Re: [PATCH V2 00/23] IOREQ feature (+ virtio-mmio) on Arm

[Masami Hiramatsu <masami.hiramatsu@linaro.org>]

Hi Oleksandr,

Thanks for sharing the virtio-disk server, I also tested with a real usb disk.

In config file:

virtio = 1
vdisk = [ 'backend=Domain-0, disks=ro:/dev/sda1' ]

And it can be mounted in DomU

[    2.892874] virtio_blk virtio0: [vda] 1875382927 512-byte logical
blocks (960 GB/894 GiB)
[    2.892925] vda: detected capacity change from 0 to 960196058624
...
root@develbox:~# cat /proc/partitions
major minor  #blocks  name

 254        0  937691463 vda
...
root@develbox:~# mount /dev/vda /mnt/
[  192.260968] EXT4-fs (vda): mounted filesystem with ordered data
mode. Opts: (null)
mount: /mnt: WARNING: source write-protected, mounted read-only.

So "ro" flag also correctly works.
Great!

Thank you!

2020年11月1日(日) 6:10 Oleksandr Tyshchenko <olekstysh@gmail.com>:
>
>
>
> On Fri, Oct 30, 2020 at 1:34 PM Masami Hiramatsu <masami.hiramatsu@linaro.org> wrote:
>>
>> Hi Oleksandr,
>
>
> Hi Masami, all
>
> [sorry for the possible format issue]
>
>>
>> >> >
>> >> >       Could you tell me how can I test it?
>> >> >
>> >> >
>> >> > I assume it is due to the lack of the virtio-disk backend (which I haven't shared yet as I focused on the IOREQ/DM support on Arm in the
>> >> > first place).
>> >> > Could you wait a little bit, I am going to share it soon.
>> >>
>> >> Do you have a quick-and-dirty hack you can share in the meantime? Even
>> >> just on github as a special branch? It would be very useful to be able
>> >> to have a test-driver for the new feature.
>> >
>> > Well, I will provide a branch on github with our PoC virtio-disk backend by the end of this week. It will be possible to test this series with it.
>>
>> Great! OK I'll be waiting for the PoC backend.
>>
>> Thank you!
>
>
> You can find the virtio-disk backend PoC (shared as is) at [1].
>
> Brief description...
>
> The virtio-disk backend PoC is a completely standalone entity (IOREQ server) which emulates a virtio-mmio disk device.
> It is based on code from DEMU [2] (for IOREQ server purposes) and some code from kvmtool [3] to implement virtio protocol,
> disk operations over underlying H/W and Xenbus code to be able to read configuration from the Xenstore
> (it is configured via domain config file). Last patch in this series (marked as RFC) actually adds required bits to the libxl code.
>
> Some notes...
>
> Backend could be used with current V2 IOREQ series [4] without any modifications, all what you need is to enable
> CONFIG_IOREQ_SERVER on Arm [5], since it is disabled by default within this series.
>
> Please note that in our system we run backend in DomD (driver domain). I haven't tested it in Dom0,
> since in our system the Dom0 is thin (without any H/W) and only used to launch VMs, so there is no underlying block H/W.
> But, I hope, it is possible to run it in Dom0 as well (at least there is nothing specific to a particular domain in the backend itself, nothing hardcoded).
> If you are going to run a backend in other than Dom0 domain you need to write your own policy (FLASK) for the backend (running in that domain)
> to be able to issue DM related requests, etc. Only for test purposes you could use this patch [6] that tweeks Xen dummy policy (not for upstream).
>
> As I mentioned elsewhere you don't need to modify Guest Linux (DomU), just enable VirtIO related configs.
> If I remember correctly, the following would be enough:
> CONFIG_BLK_MQ_VIRTIO=y
> CONFIG_VIRTIO_BLK=y
> CONFIG_VIRTIO=y
> CONFIG_VIRTIO_BALLOON=y
> CONFIG_VIRTIO_MMIO=y
> If I remember correctly, if your Host Linux (Dom0 or DomD) version >= 4.17 you don't need to modify it as well.
> Otherwise, you need to cherry-pick "xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE" from the upstream to be able
> to use the acquire interface for the resource mapping.
>
> We usually build a backend in the context of the Yocto build process and run it as a systemd service,
> but you can also build and run it manually (it should be launched before DomU creation).
>
> There are no command line options at all. Everything is configured via domain configuration file:
> # This option is mandatory, it shows that VirtIO is going to be used by guest
> virtio=1
> # Example of domain configuration (two disks are assigned to the guest, the latter is in readonly mode):
> vdisk = [ 'backend=DomD, disks=rw:/dev/mmcblk0p3;ro:/dev/mmcblk1p3' ]
>
> Hope that helps. Feel free to ask questions if any.
>
> [1] https://github.com/xen-troops/virtio-disk/commits/ioreq_v3
> [2] https://xenbits.xen.org/gitweb/?p=people/pauldu/demu.git;a=summary
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/will/kvmtool.git/
> [4] https://github.com/otyshchenko1/xen/commits/ioreq_4.14_ml3
> [5] https://github.com/otyshchenko1/xen/commit/ee221102193f0422a240832edc41d73f6f3da923
> [6] https://github.com/otyshchenko1/xen/commit/be868a63014b7aa6c9731d5692200d7f2f57c611
>
> --
> Regards,
>
> Oleksandr Tyshchenko



-- 
Masami Hiramatsu