Local discovery: Use db instead of filesystem

We mostly trust the file watchers meaning that we don't re-scan the
local tree if we have done that recently and no file watcher events
have arrived. If the file watchers invalidate a subtree, we rescan
only that subtree.

Since we're not entirely sure the file watchers are reliable, we still
do full local discoveries regularly (1h by default). There is a config
file setting as well as an environment variable to control the interval.

doc/conffile.rst

@@ -27,6 +27,8 @@ Some interesting values that can be set on the configuration file are:
 +---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+
 | ``forceSyncInterval``           | ``7200000``   | The duration of no activity after which a synchronization run shall be triggered automatically.        |
 +---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+
+| ``fullLocalDiscoveryInterval``  | ``3600000``   | The interval after which the next synchronization will perform a full local discovery.                 |
++---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+
 | ``notificationRefreshInterval`` | ``300000``    | Specifies the default interval of checking for new server notifications in milliseconds.               |
 +---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+
 
@@ -62,4 +64,4 @@ Some interesting values that can be set on the configuration file are:
 |                                 |               | ``2`` for No Proxy.                                                                                    |
 +                                 +               +--------------------------------------------------------------------------------------------------------+
 |                                 |               | ``3`` for HTTP(S) Proxy.                                                                               |
-+---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+
++---------------------------------+---------------+--------------------------------------------------------------------------------------------------------+

src/common/syncjournaldb.cpp

@@ -547,13 +547,28 @@ bool SyncJournalDb::checkConnect()
         return sqlFail("prepare _getFileRecordQueryByFileId", *_getFileRecordQueryByFileId);
     }
 
+    // This query is used to skip discovery and fill the tree from the
+    // database instead
     _getFilesBelowPathQuery.reset(new SqlQuery(_db));
     if (_getFilesBelowPathQuery->prepare(
             GET_FILE_RECORD_QUERY
-            " WHERE path > (?1||'/') AND path < (?1||'0') ORDER BY path||'/' ASC")) {
+            " WHERE path > (?1||'/') AND path < (?1||'0')"
+            // We want to ensure that the contents of a directory are sorted
+            // directly behind the directory itself. Without this ORDER BY
+            // an ordering like foo, foo-2, foo/file would be returned.
+            // With the trailing /, we get foo-2, foo, foo/file. This property
+            // is used in fill_tree_from_db().
+            " ORDER BY path||'/' ASC")) {
         return sqlFail("prepare _getFilesBelowPathQuery", *_getFilesBelowPathQuery);
     }
 
+    _getAllFilesQuery.reset(new SqlQuery(_db));
+    if (_getAllFilesQuery->prepare(
+            GET_FILE_RECORD_QUERY
+            " ORDER BY path||'/' ASC")) {
+        return sqlFail("prepare _getAllFilesQuery", *_getAllFilesQuery);
+    }
+
     _setFileRecordQuery.reset(new SqlQuery(_db));
     if (_setFileRecordQuery->prepare("INSERT OR REPLACE INTO metadata "
                                      "(phash, pathlen, path, inode, uid, gid, mode, modtime, type, md5, fileid, remotePerm, filesize, ignoredChildrenRemote, contentChecksum, contentChecksumTypeId) "
@@ -704,6 +719,7 @@ void SyncJournalDb::close()
     _getFileRecordQueryByInode.reset(0);
     _getFileRecordQueryByFileId.reset(0);
     _getFilesBelowPathQuery.reset(0);
+    _getAllFilesQuery.reset(0);
     _setFileRecordQuery.reset(0);
     _setFileRecordChecksumQuery.reset(0);
     _setFileRecordLocalMetadataQuery.reset(0);
@@ -1133,16 +1149,23 @@ bool SyncJournalDb::getFilesBelowPath(const QByteArray &path, const std::functio
     if (!checkConnect())
         return false;
 
