fix: add X connection monitoring for session logout

[mhduiy]

Added XCB dependency and implemented X server connection monitoring to detect when the X server disconnects. This ensures the session properly logs out when the X server connection is lost, preventing orphaned sessions.

1. Added libxcb1-dev to Build-Depends in debian/control
2. Added XCB pkg-config check and linking in CMakeLists.txt
3. Implemented watchXConnection() method that establishes an XCB connection and monitors the file descriptor using QSocketNotifier
4. When X connection errors are detected, the session automatically triggers logout to clean up resources
5. Only activates on X11 displays, not Wayland

This fix addresses cases where X server crashes or disconnects unexpectedly, leaving the session manager running without a display server.

fix: 添加X连接监控以实现会话登出

添加XCB依赖并实现X服务器连接监控，以检测X服务器断开连接的情况。这确保当X
服务器连接丢失时会话能正确登出，防止出现孤儿会话。

1. 在debian/control的Build-Depends中添加libxcb1-dev
2. 在CMakeLists.txt中添加XCB pkg-config检查和链接
3. 实现watchXConnection()方法，使用XCB建立连接并通过QSocketNotifier监控 文件描述符
4. 当检测到X连接错误时，会话自动触发登出以清理资源
5. 仅在X11显示环境下激活，Wayland环境下不启用

此修复解决了X服务器崩溃或意外断开连接时，会话管理器在没有显示服务器的情
况下继续运行的问题。

PMS: BUG-353461

Summary by Sourcery

Monitor the X server connection in the session manager and trigger logout when the X connection is lost on X11 displays.

Bug Fixes:

• Ensure the session manager logs out automatically when the X server disconnects or crashes to avoid orphaned sessions on X11.

Enhancements:

• Introduce X connection monitoring in SessionManager using a socket notifier, enabled only for non-Wayland displays.

Build:

• Add XCB as a pkg-config dependency and link it into the dde-session target.
• Add libxcb development dependency to the Debian packaging metadata.

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mhduiy

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• debian/deepin/OWNERS

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[sourcery-ai]

Reviewer's Guide

Implements X11 connection monitoring in the session manager using libxcb and QSocketNotifier so that when the X server disconnects, the session manager detects the error and triggers a logout, with corresponding build system and packaging updates for the new XCB dependency.

Sequence diagram for X server disconnect triggering session logout

sequenceDiagram
    participant SessionManager
    participant XCBConnection
    participant QSocketNotifier
    participant XServer

    SessionManager->>SessionManager: init()
    alt not Utils_IS_WAYLAND_DISPLAY
        SessionManager->>SessionManager: watchXConnection()
        SessionManager->>XCBConnection: xcb_connect()
        XCBConnection-->>SessionManager: connection handle and fd
        SessionManager->>QSocketNotifier: create with fd and Read
        SessionManager->>QSocketNotifier: connect activated signal
    end

    XServer--x XCBConnection: disconnect or crash
    XCBConnection-->>QSocketNotifier: fd becomes readable
    QSocketNotifier-->>SessionManager: activated(fd, Read)

    SessionManager->>XCBConnection: xcb_poll_for_event() loop
    SessionManager->>XCBConnection: xcb_connection_has_error()
    alt connection has error
        SessionManager->>QSocketNotifier: setEnabled(false)
        SessionManager->>XCBConnection: xcb_disconnect()
        SessionManager->>SessionManager: doLogout()
    else no error
        SessionManager-->>QSocketNotifier: continue monitoring
    end

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Updated class diagram for SessionManager with X connection monitoring

classDiagram
    class SessionManager {
        +init() void
        +watchXConnection() void
        +handleOSSignal() void
        +shutdown(bool force) void
        +reboot(bool force) void
        +setDPMSMode(bool on) void
        +doLogout() void
    }

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File-Level Changes

Change	Details	Files
Add X11 connection monitoring in SessionManager to trigger logout when the X server disconnects.	Introduce watchXConnection() in SessionManager that opens an xcb connection and monitors its file descriptor with QSocketNotifier On QSocketNotifier activation, drain pending X events with xcb_poll_for_event and check xcb_connection_has_error When an X connection error is detected, disable the notifier, disconnect from X, and call doLogout() Invoke watchXConnection() during SessionManager::init() only when not running on a Wayland display	src/dde-session/impl/sessionmanager.cpp src/dde-session/impl/sessionmanager.h
Wire in the new XCB dependency into the build and packaging configuration.	Add pkg_check_modules(XCB REQUIRED IMPORTED_TARGET xcb) and link PkgConfig::XCB into the dde-session target Update SPDX copyright header year range in dde-session CMakeLists Declare libxcb1-dev as a build dependency in debian/control	src/dde-session/CMakeLists.txt debian/control

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[deepin-ci-robot]

deepin pr auto review

这段代码主要实现了在非 Wayland 环境下监听 X Server 连接状态的功能，当 X Server 连接断开时触发登出操作。以下是对该代码的详细审查和改进建议：

