Support logging direct to journald, if enabled.

Instead of merely intercepting logging output from stdout/stderr from the
journal side of started processes, this has the advantage of meaning that the
origin process name will be correct.

fprintf won't work, because if a process starts children (like e.g. a
homescreen does), then their stdout/stderr are merged into their parent, and
journal has no way of differentiating the origin.

We are also able to store information about the context of logging, which might
be useful in post-mortem cases.

[ChangeLog][Platform Specific Changes][Linux] Systems with systemd may now pass
-journald to configure to send logging output to journald. Logging will still be
sent to stderr for interactive applications (run from a tty) or with
QT_NO_JOURNALD_LOG set to a non-empty value.

Change-Id: Ib260cec1ea87390bf44f267d217d795583407d00
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 48 insertions, 0 deletions

diff --git a/src/corelib/global/qlogging.cpp b/src/corelib/global/qlogging.cpp
index 076582373e..23d046acf0 100644
--- a/src/corelib/global/qlogging.cpp
+++ b/src/corelib/global/qlogging.cpp
@@ -63,6 +63,11 @@
 #include <android/log.h>
 #endif
 
+#if defined(QT_USE_JOURNALD) && !defined(QT_BOOTSTRAPPED)
+# include <systemd/sd-journal.h>
+# include <unistd.h>
+#endif
+
 #include <stdio.h>
 
 QT_BEGIN_NAMESPACE
@@ -866,6 +871,37 @@ Q_CORE_EXPORT QtMsgHandler qInstallMsgHandler(QtMsgHandler);
 static QtMsgHandler msgHandler = 0;                // pointer to debug handler (without context)
 static QtMessageHandler messageHandler = 0;         // pointer to debug handler (with context)
 
+#if defined(QT_USE_JOURNALD) && !defined(QT_BOOTSTRAPPED)
+static void systemd_default_message_handler(QtMsgType type,
+                                            const QMessageLogContext &context,
+                                            const QString &message)
+{
+    int priority = LOG_INFO; // Informational
+    switch (type) {
+    case QtDebugMsg:
+        priority = LOG_DEBUG; // Debug-level messages
+        break;
+    case QtWarningMsg:
+        priority = LOG_WARNING; // Warning conditions
+        break;
+    case QtCriticalMsg:
+        priority = LOG_CRIT; // Critical conditions
+        break;
+    case QtFatalMsg:
+        priority = LOG_ALERT; // Action must be taken immediately
+        break;
+    }
+
+    char filebuf[PATH_MAX + sizeof("CODE_FILE=")];
+    snprintf(filebuf, sizeof(filebuf), "CODE_FILE=%s", context.file ? context.file : "unknown");
+
+    char linebuf[20];
+    snprintf(linebuf, sizeof(linebuf), "CODE_LINE=%d", context.line);
+
+    sd_journal_print_with_location(priority, filebuf, linebuf, context.function ? context.function : "unknown", "%s", message.toUtf8().constData());
+}
+#endif
+
 #ifdef Q_OS_ANDROID
 static void android_default_message_handler(QtMsgType type,
                                   const QMessageLogContext &context,
@@ -902,6 +938,18 @@ static void qDefaultMessageHandler(QtMsgType type, const QMessageLogContext &con
 
 #if defined(QT_USE_SLOG2)
     slog2_default_handler(type, logMessage.toLocal8Bit().constData());
+#elif defined(QT_USE_JOURNALD) && !defined(QT_BOOTSTRAPPED)
+    // We use isatty to catch the obvious case of someone running something interactively.
+    // We also support an environment variable for Qt Creator use, or more complicated cases like subprocesses.
+    static bool logToConsole = isatty(fileno(stdin)) || !qEnvironmentVariableIsEmpty("QT_NO_JOURNALD_LOG");
+    if (Q_LIKELY(!logToConsole)) {
+        // remove trailing \n, systemd appears to want them newline-less
+        logMessage.chop(1);
+        systemd_default_message_handler(type, context, logMessage);
+    } else {
+        fprintf(stderr, "%s", logMessage.toUtf8().constData());
+        fflush(stderr);
+    }
 #elif defined(Q_OS_ANDROID)
     static bool logToAndroid = qEnvironmentVariableIsEmpty("QT_ANDROID_PLAIN_LOG");
     if (logToAndroid) {