docs: filesystems: convert ntfs.txt to ReST

- Add a SPDX header;
- Adjust document title;
- Comment out text-only ToC;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/f09ca6c9bdd4e7aa7208f3dba0b8753080b38d03.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 466 insertions, 0 deletions

diff --git a/Documentation/filesystems/ntfs.rst b/Documentation/filesystems/ntfs.rst
new file mode 100644
index 000000000000..5bb093a26485
--- /dev/null
+++ b/Documentation/filesystems/ntfs.rst
@@ -0,0 +1,466 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================================
+The Linux NTFS filesystem driver
+================================
+
+
+.. Table of contents
+
+   - Overview
+   - Web site
+   - Features
+   - Supported mount options
+   - Known bugs and (mis-)features
+   - Using NTFS volume and stripe sets
+     - The Device-Mapper driver
+     - The Software RAID / MD driver
+     - Limitations when using the MD driver
+
+
+Overview
+========
+
+Linux-NTFS comes with a number of user-space programs known as ntfsprogs.
+These include mkntfs, a full-featured ntfs filesystem format utility,
+ntfsundelete used for recovering files that were unintentionally deleted
+from an NTFS volume and ntfsresize which is used to resize an NTFS partition.
+See the web site for more information.
+
+To mount an NTFS 1.2/3.x (Windows NT4/2000/XP/2003) volume, use the file
+system type 'ntfs'.  The driver currently supports read-only mode (with no
+fault-tolerance, encryption or journalling) and very limited, but safe, write
+support.
+
+For fault tolerance and raid support (i.e. volume and stripe sets), you can
+use the kernel's Software RAID / MD driver.  See section "Using Software RAID
+with NTFS" for details.
+
+
+Web site
+========
+
+There is plenty of additional information on the linux-ntfs web site
+at http://www.linux-ntfs.org/
+
+The web site has a lot of additional information, such as a comprehensive
+FAQ, documentation on the NTFS on-disk format, information on the Linux-NTFS
+userspace utilities, etc.
+
+
+Features
+========
+
+- This is a complete rewrite of the NTFS driver that used to be in the 2.4 and
+  earlier kernels.  This new driver implements NTFS read support and is
+  functionally equivalent to the old ntfs driver and it also implements limited
+  write support.  The biggest limitation at present is that files/directories
+  cannot be created or deleted.  See below for the list of write features that
+  are so far supported.  Another limitation is that writing to compressed files
+  is not implemented at all.  Also, neither read nor write access to encrypted
+  files is so far implemented.
+- The new driver has full support for sparse files on NTFS 3.x volumes which
+  the old driver isn't happy with.
+- The new driver supports execution of binaries due to mmap() now being
+  supported.
+- The new driver supports loopback mounting of files on NTFS which is used by
+  some Linux distributions to enable the user to run Linux from an NTFS
+  partition by creating a large file while in Windows and then loopback
+  mounting the file while in Linux and creating a Linux filesystem on it that
+  is used to install Linux on it.
+- A comparison of the two drivers using::
+
+	time find . -type f -exec md5sum "{}" \;
+
+  run three times in sequence with each driver (after a reboot) on a 1.4GiB
+  NTFS partition, showed the new driver to be 20% faster in total time elapsed
+  (from 9:43 minutes on average down to 7:53).  The time spent in user space
+  was unchanged but the time spent in the kernel was decreased by a factor of
+  2.5 (from 85 CPU seconds down to 33).
+- The driver does not support short file names in general.  For backwards
+  compatibility, we implement access to files using their short file names if
+  they exist.  The driver will not create short file names however, and a
+  rename will discard any existing short file name.
+- The new driver supports exporting of mounted NTFS volumes via NFS.
+- The new driver supports async io (aio).
+- The new driver supports fsync(2), fdatasync(2), and msync(2).
+- The new driver supports readv(2) and writev(2).
+- The new driver supports access time updates (including mtime and ctime).
+- The new driver supports truncate(2) and open(2) with O_TRUNC.  But at present
+  only very limited support for highly fragmented files, i.e. ones which have
+  their data attribute split across multiple extents, is included.  Another
+  limitation is that at present truncate(2) will never create sparse files,
+  since to mark a file sparse we need to modify the directory entry for the
+  file and we do not implement directory modifications yet.
+- The new driver supports write(2) which can both overwrite existing data and
+  extend the file size so that you can write beyond the existing data.  Also,
+  writing into sparse regions is supported and the holes are filled in with
+  clusters.  But at present only limited support for highly fragmented files,
+  i.e. ones which have their data attribute split across multiple extents, is
+  included.  Another limitation is that write(2) will never create sparse
+  files, since to mark a file sparse we need to modify the directory entry for
+  the file and we do not implement directory modifications yet.
