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Mastering KVM Virtualization
Mastering KVM Virtualization

Mastering KVM Virtualization: Dive in to the cutting edge techniques of Linux KVM virtualization, and build the virtualization solutions your datacentre demands

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Mastering KVM Virtualization

Chapter 2. KVM Internals

In this chapter, we will discuss the important data structures and the internal implementation of libvirt, QEMU, and KVM. Then we will dive into the execution flow of a vCPU in the KVM context.

In this chapter, we will cover:

  • The internal workings of libvirt, QEMU, and KVM.
  • Important data structures and code paths of libvirt, QEMU, and KVM.
  • Execution flow of vCPUs
  • How all these communicate with each other to provide virtualization

Getting acquainted with libvirt and its implementation

As discussed in a previous chapter, there is an extra management layer called libvirt which can talk to various hypervisors (for example: KVM/QEMU, LXC, OpenVZ, UML, and so on) underlying it. libvirt is an open source Application Programming Interface (API). At the same time, it is a daemon and a management tool for managing different hypervisors as mentioned. libvirt is in use by various virtualization programs and platforms; for example, graphical user interfaces are provided by GNOME boxes and virt-manager (http://virt-manager.org/). Don't confuse this with virtual machine monitor/VMM which we discussed in Chapter 1, Understanding Linux Virtualization.

The command line client interface of libvirt is the binary called virsh. libvirt is also used by other higher-level management tools, such as oVirt (www.ovirt.org):

Getting acquainted with libvirt and its implementation

Most people think that libvirt is restricted to a single node or local node where it is running; it's not true...

Internal workings of libvirt

Let me give some details about the following libvirt source code. If you really want to know more about the implementation, it is good to poke around in the libvirt source code. Get the libvirt source code from the libvirt Git repository:

[root@node]# git clone git://libvirt.org/libvirt.git

Once you clone the repo, you can see the following hierarchy of files in the repo:

Internal workings of libvirt

libvirt code is based on the C programming language; however, libvirt has language bindings in different languages such as C#, Java, OCaml, Perl, PHP, Python, Ruby, and so on. For more details on these bindings, please refer to: https://libvirt.org/bindings.html. The main (and few) directories in the source code are docs, daemon, src, and so on. The libvirt project is well documented and the documentation is available in the source code repo and also at http://libvirt.org.

Let us move on. If we look at the libvirt internals, we can see libvirt operates or starts the connection path based on driver...

Time to think more about QEMU

Quick Emulator (QEMU) was written by Fabrice Bellard (creator of FFmpeg), and is free software and mainly licensed under GNU General Public License (GPL).

QEMU is a generic and open source machine emulator and virtualizer. When used as a machine emulator, QEMU can run OSs and programs made for one machine (for example: an ARM board) on a different machine (for example: your own PC). By using dynamic translation, it achieves very good performance (see www.QEMU.org).

Let me rephrase the preceding paragraph and give a more specific explanation. QEMU is actually a hosted hypervisor/VMM that performs hardware virtualization. Are you confused? If yes, don't worry. You will get a better picture by the end of this chapter, especially when you go through each of the interrelated components and correlate the entire path used here to perform virtualization. QEMU can act as an Emulator or Virtualizer:

  • Qemu as an Emulator: In Chapter 1, Understanding Linux Virtualization...

KVM in action

Time to discuss KVM! The fundamentals KVM developers followed were the same as the Linux kernel: "Don't reinvent the wheel". That said, they didn't try to change the kernel code to make a hypervisor; rather, the code was developed by following the new hardware assistance in virtualization (VMX and SVM) from hardware vendors as a loadable kernel module. There is a common kernel module called kvm.ko and there are hardware-based kernel modules such as kvm-intel.ko (Intel-based systems) or kvm-amd.ko (AMD-based systems). Accordingly, KVM will load the kvm-intel.ko (if the vmx flag is present) or kvm-amd.ko (if the svm flag is present) modules. This turns the Linux kernel into a hypervisor, thus achieving virtualization. The KVM is developed by qumranet and it has been part of the Linux kernel since version 2.6.20. Later qumranet was acquired by Red Hat.

