使用 libvirt 和 QEMU 的 9p 根文件系統

我正在嘗試使用 libvirt 啟動具有 9p 根文件系統的 Linux VM。當使用以下命令直接呼叫 QEMU 時，這非常有效：

qemu-system-x86_64 -enable-kvm \
-kernel /vmroot/trusty/boot/vmlinuz-3.13.0-24-generic \
-initrd /vmroot/trusty/boot/initrd.img-3.13.0-24-generic \
-fsdev local,id=root9p,path=/vmroot/trusty,security_model=mapped \
-device virtio-9p-pci,fsdev=root9p,mount_tag=root9p \
-nographic \
-append 'root=root9p rw rootfstype=9p rootflags=trans=virtio console=ttyS0'

現在，我試圖通過使用 XML 配置的 libvirt 獲得相同的效果。我的 XML 配置如下：

<?xml version="1.0"?>
<domain type='kvm'>
   <name>trusty</name>
   <uuid>618237b9-2f17-4dfc-ba46-dec508d31e4e</uuid>
   <os>
       <type>hvm</type>
       <kernel>/vmroot/trusty/boot/vmlinuz-3.13.0-45-generic</kernel>
       <initrd>/vmroot/trusty/boot/initrd.img-3.13.0-45-generic</initrd>
       <cmdline>root=root9p rw rootfstype=9p rootflags=trans=virtio console=ttyS0</cmdline>
   </os>
   <vcpu>2</vcpu>
   <memory unit='KiB'>524288</memory>
   <on_poweroff>destroy</on_poweroff>
   <on_reboot>restart</on_reboot>
   <on_crash>destroy</on_crash>
   <features>
       <pae/>
       <acpi/>
       <hap/>
   </features>
   <devices>
       <emulator>/usr/bin/qemu-system-x86_64</emulator>
       <serial type='pty'>
           <target port='0'/>
       </serial>
   </devices>
   <filesystem type='mount' accessmode='mapped'>
       <source dir='/vmroot/trusty'/>
       <target dir='root9p'/>
   </filesystem>
</domain>

現在，從 XML 生成的本機 QEMU 命令行不包含啟用此功能的必要選項。生成的命令行是：

qemu-system-x86_64 -name trusty -machine pc,accel=kvm,usb=off -m 512 \
-realtime mlock=off -smp 2,sockets=2,cores=1,threads=1 \
-uuid 618237b9-2f17-4dfc-ba46-dec508d31e4e -nographic -no-user-config \
-nodefaults -chardev socket,id=charmonitor,path=/home/user/.config/libvirt/qemu/lib/trusty.monitor,server,nowait \
-mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc \
-no-shutdown -boot strict=on \
-kernel /vmroot/trusty/boot/vmlinuz-3.13.0-45-generic \
-initrd /vmroot/trusty/boot/initrd.img-3.13.0-45-generic \
-append 'root=root9p rw rootfstype=9p rootflags=trans=virtio console=ttyS0' \
-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
-chardev pty,id=charserial0 \
-device isa-serial,chardev=charserial0,id=serial0 \
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x2 \
-msg timestamp=on

那麼，我怎樣才能讓 libvirt 包含-fsdev和附加-device選項？

找到了解決方案。簡單的配置錯誤。<filesystem>元素需要在元素內部<devices>，因此 XML 變為：

<?xml version="1.0"?>
<domain type='kvm'>
   <name>trusty</name>
   <uuid>618237b9-2f17-4dfc-ba46-dec508d31e4e</uuid>
   <os>
       <type>hvm</type>
       <kernel>/vmroot/trusty/boot/vmlinuz-3.13.0-45-generic</kernel>
       <initrd>/vmroot/trusty/boot/initrd.img-3.13.0-45-generic</initrd>
       <cmdline>root=root9p rw rootfstype=9p rootflags=trans=virtio console=ttyS0</cmdline>
   </os>
   <vcpu>2</vcpu>
   <memory unit='KiB'>524288</memory>
   <on_poweroff>destroy</on_poweroff>
   <on_reboot>restart</on_reboot>
   <on_crash>destroy</on_crash>
   <features>
       <pae/>
       <acpi/>
       <hap/>
   </features>
   <devices>
       <emulator>/usr/bin/qemu-system-x86_64</emulator>
       <serial type='pty'>
           <target port='0'/>
       </serial>
       <filesystem type='mount' accessmode='mapped'>
           <source dir='/vmroot/trusty'/>
           <target dir='root9p'/>
       </filesystem>
   </devices>
</domain>

引用自：https://serverfault.com/questions/673641