fuse/README - android_bootable_recovery - Gitiles

 General Information
 ===================

 FUSE (Filesystem in Userspace) is a simple interface for userspace
 programs to export a virtual filesystem to the Linux kernel.  FUSE
 also aims to provide a secure method for non privileged users to
 create and mount their own filesystem implementations.

 You can download the source code releases from

   http://sourceforge.net/projects/fuse

 or alternatively you can use CVS to get the very latest development
 version:

   cvs -d :pserver:anonymous@fuse.cvs.sourceforge.net:/cvsroot/fuse co fuse


 Dependencies
 ============

 Linux kernel version 2.6.X where X >= 9.

 Alternatively a kernel module from FUSE release 2.5.* can be used with
 this release, which supports kernels >= 2.4.21.

 Installation
 ============

 ./configure
 make
 make install
 modprobe fuse

 You may also need to add '/usr/local/lib' to '/etc/ld.so.conf' and/or
 run ldconfig.

 You'll also need a fuse kernel module, Linux kernels 2.6.14 or later
 contain FUSE support.

 For more details see the file 'INSTALL'

 How To Use
 ==========

 FUSE is made up of three main parts:

  - A kernel filesystem module

  - A userspace library

  - A mount/unmount program


 Here's how to create your very own virtual filesystem in five easy
 steps (after installing FUSE):

   1) Edit the file example/fusexmp.c to do whatever you want...

   2) Build the fusexmp program

   3) run 'example/fusexmp /mnt/fuse -d'

   4) ls -al /mnt/fuse

   5) Be glad

 If it doesn't work out, please ask!  Also see the file 'include/fuse.h' for
 detailed documentation of the library interface.

 Security
 ========

 If you run 'make install', the fusermount program is installed
 set-user-id to root.  This is done to allow normal users to mount
 their own filesystem implementations.

 There must however be some limitations, in order to prevent Bad User from
 doing nasty things.  Currently those limitations are:

   - The user can only mount on a mountpoint, for which it has write
     permission

   - The mountpoint is not a sticky directory which isn't owned by the
     user (like /tmp usually is)

   - No other user (including root) can access the contents of the mounted
     filesystem.

 Configuration
 =============

 Some options regarding mount policy can be set in the file
 '/etc/fuse.conf'

 Currently these options are:

 mount_max = NNN

   Set the maximum number of FUSE mounts allowed to non-root users.
   The default is 1000.

 user_allow_other

   Allow non-root users to specify the 'allow_other' or 'allow_root'
   mount options.


 Mount options
 =============

 Most of the generic mount options described in 'man mount' are
 supported (ro, rw, suid, nosuid, dev, nodev, exec, noexec, atime,
 noatime, sync async, dirsync).  Filesystems are mounted with
 '-onodev,nosuid' by default, which can only be overridden by a
 privileged user.

 These are FUSE specific mount options that can be specified for all
 filesystems:

 default_permissions

   By default FUSE doesn't check file access permissions, the
   filesystem is free to implement it's access policy or leave it to
   the underlying file access mechanism (e.g. in case of network
   filesystems).  This option enables permission checking, restricting
   access based on file mode.  This is option is usually useful
   together with the 'allow_other' mount option.

 allow_other

   This option overrides the security measure restricting file access
   to the user mounting the filesystem.  So all users (including root)
   can access the files.  This option is by default only allowed to
   root, but this restriction can be removed with a configuration
   option described in the previous section.

 allow_root

   This option is similar to 'allow_other' but file access is limited
   to the user mounting the filesystem and root.  This option and
   'allow_other' are mutually exclusive.

 kernel_cache

   This option disables flushing the cache of the file contents on
   every open().  This should only be enabled on filesystems, where the
   file data is never changed externally (not through the mounted FUSE
   filesystem).  Thus it is not suitable for network filesystems and
   other "intermediate" filesystems.

