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本文是一个简单的demo，基于开源qemu2.8，演示了如何添加qmp和hmp接口，同时实现从hmp命令打通到底层外设函数的通道，此处为i6300esb ¹的测试函数。注意：此处的调用路径仅供演示，实际上并不合理，会出现一些告警，而在实际云平台编译环境中，rpmbuild编译链接，是不允许的warning存在的，若想添加接口，还是应该参考已有的接口走回调函数的方式，或者使用object property方式注册处理函数。

1.添加qmp接口

1.1.添加接口原型

在qapi-schema.json末尾添加接口原型daxiatou-watchdog-set-timeout

{ 'command': 'daxiatou-watchdog-set-timeout' ,'data':{'*time':'int'}}

int对应的int64_t，正常应该是在这一步先执行编译，再进行下一步，此处节省篇幅，一步搞定，详细用法，查阅qemu官方文档《writing-qmp-commands.txt》

1.2.添加接口函数体

/*qmp.c*/void qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp){if (has_time){printf("%ld\n", time);}else{ printf("Please input time\n"); }}

1.3.测试接口

1.3.1.启动虚拟机

qemu启动脚本需要增加以下参数

-chardev socket,id=qmp,port=4444,host=localhost,server  -mon chardev=qmp,mode=control,pretty=on

这样，qemu monitor就可以接受qmp协议报文，随后另起一个shell，使用如下命令连接qemu monitor

[root@localhost qemu-2.8.0]# telnet localhost 4444Trying ::1...Connected to localhost.Escape character is '^]'.{"QMP": {"version": {"qemu": {"micro": 0,"minor": 8,"major": 2},"package": ""},"capabilities": []}}

1.3.2.执行测试命令

打开command mode

{ "execute": "qmp_capabilities" }

执行带参数命令

{ "execute": "daxiatou-watchdog-set-timeout", "arguments": { "time": 1000 } }

查看qemu端的效果

(qemu) 1000

执行不带参数的命令

{ "execute": "daxiatou-watchdog-set-timeout"}

查看qemu端的效果

(qemu) Please input time

1.3.3.查看编译后自动生成的代码

[root@localhost qemu-2.8.0]# grep -rn 'daxiatou'qapi-types.h:1936:typedef struct q_obj_daxiatou_watchdog_set_timeout_arg q_obj_daxiatou_watchdog_set_timeout_arg;qapi-types.h:5596:struct q_obj_daxiatou_watchdog_set_timeout_arg {qapi-visit.c:15673:void visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(Visitor *v, q_obj_daxiatou_watchdog_set_timeout_arg *obj, Error **errp)qapi-visit.h:986:void visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(Visitor *v, q_obj_daxiatou_watchdog_set_timeout_arg *obj, Error **errp);Binary file qmp.o matchesqmp-commands.h:97:void qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp);qmp-commands.h:98:void qmp_marshal_daxiatou_watchdog_set_timeout(QDict *args, QObject **ret, Error **errp);qmp.c:719:void qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp)Binary file qemu-nbd matchesqmp-introspect.c:91:    "{\"arg-type\": \"67\", \"meta-type\": \"command\", \"name\": \"daxiatou-watchdog-set-timeout\", \"ret-type\": \"17\"}, "Binary file x86_64-softmmu/qemu-system-x86_64 matchesqmp-marshal.c:1286:void qmp_marshal_daxiatou_watchdog_set_timeout(QDict *args, QObject **ret, Error **errp)qmp-marshal.c:1290:    q_obj_daxiatou_watchdog_set_timeout_arg arg = {0};qmp-marshal.c:1297:    visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(v, &arg, &err);qmp-marshal.c:1306:    qmp_daxiatou_watchdog_set_timeout(arg.has_time, arg.time, &err);qmp-marshal.c:1313:    visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(v, &arg, NULL);qmp-marshal.c:6147:    qmp_register_command("daxiatou-watchdog-set-timeout", qmp_marshal_daxiatou_watchdog_set_timeout, QCO_NO_OPTIONS);Binary file qapi-visit.o matchesBinary file qemu-io matchesBinary file qmp-introspect.o matchesBinary file qemu-img matchesBinary file qmp-marshal.o matchesqapi-schema.json:4779:{ 'command': 'daxiatou-watchdog-set-timeout' ,'data':{'*time':'int'}}Binary file i386-softmmu/qemu-system-i386 matchesBinary file libqemuutil.a matchesBinary file qemu-ga matches

