CTF: Fix minor problems in the implementation

- Check if trace location is writable
- Call fclose only if file is opened
- Convert metadata to QByteArray in one place.
- Add constraint to array operator.

Change-Id: Id01998fe8e754dab7a4b7d8ce1361ac822d01390
Reviewed-by: Antti Määttä <antti.maatta@qt.io>
(cherry picked from commit 1d0da1d683cc71ea14cfd85f5e9aa227d7f75762)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/tracing/qctflib.cpp

@@ -16,6 +16,8 @@
 
 QT_BEGIN_NAMESPACE
 
+using namespace Qt::StringLiterals;
+
 Q_LOGGING_CATEGORY(lcDebugTrace, "qt.core.ctf");
 
 static const size_t packetHeaderSize = 24 + 6 * 8 + 4;
@@ -29,6 +31,7 @@ static const size_t traceMetadataSize = sizeof(traceMetadataTemplate);
 template <typename T>
 QByteArray &operator<<(QByteArray &arr, T val)
 {
+    static_assert(std::is_arithmetic_v<T>);
     arr.append((char *)&val, sizeof(val));
     return arr;
 }
@@ -55,19 +58,28 @@ QCtfLibImpl::QCtfLibImpl()
         qCWarning (lcDebugTrace) << "QTRACE_LOCATION not set";
         return;
     }
+
+    // Check if the location is writable
     FILE *file = nullptr;
-    file = fopen(qPrintable(location + QStringLiteral("/session.json")), "rb");
+    file = fopen(qPrintable(location + "/metadata"_L1), "w+b");
     if (!file) {
-        qCWarning (lcDebugTrace) << "unable to open session file: " << (location + QStringLiteral("/session.json"));
+        qCWarning (lcDebugTrace) << "Unable to write to location";
+        return;
+    }
+    fclose(file);
+
+    const QString filename = location + QStringLiteral("/session.json");
+    file = fopen(qPrintable(filename), "rb");
+    if (!file) {
+        qCWarning (lcDebugTrace) << "unable to open session file: " << filename;
         m_location = location;
         m_session.tracepoints.append(QStringLiteral("all"));
         m_session.name = QStringLiteral("default");
     } else {
-        QByteArray data;
         fseek(file, 0, SEEK_END);
         long pos = ftell(file);
         fseek(file, 0, SEEK_SET);
-        data.resize(pos);
+        QByteArray data(pos, Qt::Uninitialized);
         long size = (long)fread(data.data(), pos, 1, file);
         fclose(file);
         if (size != 1)
@@ -104,20 +116,23 @@ QCtfLibImpl::QCtfLibImpl()
 #else
     metadata.replace(QStringLiteral("$ENDIANNESS"), QStringLiteral("le"));
 #endif
-    writeMetadata(metadata.toUtf8(), true);
+    writeMetadata(metadata, true);
 
     m_timer.start();
 }
 
-void QCtfLibImpl::writeMetadata(const QByteArray &data, bool overwrite)
+void QCtfLibImpl::writeMetadata(const QString &metadata, bool overwrite)
 {
     FILE *file = nullptr;
-    file = fopen(qPrintable(m_location + QStringLiteral("/metadata")), overwrite ? "w+b": "ab");
+    file = fopen(qPrintable(m_location + "/metadata"_L1), overwrite ? "w+b": "ab");
     if (!file)
         return;
 
     if (!overwrite)
         fputs("\n", file);
+
+    // data contains zero at the end, hence size - 1.
+    const QByteArray data = metadata.toUtf8();
     fwrite(data.data(), data.size() - 1, 1, file);
     fclose(file);
 }
@@ -154,9 +169,9 @@ void QCtfLibImpl::writeCtfPacket(QCtfLibImpl::Channel &ch)
         fwrite(packet.data(), packet.size(), 1, file);
         ch.data.resize(packetSize - packet.size(), 0);
         fwrite(ch.data.data(), ch.data.size(), 1, file);
-    }
         fclose(file);
     }
+}
 
 QCtfLibImpl::~QCtfLibImpl()
 {
@@ -229,10 +244,10 @@ void QCtfLibImpl::doTracepoint(const QCtfTracePointEvent &point, const QByteArra
             }
             if (m_newAdditionalMetadata.size()) {
                 for (const QString &name : m_newAdditionalMetadata)
-                    writeMetadata(m_additionalMetadata[name]->metadata.toUtf8());
+                    writeMetadata(m_additionalMetadata[name]->metadata);
                 m_newAdditionalMetadata.clear();
             }
-            writeMetadata(priv->metadata.toUtf8());
+            writeMetadata(priv->metadata);
         }
         timestamp = m_timer.nsecsElapsed();
     }
@@ -254,6 +269,7 @@ void QCtfLibImpl::doTracepoint(const QCtfTracePointEvent &point, const QByteArra
         sprintf(ch.channelName, "%s/channel_%d", qPrintable(m_location), m_threadIndices[thread]);
         FILE *f = nullptr;
         f = fopen(ch.channelName, "wb");
+        if (f)
             fclose(f);
         ch.minTimestamp = ch.maxTimestamp = timestamp;
         ch.thread = thread;

src/corelib/tracing/qctflib_p.h

@@ -85,7 +85,7 @@ private:
     static QCtfLibImpl *s_instance;
     QHash<QString, QCtfTracePointPrivate *> m_eventPrivs;
     void updateMetadata(const QCtfTracePointEvent &point);
-    void writeMetadata(const QByteArray &data, bool overwrite = false);
+    void writeMetadata(const QString &metadata, bool overwrite = false);
     static void writeCtfPacket(Channel &ch);
 
     static constexpr QUuid s_TraceUuid = QUuid(0x3e589c95, 0xed11, 0xc159, 0x42, 0x02, 0x6a, 0x9b, 0x02, 0x00, 0x12, 0xac);