Display: Do not offer a tty if it's already taken by a logind session

Otherwise, it all freezes and nothing works as it should.

Fixes #1588

CMakeLists.txt

@@ -35,6 +35,9 @@ option(ENABLE_PAM "Enable PAM support" ON)
 option(NO_SYSTEMD "Disable systemd support" OFF)
 option(USE_ELOGIND "Use elogind instead of logind" OFF)
 
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
 # ECM
 find_package(ECM 1.4.0 REQUIRED NO_MODULE)
 set(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake;${CMAKE_MODULE_PATH};${ECM_MODULE_PATH}")

src/common/VirtualTerminal.cpp

@@ -31,6 +31,7 @@
 #include <linux/kd.h>
 #include <sys/ioctl.h>
 #include <qscopeguard.h>
+#include <QFileInfo>
 
 #define RELEASE_DISPLAY_SIGNAL (SIGRTMAX)
 #define ACQUIRE_DISPLAY_SIGNAL (SIGRTMAX - 1)
@@ -116,8 +117,8 @@ out:
                 qDebug() << "VT mode didn't need to be fixed";
         }
 
-        int fetchAvailableVt() {
-            // open VT master
+        int currentVt()
+        {
             int fd = open("/dev/tty0", O_RDWR | O_NOCTTY);
             if (fd < 0) {
                 qCritical() << "Failed to open VT master:" << strerror(errno);
@@ -129,19 +130,12 @@ out:
 
             vt_stat vtState = { 0 };
             if (ioctl(fd, VT_GETSTATE, &vtState) < 0) {
-                qCritical() << "Failed to get current VT:" << strerror(errno);
-
-                int vt = 0;
-                // If there's no current tty, request the next to open
-                if (ioctl(fd, VT_OPENQRY, &vt) < 0) {
-                    qCritical() << "Failed to open new VT:" << strerror(errno);
-                    return -1;
-                }
-                return vt;
+                return -1;
             }
             return vtState.v_active;
         }
 
+
         int setUpNewVt() {
             // open VT master
             int fd = open("/dev/tty0", O_RDWR | O_NOCTTY);

src/common/VirtualTerminal.h

@@ -22,7 +22,7 @@
 
 namespace SDDM {
     namespace VirtualTerminal {
-        int fetchAvailableVt();
+        int currentVt();
         int setUpNewVt();
         void jumpToVt(int vt, bool vt_auto);
     }

src/common/VirtualTerminal_FreeBSD.cpp

@@ -35,10 +35,9 @@ namespace SDDM {
         static char ttyvX[] = "/dev/ttyvX";
         static const char ttyvs[] = "0123456789ab";
 
-        int setUpNewVt() {
-            // there is no way to create VTs on FreeBSD, so
-            // just try to fetch any available
-            return fetchAvailableVt();
+        int currentVt()
+        {
+            return -1;
         }
 
         void jumpToVt(int vt, bool vt_auto) {
@@ -64,7 +63,7 @@ namespace SDDM {
             }
         }
 
-        int fetchAvailableVt() {
+        int setUpNewVt() {
             int fd = ::open("/dev/console", O_RDONLY);
             if(fd == -1) {
                 qWarning() << "Failed to open /dev/console: " << strerror(errno);

src/daemon/Display.cpp

@@ -40,6 +40,10 @@
 #include <unistd.h>
 #include <sys/time.h>
 
+#include <sys/ioctl.h>
+#include <fcntl.h>
+#include <linux/vt.h>
+
 #include <QDBusConnection>
 #include <QDBusMessage>
 #include <QDBusReply>
@@ -51,6 +55,35 @@
 
 
 namespace SDDM {
+    bool isTtyInUse(const QString &desiredTty) {
+        if (Logind::isAvailable()) {
+            OrgFreedesktopLogin1ManagerInterface manager(Logind::serviceName(), Logind::managerPath(), QDBusConnection::systemBus());
+            auto reply = manager.ListSessions();
+            reply.waitForFinished();
+
+            const auto info = reply.value();
+            for(const SessionInfo &s : info) {
+                OrgFreedesktopLogin1SessionInterface session(Logind::serviceName(), s.sessionPath.path(), QDBusConnection::systemBus());
+                if (desiredTty == session.tTY() && session.state() != QLatin1String("closing")) {
+                    qDebug() << "tty" << desiredTty << "already in use by" << session.user().path << session.state()
+                                      << session.display() << session.desktop() << session.vTNr();
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+
+    int fetchAvailableVt() {
+        const auto vt = VirtualTerminal::currentVt();
+        if (vt > 0) {
+            if (!isTtyInUse(QStringLiteral("tty%1").arg(vt))) {
+                return vt;
+            }
+        }
+        return VirtualTerminal::setUpNewVt();
+    }
+
     Display::Display(Seat *parent) : QObject(parent),
         m_auth(new Auth(this)),
         m_seat(parent),
@@ -62,10 +95,10 @@ namespace SDDM {
         const QString &displayServerType = mainConfig.DisplayServer.get().toLower();
         if (displayServerType == QStringLiteral("x11-user")) {
             m_displayServerType = X11UserDisplayServerType;
-            m_terminalId = VirtualTerminal::fetchAvailableVt();
+            m_terminalId = fetchAvailableVt();
         } else if (displayServerType == QStringLiteral("wayland")) {
             m_displayServerType = WaylandDisplayServerType;
-            m_terminalId = VirtualTerminal::fetchAvailableVt();
+            m_terminalId = fetchAvailableVt();
         } else {
             if (displayServerType != QLatin1String("x11")) {
                 qWarning("\"%s\" is an invalid value for General.DisplayServer: fall back to \"x11\"",