libvirt users - Jan 2022 - Backend memory object creation - query

Hello,


For our use-case with Libvirt we want to create the Memory backend object ,

Expected QEMU args would be
-object memory-backend-memfd,id=mem1,size=4096M

Request you to please help us to specify this arg in the libvirt XML.

Thanks,
Shiv
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On Thu, Jan 27, 2022 at 04:05:19 +0000, M, Shivakumar
wrote:
> Hello,
Hi,

note that there's no need to CC both libvir-list and libvirt-users
maling lists.
> 
> 
> For our use-case with Libvirt we want to create the Memory backend object ,
> 
> Expected QEMU args would be
> -object memory-backend-memfd,id=mem1,size=4096M
Your description is a bit vague. Do you want to use it to back the guest
memory?

As by itself a memory object itself is useless without being attached
somewhere

In case you want to configure qemu to back the default memory of the VM
by a memfd:

Per https://www.libvirt.org/formatdomain.html#memory-backing

<domain type='kvm'>
 ...

 <memoryBacking>
   <source type='memfd'/>
 </memoryBacking>
...
</domain>

Results into invoking qemu with:

-machine
pc-i440fx-2.9,usb=off,vmport=off,dump-guest-core=off,memory-backend=pc.ram \
...
-object
'{"qom-type":"memory-backend-memfd","id":"pc.ram","x-use-canonical-path-for-ramblock-id":false,"size":1048576000,"host-nodes":[0],"policy":"bind"}'
\

> 
> Request you to please help us to specify this arg in the libvirt XML.
> 
> Thanks,
> Shiv