-    _getFilesBelowPathQuery->reset_and_clear_bindings();
-    _getFilesBelowPathQuery->bindValue(1, path);
+    // Since the path column doesn't store the starting /, the getFilesBelowPathQuery
+    // can't be used for the root path "". It would scan for (path > '/' and path < '0')
+    // and find nothing. So, unfortunately, we have to use a different query for
+    // retrieving the whole tree.
+    auto &query = path.isEmpty() ? _getAllFilesQuery : _getFilesBelowPathQuery;
 
-    if (!_getFilesBelowPathQuery->exec()) {
+    query->reset_and_clear_bindings();
+    if (query == _getFilesBelowPathQuery)
+        query->bindValue(1, path);
+
+    if (!query->exec()) {
         return false;
     }
 
-    while (_getFilesBelowPathQuery->next()) {
+    while (query->next()) {
         SyncJournalFileRecord rec;
-        fillFileRecordFromGetQuery(rec, *_getFilesBelowPathQuery);
+        fillFileRecordFromGetQuery(rec, *query);
         rowCallback(rec);
     }
 

src/common/syncjournaldb.h

@@ -244,6 +244,7 @@ private:
     QScopedPointer<SqlQuery> _getFileRecordQueryByInode;
     QScopedPointer<SqlQuery> _getFileRecordQueryByFileId;
     QScopedPointer<SqlQuery> _getFilesBelowPathQuery;
+    QScopedPointer<SqlQuery> _getAllFilesQuery;
     QScopedPointer<SqlQuery> _setFileRecordQuery;
     QScopedPointer<SqlQuery> _setFileRecordChecksumQuery;
     QScopedPointer<SqlQuery> _setFileRecordLocalMetadataQuery;

src/csync/csync.cpp

@@ -314,6 +314,9 @@ int csync_s::reinitialize() {
   local.files.clear();
   remote.files.clear();
 
+  local_discovery_style = LocalDiscoveryStyle::FilesystemOnly;
+  locally_touched_dirs.clear();
+
   status = CSYNC_STATUS_INIT;
   SAFE_FREE(error_string);
 

src/csync/csync_private.h

@@ -38,6 +38,7 @@
 #include <stdbool.h>
 #include <sqlite3.h>
 #include <map>
+#include <set>
 
 #include "common/syncjournaldb.h"
 #include "config_csync.h"
@@ -70,6 +71,11 @@ enum csync_replica_e {
   REMOTE_REPLICA
 };
 
+enum class LocalDiscoveryStyle {
+    FilesystemOnly, //< read all local data from the filesystem
+    DatabaseAndFilesystem, //< read from the db, except for listed paths
+};
+
 
 /*
  * This is a structurere similar to QStringRef
@@ -190,6 +196,16 @@ struct OCSYNC_EXPORT csync_s {
    */
   bool read_remote_from_db = false;
 
+  LocalDiscoveryStyle local_discovery_style = LocalDiscoveryStyle::FilesystemOnly;
+
+  /**
+   * List of folder-relative directory paths that should be scanned on the
+   * filesystem if the local_discovery_style suggests it.
+   *
+   * Their parents will be scanned too. The paths don't start with a /.
+   */
+  std::set<QByteArray> locally_touched_dirs;
+
   bool ignore_hidden_files = true;
 
   csync_s(const char *localUri, OCC::SyncJournalDb *statedb);

src/csync/csync_update.cpp

@@ -435,28 +435,31 @@ static bool fill_tree_from_db(CSYNC *ctx, const char *uri)
 {
     int64_t count = 0;
     QByteArray skipbase;
-    auto rowCallback = [ctx, &count, &skipbase](const OCC::SyncJournalFileRecord &rec) {
-        /* When selective sync is used, the database may have subtrees with a parent
-         * whose etag (md5) is _invalid_. These are ignored and shall not appear in the
-         * remote tree.
-         * Sometimes folders that are not ignored by selective sync get marked as
-         * _invalid_, but that is not a problem as the next discovery will retrieve
-         * their correct etags again and we don't run into this case.
-         */
-        if( rec._etag == "_invalid_") {
-            qCDebug(lcUpdate, "%s selective sync excluded", rec._path.constData());
-            skipbase = rec._path;
-            skipbase += '/';
-            return;
-        }
+    auto &files = ctx->current == LOCAL_REPLICA ? ctx->local.files : ctx->remote.files;
+    auto rowCallback = [ctx, &count, &skipbase, &files](const OCC::SyncJournalFileRecord &rec) {
+        if (ctx->current == REMOTE_REPLICA) {
+            /* When selective sync is used, the database may have subtrees with a parent
+             * whose etag is _invalid_. These are ignored and shall not appear in the
+             * remote tree.
+             * Sometimes folders that are not ignored by selective sync get marked as
+             * _invalid_, but that is not a problem as the next discovery will retrieve
+             * their correct etags again and we don't run into this case.
+             */
+            if (rec._etag == "_invalid_") {
+                qCDebug(lcUpdate, "%s selective sync excluded", rec._path.constData());
+                skipbase = rec._path;
+                skipbase += '/';
+                return;
+            }
 