   NOTE: if this option is not specified (and neither 'direct_io') data
   is still cached after the open(), so a read() system call will not
   always initiate a read operation.

 auto_cache

   This option enables automatic flushing of the data cache on open().
   The cache will only be flushed if the modification time or the size
   of the file has changed.

 large_read

   Issue large read requests.  This can improve performance for some
   filesystems, but can also degrade performance.  This option is only
   useful on 2.4.X kernels, as on 2.6 kernels requests size is
   automatically determined for optimum performance.

 direct_io

   This option disables the use of page cache (file content cache) in
   the kernel for this filesystem.  This has several affects:

      - Each read() or write() system call will initiate one or more
        read or write operations, data will not be cached in the
        kernel.

      - The return value of the read() and write() system calls will
        correspond to the return values of the read and write
        operations.  This is useful for example if the file size is not
        known in advance (before reading it).

 max_read=N

   With this option the maximum size of read operations can be set.
   The default is infinite.  Note that the size of read requests is
   limited anyway to 32 pages (which is 128kbyte on i386).

 max_readahead=N

   Set the maximum number of bytes to read-ahead.  The default is
   determined by the kernel.  On linux-2.6.22 or earlier it's 131072
   (128kbytes)

 max_write=N

   Set the maximum number of bytes in a single write operation.  The
   default is 128kbytes.  Note, that due to various limitations, the
   size of write requests can be much smaller (4kbytes).  This
   limitation will be removed in the future.

 async_read

   Perform reads asynchronously. This is the default

 sync_read

   Perform all reads (even read-ahead) synchronously.

 hard_remove

   The default behavior is that if an open file is deleted, the file is
   renamed to a hidden file (.fuse_hiddenXXX), and only removed when
   the file is finally released.  This relieves the filesystem
   implementation of having to deal with this problem.  This option
   disables the hiding behavior, and files are removed immediately in
   an unlink operation (or in a rename operation which overwrites an
   existing file).

   It is recommended that you not use the hard_remove option. When
   hard_remove is set, the following libc functions fail on unlinked
   files (returning errno of ENOENT):
      - read()
      - write()
      - fsync()
      - close()
      - f*xattr()
      - ftruncate()
      - fstat()
      - fchmod()
      - fchown()

 debug

   Turns on debug information printing by the library.

 fsname=NAME

   Sets the filesystem source (first field in /etc/mtab).  The default
   is the program name.

 subtype=TYPE

   Sets the filesystem type (third field in /etc/mtab).  The default is
   the program name.

   If the kernel suppports it, /etc/mtab and /proc/mounts will show the
   filesystem type as "fuse.TYPE"

   If the kernel doesn't support subtypes, the source filed will be
   "TYPE#NAME", or if fsname option is not specified, just "TYPE".

 use_ino

   Honor the 'st_ino' field in getattr() and fill_dir().  This value is
   used to fill in the 'st_ino' field in the stat()/lstat()/fstat()
   functions and the 'd_ino' field in the readdir() function.  The
   filesystem does not have to guarantee uniqueness, however some
   applications rely on this value being unique for the whole
   filesystem.

 readdir_ino

   If 'use_ino' option is not given, still try to fill in the 'd_ino'
   field in readdir().  If the name was previously looked up, and is
   still in the cache, the inode number found there will be used.
   Otherwise it will be set to '-1'.  If 'use_ino' option is given,
   this option is ignored.

 nonempty

   Allows mounts over a non-empty file or directory.  By default these
   mounts are rejected (from version 2.3.1) to prevent accidental
   covering up of data, which could for example prevent automatic
   backup.

 umask=M

   Override the permission bits in 'st_mode' set by the filesystem.
   The resulting permission bits are the ones missing from the given
   umask value.  The value is given in octal representation.

 uid=N

   Override the 'st_uid' field set by the filesystem.

 gid=N

   Override the 'st_gid' field set by the filesystem.

 blkdev

   Mount a filesystem backed by a block device.  This is a privileged
   option.  The device must be specified with the 'fsname=NAME' option.

