Shulou(Shulou.com)06/02 Report--

QEMU

Qemu is an independent virtualization solution, virtualizing through inter-VT or AMD SVM, installing qemu system, you can directly simulate a completely different system around the river, and the creation of virtual machines can be completed through qemu-image. Qemu itself can be independent of KVM, but if KVM exists and the hardware (processor) supports functions such as Inter VT, then QEMU can use the functions provided by KVM to improve performance in virtualizing the processor.

KVM

KVM is a fully virtualized solution for Linux integrated into the Linux kernel with an X86 architecture and hardware support for virtualization technologies (IntelVT or AMD-V). It is a very small module of Linux, using Linux to do a lot of things, such as task scheduling, memory management and hardware device interaction. To be exact, KVM is a module of Linux kernel. You can use the command modprobe to load the KVM module. After the module is loaded, you can further create the virtual machine through other tools. But the KVM module is far from enough, because the user cannot directly control the kernel module to do things, and you must have a tool that runs in user space. As a user-space tool, kvm developers chose the established open source virtualization software QEMU. QEMU is also a virtualization software. Its characteristic is that it can virtualize different CPU. For example, you can virtualize a Power CPU on x86 CPU, and use it to compile programs that can run on Power. KVM uses part of QEMU and is slightly modified to become a user space tool that can control KVM. So you will see that the official KVM download has two major parts (qemu and kvm) and three files (the KVM module, the QEMU tool, and a collection of both). In other words, you can only upgrade the KVM module, or you can upgrade only the QEMU tool. This is the relationship between KVM and QEMU. The KVM kernel module itself can only provide virtualization of CPU and memory, so it must be combined with QEMU to form a complete virtualization technology, which is called qemu-kvm.

KVM-QEMU

Qemu integrates KVM, calls the / dev/kvm interface through ioctl, and hands over the part of the CPU instruction to the kernel module. Kvm is responsible for cpu Virtualization + memory Virtualization, which virtualizes cpu and memory, but kvm cannot simulate other devices. Qemu simulates IO devices (network cards, disks, etc.), kvm plus qemu can achieve real server virtualization. Because the above two things are used, it is called qemu-kvm. Qemu simulates other hardware, such as Network and Disk, which will also affect the performance of these devices, so pass through paravirtualized devices virtio_blk and virtio_net are produced to improve device performance.

LIBVIRT

Libvirt is a collection of software that manages virtual machines and other virtualization functions, such as storage management and network management. It includes an API library, a daemon (libvirtd), and a command line tool (virsh); libvirt itself is built on an abstract concept. It provides a common API for common functions implemented by supported hypervisors. The main goal of libvirt is to provide a convenient and reliable programming interface for various virtualization tools to manage many different virtualization providers in a single way.

Functional virtual machine management: includes different domain lifecycle operations, such as start, stop, pause, save, restore, and migrate. Supports hot-swappable operations for multiple device types, including disks, network cards, memory and CPU. Remote machine support: as long as libvirt daemon is running on the machine, including remote machines, all libvirt functions can be accessed and used. Support a variety of network remote transmission, using the simplest SSH, no additional configuration work is required. Storage management: any host running libvirt daemon can be used to manage different types of storage: create file images of different formats (qcow2, vmdk, raw, etc.), attach NFS shares, list existing LVM volume groups, create new LVM volume groups and logical volumes, partition unprocessed disk devices, mount iSCSI shares, and so on. Because libvirt can work remotely, all of these can be used by remote hosts. Network interface management: any host running libvirt daemon can be used to manage physical and logical network interfaces. Virtual NAT and routing-based networks: any host running libvirt daemon can be used to manage and create virtual networks. The relationship between openstack, kvm, qemu-kvm and libvirt (copied from the network)

KVM is the lowest-level hypervisor, which is used to simulate the operation of CPU. It lacks support for network and surrounding Iripple O, so we can't use it directly. QEMU-KVM is a complete simulator, it is built on top of KVM, it provides complete network and IMaguo support. Openstack does not directly control qemu-kvm, it uses a library called libvirt to indirectly control qemu-kvm. Libvirt provides cross-VM platform functionality, which can control simulators other than QEMU, including vmware, virtualbox, xen, and so on. So for the sake of the cross-VM nature of openstack, openstack will only use libvirt instead of qemu-kvm. Libvirt also provides some advanced features, such as pool/vol management.

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