+
+Supported mount options
+=======================
+
+In addition to the generic mount options described by the manual page for the
+mount command (man 8 mount, also see man 5 fstab), the NTFS driver supports the
+following mount options:
+
+======================= =======================================================
+iocharset=name		Deprecated option.  Still supported but please use
+			nls=name in the future.  See description for nls=name.
+
+nls=name		Character set to use when returning file names.
+			Unlike VFAT, NTFS suppresses names that contain
+			unconvertible characters.  Note that most character
+			sets contain insufficient characters to represent all
+			possible Unicode characters that can exist on NTFS.
+			To be sure you are not missing any files, you are
+			advised to use nls=utf8 which is capable of
+			representing all Unicode characters.
+
+utf8=<bool>		Option no longer supported.  Currently mapped to
+			nls=utf8 but please use nls=utf8 in the future and
+			make sure utf8 is compiled either as module or into
+			the kernel.  See description for nls=name.
+
+uid=
+gid=
+umask=			Provide default owner, group, and access mode mask.
+			These options work as documented in mount(8).  By
+			default, the files/directories are owned by root and
+			he/she has read and write permissions, as well as
+			browse permission for directories.  No one else has any
+			access permissions.  I.e. the mode on all files is by
+			default rw------- and for directories rwx------, a
+			consequence of the default fmask=0177 and dmask=0077.
+			Using a umask of zero will grant all permissions to
+			everyone, i.e. all files and directories will have mode
+			rwxrwxrwx.
+
+fmask=
+dmask=			Instead of specifying umask which applies both to
+			files and directories, fmask applies only to files and
+			dmask only to directories.
+
+sloppy=<BOOL>		If sloppy is specified, ignore unknown mount options.
+			Otherwise the default behaviour is to abort mount if
+			any unknown options are found.
+
+show_sys_files=<BOOL>	If show_sys_files is specified, show the system files
+			in directory listings.  Otherwise the default behaviour
+			is to hide the system files.
+			Note that even when show_sys_files is specified, "$MFT"
+			will not be visible due to bugs/mis-features in glibc.
+			Further, note that irrespective of show_sys_files, all
+			files are accessible by name, i.e. you can always do
+			"ls -l \$UpCase" for example to specifically show the
+			system file containing the Unicode upcase table.
+
+case_sensitive=<BOOL>	If case_sensitive is specified, treat all file names as
+			case sensitive and create file names in the POSIX
+			namespace.  Otherwise the default behaviour is to treat
+			file names as case insensitive and to create file names
+			in the WIN32/LONG name space.  Note, the Linux NTFS
+			driver will never create short file names and will
+			remove them on rename/delete of the corresponding long
+			file name.
+			Note that files remain accessible via their short file
+			name, if it exists.  If case_sensitive, you will need
+			to provide the correct case of the short file name.
+
+disable_sparse=<BOOL>	If disable_sparse is specified, creation of sparse
+			regions, i.e. holes, inside files is disabled for the
+			volume (for the duration of this mount only).  By
+			default, creation of sparse regions is enabled, which
+			is consistent with the behaviour of traditional Unix
+			filesystems.
+
+errors=opt		What to do when critical filesystem errors are found.
+			Following values can be used for "opt":
+
+			  ========  =========================================
+			  continue  DEFAULT, try to clean-up as much as
+				    possible, e.g. marking a corrupt inode as
+				    bad so it is no longer accessed, and then
+				    continue.
+			  recover   At present only supported is recovery of
+				    the boot sector from the backup copy.
+				    If read-only mount, the recovery is done
+				    in memory only and not written to disk.
+			  ========  =========================================
+
+			Note that the options are additive, i.e. specifying::
+
+			   errors=continue,errors=recover
+
+			means the driver will attempt to recover and if that
+			fails it will clean-up as much as possible and
+			continue.
+
+mft_zone_multiplier=	Set the MFT zone multiplier for the volume (this
+			setting is not persistent across mounts and can be
+			changed from mount to mount but cannot be changed on
+			remount).  Values of 1 to 4 are allowed, 1 being the
+			default.  The MFT zone multiplier determines how much
+			space is reserved for the MFT on the volume.  If all
+			other space is used up, then the MFT zone will be
+			shrunk dynamically, so this has no impact on the
+			amount of free space.  However, it can have an impact
+			on performance by affecting fragmentation of the MFT.
