[sensord] Use pipe to trasfer posix signals to mainloop

Sensord does async signal unsafe operations from posix signal handlers.

Use pipe and QSocketNotifier() to transfer async signals from signal
handler context to qt mainloop.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

sensord/main.cpp

@@ -1,5 +1,3 @@
-
-
 /**
    @file main.cpp
    @brief Sensord initiation point
@@ -32,13 +30,16 @@
 
 #include <QtCore/QCoreApplication>
 #include <QtCore/QDebug>
+#include <QSocketNotifier>
 
 #include <systemd/sd-daemon.h>
 
+#include <unistd.h>
 #include <signal.h>
 #include <iostream>
 #include <errno.h>
 #include <unistd.h>
+#include <fcntl.h>
 
 #include "config.h"
 #include "sensormanager.h"
@@ -81,11 +82,14 @@ void printUsage();
 void signalUSR1(int param)
 {
     Q_UNUSED(param);
-
-    logLevel = QtMsgType(logLevel + 1);
-    if (logLevel > QtSystemMsg)
+    if (logLevel != QtDebugMsg) {
         logLevel = QtDebugMsg;
-    qDebug() << "New debugging level: " << logLevel;
+        sensordLogW() << "Debug logging enabled";
+    }
+    else {
+        logLevel = QtWarningMsg;
+        sensordLogW() << "Debug logging disabled";
+    }
 }
 
 void signalUSR2(int param)
@@ -105,10 +109,92 @@ void signalUSR2(int param)
 
 void signalINT(int param)
 {
-    Q_UNUSED(param);
+    signal(param, SIG_DFL);
+    sensordLogD() << "Terminating ...";
     QCoreApplication::exit(0);
 }
 
+class SignalNotifier : public QObject
+{
+public:
+     SignalNotifier();
+     ~SignalNotifier();
+private slots:
+     void handleSignalInput(int socket);
+private:
+     static void handleAsyncSignal(int sig);
+     QSocketNotifier *m_socketNotifier;
+     static int s_pipe[2];
+     static const int s_signals[];
+};
+
+SignalNotifier::SignalNotifier()
+    : m_socketNotifier(0)
+{
+    sensordLogD() << "Setup async signal handlers";
+    if (pipe2(s_pipe, O_CLOEXEC) == -1) {
+        qFatal("Failed to create a pipe for signal passunc");
+    }
+    m_socketNotifier = new QSocketNotifier(s_pipe[0], QSocketNotifier::Read, this);
+    connect(m_socketNotifier, &QSocketNotifier::activated,
+            this, &SignalNotifier::handleSignalInput);
+    struct sigaction action;
+    memset(&action, 0, sizeof action);
+    action.sa_handler = handleAsyncSignal;
+    sigemptyset(&action.sa_mask);
+    action.sa_flags = SA_RESTART;
+    for (size_t i = 0; s_signals[i] != -1; ++i )
+        sigaction(s_signals[i], &action, 0);
+}
+
+SignalNotifier::~SignalNotifier()
+{
+    sensordLogD() << "Reset async signal handlers";
+    for (size_t i = 0; s_signals[i] != -1; ++i )
+        signal(s_signals[i], SIG_DFL);
+    delete m_socketNotifier; m_socketNotifier = 0;
+    close(s_pipe[1]), s_pipe[1] = -1;
+    close(s_pipe[0]), s_pipe[0] = -1;
+}
+
+void SignalNotifier::handleAsyncSignal(int sig)
+{
+    /* Can call only async-signal safe functions! */
+    if (write(s_pipe[1], &sig, sizeof sig) == -1) {
+        _exit(EXIT_FAILURE);
+    }
+}
+
+void SignalNotifier::handleSignalInput(int socket)
+{
+    Q_UNUSED(socket);
+    int sig = SIGTERM;
+    uint64_t tmp = 0;
+    if (read(s_pipe[0], &sig, sizeof sig) == -1) {
+        // dontcare
+    }
+    sensordLogD() << "Caught async signal"  << strsignal(sig);
+    switch (sig) {
+    case SIGINT:
+    case SIGTERM:
+        signalINT(sig);
+        break;
+    case SIGUSR1:
+        signalUSR1(sig);
+        break;
+    case SIGUSR2:
+        signalUSR2(sig);
+        break;
+    };
+}
+
+int SignalNotifier::s_pipe[2] = { -1, -1 };
+
+const int SignalNotifier::s_signals[] =
+{
+    SIGINT, SIGTERM, SIGUSR1, SIGUSR2, -1
+};
+
 int main(int argc, char *argv[])
 {
     previousMessageHandler = qInstallMessageHandler(messageOutput);
@@ -151,10 +237,6 @@ int main(int argc, char *argv[])
         }
     }
 
-    signal(SIGUSR1, signalUSR1);
-    signal(SIGUSR2, signalUSR2);
-    signal(SIGINT, signalINT);
-
     if (parser.createDaemon())
     {
         fflush(0);
@@ -200,7 +282,10 @@ int main(int argc, char *argv[])
         sd_notify(0, "READY=1");
     }
 
+    SignalNotifier *signalNotifier = new SignalNotifier();
     int ret = app.exec();
+    delete signalNotifier; signalNotifier = 0;
+
     sensordLogD() << "Exiting...";
     Config::close();
     return ret;