会生成很多东西，绝大多数不用理会，主要看这两个地方，

/* qmp-marshal.c*/void qmp_marshal_daxiatou_watchdog_set_timeout(QDict *args, QObject **ret, Error **errp){Error *err = NULL;Visitor *v;q_obj_daxiatou_watchdog_set_timeout_arg arg = {0};v = qobject_input_visitor_new(QOBJECT(args), true);visit_start_struct(v, NULL, NULL, 0, &err);if (err) {goto out;}visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(v, &arg, &err);if (!err) {visit_check_struct(v, &err);}visit_end_struct(v, NULL);if (err) {goto out;}qmp_daxiatou_watchdog_set_timeout(arg.has_time, arg.time, &err);out:error_propagate(errp, err);visit_free(v);v = qapi_dealloc_visitor_new();visit_start_struct(v, NULL, NULL, 0, NULL);visit_type_q_obj_daxiatou_watchdog_set_timeout_arg_members(v, &arg, NULL);visit_end_struct(v, NULL);visit_free(v);}qmp_register_command("daxiatou-watchdog-set-timeout", qmp_marshal_daxiatou_watchdog_set_timeout, QCO_NO_OPTIONS);

qmp_register_command会注册一个qmp命令行"daxiatou-watchdog-set-timeout"，上一节中使用到的命令，就是这里注册的，相关联的函数qmp_marshal_daxiatou_watchdog_set_timeout，会调用1.2节里面添加的自定义函数qmp_daxiatou_watchdog_set_timeout，这种设计方式，可以让’qmp_'开头的函数在另外的文件内单独定义函数体，而不影响框架自动生成的代码。

2.添加hmp命令

HMP就是humanmonitor,在qemu monitor敲的命令就属于这一类，这是面向用户直接使用的命令

2.1.添加命令行

/*hmp-commands.hx */{.name       = "daxiatou-watchdog-set-timeout",.args_type  = "time:i?",.params     = "daxiatou2 [time]",.help       = "set timeout of i6300esb",.cmd        = hmp_daxiatou_watchdog_set_timeout,},STEXI@item daxiatou-watchdog-set-timeout @var{message}Print message to the standard outputETEXI

第一个参数.name代表命令本身的名字

第三个参数.params的作用是显示使用方式，如下所示

(qemu) help daxiatou-watchdog-set-timeoutdaxiatou-watchdog-set-timeout daxiatou2 [time] -- set timeout of i6300esb

2.2.添加调用函数

添加函数声明

/*hmp.h*/void hmp_daxiatou_watchdog_set_timeout(Monitor *mon, const QDict *qdict);

添加函数体

/*hmp.c*/void hmp_daxiatou_watchdog_set_timeout(Monitor *mon, const QDict *qdict){int time = qdict_get_try_int(qdict, "time",30);Error *err = NULL;qmp_daxiatou_watchdog_set_timeout(!!time, time, &err);if (err) {monitor_printf(mon, "%s\n", error_get_pretty(err));error_free(err);return;}}

查看运行效果

(qemu) daxiatou-watchdog-set-timeout 100100(qemu) daxiatou-watchdog-set-timeout30

3.增加外设接口

此处希望通过命令行，能直接操作i6300esb的相关变量，首先，需要让命令行的函数感知到设备的存在

3.1.在设备代码文件中增加测试函数

/*code 3-1*//*hw/watchdog/wdt_i6300esb.c*/static void i6300esb_test(void){i6300esb_debug("daxiatou-i6300esb\n");}

在命令行中直接增加以上函数i6300esb_test()的调用

/*code 3-2 qmp.c*/void qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp){if (has_time){printf("%ld\n", time);i6300esb_test();}else{ printf("Please input time\n"); }}

