Re: [PATCH v4 8/8] hw/i386: Introduce the microvm machine type

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 24, 2019 at 02:44:33PM +0200, Sergio Lopez wrote:
> +static void microvm_fix_kernel_cmdline(MachineState *machine)
> +{
> +    X86MachineState *x86ms = X86_MACHINE(machine);
> +    BusState *bus;
> +    BusChild *kid;
> +    char *cmdline;
> +
> +    /*
> +     * Find MMIO transports with attached devices, and add them to the kernel
> +     * command line.
> +     *
> +     * Yes, this is a hack, but one that heavily improves the UX without
> +     * introducing any significant issues.
> +     */
> +    cmdline = g_strdup(machine->kernel_cmdline);
> +    bus = sysbus_get_default();
> +    QTAILQ_FOREACH(kid, &bus->children, sibling) {
> +        DeviceState *dev = kid->child;
> +        ObjectClass *class = object_get_class(OBJECT(dev));
> +
> +        if (class == object_class_by_name(TYPE_VIRTIO_MMIO)) {
> +            VirtIOMMIOProxy *mmio = VIRTIO_MMIO(OBJECT(dev));
> +            VirtioBusState *mmio_virtio_bus = &mmio->bus;
> +            BusState *mmio_bus = &mmio_virtio_bus->parent_obj;
> +
> +            if (!QTAILQ_EMPTY(&mmio_bus->children)) {
> +                gchar *mmio_cmdline = microvm_get_mmio_cmdline(mmio_bus->name);
> +                if (mmio_cmdline) {
> +                    char *newcmd = g_strjoin(NULL, cmdline, mmio_cmdline, NULL);
> +                    g_free(mmio_cmdline);
> +                    g_free(cmdline);
> +                    cmdline = newcmd;
> +                }
> +            }
> +        }
> +    }
> +
> +    fw_cfg_modify_i32(x86ms->fw_cfg, FW_CFG_CMDLINE_SIZE, strlen(cmdline) + 1);
> +    fw_cfg_modify_string(x86ms->fw_cfg, FW_CFG_CMDLINE_DATA, cmdline);
> +}

Can we rearrange this somewhat? Maybe the mmio constructor
would format the device description and add to some list,
and then microvm would just get stuff from that list
and add it to kernel command line?
This way it can also be controlled by a virtio-mmio property, so
e.g. you can disable it per device if you like.
In particular, this seems like a handy trick for any machine type
using mmio.

-- 
MST