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

[Peter Xu <peterx@redhat.com>]

On Tue, Nov 04, 2025 at 10:53:54AM +0000, Peter Maydell wrote:
> 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 for reporting, sent "[PATCH] machine: Provide a description for
aux-ram-share property" just now.

PS: for q35 there's another one fd-bootchk=..

-- 
Peter Xu