core/command: allow qs log to retrieve logs of dead instances

If no live instances are found matching the current config, the
youngest dead instance will be used instead.

Author: outfoxxed

src/core/paths.cpp

@@ -262,7 +262,7 @@ void QsPaths::createLock() {
 	}
 }
 
-bool QsPaths::checkLock(const QString& path, InstanceLockInfo* info) {
+bool QsPaths::checkLock(const QString& path, InstanceLockInfo* info, bool allowDead) {
 	auto file = QFile(QDir(path).filePath("instance.lock"));
 	if (!file.open(QFile::ReadOnly)) return false;
 
@@ -275,10 +275,12 @@ bool QsPaths::checkLock(const QString& path, InstanceLockInfo* info) {
 	};
 
 	fcntl(file.handle(), F_GETLK, &lock); // NOLINT
-	if (lock.l_type == F_UNLCK) return false;
+	auto isLocked = lock.l_type != F_UNLCK;
+
+	if (!isLocked && !allowDead) return false;
 
 	if (info) {
-		info->pid = lock.l_pid;
+		info->pid = isLocked ? lock.l_pid : -1;
 
 		auto stream = QDataStream(&file);
 		stream >> info->instance;
@@ -287,7 +289,7 @@ bool QsPaths::checkLock(const QString& path, InstanceLockInfo* info) {
 	return true;
 }
 
-QVector<InstanceLockInfo> QsPaths::collectInstances(const QString& path) {
+QVector<InstanceLockInfo> QsPaths::collectInstances(const QString& path, bool fallbackDead) {
 	qCDebug(logPaths) << "Collecting instances from" << path;
 	auto instances = QVector<InstanceLockInfo>();
 	auto dir = QDir(path);
@@ -296,13 +298,18 @@ QVector<InstanceLockInfo> QsPaths::collectInstances(const QString& path) {
 	for (auto& entry: dir.entryList(QDir::Dirs | QDir::NoDotAndDotDot)) {
 		auto path = dir.filePath(entry);
 
-		if (QsPaths::checkLock(path, &info)) {
-			qCDebug(logPaths).nospace() << "Found live instance " << info.instance.instanceId << " (pid "
+		if (QsPaths::checkLock(path, &info, fallbackDead)) {
+			if (fallbackDead && info.pid != -1) {
+				fallbackDead = false;
+				instances.clear();
+			}
+
+			qCDebug(logPaths).nospace() << "Found instance " << info.instance.instanceId << " (pid "
 			                            << info.pid << ") at " << path;
 
 			instances.push_back(info);
 		} else {
-			qCDebug(logPaths) << "Skipped dead instance at" << path;
+			qCDebug(logPaths) << "Skipped potential instance at" << path;
 		}
 	}
 

src/core/paths.hpp

@@ -20,8 +20,9 @@ class QsPaths {
 	static QDir crashDir(const QString& id);
 	static QString basePath(const QString& id);
 	static QString ipcPath(const QString& id);
-	static bool checkLock(const QString& path, InstanceLockInfo* info = nullptr);
-	static QVector<InstanceLockInfo> collectInstances(const QString& path);
+	static bool
+	checkLock(const QString& path, InstanceLockInfo* info = nullptr, bool allowDead = false);
+	static QVector<InstanceLockInfo> collectInstances(const QString& path, bool fallbackDead = false);
 
 	QDir* cacheDir();
 	QDir* baseRunDir();

src/launch/command.cpp

@@ -109,21 +109,21 @@ void sortInstances(QVector<InstanceLockInfo>& list, bool newestFirst) {
 	});
 };
 
-int selectInstance(CommandState& cmd, InstanceLockInfo* instance) {
+int selectInstance(CommandState& cmd, InstanceLockInfo* instance, bool deadFallback = false) {
 	auto* basePath = QsPaths::instance()->baseRunDir();
 	if (!basePath) return -1;
 
 	QString path;
 
 	if (cmd.instance.pid != -1) {
 		path = QDir(basePath->filePath("by-pid")).filePath(QString::number(cmd.instance.pid));
-		if (!QsPaths::checkLock(path, instance)) {
+		if (!QsPaths::checkLock(path, instance, deadFallback)) {
 			qCInfo(logBare) << "No instance found for pid" << cmd.instance.pid;
 			return -1;
 		}
 	} else if (!cmd.instance.id->isEmpty()) {
 		path = basePath->filePath("by-pid");
-		auto instances = QsPaths::collectInstances(path);
+		auto instances = QsPaths::collectInstances(path, deadFallback);
 
 		instances.removeIf([&](const InstanceLockInfo& info) {
 			return !info.instance.instanceId.startsWith(*cmd.instance.id);
@@ -136,7 +136,8 @@ int selectInstance(CommandState& cmd, InstanceLockInfo* instance) {
 			qCInfo(logBare) << "More than one instance starts with" << *cmd.instance.id;
 
 			for (auto& instance: instances) {
-				qCInfo(logBare).noquote() << " -" << instance.instance.instanceId;
+				qCInfo(logBare).noquote() << " -" << instance.instance.instanceId
+				                          << (instance.pid == -1 ? " (dead)" : "");
 			}
 
 			return -1;
@@ -153,8 +154,11 @@ int selectInstance(CommandState& cmd, InstanceLockInfo* instance) {
 
 		path = QDir(basePath->filePath("by-path")).filePath(pathId);
 
-		auto instances = QsPaths::collectInstances(path);
-		sortInstances(instances, cmd.config.newest);
+		auto instances = QsPaths::collectInstances(path, deadFallback);
+		sortInstances(
+		    instances,
+		    cmd.config.newest || (!instances.empty() && instances.first().pid == -1)
+		);
 
 		if (instances.isEmpty()) {
 			qCInfo(logBare) << "No running instances for" << configFilePath;
@@ -172,7 +176,7 @@ int readLogFile(CommandState& cmd) {
 
 	if (path.isEmpty()) {
 		InstanceLockInfo instance;
-		auto r = selectInstance(cmd, &instance);
+		auto r = selectInstance(cmd, &instance, true);
 		if (r != 0) return r;
 
 		path = QDir(QsPaths::basePath(instance.instance.instanceId)).filePath("log.qslog");