编译失败

[root@localhost qemu-2.8.0]# make -j4CHK version_gen.hCC      hw/watchdog/wdt_i6300esb.ohw/watchdog/wdt_i6300esb.c:467:13: warning: ‘i6300esb_test’ defined but not used [-Wunused-function]static void i6300esb_test(void)^LINK    i386-softmmu/qemu-system-i386LINK    x86_64-softmmu/qemu-system-x86_64../qmp.o: In function `qmp_daxiatou_watchdog_set_timeout':/home/qemu-2.8.0/qmp.c:741: undefined reference to `i6300esb_test'collect2: error: ld returned 1 exit statusmake[1]: *** [qemu-system-i386] Error 1make: *** [subdir-i386-softmmu] Error 2make: *** Waiting for unfinished jobs....../qmp.o: In function `qmp_daxiatou_watchdog_set_timeout':/home/qemu-2.8.0/qmp.c:741: undefined reference to `i6300esb_test'collect2: error: ld returned 1 exit statusmake[1]: *** [qemu-system-x86_64] Error 1make: *** [subdir-x86_64-softmmu] Error 2

说明，这两个c文件无法直接感知对方的存在，中间走了很多层，现在需要借助qemu自带的接口，一级级寻找能够操作到设备的路线

//qmp.cvoid qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp){const char *id = "watchdog0";Error *err = NULL;qmp_device_del(id, &err);if (has_time){printf("%ld\n", time);//i6300esb_test();}else{ printf("Please input time\n"); }}

可以成功调用删除函数，，但是qmp_device_del内部的语句，无法被识别，因此，只能模仿qmp_device_del函数，移动到qdev-monitor.c中定义，顺着这条路往下跟

3.2.在qdev中调用pci函数

//qdev-monitor.cvoid qmp_daxiatou_watchdog_set_timeout(bool has_time, int64_t time, Error **errp){const char *id = "watchdog0";Error *err = NULL;DeviceState *dev = find_device_state(id, errp);PCIDevice *pci_dev = (PCIDevice *)dev;//PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(pci_dev);qdev_daxiatou_watchdog_set_timeout(dev,errp);//    qmp_device_del(id, &err);if (has_time){printf("%ld\n", time);//i6300esb_test();}else{ printf("Please input time\n"); }}

//include/hw/qdev-core.hvoid qdev_daxiatou_watchdog_set_timeout(DeviceState *dev, Error **errp);

//hw/core/qdev.cvoid qdev_daxiatou_watchdog_set_timeout(DeviceState *dev, Error **errp){PCIDevice *pci_dev = (PCIDevice *)dev;DeviceClass *dc = DEVICE_GET_CLASS(dev);printf("daxiatou = %p\n",dc);pci_daxiatou();}

//include/hw/pci/pci.hvoid pci_daxiatou( );

//hw/pci/pci.cvoid pci_daxiatou( ){printf("daxiatou-pci-test\n");}

说明在以上代码块中定义函数，qdev可以调用，下一步就是要在pci的函数里面，调用到具体设备的函数了，此处是i6300esb，测试效果如下，

(qemu) daxiatou-watchdog-set-timeoutdaxiatou = 0x558e01bdb090daxiatou-pci-test30

3.3.在pci中调用设备函数

和3.2节中的方式一样，直接调用i6300esb_test函数

//hw/pci/pci.c//extern void i6300esb_test(void);如果不添加这个，会告警void pci_daxiatou(){printf("daxiatou-pci-test\n");i6300esb_test();}

编译会产生告警，这是因为没有在头文件中声明，此处没有同名的头文件，先暂时忽略告警，强行安装运行

[root@localhost qemu-2.8.0]# make -j4CHK version_gen.hCC      hw/watchdog/wdt_i6300esb.ohw/watchdog/wdt_i6300esb.c:467:6: warning: no previous prototype for ‘i6300esb_test’ [-Wmissing-prototypes]void i6300esb_test(void)^LINK    x86_64-softmmu/qemu-system-x86_64LINK    i386-softmmu/qemu-system-i386

成功调用到设备源代码中的函数

(qemu) daxiatou-watchdog-set-timeoutdaxiatou = 0x55b4dff00090daxiatou-pci-testi6300esb: i6300esb_test: daxiatou-i6300esb30

reference

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1. qemu intel i6300esb watchdog虚拟外设分析 ↩︎