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VirtFS - A virtualization aware File System pass-through.

Venkateswararao Jujjuri (jvrao@linux.vnet.ibm.com)

Virtualization in Linux was a hot buzz in the last decade and now it is a reality. Many components like KVM and QEMU are converging to produce practical systems. While the hardware and software technologies are coming together, industry and customers are embracing the idea of virtualization on Linux and deploying virtual machines as a feasible alternative to physical machines.

Historically, Linux has focused on improving and para-virtualizing underlying devices like disks and networks. Virtualizing a disk has many drawbacks as a great amount of information is lost between the applications running in a guest interacting with the guest's file system and the hypervisor which only sees operations to a disk.

In this paradigm there lies a need for virtualization aware (para-virtual) system services like File Systems. We are introducing one of the first examples of paravirtualizing system services: Virtualization aware File System pass-through - VirtFS.

VirtFS consists of 9P client and server portions and offers a file system pass-through mechanism between KVM host and guest operating systems. It is positioned to exploit the current technologies and is being built on their strengths.

* Uses 9P protocol by defining Linux extension (9P2000.L).

* Client is already part of mainline kernel and seamlessly plugs into VFS layer.

* Server will be part of QEMU, a natural way to share data between the host and the guest.

* Uses virtIO as its transport mechanism.

This paper details the VirtFS design, how it is being built to take advantage of existing technologies like 9P, QEMU, and VirtIO. The paper also goes on explaining how it can offer some of the most desirables that the virtualization world has to offer - host and guest isolation, secure access of host file systems on guest, close to native file system performance, multi tenancy, etc.

We conclude with the future of this technology on how it is poised to take advantage of the fact that the guest and host are running on the same hardware and how various caches and memory can be shared between them.



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