2 .\" SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 .\" Copyright (c) 2019 The FreeBSD Foundation
6 .\" This software was developed by BFF Storage Systems, LLC under sponsorship
7 .\" from the FreeBSD Foundation.
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36 .Nd "File system in USErspace"
38 To link into the kernel:
39 .Bd -ragged -offset indent
43 To load as a loadable kernel module:
49 driver implements a file system that is serviced by a userspace program.
51 There are many uses for
53 Userspace daemons can access libraries or programming languages that cannot run
54 in kernel-mode, for example.
56 is also useful for developing and debugging file systems, because a crash of
57 the daemon will not take down the entire operating system.
61 Many daemons can run on multiple operating systems with minimal modifications.
63 The following variables are available as both
68 .Bl -tag -width indent
69 .It Va vfs.fusefs.kernelabi_major
70 Major version of the FUSE kernel ABI supported by this driver.
71 .It Va vfs.fusefs.kernelabi_minor
72 Minor version of the FUSE kernel ABI supported by this driver.
73 .It Va vfs.fusefs.data_cache_mode
77 A value of 0 will disable caching entirely.
78 Every data access will be forwarded to the daemon.
79 A value of 1 will select write-through caching.
80 Reads will be cached in the VFS layer as usual.
81 Writes will be immediately forwarded to the daemon, and also added to the cache.
82 A value of 2 will select write-back caching.
83 Reads and writes will both be cached, and writes will occasionally be flushed
84 to the daemon by the page daemon.
85 Write-back caching is usually unsafe, especially for FUSE file systems that
86 require network access.
87 .It Va vfs.fusefs.lookup_cache_enable
90 will cache lookup responses from the file system.
91 FUSE file systems indicate whether lookup responses should be cacheable, but
92 it may be useful to globally disable caching them if a file system is
94 .\" Undocumented sysctls
95 .\" ====================
96 .\" Counters: I intend to rename to vfs.fusefs.stats.* for clarity
97 .\" vfs.fusefs.lookup_cache_{hits, misses}
98 .\" vfs.fusefs.filehandle_count
99 .\" vfs.fusefs.ticker_count
100 .\" vfs.fusefs.node_count
102 .\" vfs.fusefs.version - useless since the driver moved in-tree
103 .\" vfs.fusefs.reclaim_revoked: I don't understand it well-enough
104 .\" vfs.fusefs.enforce_dev_perms: I don't understand it well enough.
105 .\" vfs.fusefs.iov_credit: I don't understand it well enough
106 .\" vfs.fusefs.iov_permanent_bufsize: I don't understand it well enough
107 .\" vfs.fusefs.fix_broken_io: I don't understand it well enough
108 .\" vfs.fusefs.sync_resize: useless and should be removed
109 .\" vfs.fusefs.refresh_size: probably useless?
110 .\" vfs.fusefs.mmap_enable: why is this optional?
111 .\" vfs.fusefs.data_cache_invalidate: what is this needed for?
117 driver was written as the part of the
119 implementation of the FUSE userspace file system framework (see
120 .Xr https://github.com/libfuse/libfuse )
121 and first appeared in the
122 .Pa sysutils/fusefs-kmod
125 It was added to the base system in
135 driver was originally written by
137 as a Google Summer of Code project in 2005.
138 It was further developed by
140 during Google Summer of Code 2011, and that version was integrated into the
142 .An Attilio Rao Aq Mt attilio@FreeBSD.org .
144 This manual page was written by
145 .An Alan Somers Aq Mt asomers@FreeBSD.org .