 entry_timeout=T

   The timeout in seconds for which name lookups will be cached. The
   default is 1.0 second.  For all the timeout options, it is possible
   to give fractions of a second as well (e.g. "-oentry_timeout=2.8")

 negative_timeout=T

   The timeout in seconds for which a negative lookup will be cached.
   This means, that if file did not exist (lookup retuned ENOENT), the
   lookup will only be redone after the timeout, and the file/directory
   will be assumed to not exist until then.  The default is 0.0 second,
   meaning that caching negative lookups are disabled.

 attr_timeout=T

   The timeout in seconds for which file/directory attributes are
   cached.  The default is 1.0 second.

 ac_attr_timeout=T

   The timeout in seconds for which file attributes are cached for the
   purpose of checking if "auto_cache" should flush the file data on
   open.   The default is the value of 'attr_timeout'

 intr

   Allow requests to be interrupted.  Turning on this option may result
   in unexpected behavior, if the filesystem does not support request
   interruption.

 intr_signal=NUM

   Specify which signal number to send to the filesystem when a request
   is interrupted.  The default is 10 (USR1).

 modules=M1[:M2...]

   Add modules to the filesystem stack.  Modules are pushed in the
   order they are specified, with the original filesystem being on the
   bottom of the stack.


 Modules distributed with fuse
 -----------------------------

 iconv
 `````
 Perform file name character set conversion.  Options are:

 from_code=CHARSET

   Character set to convert from (see iconv -l for a list of possible
   values).  Default is UTF-8.

 to_code=CHARSET

   Character set to convert to.  Default is determined by the current
   locale.


 subdir
 ``````
 Prepend a given directory to each path. Options are:

 subdir=DIR

   Directory to prepend to all paths.  This option is mandatory.

 rellinks

   Transform absolute symlinks into relative

 norellinks

   Do not transform absolute symlinks into relative.  This is the default.


 Reporting bugs
 ==============

 Please send bug reports to the <fuse-devel@lists.sourceforge.net>
 mailing list.

 The list is open, you need not be subscribed to post.
	General Information
	===================

	FUSE (Filesystem in Userspace) is a simple interface for userspace
	programs to export a virtual filesystem to the Linux kernel. FUSE
	also aims to provide a secure method for non privileged users to
	create and mount their own filesystem implementations.

	You can download the source code releases from

	http://sourceforge.net/projects/fuse

	or alternatively you can use CVS to get the very latest development
	version:

	cvs -d :pserver:anonymous@fuse.cvs.sourceforge.net:/cvsroot/fuse co fuse


	Dependencies
	============

	Linux kernel version 2.6.X where X >= 9.

	Alternatively a kernel module from FUSE release 2.5.* can be used with
	this release, which supports kernels >= 2.4.21.

	Installation
	============

	./configure
	make
	make install
	modprobe fuse

	You may also need to add '/usr/local/lib' to '/etc/ld.so.conf' and/or
	run ldconfig.

	You'll also need a fuse kernel module, Linux kernels 2.6.14 or later
	contain FUSE support.

	For more details see the file 'INSTALL'

	How To Use
	==========

	FUSE is made up of three main parts:

	- A kernel filesystem module

	- A userspace library

	- A mount/unmount program


	Here's how to create your very own virtual filesystem in five easy
	steps (after installing FUSE):

	1) Edit the file example/fusexmp.c to do whatever you want...

	2) Build the fusexmp program

	3) run 'example/fusexmp /mnt/fuse -d'

	4) ls -al /mnt/fuse

	5) Be glad

	If it doesn't work out, please ask! Also see the file 'include/fuse.h' for
	detailed documentation of the library interface.

	Security
	========

	If you run 'make install', the fusermount program is installed
	set-user-id to root. This is done to allow normal users to mount
	their own filesystem implementations.