+			In general use the default.  If you have a lot of small
+			files then use a higher value.  The values have the
+			following meaning:
+
+			      =====	    =================================
+			      Value	     MFT zone size (% of volume size)
+			      =====	    =================================
+				1		12.5%
+				2		25%
+				3		37.5%
+				4		50%
+			      =====	    =================================
+
+			Note this option is irrelevant for read-only mounts.
+======================= =======================================================
+
+
+Known bugs and (mis-)features
+=============================
+
+- The link count on each directory inode entry is set to 1, due to Linux not
+  supporting directory hard links.  This may well confuse some user space
+  applications, since the directory names will have the same inode numbers.
+  This also speeds up ntfs_read_inode() immensely.  And we haven't found any
+  problems with this approach so far.  If you find a problem with this, please
+  let us know.
+
+
+Please send bug reports/comments/feedback/abuse to the Linux-NTFS development
+list at sourceforge: linux-ntfs-dev@lists.sourceforge.net
+
+
+Using NTFS volume and stripe sets
+=================================
+
+For support of volume and stripe sets, you can either use the kernel's
+Device-Mapper driver or the kernel's Software RAID / MD driver.  The former is
+the recommended one to use for linear raid.  But the latter is required for
+raid level 5.  For striping and mirroring, either driver should work fine.
+
+
+The Device-Mapper driver
+------------------------
+
+You will need to create a table of the components of the volume/stripe set and
+how they fit together and load this into the kernel using the dmsetup utility
+(see man 8 dmsetup).
+
+Linear volume sets, i.e. linear raid, has been tested and works fine.  Even
+though untested, there is no reason why stripe sets, i.e. raid level 0, and
+mirrors, i.e. raid level 1 should not work, too.  Stripes with parity, i.e.
+raid level 5, unfortunately cannot work yet because the current version of the
+Device-Mapper driver does not support raid level 5.  You may be able to use the
+Software RAID / MD driver for raid level 5, see the next section for details.
+
+To create the table describing your volume you will need to know each of its
+components and their sizes in sectors, i.e. multiples of 512-byte blocks.
+
+For NT4 fault tolerant volumes you can obtain the sizes using fdisk.  So for
+example if one of your partitions is /dev/hda2 you would do::
+
+    $ fdisk -ul /dev/hda
+
+    Disk /dev/hda: 81.9 GB, 81964302336 bytes
+    255 heads, 63 sectors/track, 9964 cylinders, total 160086528 sectors
+    Units = sectors of 1 * 512 = 512 bytes
+
+	Device Boot      Start         End      Blocks   Id  System
+	/dev/hda1   *          63     4209029     2104483+  83  Linux
+	/dev/hda2         4209030    37768814    16779892+  86  NTFS
+	/dev/hda3        37768815    46170809     4200997+  83  Linux
+
+And you would know that /dev/hda2 has a size of 37768814 - 4209030 + 1 =
+33559785 sectors.
+
+For Win2k and later dynamic disks, you can for example use the ldminfo utility
+which is part of the Linux LDM tools (the latest version at the time of
+writing is linux-ldm-0.0.8.tar.bz2).  You can download it from:
+
+	http://www.linux-ntfs.org/
+
+Simply extract the downloaded archive (tar xvjf linux-ldm-0.0.8.tar.bz2), go
+into it (cd linux-ldm-0.0.8) and change to the test directory (cd test).  You
+will find the precompiled (i386) ldminfo utility there.  NOTE: You will not be
+able to compile this yourself easily so use the binary version!
+
+Then you would use ldminfo in dump mode to obtain the necessary information::
+
+    $ ./ldminfo --dump /dev/hda
+
+This would dump the LDM database found on /dev/hda which describes all of your
+dynamic disks and all the volumes on them.  At the bottom you will see the
+VOLUME DEFINITIONS section which is all you really need.  You may need to look
+further above to determine which of the disks in the volume definitions is
+which device in Linux.  Hint: Run ldminfo on each of your dynamic disks and
+look at the Disk Id close to the top of the output for each (the PRIVATE HEADER
+section).  You can then find these Disk Ids in the VBLK DATABASE section in the
+<Disk> components where you will get the LDM Name for the disk that is found in
+the VOLUME DEFINITIONS section.
+
+Note you will also need to enable the LDM driver in the Linux kernel.  If your
+distribution did not enable it, you will need to recompile the kernel with it
+enabled.  This will create the LDM partitions on each device at boot time.  You
+would then use those devices (for /dev/hda they would be /dev/hda1, 2, 3, etc)
+in the Device-Mapper table.
