Re: [Xen-devel] [PATCH v2 05/21] xen/arm: extend device tree based multiboot protocol

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 07/07/18 00:12, Stefano Stabellini wrote:
> Extend the existing device tree based multiboot protocol to include
> information regarding multiple domains to boot.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
>
> ---
> Changes in v2:
> - lower case kernel
> - rename mem to memory
> - mandate cpus and memory
> - replace domU-kernel with kernel and domU-ramdisk with ramdisk
> - rename xen,domU with xen,domain
> - add info about dom0
> - switch memory and cpus to integers
> - remove defaults
> - add vpl011
> ---
>   docs/misc/arm/device-tree/booting.txt | 108 ++++++++++++++++++++++++++++++++++
>   1 file changed, 108 insertions(+)
>
> diff --git a/docs/misc/arm/device-tree/booting.txt 
> b/docs/misc/arm/device-tree/booting.txt
> index ce2d0dc..5c3b8da 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -119,3 +119,111 @@ For those you would hardcode the Xen commandline in the 
> DTB under
>   line by writing bootargs (as for native Linux).
>   A Xen-aware bootloader would set xen,xen-bootargs for Xen, xen,dom0-bootargs
>   for Dom0 and bootargs for native Linux.
> +
> +
> +Creating Multiple Domains directly from Xen
> +===========================================
> +
> +It is possible to have Xen create other domains, in addition to dom0,
> +out of the information provided via device tree. A kernel and initrd
> +(optional) need to be specified for each guest.
> +
> +For each domain to be created there needs to be one node under /chosen
> +with the following properties:
> +
> +- compatible
> +
> +    For domUs: "xen,domain"
> +    For dom0: "xen,domain", "xen,initial-domain"
Looking briefly at the code, I don't see any support of 
"xen,initial-domain". Did I miss anything?
But, it is a bit strange to put that in compatible. Shouldn't this be a 
property?

> +
> +- memory
> +
> +    An integer specifying the amount of megabytes of RAM to allocate to
> +    the guest.
I would define this a KB. With Dom0less it would be easy to spawn a 
guest with less than a MB of memory. What matter is the amount of memory 
should be page-aligned.
> +
> +- cpus
> +
> +    An integer specifying the number of vcpus to allocate to the guest.
> +
> +- vpl011
> +
> +    An integer to enable/disable a virtual pl011 for the guest to use.
The interrupt is a bit confusing here. What value will enable? What 
value will disable?
I think you can just make an empty property.

> +
> +- #address-cells and #size-cells
> +
> +    Both #address-cells and #size-cells need to be specified because
> +    both sub-nodes (described shortly) have reg properties.
> +
> +Under the "xen,domain" compatible node, one or more sub-nodes are present
> +for the DomU kernel and ramdisk.
> +
> +The kernel sub-node has the following properties:
> +
> +- compatible
> +
> +    "multiboot,kernel"
> +
> +- reg
> +
> +    Specifies the physical address of the kernel in RAM and its
> +    length.
> +
> +- bootargs (optional)
> +
> +    Command line parameters for the guest kernel.
> +
> +The ramdisk sub-node has the following properties:
> +
> +- compatible
> +
> +    "multiboot,ramdisk"
> +
> +- reg
> +
> +    Specifies the physical address of the ramdisk in RAM and its
> +    length.
> +
> +
> +Example
> +=======
> +
> +chosen {
> +    domU1 {
> +        compatible = "xen,domain";
> +        #address-cells = <0x2>;
> +        #size-cells = <0x1>;
> +        memory = <128>;
> +        cpus = <2>;
> +        vpl011 = <1>;
> +
> +        module@0x4a000000 {
> +            compatible = "multiboot,kernel";
> +            reg = <0x0 0x4a000000 0xffffff>;
> +            bootargs = "console=ttyAMA0 init=/bin/sh";
> +        };
> +
> +        module@0x4b000000 {
> +            compatible = "multiboot,ramdisk";
> +            reg = <0x0 0x4b000000 0xffffff>;
> +        };
> +    };
> +
> +    domU2 {
> +        compatible = "xen,domain";
> +        #address-cells = <0x2>;
> +        #size-cells = <0x1>;
> +        memory = <64>;
> +        cpus = <1>;
> +
> +        module@0x4c000000 {
> +            compatible = "multiboot,kernel";
> +            reg = <0x0 0x4c000000 0xffffff>;
> +            bootargs = "console=ttyAMA0 init=/bin/sh";
> +        };
> +
> +        module@0x4d000000 {
> +            compatible = "multiboot,ramdisk";
> +            reg = <0x0 0x4d000000 0xffffff>;
> +        };
> +    };
> +};
Cheers,

--
Julien Grall

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