one qustion about the snapshot of the libvirt, thanks.

[Guozhonghua]

Hello, 

When we test snapshot features and review the code of libvirt, there is one 
question, not an issue. 

    /* do the memory snapshot if necessary */
    if (memory) {
        /* check if migration is possible */
        if (!qemuMigrationSrcIsAllowed(driver, vm, false, 0))
            goto cleanup;

While making one snapshot with memory on one vm, but it is not allowed while 
the vm which has some src devices, such as pci devs, with which the vm is not 
allowed to be migrated.
I want to known the reason, why should  it check this conditions? 


Thank You!