1.Description of problem:

     It report use migration with shmem device is not supported , when I use the command "virsh migrate --live" to migrate a VM to another host.  
 
2.Version-Release number of selected component (if applicable):
     libvirt 3.9.0
     qemu-kvm  2.8.1
 
3.Steps to Reproduce:
1) Add serveral lines below to guest configuration

    <shmem name='my_shmem1'>
      <model type='ivshmem-plain'/>
      <size unit='M'>4</size>
    </shmem>

 
2) virsh start guest-1
 
3) virsh migrate --live guest-1 qemu+ssh://target/system
 
Actual results:
     error: Requested operation is not valid: migration with shmem device is not supported
 
4.Code Review
   When using the command “virsh create guset-1.xml,it produce corresponding command below.
   “qemu-kvm -device ivshmem-plain, id=shmem0,memdev=shmmem-shmem0,bus=pci.0,addr=0xa”
 
I read qemu-doc.texi in qemu-2.8.1 source code, which have a explain of migrating ivshmem below 
   “With device property @option{master=on}, the guest will copy the shared
   memory on migration to the destination host.  With @option{master=off},
   the guest will not be able to migrate with the device attached.” 
 
But libvirt library can not recognize the property “master=on”. When I directly used command "qemu-kvm -device ivshmem-plain,id=shmem0,memdev=shmmem-shmem0,master=on,bus=pci.0,addr=0xa” to launch a guest, it can migrate in live.
 
    I review the code about qemu code with branch 2.8.1 and master from https://github.com/libvirt/libvirt, it have no configuration definition for “master=on”
    The below is the part of source code
 
domain_conf.h
struct _virDomainShmemDef {
    char *name;
    unsigned long long size;
    int model; /* enum virDomainShmemModel */
    struct {
        bool enabled;
        virDomainChrSourceDef chr;
    } server;
    struct {
        bool enabled;
        unsigned vectors;
        virTristateSwitch ioeventfd;
    } msi;
    virDomainDeviceInfo info;
};