-        /* Skip over all entries with the same base path. Note that this depends
-         * strongly on the ordering of the retrieved items. */
-        if( !skipbase.isEmpty() && rec._path.startsWith(skipbase) ) {
-            qCDebug(lcUpdate, "%s selective sync excluded because the parent is", rec._path.constData());
-            return;
-        } else {
-            skipbase.clear();
+            /* Skip over all entries with the same base path. Note that this depends
+             * strongly on the ordering of the retrieved items. */
+            if (!skipbase.isEmpty() && rec._path.startsWith(skipbase)) {
+                qCDebug(lcUpdate, "%s selective sync excluded because the parent is", rec._path.constData());
+                return;
+            } else {
+                skipbase.clear();
+            }
         }
 
         std::unique_ptr<csync_file_stat_t> st = csync_file_stat_t::fromSyncJournalFileRecord(rec);
@@ -477,7 +480,7 @@ static bool fill_tree_from_db(CSYNC *ctx, const char *uri)
         }
 
         /* store into result list. */
-        ctx->remote.files[rec._path] = std::move(st);
+        files[rec._path] = std::move(st);
         ++count;
     };
 
@@ -522,6 +525,26 @@ int csync_ftw(CSYNC *ctx, const char *uri, csync_walker_fn fn,
   int rc = 0;
 
   bool do_read_from_db = (ctx->current == REMOTE_REPLICA && ctx->remote.read_from_db);
+  const char *db_uri = uri;
+
+  if (ctx->current == LOCAL_REPLICA
+      && ctx->local_discovery_style == LocalDiscoveryStyle::DatabaseAndFilesystem) {
+      const char *local_uri = uri + strlen(ctx->local.uri);
+      if (*local_uri == '/')
+          ++local_uri;
+      db_uri = local_uri;
+      do_read_from_db = true;
+
+      // Minor bug: local_uri doesn't have a trailing /. Example: Assume it's "d/foo"
+      // and we want to check whether we should read from the db. Assume "d/foo a" is
+      // in locally_touched_dirs. Then this check will say no, don't read from the db!
+      // (because "d/foo" < "d/foo a" < "d/foo/bar")
+      // C++14: Could skip the conversion to QByteArray here.
+      auto it = ctx->locally_touched_dirs.lower_bound(QByteArray(local_uri));
+      if (it != ctx->locally_touched_dirs.end() && it->startsWith(local_uri)) {
+          do_read_from_db = false;
+      }
+  }
 
   if (!depth) {
     mark_current_item_ignored(ctx, previous_fs, CSYNC_STATUS_INDIVIDUAL_TOO_DEEP);
@@ -533,7 +556,7 @@ int csync_ftw(CSYNC *ctx, const char *uri, csync_walker_fn fn,
   // if the etag of this dir is still the same, its content is restored from the
   // database.
   if( do_read_from_db ) {
-      if( ! fill_tree_from_db(ctx, uri) ) {
+      if( ! fill_tree_from_db(ctx, db_uri) ) {
         errno = ENOENT;
         ctx->status_code = CSYNC_STATUS_OPENDIR_ERROR;
         goto error;

src/gui/folder.cpp

@@ -448,12 +448,26 @@ int Folder::slotWipeErrorBlacklist()
 
