virtio-fs: add Documentation/filesystems/virtiofs.rst (2d1d25d0) · Commits · e / devices / android_kernel_fairphone_FP5

Documentation/filesystems/index.rst

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		journalling
		fscrypt

		Filesystems
		===========

		Documentation for filesystem implementations.

		.. toctree::
		:maxdepth: 2

		virtiofs

Documentation/filesystems/virtiofs.rst

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		.. SPDX-License-Identifier: GPL-2.0

		===================================================
		virtiofs: virtio-fs host<->guest shared file system
		===================================================

		- Copyright (C) 2019 Red Hat, Inc.

		Introduction
		============
		The virtiofs file system for Linux implements a driver for the paravirtualized
		VIRTIO "virtio-fs" device for guest<->host file system sharing. It allows a
		guest to mount a directory that has been exported on the host.

		Guests often require access to files residing on the host or remote systems.
		Use cases include making files available to new guests during installation,
		booting from a root file system located on the host, persistent storage for
		stateless or ephemeral guests, and sharing a directory between guests.

		Although it is possible to use existing network file systems for some of these
		tasks, they require configuration steps that are hard to automate and they
		expose the storage network to the guest. The virtio-fs device was designed to
		solve these problems by providing file system access without networking.

		Furthermore the virtio-fs device takes advantage of the co-location of the
		guest and host to increase performance and provide semantics that are not
		possible with network file systems.

		Usage
		=====
		Mount file system with tag ``myfs`` on ``/mnt``:

		.. code-block:: sh

		guest# mount -t virtiofs myfs /mnt

		Please see https://virtio-fs.gitlab.io/ for details on how to configure QEMU
		and the virtiofsd daemon.

		Internals
		=========
		Since the virtio-fs device uses the FUSE protocol for file system requests, the
		virtiofs file system for Linux is integrated closely with the FUSE file system
		client. The guest acts as the FUSE client while the host acts as the FUSE
		server. The /dev/fuse interface between the kernel and userspace is replaced
		with the virtio-fs device interface.

		FUSE requests are placed into a virtqueue and processed by the host. The
		response portion of the buffer is filled in by the host and the guest handles
		the request completion.

		Mapping /dev/fuse to virtqueues requires solving differences in semantics
		between /dev/fuse and virtqueues. Each time the /dev/fuse device is read, the
		FUSE client may choose which request to transfer, making it possible to
		prioritize certain requests over others. Virtqueues have queue semantics and
		it is not possible to change the order of requests that have been enqueued.
		This is especially important if the virtqueue becomes full since it is then
		impossible to add high priority requests. In order to address this difference,
		the virtio-fs device uses a "hiprio" virtqueue specifically for requests that
		have priority over normal requests.

MAINTAINERS

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		F: drivers/s390/virtio/
		F: arch/s390/include/uapi/asm/virtio-ccw.h

		VIRTIO FILE SYSTEM
		M: Vivek Goyal <vgoyal@redhat.com>
		M: Stefan Hajnoczi <stefanha@redhat.com>
		M: Miklos Szeredi <miklos@szeredi.hu>
		L: virtualization@lists.linux-foundation.org
		L: linux-fsdevel@vger.kernel.org
		W: https://virtio-fs.gitlab.io/
		S: Supported
		F: fs/fuse/virtio_fs.c
		F: include/uapi/linux/virtio_fs.h
		F: Documentation/filesystems/virtiofs.rst

		VIRTIO GPU DRIVER
		M: David Airlie <airlied@linux.ie>
		M: Gerd Hoffmann <kraxel@redhat.com>