Re: [PATCH V4 04/19] machine: aux-ram-share option

[Steven Sistare]

On 12/5/2024 7:19 AM, Markus Armbruster wrote:
> Markus Armbruster <armbru@redhat.com> writes:
>
> > Steve Sistare <steven.sistare@oracle.com> writes:
> >
> > > 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.
> > >
> > > Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> >
> > [...]
> >
> > > diff --git a/qemu-options.hx b/qemu-options.hx
> > > index dacc979..02b9118 100644
> > > --- a/qemu-options.hx
> > > +++ b/qemu-options.hx
> > > @@ -38,6 +38,9 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> > >       "                nvdimm=on|off controls NVDIMM support (default=off)\n"
> > >       "                memory-encryption=@var{} memory encryption object to use 
> > > (default=none)\n"
> > >       "                hmat=on|off controls ACPI HMAT support (default=off)\n"
> > > +#ifdef CONFIG_POSIX
> > > +    "                aux-ram-share=on|off allocate auxiliary guest RAM as shared 
> > > (default: off)\n"
> > > +#endif
> > >       "                memory-backend='backend-id' specifies explicitly provided 
> > > backend for main RAM (default=none)\n"
> > >       "                
> > > cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n",
> > >       QEMU_ARCH_ALL)
> > > @@ -101,6 +104,18 @@ SRST
> > >           Enables or disables ACPI Heterogeneous Memory Attribute Table
> > >           (HMAT) support. The default is off.
> > >   
> > > +#ifdef CONFIG_POSIX
> > > +    ``aux-ram-share=on|off``
> > > +        Allocate auxiliary 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.
> > > +
> > > +        Some migration modes require aux-ram-share=on.
> > > +#endif
> > > +
> >
> > I get
> >
> >      Warning, treated as error:
> >      .../qemu-options.hx:117:Definition list ends without a blank line; 
> > unexpected unindent.
> >
> > Putting the blank line before #endif works for me.
>
> Actually, #ifdef does not work within SRST ... ERST.
>
> Elsewhere, we document build-time optional features unconditionally.
> Simply drop the #ifdef here.

Thanks Markus.  I see the "#ifdef" literal emitted in the man page.  I'll 
delete it.

- Steve