 void Folder::slotWatchedPathChanged(const QString &path)
 {
+    if (!path.startsWith(this->path())) {
+        qCDebug(lcFolder) << "Changed path is not contained in folder, ignoring:" << path;
+        return;
+    }
+
+    auto relativePath = path.midRef(this->path().size());
+
+    // Add to list of locally modified paths
+    //
+    // We do this before checking for our own sync-related changes to make
+    // extra sure to not miss relevant changes.
+    auto relativePathBytes = relativePath.toUtf8();
+    _localDiscoveryPaths.insert(relativePathBytes);
+    qCDebug(lcFolder) << "local discovery: inserted" << relativePath << "due to file watcher";
+
 // The folder watcher fires a lot of bogus notifications during
 // a sync operation, both for actual user files and the database
 // and log. Therefore we check notifications against operations
 // the sync is doing to filter out our own changes.
 #ifdef Q_OS_MAC
-    Q_UNUSED(path)
 // On OSX the folder watcher does not report changes done by our
 // own process. Therefore nothing needs to be done here!
 #else
@@ -465,15 +479,12 @@ void Folder::slotWatchedPathChanged(const QString &path)
 #endif
 
     // Check that the mtime actually changed.
-    if (path.startsWith(this->path())) {
-        auto relativePath = path.mid(this->path().size());
-        SyncJournalFileRecord record;
-        if (_journal.getFileRecord(relativePath, &record)
-            && record.isValid()
-            && !FileSystem::fileChanged(path, record._fileSize, record._modtime)) {
-            qCInfo(lcFolder) << "Ignoring spurious notification for file" << relativePath;
-            return; // probably a spurious notification
-        }
+    SyncJournalFileRecord record;
+    if (_journal.getFileRecord(relativePathBytes, &record)
+        && record.isValid()
+        && !FileSystem::fileChanged(path, record._fileSize, record._modtime)) {
+        qCInfo(lcFolder) << "Ignoring spurious notification for file" << relativePath;
+        return; // probably a spurious notification
     }
 
     emit watchedFileChangedExternally(path);
@@ -645,6 +656,36 @@ void Folder::startSync(const QStringList &pathList)
     setDirtyNetworkLimits();
     setSyncOptions();
 
+    static qint64 fullLocalDiscoveryInterval = []() {
+        auto interval = ConfigFile().fullLocalDiscoveryInterval();
+        QByteArray env = qgetenv("OWNCLOUD_FULL_LOCAL_DISCOVERY_INTERVAL");
+        if (!env.isEmpty()) {
+            interval = env.toLongLong();
+        }
+        return interval;
+    }();
+    if (_folderWatcher && _folderWatcher->isReliable()
+        && _timeSinceLastFullLocalDiscovery.isValid()
+        && (fullLocalDiscoveryInterval < 0
+               || _timeSinceLastFullLocalDiscovery.elapsed() < fullLocalDiscoveryInterval)) {
+        qCInfo(lcFolder) << "Allowing local discovery to read from the database";
+        _engine->setLocalDiscoveryOptions(LocalDiscoveryStyle::DatabaseAndFilesystem, _localDiscoveryPaths);
+
+        if (lcFolder().isDebugEnabled()) {
+            QByteArrayList paths;
+            for (auto &path : _localDiscoveryPaths)
+                paths.append(path);
+            qCDebug(lcFolder) << "local discovery paths: " << paths;
+        }
+
+        _previousLocalDiscoveryPaths = std::move(_localDiscoveryPaths);
+    } else {
+        qCInfo(lcFolder) << "Forbidding local discovery to read from the database";
+        _engine->setLocalDiscoveryOptions(LocalDiscoveryStyle::FilesystemOnly);
+        _previousLocalDiscoveryPaths.clear();
+    }
+    _localDiscoveryPaths.clear();
+
     _engine->setIgnoreHiddenFiles(_definition.ignoreHiddenFiles);
 
