Documentation/filesystems/fuse.rst

10 Userspace filesystem:
11   A filesystem in which data and metadata are provided by an ordinary
12   userspace process.  The filesystem can be accessed normally through
16   The process(es) providing the data and metadata of the filesystem.
19   A userspace filesystem mounted by a non-privileged (non-root) user.
20   The filesystem daemon is running with the privileges of the mounting
25   A connection between the filesystem daemon and the kernel.  The
26   connection exists until either the daemon dies, or the filesystem is
27   umounted.  Note that detaching (or lazy umounting) the filesystem
29   the last reference to the filesystem is released.
35   The user who is performing filesystem operations.
40 FUSE is a userspace filesystem framework.  It consists of a kernel
46 filesystems.  A good example is sshfs: a secure network filesystem
55 The filesystem type given to mount(2) can be one of the following:
58       This is the usual way to mount a FUSE filesystem.  The first
63       The filesystem is block device based.  The first argument of the
71   filesystem and the kernel.  The file descriptor must have been
75   The file mode of the filesystem's root in octal representation.
85   filesystem is free to implement its access policy or leave it to
93   to the user mounting the filesystem.  This option is by default only
103   Set the block size for the filesystem.  The default is 512.  This
106 Control filesystem
109 There's a control filesystem for FUSE, which can be mounted by::
116 Under the fuse control filesystem each connection has a directory
123 	  userspace or being processed by the filesystem daemon.  If there is
124 	  no filesystem activity and 'waiting' is non-zero, then the
125 	  filesystem is hung or deadlocked.
128 	  Writing anything into this file will abort the filesystem
134 Interrupting filesystem operations
137 If a process issuing a FUSE filesystem request is interrupted, the
153 userspace filesystem will receive queued INTERRUPTs before any others.
155 The userspace filesystem may ignore the INTERRUPT requests entirely,
168 If the filesystem cannot find the original request, it should wait for
174 Aborting a filesystem connection
177 It is possible to get into certain situations where the filesystem is
180   a) Broken userspace filesystem implementation
191 the filesystem.  There are several ways to do this:
193   - Kill the filesystem daemon.  Works in case of a) and b)
195   - Kill the filesystem daemon and all users of the filesystem.  Works
199     filesystem is still attached (it hasn't been lazy unmounted)
201   - Abort filesystem through the FUSE control filesystem.  Most
215     help of the mounted filesystem
228     1. creating a filesystem containing a device file, then opening this device
230     2. creating a filesystem containing a suid or sgid application, then executing this application
238     filesystem, the filesystem daemon serving requests can record the
248      1) mounting a filesystem over a file or directory which the mount
262             filesystem operation creating a DoS against the user or the
265             filesystem could be stopped, and thus causing the system
274 	to access the filesystem, which could otherwise not be
279 	the filesystem or not.
284 	filesystem, since *SIGSTOP* can be used to get a similar effect.
318 The following diagram shows how a filesystem operation (in this
322  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
364 There are a couple of ways in which to deadlock a FUSE filesystem.
370  |  "rm /mnt/fuse/file"               |  FUSE filesystem daemon
383 The solution for this is to allow the filesystem to be aborted.
388 This one needs a carefully crafted filesystem.  It's a variation on
389 the above, only the call back to the filesystem is not explicit,
392  |  Kamikaze filesystem thread 1      |  Kamikaze filesystem thread 2