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Commit 8f744bde authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'virtio-fs-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse 

Pull fuse virtio-fs support from Miklos Szeredi:
 "Virtio-fs allows exporting directory trees on the host and mounting
  them in guest(s).

  This isn't actually a new filesystem, but a glue layer between the
  fuse filesystem and a virtio based back-end.

  It's similar in functionality to the existing virtio-9p solution, but
  significantly faster in benchmarks and has better POSIX compliance.
  Further permformance improvements can be achieved by sharing the page
  cache between host and guest, allowing for faster I/O and reduced
  memory use.

  Kata Containers have been including the out-of-tree virtio-fs (with
  the shared page cache patches as well) since version 1.7 as an
  experimental feature. They have been active in development and plan to
  switch from virtio-9p to virtio-fs as their default solution. There
  has been interest from other sources as well.

  The userspace infrastructure is slated to be merged into qemu once the
  kernel part hits mainline.

  This was developed by Vivek Goyal, Dave Gilbert and Stefan Hajnoczi"

* tag 'virtio-fs-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse:
  virtio-fs: add virtiofs filesystem
  virtio-fs: add Documentation/filesystems/virtiofs.rst
  fuse: reserve values for mapping protocol
parents 9977b1a7 a62a8ef9

Documentation/filesystems/index.rst

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@@ -37,3 +37,13 @@ filesystem implementations. 
   journalling

   fscrypt

   fsverity



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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@@ -17280,6 +17280,18 @@ S: Supported 
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>

































fs/fuse/Kconfig



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@@ -27,3 +27,14 @@ config CUSE





























	  If you want to develop or use a userspace character device















	  based on CUSE, answer Y or M.



























config VIRTIO_FS













	tristate "Virtio Filesystem"













	depends on FUSE_FS













	select VIRTIO













	help













	  The Virtio Filesystem allows guests to mount file systems from the













          host.



























	  If you want to share files between guests or with the host, answer Y













          or M.
























fs/fuse/Makefile



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@@ -5,5 +5,6 @@





























obj-$(CONFIG_FUSE_FS) += fuse.o















obj-$(CONFIG_CUSE) += cuse.o













obj-$(CONFIG_VIRTIO_FS) += virtio_fs.o































fuse-objs := dev.o dir.o file.o inode.o control.o xattr.o acl.o readdir.o