     QMetaObject::invokeMethod(_engine.data(), "startSync", Qt::QueuedConnection);
@@ -783,6 +824,24 @@ void Folder::slotSyncFinished(bool success)
         journalDb()->setSelectiveSyncList(SyncJournalDb::SelectiveSyncWhiteList, QStringList());
     }
 
+    // bug: This function uses many different criteria for "sync was successful" - investigate!
+    if ((_syncResult.status() == SyncResult::Success
+            || _syncResult.status() == SyncResult::Problem)
+        && success) {
+        if (_engine->lastLocalDiscoveryStyle() == LocalDiscoveryStyle::FilesystemOnly) {
+            _timeSinceLastFullLocalDiscovery.start();
+        }
+        qCDebug(lcFolder) << "Sync success, forgetting last sync's local discovery path list";
+    } else {
+        // On overall-failure we can't forget about last sync's local discovery
+        // paths yet, reuse them for the next sync again.
+        // C++17: Could use std::set::merge().
+        _localDiscoveryPaths.insert(
+            _previousLocalDiscoveryPaths.begin(), _previousLocalDiscoveryPaths.end());
+        qCDebug(lcFolder) << "Sync failed, keeping last sync's local discovery path list";
+    }
+    _previousLocalDiscoveryPaths.clear();
+
     emit syncStateChange();
 
     // The syncFinished result that is to be triggered here makes the folderman
@@ -851,6 +910,25 @@ void Folder::slotItemCompleted(const SyncFileItemPtr &item)
             _folderWatcher->removePath(path() + item->_file);
     }
 
+    // Success and failure of sync items adjust what the next sync is
+    // supposed to do.
+    //
+    // For successes, we want to wipe the file from the list to ensure we don't
+    // rediscover it even if this overall sync fails.
+    //
+    // For failures, we want to add the file to the list so the next sync
+    // will be able to retry it.
+    if (item->_status == SyncFileItem::Success
+        || item->_status == SyncFileItem::FileIgnored
+        || item->_status == SyncFileItem::Restoration
+        || item->_status == SyncFileItem::Conflict) {
+        if (_previousLocalDiscoveryPaths.erase(item->_file.toUtf8()))
+            qCDebug(lcFolder) << "local discovery: wiped" << item->_file;
+    } else {
+        _localDiscoveryPaths.insert(item->_file.toUtf8());
+        qCDebug(lcFolder) << "local discovery: inserted" << item->_file << "due to sync failure";
+    }
+
     _syncResult.processCompletedItem(item);
 
     _fileLog->logItem(*item);
@@ -903,6 +981,11 @@ void Folder::slotScheduleThisFolder()
     FolderMan::instance()->scheduleFolder(this);
 }
 
+void Folder::slotNextSyncFullLocalDiscovery()
+{
+    _timeSinceLastFullLocalDiscovery.invalidate();
+}
+
 void Folder::scheduleThisFolderSoon()
 {
     if (!_scheduleSelfTimer.isActive()) {
@@ -925,6 +1008,8 @@ void Folder::registerFolderWatcher()
     _folderWatcher.reset(new FolderWatcher(path(), this));
     connect(_folderWatcher.data(), &FolderWatcher::pathChanged,
         this, &Folder::slotWatchedPathChanged);
+    connect(_folderWatcher.data(), &FolderWatcher::lostChanges,
+        this, &Folder::slotNextSyncFullLocalDiscovery);
 }
 
 void Folder::slotAboutToRemoveAllFiles(SyncFileItem::Direction dir, bool *cancel)

src/gui/folder.h

@@ -27,6 +27,7 @@
 
 #include <QObject>
 #include <QStringList>
+#include <set>
 
 class QThread;
 class QSettings;
@@ -312,6 +313,9 @@ private slots:
      */
     void slotScheduleThisFolder();
 
+    /** Ensures that the next sync performs a full local discovery. */
+    void slotNextSyncFullLocalDiscovery();
+
 private:
     bool setIgnoredFiles();
 
@@ -346,6 +350,7 @@ private:
     QString _lastEtag;
     QElapsedTimer _timeSinceLastSyncDone;
     QElapsedTimer _timeSinceLastSyncStart;
+    QElapsedTimer _timeSinceLastFullLocalDiscovery;
     qint64 _lastSyncDuration;
 