	There must however be some limitations, in order to prevent Bad User from
	doing nasty things. Currently those limitations are:

	- The user can only mount on a mountpoint, for which it has write
	permission

	- The mountpoint is not a sticky directory which isn't owned by the
	user (like /tmp usually is)

	- No other user (including root) can access the contents of the mounted
	filesystem.

	Configuration
	=============

	Some options regarding mount policy can be set in the file
	'/etc/fuse.conf'

	Currently these options are:

	mount_max = NNN

	Set the maximum number of FUSE mounts allowed to non-root users.
	The default is 1000.

	user_allow_other

	Allow non-root users to specify the 'allow_other' or 'allow_root'
	mount options.


	Mount options
	=============

	Most of the generic mount options described in 'man mount' are
	supported (ro, rw, suid, nosuid, dev, nodev, exec, noexec, atime,
	noatime, sync async, dirsync). Filesystems are mounted with
	'-onodev,nosuid' by default, which can only be overridden by a
	privileged user.

	These are FUSE specific mount options that can be specified for all
	filesystems:

	default_permissions

	By default FUSE doesn't check file access permissions, the
	filesystem is free to implement it's access policy or leave it to
	the underlying file access mechanism (e.g. in case of network
	filesystems). This option enables permission checking, restricting
	access based on file mode. This is option is usually useful
	together with the 'allow_other' mount option.

	allow_other

	This option overrides the security measure restricting file access
	to the user mounting the filesystem. So all users (including root)
	can access the files. This option is by default only allowed to
	root, but this restriction can be removed with a configuration
	option described in the previous section.

	allow_root

	This option is similar to 'allow_other' but file access is limited
	to the user mounting the filesystem and root. This option and
	'allow_other' are mutually exclusive.

	kernel_cache

	This option disables flushing the cache of the file contents on
	every open(). This should only be enabled on filesystems, where the
	file data is never changed externally (not through the mounted FUSE
	filesystem). Thus it is not suitable for network filesystems and
	other "intermediate" filesystems.

	NOTE: if this option is not specified (and neither 'direct_io') data
	is still cached after the open(), so a read() system call will not
	always initiate a read operation.

	auto_cache

	This option enables automatic flushing of the data cache on open().
	The cache will only be flushed if the modification time or the size
	of the file has changed.

	large_read

	Issue large read requests. This can improve performance for some
	filesystems, but can also degrade performance. This option is only
	useful on 2.4.X kernels, as on 2.6 kernels requests size is
	automatically determined for optimum performance.

	direct_io

	This option disables the use of page cache (file content cache) in
	the kernel for this filesystem. This has several affects:

	- Each read() or write() system call will initiate one or more
	read or write operations, data will not be cached in the
	kernel.

	- The return value of the read() and write() system calls will
	correspond to the return values of the read and write
	operations. This is useful for example if the file size is not
	known in advance (before reading it).

	max_read=N

	With this option the maximum size of read operations can be set.
	The default is infinite. Note that the size of read requests is
	limited anyway to 32 pages (which is 128kbyte on i386).

	max_readahead=N

	Set the maximum number of bytes to read-ahead. The default is
	determined by the kernel. On linux-2.6.22 or earlier it's 131072
	(128kbytes)

	max_write=N

	Set the maximum number of bytes in a single write operation. The
	default is 128kbytes. Note, that due to various limitations, the
	size of write requests can be much smaller (4kbytes). This
	limitation will be removed in the future.

	async_read

	Perform reads asynchronously. This is the default

	sync_read

	Perform all reads (even read-ahead) synchronously.

	hard_remove

	The default behavior is that if an open file is deleted, the file is
	renamed to a hidden file (.fuse_hiddenXXX), and only removed when
	the file is finally released. This relieves the filesystem
	implementation of having to deal with this problem. This option
	disables the hiding behavior, and files are removed immediately in
	an unlink operation (or in a rename operation which overwrites an
	existing file).

