Re: [PULL 07/42] machine: aux-ram-share option

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 29 Jan 2025 at 16:03, Fabiano Rosas <farosas@suse.de> wrote:
>
> From: Steve Sistare <steven.sistare@oracle.com>
>
> Allocate auxilliary guest RAM as an anonymous file that is shareable
> with an external process.  This option applies to memory allocated as
> a side effect of creating various devices. It does not apply to
> memory-backend-objects, whether explicitly specified on the command
> line, or implicitly created by the -m command line option.
>
> This option is intended to support new migration modes, in which the
> memory region can be transferred in place to a new QEMU process, by sending
> the memfd file descriptor to the process.  Memory contents are preserved,
> and if the mode also transfers device descriptors, then pages that are
> locked in memory for DMA remain locked.  This behavior is a pre-requisite
> for supporting vfio, vdpa, and iommufd devices with the new modes.

Hi; I've just noticed that in this patch:


> @@ -1162,6 +1178,12 @@ static void machine_class_init(ObjectClass *oc, void *data)
>      object_class_property_set_description(oc, "mem-merge",
>          "Enable/disable memory merge support");
>
> +#ifdef CONFIG_POSIX
> +    object_class_property_add_bool(oc, "aux-ram-share",
> +                                   machine_get_aux_ram_share,
> +                                   machine_set_aux_ram_share);
> +#endif

we added a new class property to the machine, but we don't
call object_class_property_set_description() to give it any
help text (compare how we handle the other properties in this
function).

> +
>      object_class_property_add_bool(oc, "usb",
>          machine_get_usb, machine_set_usb);
>      object_class_property_set_description(oc, "usb",

This means that if you run "qemu-system-x86_64 -M q35,help"
you'll see that this option is missing help text:

pc-q35-10.2-machine options:
  acpi=<OnOffAuto>       - Enable ACPI
  append=<string>        - Linux kernel command line
  aux-ram-share=<bool>
  boot=<BootConfiguration> - Boot configuration
  bus-lock-ratelimit=<uint64_t> - Set the ratelimit for the bus locks
acquired in VMs
  confidential-guest-support=<link<confidential-guest-support>> - Set
confidential guest scheme to support
  default-bus-bypass-iommu=<bool>
[etc]

Would somebody like to write a patch to add the missing
description ?

thanks
-- PMM