     /// The number of syncs that failed in a row.
@@ -380,6 +385,22 @@ private:
      * Created by registerFolderWatcher(), triggers slotWatchedPathChanged()
      */
     QScopedPointer<FolderWatcher> _folderWatcher;
+
+    /**
+     * The paths that should be checked by the next local discovery.
+     *
+     * Mostly a collection of files the filewatchers have reported as touched.
+     * Also includes files that have had errors in the last sync run.
+     */
+    std::set<QByteArray> _localDiscoveryPaths;
+
+    /**
+     * The paths that the current sync run used for local discovery.
+     *
+     * For failing syncs, this list will be merged into _localDiscoveryPaths
+     * again when the sync is done to make sure everything is retried.
+     */
+    std::set<QByteArray> _previousLocalDiscoveryPaths;
 };
 }
 

src/libsync/configfile.cpp

@@ -36,6 +36,7 @@
 #include <QNetworkProxy>
 
 #define DEFAULT_REMOTE_POLL_INTERVAL 30000 // default remote poll time in milliseconds
+#define DEFAULT_FULL_LOCAL_DISCOVERY_INTERVAL (60 * 60 * 1000) // 1 hour
 #define DEFAULT_MAX_LOG_LINES 20000
 
 namespace OCC {
@@ -45,6 +46,7 @@ Q_LOGGING_CATEGORY(lcConfigFile, "sync.configfile", QtInfoMsg)
 //static const char caCertsKeyC[] = "CaCertificates"; only used from account.cpp
 static const char remotePollIntervalC[] = "remotePollInterval";
 static const char forceSyncIntervalC[] = "forceSyncInterval";
+static const char fullLocalDiscoveryIntervalC[] = "fullLocalDiscoveryInterval";
 static const char notificationRefreshIntervalC[] = "notificationRefreshInterval";
 static const char monoIconsC[] = "monoIcons";
 static const char promptDeleteC[] = "promptDeleteAllFiles";
@@ -406,6 +408,13 @@ quint64 ConfigFile::forceSyncInterval(const QString &connection) const
     return interval;
 }
 
+qint64 ConfigFile::fullLocalDiscoveryInterval() const
+{
+    QSettings settings(configFile(), QSettings::IniFormat);
+    settings.beginGroup(defaultConnection());
+    return settings.value(QLatin1String(fullLocalDiscoveryIntervalC), DEFAULT_FULL_LOCAL_DISCOVERY_INTERVAL).toLongLong();
+}
+
 quint64 ConfigFile::notificationRefreshInterval(const QString &connection) const
 {
     QString con(connection);

src/libsync/configfile.h

@@ -72,6 +72,13 @@ public:
     /* Force sync interval, in milliseconds */
     quint64 forceSyncInterval(const QString &connection = QString()) const;
 
+    /**
+     * Interval in milliseconds within which full local discovery is required
+     *
+     * Use -1 to disable regular full local discoveries.
+     */
+    qint64 fullLocalDiscoveryInterval() const;
+
     bool monoIcons() const;
     void setMonoIcons(bool);
 

src/libsync/syncengine.cpp

@@ -813,6 +813,7 @@ void SyncEngine::startSync()
     }
 
     _csync_ctx->read_remote_from_db = true;
+    _lastLocalDiscoveryStyle = _csync_ctx->local_discovery_style;
 
     bool ok;
     auto selectiveSyncBlackList = _journal->getSelectiveSyncList(SyncJournalDb::SelectiveSyncBlackList, &ok);
@@ -1555,6 +1556,12 @@ AccountPtr SyncEngine::account() const
     return _account;
 }
 
+void SyncEngine::setLocalDiscoveryOptions(LocalDiscoveryStyle style, std::set<QByteArray> dirs)
+{
+    _csync_ctx->local_discovery_style = style;
+    _csync_ctx->locally_touched_dirs = std::move(dirs);
+}
+
 void SyncEngine::abort()
 {
     if (_propagator)

src/libsync/syncengine.h

@@ -25,6 +25,7 @@
 #include <QMap>
 #include <QStringList>
 #include <QSharedPointer>
+#include <set>
 