	It is recommended that you not use the hard_remove option. When
	hard_remove is set, the following libc functions fail on unlinked
	files (returning errno of ENOENT):
	- read()
	- write()
	- fsync()
	- close()
	- f*xattr()
	- ftruncate()
	- fstat()
	- fchmod()
	- fchown()

	debug

	Turns on debug information printing by the library.

	fsname=NAME

	Sets the filesystem source (first field in /etc/mtab). The default
	is the program name.

	subtype=TYPE

	Sets the filesystem type (third field in /etc/mtab). The default is
	the program name.

	If the kernel suppports it, /etc/mtab and /proc/mounts will show the
	filesystem type as "fuse.TYPE"

	If the kernel doesn't support subtypes, the source filed will be
	"TYPE#NAME", or if fsname option is not specified, just "TYPE".

	use_ino

	Honor the 'st_ino' field in getattr() and fill_dir(). This value is
	used to fill in the 'st_ino' field in the stat()/lstat()/fstat()
	functions and the 'd_ino' field in the readdir() function. The
	filesystem does not have to guarantee uniqueness, however some
	applications rely on this value being unique for the whole
	filesystem.

	readdir_ino

	If 'use_ino' option is not given, still try to fill in the 'd_ino'
	field in readdir(). If the name was previously looked up, and is
	still in the cache, the inode number found there will be used.
	Otherwise it will be set to '-1'. If 'use_ino' option is given,
	this option is ignored.

	nonempty

	Allows mounts over a non-empty file or directory. By default these
	mounts are rejected (from version 2.3.1) to prevent accidental
	covering up of data, which could for example prevent automatic
	backup.

	umask=M

	Override the permission bits in 'st_mode' set by the filesystem.
	The resulting permission bits are the ones missing from the given
	umask value. The value is given in octal representation.

	uid=N

	Override the 'st_uid' field set by the filesystem.

	gid=N

	Override the 'st_gid' field set by the filesystem.

	blkdev

	Mount a filesystem backed by a block device. This is a privileged
	option. The device must be specified with the 'fsname=NAME' option.

	entry_timeout=T

	The timeout in seconds for which name lookups will be cached. The
	default is 1.0 second. For all the timeout options, it is possible
	to give fractions of a second as well (e.g. "-oentry_timeout=2.8")

	negative_timeout=T

	The timeout in seconds for which a negative lookup will be cached.
	This means, that if file did not exist (lookup retuned ENOENT), the
	lookup will only be redone after the timeout, and the file/directory
	will be assumed to not exist until then. The default is 0.0 second,
	meaning that caching negative lookups are disabled.

	attr_timeout=T

	The timeout in seconds for which file/directory attributes are
	cached. The default is 1.0 second.

	ac_attr_timeout=T

	The timeout in seconds for which file attributes are cached for the
	purpose of checking if "auto_cache" should flush the file data on
	open. The default is the value of 'attr_timeout'

	intr

	Allow requests to be interrupted. Turning on this option may result
	in unexpected behavior, if the filesystem does not support request
	interruption.

	intr_signal=NUM

	Specify which signal number to send to the filesystem when a request
	is interrupted. The default is 10 (USR1).

	modules=M1[:M2...]

	Add modules to the filesystem stack. Modules are pushed in the
	order they are specified, with the original filesystem being on the
	bottom of the stack.


	Modules distributed with fuse
	-----------------------------

	iconv
	`````
	Perform file name character set conversion. Options are:

	from_code=CHARSET

	Character set to convert from (see iconv -l for a list of possible
	values). Default is UTF-8.

	to_code=CHARSET

	Character set to convert to. Default is determined by the current
	locale.


	subdir
	``````
	Prepend a given directory to each path. Options are:

	subdir=DIR

	Directory to prepend to all paths. This option is mandatory.

	rellinks

	Transform absolute symlinks into relative

	norellinks

	Do not transform absolute symlinks into relative. This is the default.


	Reporting bugs
	==============

	Please send bug reports to the <fuse-devel@lists.sourceforge.net>
	mailing list.

	The list is open, you need not be subscribed to post.