QEMU and virt xml specifications for newbies

[Ruben Safir]

Greetings

I'm relatively new to the virtualization scene and I am trying to learn
how to use KVM with QEMU and libvirt.  Looking for tutorials, I ended up
on an IBM resource which has a sample XML file for a quick start, but it
is not well documented and doing a websearch for details has had limited
succuss.

The suggested XML file they give looks like this:
<domain type="kvm">
        <name>firsttemplate</name>
        <memory unit="GiB">16</memory>
        <vcpu>2</vcpu>
        <os>
                <type>hvm</type>
        </os>
        <iothreads>1</iothreads>
        <on_crash>preserve</on_crash>
        <devices>
                <disk type="block" device="disk">
                        <driver name="qemu" type="qcow2" cache="none"
iothread="1" io="native"/>
                        <source
dev="/dev/mapper/36005076305ffc1ae00000000000020d3"/>
                        <target dev="vda" bus="virtio"/>
                        <boot order="1"/>
                </disk>
                <interface type="direct">
                        <source dev="bond0" mode="bridge"/>
                </interface>
                <console type="pty">
                        <target type="sclp">
                </console>
                <memballon mode="none"\>
        </devices>
</domain>

They have certain aspects in bold type that shouldn't be altered,
according to them.

I'm having a difficult time understanding what should be entered into
the <disk> <source > section.  It looks like it is actually defining 
a drive, but I have no idea what /dev/mapper is.  I would think one
would need to create some for a virtual disk image

In this example, they use a disk file
https://askaralikhan.blogspot.com/2011/01/creating-kvm-guests-using-virsh-tool.html

which is defined as a file and not a block device.  That brings up a
general puzzle, do these uml descriptions describe the host view or what
you want to create in the guest view?

I'd appreciate some direction on this.  Thanks

Ruben
-- 
So many immigrant groups have swept through our town
that Brooklyn, like Atlantis, reaches mythological
proportions in the mind of the world - RI Safir 1998
http://www.mrbrklyn.com 

DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
http://www.nylxs.com - Leadership Development in Free Software
http://www2.mrbrklyn.com/resources - Unpublished Archive 
http://www.coinhangout.com - coins!
http://www.brooklyn-living.com 

Being so tracked is for FARM ANIMALS and extermination camps, 
but incompatible with living as a free human being. -RI Safir 2013