 #include <csync.h>
 
@@ -92,6 +93,7 @@ public:
     AccountPtr account() const;
     SyncJournalDb *journal() const { return _journal; }
     QString localPath() const { return _localPath; }
+
     /**
      * Minimum age, in milisecond, of a file that can be uploaded.
      * Files more recent than that are not going to be uploaeded as they are considered
@@ -99,6 +101,22 @@ public:
      */
     static qint64 minimumFileAgeForUpload; // in ms
 
+    /**
+     * Control whether local discovery should read from filesystem or db.
+     *
+     * If style is Partial, the paths is a set of file paths relative to
+     * the synced folder. All the parent directories of these paths will not
+     * be read from the db and scanned on the filesystem.
+     *
+     * Note, the style and paths are only retained for the next sync and
+     * revert afterwards. Use _lastLocalDiscoveryStyle to discover the last
+     * sync's style.
+     */
+    void setLocalDiscoveryOptions(LocalDiscoveryStyle style, std::set<QByteArray> dirs = {});
+
+    /** Access the last sync run's local discovery style */
+    LocalDiscoveryStyle lastLocalDiscoveryStyle() const { return _lastLocalDiscoveryStyle; }
+
 signals:
     void csyncUnavailable();
 
@@ -272,6 +290,9 @@ private:
 
     /** List of unique errors that occurred in a sync run. */
     QSet<QString> _uniqueErrors;
+
+    /** The kind of local discovery the last sync run used */
+    LocalDiscoveryStyle _lastLocalDiscoveryStyle = LocalDiscoveryStyle::DatabaseAndFilesystem;
 };
 }
 

test/testsyncengine.cpp

@@ -613,6 +613,40 @@ private slots:
         QCOMPARE(nDELETE, 5);
         QCOMPARE(fakeFolder.currentLocalState(), remoteInfo);
     }
+
+    // Check correct behavior when local discovery is partially drawn from the db
+    void testLocalDiscoveryStyle()
+    {
+        FakeFolder fakeFolder{ FileInfo::A12_B12_C12_S12() };
+
+        // More subdirectories are useful for testing
+        fakeFolder.localModifier().mkdir("A/X");
+        fakeFolder.localModifier().mkdir("A/Y");
+        fakeFolder.localModifier().insert("A/X/x1");
+        fakeFolder.localModifier().insert("A/Y/y1");
+        QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+
+        // Test begins
+        fakeFolder.localModifier().insert("A/a3");
+        fakeFolder.localModifier().insert("A/X/x2");
+        fakeFolder.localModifier().insert("A/Y/y2");
+        fakeFolder.localModifier().insert("B/b3");
+        fakeFolder.remoteModifier().insert("C/c3");
+
+        fakeFolder.syncEngine().setLocalDiscoveryOptions(LocalDiscoveryStyle::DatabaseAndFilesystem, { "A/X" });
+        QVERIFY(fakeFolder.syncOnce());
+        QVERIFY(fakeFolder.currentRemoteState().find("A/a3"));
+        QVERIFY(fakeFolder.currentRemoteState().find("A/X/x2"));
+        QVERIFY(!fakeFolder.currentRemoteState().find("A/Y/y2"));
+        QVERIFY(!fakeFolder.currentRemoteState().find("B/b3"));
+        QVERIFY(fakeFolder.currentLocalState().find("C/c3"));
+        QCOMPARE(fakeFolder.syncEngine().lastLocalDiscoveryStyle(), LocalDiscoveryStyle::DatabaseAndFilesystem);
+
+        QVERIFY(fakeFolder.syncOnce());
+        QCOMPARE(fakeFolder.currentLocalState(), fakeFolder.currentRemoteState());
+        QCOMPARE(fakeFolder.syncEngine().lastLocalDiscoveryStyle(), LocalDiscoveryStyle::FilesystemOnly);
+    }
 };
 
 QTEST_GUILESS_MAIN(TestSyncEngine)