Fsync parent directory after atomic save

src/sessionmanager.cpp

@@ -17,6 +17,9 @@
 #include <QDateTime>
 #include <QElapsedTimer>
 #include <algorithm>
+#include <cerrno>
+#include <cstring>
+#include <fcntl.h>
 #include <unistd.h>
 
 static constexpr int kMaxSessionCount = 100;
@@ -985,6 +988,16 @@ void SessionManager::saveSessionScrollback(SessionInfo &info)
             ::fsync(saveFile.handle());
             if (saveFile.commit()) {
                 info.scrollbackDirty = false;
+                // fsync the parent directory so the rename's dirent update
+                // survives a power loss (file content is already durable).
+                int dirFd = ::open(scrollbackDir().toUtf8().constData(), O_RDONLY);
+                if (dirFd >= 0) {
+                    if (::fsync(dirFd) != 0)
+                        qWarning() << "Scrollback: dir fsync failed:" << std::strerror(errno);
+                    ::close(dirFd);
+                } else {
+                    qWarning() << "Scrollback: dir fsync open failed:" << std::strerror(errno);
+                }
             } else {
                 qWarning() << "Failed to commit scrollback:" << saveFile.errorString();
             }

src/settings.cpp

@@ -2,11 +2,13 @@
 
 #include <QStandardPaths>
 #include <QFile>
+#include <QFileInfo>
 #include <QDebug>
 
 #include <cerrno>
 #include <cstdio>
 #include <cstring>
+#include <fcntl.h>
 #include <unistd.h>
 
 Settings::Settings(QObject *parent)
@@ -89,6 +91,17 @@ void Settings::save()
             qWarning() << "Settings: atomic save failed:" << std::strerror(errno);
             QFile::remove(tmpPath);
             m_settings.sync();
+        } else {
+            // fsync the parent directory so the rename's dirent update
+            // survives a power loss (file content is already durable).
+            int dirFd = ::open(QFileInfo(path).absolutePath().toUtf8().constData(), O_RDONLY);
+            if (dirFd >= 0) {
+                if (::fsync(dirFd) != 0)
+                    qWarning() << "Settings: dir fsync failed:" << std::strerror(errno);
+                ::close(dirFd);
+            } else {
+                qWarning() << "Settings: dir fsync open failed:" << std::strerror(errno);
+            }
         }
     } else {
         m_settings.sync();