虚拟机配置中：

<channel type='unix'>

<target type='virtio' name='org.qemu.guest_agent.0'/>

<address type='virtio-serial' controller='0' bus='0' port='1'/>

</channel>

With qemu, if name is "org.qemu.guest_agent.0", then libvirt can interact with a guest agent installed in the guest, for actions such as guest shutdown or file system quiescing.

虚拟机启动命令行：

/usr/libexec/qemu-kvm

-chardev socket,id=charmonitor,fd=35,server,nowait

-mon chardev=charmonitor,id=monitor,mode=control

-chardev socket,id=charchannel0,fd=42,server,nowait

-device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0

启动虚拟机时libvirt会创建一个qemu monitor的unix socket和一个qemu agent的unix socket：

srwxrwxr-x 1 root root 0 Jan 11 16:13 /var/lib/libvirt/qemu/domain-28-Centos7/monitor.sock

srwxrwxr-x 1 qemu qemu 0 Jan 11 16:13 /var/lib/libvirt/qemu/channel/target/domain-28-Centos7/org.qemu.guest_agent.0

qemu monitor和qemu agent通道创建过程

Libvirt-6.9

libvirt启动虚拟机时会打开两个unix socket，作为server，一个用作qemu monitor，一个用作qemu agent，然后启动qemu子进程。

qemuProcessStart

->qemuProcessPrepareDomain

->for循环执行qemuDomainPrepareChannel # 设置channel->source->data.nix.path，例如：/var/lib/libvirt/qemu/channel/target/domain-28-Centos7/org.qemu.guest_agent.0

qemuProcessLaunch

->qemuBuildCommandLine

->qemuBuildMonitorCommandLine

->qemuBuildChrChardevStr

->fd = qemuOpenChrChardevUNIXSocket # dev->type == VIR_DOMAIN_CHR_TYPE_UNIX

->virCommandPassFD(cmd, fd, VIR_COMMAND_PASS_FD_CLOSE_PARENT); # 将要传递的fd放在cmd->passfd中

->qemuBuildChannelsCommandLine

->qemuBuildChrChardevStr # VIR_DOMAIN_CHR_CHANNEL_TARGET_TYPE_VIRTIO

->fd = qemuOpenChrChardevUNIXSocket(dev); # VIR_DOMAIN_CHR_TYPE_UNIX，打开unix socker listen

->virCommandPassFD(cmd, fd, VIR_COMMAND_PASS_FD_CLOSE_PARENT);

->qemuBuildChrDeviceCommandLine # 生成-device参数

->virCommandRun # 启动qemu子进程，之后libvirt进程关闭cmd->passfd中的fd

->qemuProcessWaitForMonitor

->qemuConnectMonitor

->qemuMonitorOpen # 连接unix socket

->qemuProcessInitMonitor # 发送qmp_capabilities

->qemuMigrationCapsCheck # 发送query-migrate-capabilities

->qemuMonitorGetChardevInfo # 发送query-chardev

->qemuProcessRefreshChannelVirtioState # 增加domain agent生命周期事件

->qemuConnectAgent

->agent = qemuAgentOpen(...)

->agent->fd = qemuAgentOpenUnix(config->data.nix.path); # 通过unix socket连接到qemu agent，config->data.nix.path在之前的qemuDomainPrepareChannel 函数中已经设置好

->qemuAgentRegister(agent); # 使用glib事件循环监测qemu agent事件，处理函数为qemuAgentIO

qemu-5.0

qemu_init

->for循环执行chardev_init_func

->qemu_chr_new_from_opts

->backend = qemu_chr_parse_opts(opts, errp);

->qemu_chr_parse_socket # SOCKET_ADDRESS_LEGACY_KIND_FD

->chr = qemu_chardev_new(...)

->chardev_new

->qemu_char_open

->qmp_chardev_open_socket

->qmp_chardev_open_socket_server

qemu-5.0对qmp命令和qga命令的处理

全局变量qmp_dispatcher_bh用于进行qmp命令

/* Bottom half to dispatch the requests received from I/O thread */
QEMUBH *qmp_dispatcher_bh;

函数monitor_init_globals_core初始化qmp_dispatcher_bh并将其处理函数设置为monitor_qmp_bh_dispatcher

void monitor_init_globals_core(void)
{monitor_qapi_event_init();qemu_mutex_init(&monitor_lock);/** The dispatcher BH must run in the main loop thread, since we* have commands assuming that context.  It would be nice to get* rid of those assumptions.*/qmp_dispatcher_bh = aio_bh_new(iohandler_get_aio_context(),monitor_qmp_bh_dispatcher,NULL);
}

qmp命令的入口函数是qmp_dispatch:

virsh qemu-monitor-command --hmp info block调用堆栈如下：

Breakpoint 1, 0x000055fdab6f88a0 in hmp_info_block ()

(gdb) bt

#0 0x000055fdab6f88a0 in hmp_info_block ()

#1 0x000055fdab7e3dd6 in handle_hmp_command ()

#2 0x000055fdab674d12 in qmp_human_monitor_command ()

#3 0x000055fdab807019 in qmp_marshal_human_monitor_command ()

#4 0x000055fdab8c14b0 in qmp_dispatch ()

#5 0x000055fdab7e1111 in monitor_qmp_dispatch ()

#6 0x000055fdab7e17d0 in monitor_qmp_bh_dispatcher ()

#7 0x000055fdab9081e3 in aio_bh_poll ()

#8 0x000055fdab90b59e in aio_dispatch ()

#9 0x000055fdab90807e in aio_ctx_dispatch ()

#10 0x00007f25d5f15099 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0

#11 0x000055fdab90a8e3 in main_loop_wait ()

#12 0x000055fdab67b269 in qemu_main_loop ()

#13 0x000055fdab59c08e in main ()

virsh qemu-monitor-command '{"execute": "query-block"}'调用堆栈如下：

#0 0x000055fdab87b5a0 in qmp_query_block ()

#1 0x000055fdab7fc797 in qmp_marshal_query_block ()

#2 0x000055fdab8c1536 in qmp_dispatch ()

#3 0x000055fdab7e1111 in monitor_qmp_dispatch ()

#4 0x000055fdab7e17d0 in monitor_qmp_bh_dispatcher ()

#5 0x000055fdab9081e3 in aio_bh_poll ()

#6 0x000055fdab90b59e in aio_dispatch ()

#7 0x000055fdab90807e in aio_ctx_dispatch ()

#8 0x00007f25d5f15099 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0

#9 0x000055fdab90a8e3 in main_loop_wait ()

#10 0x000055fdab67b269 in qemu_main_loop ()

#11 0x000055fdab59c08e in main ()

qga命令的入口函数是tcp_chr_read:

tcp_chr_read

->qemu_chr_be_write

->chr_read # virtconsole_realize中调用qemu_chr_fe_set_handlers将backend的读函数设置为chr_read(virtio-console.c)

->virtio_serial_write

->virtqueue_push

->virtio_notify

之后就是通过virtio机制通知到虚拟机内部，虚拟机内部的qemu guest agent打开的virtio串口收到消息进行处理。

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qemu monitor和qemu agent的实现

qemu monitor和qemu agent通道创建过程

Libvirt-6.9

qemu-5.0

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