1. 语法与逻辑审查

• 逻辑正确性：
  • xcb_connect(nullptr, nullptr)：逻辑正确。传入 nullptr 会使用 DISPLAY 环境变量，符合预期。
  • xcb_poll_for_event 循环：逻辑正确。在 Qt 事件循环触发 Socket 可读时，必须排空 XCB 的队列，否则 Socket 会一直处于可读状态导致死循环（Busy Loop）。
  • xcb_connection_has_error 检查：逻辑正确。这是检测 X Server 断开的标准方法。
• 语法：
  • C++ 语法和 Qt 信号槽连接语法均无误。

2. 代码质量与规范

• 头文件包含：
  • sessionmanager.cpp 中增加了 #include <QSocketNotifier> 和 #include <xcb/xcb.h>，这是必要的。
• 版权年份：
  • CMakeLists.txt 中的版权年份从 2023 修改为 2023 - 2026。这通常是合理的，表示维护周期的预期，但需确认是否符合项目规范。
• 内存管理：
  • new QSocketNotifier(...) 创建在堆上，且指定了 this 作为父对象。Qt 的对象树机制会确保在 SessionManager 析构时自动删除该对象，符合 Qt 内存管理规范。
• 注释：
  • // 排空所有待处理事件 和 // 若连接已断开则触发登出 注释清晰，有助于理解代码意图。

3. 代码性能

• 事件排空效率：
  • while ((ev = xcb_poll_for_event(conn)) != nullptr) 循环是必要的。虽然看起来是在循环处理，但它是在消耗掉缓冲区中的数据，防止 QSocketNotifier 频繁触发，实际上避免了性能浪费。
• 资源占用：
  • 增加了一个 XCB 连接和一个文件描述符监听，资源开销极小，对性能影响可忽略不计。

4. 代码安全

• 潜在的内存泄漏风险：

  • 问题点：在 watchXConnection 函数中，如果 xcb_connection_has_error(conn) 检测到错误，代码执行了 xcb_disconnect(conn) 并返回。但是，之前创建的 notifier 对象（new QSocketNotifier）并没有被显式删除或禁用。
  • 后果：虽然 notifier 的父对象是 this，最终会被析构，但在 watchXConnection 返回后，该 notifier 对象仍然存活且处于启用状态。如果此时 fd 变为可读（由于连接断开或系统行为），activated 信号可能会被触发，导致访问已断开或无效的 conn 指针，引发 段错误（Segmentation Fault） 或未定义行为。
  • 改进建议：在连接失败或断开时，应确保 notifier 被禁用或删除。

• 竞态条件：

  • 问题点：xcb_connect 和 xcb_get_file_descriptor 之间，或者 xcb_poll_for_event 和 xcb_connection_has_error 之间，理论上存在极微小的竞态窗口。但在实际应用中，X Server 的断开通常是相对"慢"的事件，且 xcb_poll_for_event 本身会检查错误，这种风险在单线程 Qt 事件循环模型下较低。
  • 改进建议：保持现状即可，现有逻辑已经足够健壮。

• 空指针解引用：

  • 代码中检查了 xcb_connection_has_error，确保 conn 有效后才使用 xcb_get_file_descriptor，安全性良好。

5. 改进后的代码建议

针对上述提到的安全风险（主要是 notifier 对象的生命周期管理），建议对 watchXConnection 进行如下微调：

void SessionManager::watchXConnection()
{
    xcb_connection_t *conn = xcb_connect(nullptr, nullptr);
    if (xcb_connection_has_error(conn) || !conn) {
        qWarning() << "watchXConnection: failed to connect to X server";
        if (conn) xcb_disconnect(conn);
        return;
    }

    int fd = xcb_get_file_descriptor(conn);
    auto *notifier = new QSocketNotifier(fd, QSocketNotifier::Read, this);
    
    // 使用 trackConnection 确保在 lambda 中安全捕获
    // 使用 QPointer 防止悬垂指针（虽然 notifier 父对象是 this，但为了更严谨的代码习惯）
    QPointer<QSocketNotifier> safeNotifier = notifier;

    connect(notifier, &QSocketNotifier::activated, this, [=]() {
        // 如果 notifier 已经被标记为删除或无效，直接返回
        if (!safeNotifier) return;

        // 排空所有待处理事件
        xcb_generic_event_t *ev;
        while ((ev = xcb_poll_for_event(conn)) != nullptr) {
            free(ev);
        }

        // 若连接已断开则触发登出
        if (xcb_connection_has_error(conn)) {
            qWarning() << "X connection closed, logging out";
            // 立即禁用 notifier 防止重复触发
            if (safeNotifier) {
                safeNotifier->setEnabled(false);
                safeNotifier->deleteLater(); // 安全地标记删除
            }
            xcb_disconnect(conn);
            doLogout();
        }
    });
}

总结

这段代码整体质量不错，逻辑清晰，能够解决检测 X Server 断开的问题。主要需要改进的地方是在错误处理路径上加强对 QSocketNotifier 对象的管理，防止在连接失效后继续触发回调导致访问无效内存。此外，依赖项的添加是合理且必要的。

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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