Re: [Qemu-devel] [PATCH v3 0/4] Introduce the microvm machine type

[Jing Liu <jing2.liu@linux.intel.com>]

On 8/30/2019 10:27 PM, Sergio Lopez wrote:
> 
> Jing Liu <jing2.liu@linux.intel.com> writes:
> 
>> Hi Sergio,
>>
>> On 8/29/2019 11:46 PM, Sergio Lopez wrote:
>>>
>>> Jing Liu <jing2.liu@linux.intel.com> writes:
>>>
>>>> Hi Sergio,
>>>>
>>>> The idea is interesting and I tried to launch a guest by your
>>>> guide but seems failed to me. I tried both legacy and normal modes,
>>>> but the vncviewer connected and told me that:
>>>> The vm has no graphic display device.
>>>> All the screen in vnc is just black.
>>>
>>> The microvm machine type doesn't support any graphics device, so you
>>> need to rely on the serial console.
>> Got it.
>>
>>>
>>>> kernel config:
>>>> CONFIG_KVM_MMIO=y
>>>> CONFIG_VIRTIO_MMIO=y
>>>>
>>>> I don't know if any specified kernel version/patch/config
>>>> is needed or anything I missed.
>>>> Could you kindly give some tips?
>>>
>>> I'm testing it with upstream vanilla Linux. In addition to MMIO, you
>>> need to add support for PVH (the next version of this patchset, v4, will
>>> support booting from FW, so it'll be possible to use non-PVH ELF kernels
>>> and bzImages too).
>>>
>>> I've just uploaded a working kernel config here:
>>>
>>> https://gist.github.com/slp/1060ba3aaf708584572ad4109f28c8f9
>>>
>> Thanks very much and this config is helpful to me.
>>
>>> As for the QEMU command line, something like this should do the trick:
>>>
>>> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm,legacy -kernel vmlinux -append "earlyprintk=ttyS0 console=ttyS0 reboot=k panic=1" -nodefaults -no-user-config -nographic -serial stdio
>>>
>>> If this works, you can move to non-legacy mode with a virtio-console:
>>>
>>> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm -kernel vmlinux -append "console=hvc0 reboot=k panic=1" -nodefaults -no-user-config -nographic -serial pty -chardev stdio,id=virtiocon0,server -device virtio-serial-device -device virtconsole,chardev=virtiocon0
>>>
>> I tried the above two ways and it works now. Thanks!
>>
>>> If is still working, you can try adding some devices too:
>>>
>>> ./x86_64-softmmu/qemu-system-x86_64 -smp 1 -m 1g -enable-kvm -M microvm -kernel vmlinux -append "console=hvc0 reboot=k panic=1 root=/dev/vda" -nodefaults -no-user-config -nographic -serial pty -chardev stdio,id=virtiocon0,server -device virtio-serial-device -device virtconsole,chardev=virtiocon0 -netdev user,id=testnet -device virtio-net-device,netdev=testnet -drive id=test,file=alpine-rootfs-x86_64.raw,format=raw,if=none -device virtio-blk-device,drive=test
>>>
>> But I'm wondering why the image I used can not be found.
>> root=/dev/vda3 and the same image worked well on normal qemu/guest-
>> config bootup, but didn't work here. The details are,
>>
>> -append "console=hvc0 reboot=k panic=1 root=/dev/vda3 rw rootfstype=ext4" \
>>
>> [    0.022784] Key type encrypted registered
>> [    0.022988] VFS: Cannot open root device "vda3" or
>> unknown-block(254,3): error -6
>> [    0.023041] Please append a correct "root=" boot option; here are
>> the available partitions:
>> [    0.023089] fe00         8946688 vda
>> [    0.023090]  driver: virtio_blk
>> [    0.023143] Kernel panic - not syncing: VFS: Unable to mount root
>> fs on unknown-block(254,3)
>> [    0.023201] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.3.0-rc3 #23
>>
>>
>> BTW, root=/dev/vda is also tried and didn't work. The dmesg is a
>> little different:
>>
>> [    0.028050] Key type encrypted registered
>> [    0.028484] List of all partitions:
>> [    0.028529] fe00         8946688 vda
>> [    0.028529]  driver: virtio_blk
>> [    0.028615] No filesystem could mount root, tried:
>> [    0.028616]  ext4
>> [    0.028670]
>> [    0.028712] Kernel panic - not syncing: VFS: Unable to mount root
>> fs on unknown-block(254,0)
>>
>> I tried another ext4 img but still doesn't work.
>> Is there any limitation of blk image? Could I copy your image for simple
>> test?
> 
> The kernel config I posted lacks support for DOS partitions. Adding
> CONFIG_MSDOS_PARTITION=y should allow you to boot from /dev/vda3.
> 
> Anyway, in case you also want to try booting from /dev/vda (without
> partitions), this is the recipe I use to quickly create a minimal rootfs
> image:
> 
> # wget http://dl-cdn.alpinelinux.org/alpine/v3.10/releases/x86_64/alpine-minirootfs-3.10.2-x86_64.tar.gz
> # qemu-img create -f raw alpine-rootfs-x86_64.raw 1G
> # sudo losetup /dev/loop0 alpine-rootfs-x86_64.raw
> # sudo mkfs.ext4 /dev/loop0
> # sudo mount /dev/loop0 /mnt
> # sudo tar xpf alpine-minirootfs-3.10.2-x86_64.tar.gz -C /mnt
> # sudo umount /mnt
> # sudo losetup -d /dev/loop0
> 
> The rootfs will be missing openrc, so you'll need to add "init=/bin/sh"
> to the command line.
> 

Thank you Sergio. I'll try that.

Jing
> Sergio.
> 
>> Thanks in advance,
>> Jing
>>
>>> Sergio.