qemu-system-i386: -mem-path not supported with Xen when try to use memory-backend-memfd to share the memory with external processes on qemu-xen stable-4.16

[Trigger Huang]

Hello,

The QEMU Documentation suggests to use memory-backend-memfd to share the
memory with external processes, so I  add the following patch to
libxl__build_device_model_args_new() @ tools/libs/light/libxl_dm.c

*+               flexarray_append_pair(dm_args, "-object",
"memory-backend-memfd,id=mem1,size=4G");+
flexarray_append_pair(dm_args, "-machine", "memory-backend=mem1");*

However, I always got error '*qemu-system-i386: -mem-path not supported
with Xen*'
After check the qemu-xen source, the error is from
'qemu_ram_alloc_from_fd() @ softmmu/physmem.c



* if (xen_enabled()) {        error_setg(errp, "-mem-path not supported
with Xen");        return NULL;    }*

So, any suggestions on how to enable  *-mem-path* on Xen?

Thanks,
Trigger