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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.
65 variables are available:
66 .Bl -tag -width indent
67 .It Va vfs.fusefs.kernelabi_major
68 Major version of the FUSE kernel ABI supported by this driver.
69 .It Va vfs.fusefs.kernelabi_minor
70 Minor version of the FUSE kernel ABI supported by this driver.
71 .It Va vfs.fusefs.data_cache_mode
74 will cache file data for pre-7.23 file systems.
75 A value of 0 will disable caching entirely.
76 Every data access will be forwarded to the daemon.
77 A value of 1 will select write-through caching.
78 Reads will be cached in the VFS layer as usual.
79 Writes will be immediately forwarded to the daemon, and also added to the cache.
80 A value of 2 will select write-back caching.
81 Reads and writes will both be cached, and writes will occasionally be flushed
82 to the daemon by the page daemon.
83 Write-back caching is usually unsafe, especially for FUSE file systems that
84 require network access.
86 FUSE file systems using protocol 7.23 or later specify their cache behavior
87 on a per-mountpoint basis, ignoring this sysctl.
88 .It Va vfs.fusefs.stats.filehandle_count
89 Current number of open FUSE file handles.
90 .It Va vfs.fusefs.stats.lookup_cache_hits
91 Total number of lookup cache hits.
92 .It Va vfs.fusefs.stats.lookup_cache_misses
93 Total number of lookup cache misses.
94 .It Va vfs.fusefs.stats.node_count
95 Current number of allocated FUSE vnodes.
96 .It Va vfs.fusefs.stats.ticket_count
97 Current number of allocated FUSE tickets, which is roughly equal to the number
98 of FUSE operations currently being processed by daemons.
99 .\" Undocumented sysctls
100 .\" ====================
101 .\" vfs.fusefs.enforce_dev_perms: I don't understand it well enough.
102 .\" vfs.fusefs.iov_credit: I don't understand it well enough
103 .\" vfs.fusefs.iov_permanent_bufsize: I don't understand it well enough
110 driver was written as the part of the
112 implementation of the FUSE userspace file system framework (see
113 .Lk https://github.com/libfuse/libfuse )
114 and first appeared in the
115 .Pa sysutils/fusefs-kmod
118 It was added to the base system in
128 driver was originally written by
130 as a Google Summer of Code project in 2005.
131 It was further developed by
133 during Google Summer of Code 2011, and that version was integrated into the
135 .An Attilio Rao Aq Mt attilio@FreeBSD.org .
137 This manual page was written by
138 .An Alan Somers Aq Mt asomers@FreeBSD.org .