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

[Steven Sistare <steven.sistare@oracle.com>]

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