KVM exposes a device file called /dev/kvm to applications to make use of the ioctls() provided. QEMU makes...

Anonymous inodes and file structures

Previously, when we discussed QEMU, we said the Linux kernel allocates file structures and sets its f_ops and anonymous inodes. Let's look into the kvm-main.c file:

static struct file_operations kvm_chardev_ops = {
      .unlocked_ioctl = kvm_dev_ioctl,
      .compat_ioctl   = kvm_dev_ioctl,
      .llseek         = noop_llseek,
};
 kvm_dev_ioctl () 
    switch (ioctl) {
          case KVM_GET_API_VERSION:
              if (arg)
                    	goto out;
              r = KVM_API_VERSION;
              break;
          case KVM_CREATE_VM:
              r = kvm_dev_ioctl_create_vm(arg);
              break;
          case KVM_CHECK_EXTENSION:
              r = kvm_vm_ioctl_check_extension_generic(NULL, arg);
              break;
          case KVM_GET_VCPU_MMAP_SIZE:
  .    …..
}

As such as kvm_chardev_fops, there exist kvm_vm_fops and kvm_vcpu_fops:

static struct file_operations kvm_vm_fops = {
        .release        = kvm_vm_release,
...

Getting acquainted with libvirt and its implementation


As discussed in a previous chapter, there is an extra management layer called libvirt which can talk to various hypervisors (for example: KVM/QEMU, LXC, OpenVZ, UML, and so on) underlying it. libvirt is an open source Application Programming Interface (API). At the same time, it is a daemon and a management tool for managing different hypervisors as mentioned. libvirt is in use by various virtualization programs and platforms; for example, graphical user interfaces are provided by GNOME boxes and virt-manager (http://virt-manager.org/). Don't confuse this with virtual machine monitor/VMM which we discussed in Chapter 1, Understanding Linux Virtualization.

The command line client interface of libvirt is the binary called virsh. libvirt is also used by other higher-level management tools, such as oVirt (www.ovirt.org):

Most people think that libvirt is restricted to a single node or local node where it is running; it's not true. libvirt...

Internal workings of libvirt


Let me give some details about the following libvirt source code. If you really want to know more about the implementation, it is good to poke around in the libvirt source code. Get the libvirt source code from the libvirt Git repository:

[root@node]# git clone git://libvirt.org/libvirt.git

Once you clone the repo, you can see the following hierarchy of files in the repo:

libvirt code is based on the C programming language; however, libvirt has language bindings in different languages such as C#, Java, OCaml, Perl, PHP, Python, Ruby, and so on. For more details on these bindings, please refer to: https://libvirt.org/bindings.html. The main (and few) directories in the source code are docs, daemon, src, and so on. The libvirt project is well documented and the documentation is available in the source code repo and also at http://libvirt.org.

Let us move on. If we look at the libvirt internals, we can see libvirt operates or starts the connection path based on driver...

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Key benefits

  • Become an expert in Linux virtualization
  • Migrate your virtualized datacenter to the cloud
  • Find out how to build a large scale virtualization solution that will transform your organization

Description

A robust datacenter is essential for any organization – but you don’t want to waste resources. With KVM you can virtualize your datacenter, transforming a Linux operating system into a powerful hypervisor that allows you to manage multiple OS with minimal fuss. This book doesn’t just show you how to virtualize with KVM – it shows you how to do it well. Written to make you an expert on KVM, you’ll learn to manage the three essential pillars of scalability, performance and security – as well as some useful integrations with cloud services such as OpenStack. From the fundamentals of setting up a standalone KVM virtualization platform, and the best tools to harness it effectively, including virt-manager, and kimchi-project, everything you do is built around making KVM work for you in the real-world, helping you to interact and customize it as you need it. With further guidance on performance optimization for Microsoft Windows and RHEL virtual machines, as well as proven strategies for backup and disaster recovery, you’ll can be confident that your virtualized data center is working for your organization – not hampering it. Finally, the book will empower you to unlock the full potential of cloud through KVM. Migrating your physical machines to the cloud can be challenging, but once you’ve mastered KVM, it’s a little easie.

