list_files(false)?;
@@ -554,12 +534,11 @@ impl TaskListInfoIterator {
             Some(logrotate.files())
         };
 
-        let file = if active_only { TaskFile::End } else { TaskFile::Active };
         let lock = if active_only { None } else { Some(read_lock) };
 
         Ok(Self {
             list: active_list.into(),
-            file,
+            end: active_only,
             archive,
             lock,
         })
@@ -573,17 +552,9 @@ impl Iterator for TaskListInfoIterator {
         loop {
             if let Some(element) = self.list.pop_back() {
                 return Some(Ok(element));
+            } else if self.end {
+                    return None;
             } else {
-                match self.file {
-                    TaskFile::Active => {
-                        let index = match read_task_file_from_path(PROXMOX_BACKUP_INDEX_TASK_FN) {
-                            Ok(index) => index,
-                            Err(err) => return Some(Err(err)),
-                        };
-                        self.list.append(&mut index.into());
-                        self.file = TaskFile::Index;
-                    },
-                    TaskFile::Index | TaskFile::Archive => {
                 if let Some(mut archive) = self.archive.take() {
                     if let Some(file) = archive.next() {
                         let list = match read_task_file(file) {
@@ -592,16 +563,12 @@ impl Iterator for TaskListInfoIterator {
                         };
                         self.list.append(&mut list.into());
                         self.archive = Some(archive);
-                                self.file = TaskFile::Archive;
                         continue;
                     }
                 }
-                        self.file = TaskFile::End;
+
+                self.end = true;
                 self.lock.take();
-                        return None;
-                    }
-                    TaskFile::End => return None,
-                }
             }
         }
     }