1 .. SPDX-License-Identifier: GPL-2.0
2
3 .. _virtiofs_index:
4
5 ==============================================
6 virtiofs: virtio-fs host<->guest shared file s
7 ==============================================
8
9 - Copyright (C) 2019 Red Hat, Inc.
10
11 Introduction
12 ============
13 The virtiofs file system for Linux implements
14 VIRTIO "virtio-fs" device for guest<->host fil
15 guest to mount a directory that has been expor
16
17 Guests often require access to files residing
18 Use cases include making files available to ne
19 booting from a root file system located on the
20 stateless or ephemeral guests, and sharing a d
21
22 Although it is possible to use existing networ
23 tasks, they require configuration steps that a
24 expose the storage network to the guest. The
25 solve these problems by providing file system
26
27 Furthermore the virtio-fs device takes advanta
28 guest and host to increase performance and pro
29 possible with network file systems.
30
31 Usage
32 =====
33 Mount file system with tag ``myfs`` on ``/mnt`
34
35 .. code-block:: sh
36
37 guest# mount -t virtiofs myfs /mnt
38
39 Please see https://virtio-fs.gitlab.io/ for de
40 and the virtiofsd daemon.
41
42 Mount options
43 -------------
44
45 virtiofs supports general VFS mount options, f
46 ro, rw, context, etc. It also supports FUSE mo
47
48 atime behavior
49 ^^^^^^^^^^^^^^
50
51 The atime-related mount options, for example,
52 are ignored. The atime behavior for virtiofs i
53 underlying filesystem of the directory that ha
54 on the host.
55
56 Internals
57 =========
58 Since the virtio-fs device uses the FUSE proto
59 virtiofs file system for Linux is integrated c
60 client. The guest acts as the FUSE client whi
61 server. The /dev/fuse interface between the k
62 with the virtio-fs device interface.
63
64 FUSE requests are placed into a virtqueue and
65 response portion of the buffer is filled in by
66 the request completion.
67
68 Mapping /dev/fuse to virtqueues requires solvi
69 between /dev/fuse and virtqueues. Each time t
70 FUSE client may choose which request to transf
71 prioritize certain requests over others. Virt
72 it is not possible to change the order of requ
73 This is especially important if the virtqueue
74 impossible to add high priority requests. In
75 the virtio-fs device uses a "hiprio" virtqueue
76 have priority over normal requests.
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