Who is this book for?

Linux administrators – if you want to build incredible, yet manageable virtualization solutions with KVM this is the book to get you there. It will help you apply what you already know to some tricky virtualization tasks.

What you will learn

  • Explore the ecosystem of tools that support Linux virtualization
  • Find out why KVM offers you a smarter way to unlock the potential of virtualization
  • Implement KVM virtualization using oVirt
  • Explore the KVM architecture – so you can manage, scale and optimize it with ease
  • Migrate your virtualized datacenter to the cloud for truly resource-efficient computing
  • Find out how to integrate OpenStack with KVM to take full control of the cloud

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Aug 19, 2016
Length: 468 pages
Edition : 1st
Language : English
ISBN-13 : 9781784399054
Vendor :
Red Hat
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Product Details

Publication date : Aug 19, 2016
Length: 468 pages
Edition : 1st
Language : English
ISBN-13 : 9781784399054
Vendor :
Red Hat
Tools :

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Table of Contents

16 Chapters
1. Understanding Linux Virtualization Chevron down icon Chevron up icon
2. KVM Internals Chevron down icon Chevron up icon
3. Setting Up Standalone KVM Virtualization Chevron down icon Chevron up icon
4. Getting Started with libvirt and Creating Your First Virtual Machines Chevron down icon Chevron up icon
5. Network and Storage Chevron down icon Chevron up icon
6. Virtual Machine Lifecycle Management Chevron down icon Chevron up icon
7. Templates and Snapshots Chevron down icon Chevron up icon
8. Kimchi – An HTML5-Based Management Tool for KVM/libvirt Chevron down icon Chevron up icon
9. Software-Defined Networking for KVM Virtualization Chevron down icon Chevron up icon
10. Installing and Configuring the Virtual Datacenter Using oVirt Chevron down icon Chevron up icon
11. Starting Your First Virtual Machine in oVirt Chevron down icon Chevron up icon
12. Deploying OpenStack Private Cloud backed by KVM Virtualization Chevron down icon Chevron up icon
13. Performance Tuning and Best Practices in KVM Chevron down icon Chevron up icon
14. V2V and P2V Migration Tools Chevron down icon Chevron up icon
A. Converting a Virtual Machine into a Hypervisor Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Top Reviews
Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.2
(16 Ratings)
5 star 62.5%
4 star 6.3%
3 star 18.8%
2 star 12.5%
1 star 0%
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Amazon Customer Jan 04, 2019
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Excellent book!
Amazon Verified review Amazon
Jivan Nisargam Mar 10, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I read the whole book and found so much information on topics like KVM internal, Software Defined Networking, Ovirt, Openstack, Performance issues, V2V/P2V. I have never found a single book which covers all topics related to KVM. This book deserves more then 5 stars.
Amazon Verified review Amazon
D Caughey Apr 05, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
The best KVM book out there to get a really good foundation and pretty good knowledge. Pretty well written but would have liked more in depth examples. Chap1 is far too long and is pointed directly at developers.
Amazon Verified review Amazon
Amazon Customer May 20, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Awesome Book About Linux Virtualiaztion, KVM , Qemu, libvirt, Ovirt and its integration.
Amazon Verified review Amazon
Joao Rodrigues May 23, 2017
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book is a very valuable resource! It takes you from the inner works of Linux KVM, what happens under the hood, explores the different types of hypervisors, and sets out to explain how and why Linux is a very solid choice for the datacentre virtualization layer. It takes the reader from the most basic level, and builds up the knowledge to explore more advanced features such as SDN, OpenStack, as well as operational topics such as VM Lifecycle management. Everything is very clearly explained and nicely structured! Five stars! :-)
Amazon Verified review Amazon
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