+
+You can also bypass using the LDM driver by using the main device (e.g.
+/dev/hda) and then using the offsets of the LDM partitions into this device as
+the "Start sector of device" when creating the table.  Once again ldminfo would
+give you the correct information to do this.
+
+Assuming you know all your devices and their sizes things are easy.
+
+For a linear raid the table would look like this (note all values are in
+512-byte sectors)::
+
+    # Offset into	Size of this	Raid type	Device		Start sector
+    # volume	device						of device
+    0		1028161		linear		/dev/hda1	0
+    1028161		3903762		linear		/dev/hdb2	0
+    4931923		2103211		linear		/dev/hdc1	0
+
+For a striped volume, i.e. raid level 0, you will need to know the chunk size
+you used when creating the volume.  Windows uses 64kiB as the default, so it
+will probably be this unless you changes the defaults when creating the array.
+
+For a raid level 0 the table would look like this (note all values are in
+512-byte sectors)::
+
+    # Offset   Size	    Raid     Number   Chunk  1st        Start	2nd	  Start
+    # into     of the   type     of	      size   Device	in	Device	  in
+    # volume   volume	     stripes			device		  device
+    0	   2056320  striped  2	      128    /dev/hda1	0	/dev/hdb1 0
+
+If there are more than two devices, just add each of them to the end of the
+line.
+
+Finally, for a mirrored volume, i.e. raid level 1, the table would look like
+this (note all values are in 512-byte sectors)::
+
+    # Ofs Size   Raid   Log  Number Region Should Number Source  Start Target Start
+    # in  of the type   type of log size   sync?  of     Device  in    Device in
+    # vol volume		 params		     mirrors	     Device	  Device
+    0    2056320 mirror core 2	16     nosync 2	   /dev/hda1 0   /dev/hdb1 0
+
+If you are mirroring to multiple devices you can specify further targets at the
+end of the line.
+
+Note the "Should sync?" parameter "nosync" means that the two mirrors are
+already in sync which will be the case on a clean shutdown of Windows.  If the
+mirrors are not clean, you can specify the "sync" option instead of "nosync"
+and the Device-Mapper driver will then copy the entirety of the "Source Device"
+to the "Target Device" or if you specified multiple target devices to all of
+them.
+
+Once you have your table, save it in a file somewhere (e.g. /etc/ntfsvolume1),
+and hand it over to dmsetup to work with, like so::
+
+    $ dmsetup create myvolume1 /etc/ntfsvolume1
+
+You can obviously replace "myvolume1" with whatever name you like.
+
+If it all worked, you will now have the device /dev/device-mapper/myvolume1
+which you can then just use as an argument to the mount command as usual to
+mount the ntfs volume.  For example::
+
+    $ mount -t ntfs -o ro /dev/device-mapper/myvolume1 /mnt/myvol1
+
+(You need to create the directory /mnt/myvol1 first and of course you can use
+anything you like instead of /mnt/myvol1 as long as it is an existing
+directory.)
+
+It is advisable to do the mount read-only to see if the volume has been setup
+correctly to avoid the possibility of causing damage to the data on the ntfs
+volume.
+
+
+The Software RAID / MD driver
+-----------------------------
+
+An alternative to using the Device-Mapper driver is to use the kernel's
+Software RAID / MD driver.  For which you need to set up your /etc/raidtab
+appropriately (see man 5 raidtab).
+
+Linear volume sets, i.e. linear raid, as well as stripe sets, i.e. raid level
+0, have been tested and work fine (though see section "Limitations when using
+the MD driver with NTFS volumes" especially if you want to use linear raid).
+Even though untested, there is no reason why mirrors, i.e. raid level 1, and
+stripes with parity, i.e. raid level 5, should not work, too.
+
+You have to use the "persistent-superblock 0" option for each raid-disk in the
+NTFS volume/stripe you are configuring in /etc/raidtab as the persistent
+superblock used by the MD driver would damage the NTFS volume.
+
+Windows by default uses a stripe chunk size of 64k, so you probably want the
+"chunk-size 64k" option for each raid-disk, too.
+
+For example, if you have a stripe set consisting of two partitions /dev/hda5
+and /dev/hdb1 your /etc/raidtab would look like this::
+
+    raiddev /dev/md0
+	    raid-level	0
+	    nr-raid-disks	2
+	    nr-spare-disks	0
+	    persistent-superblock	0
+	    chunk-size	64k
+	    device		/dev/hda5
+	    raid-disk	0
+	    device		/dev/hdb1
+	    raid-disk	1
+
+For linear raid, just change the raid-level above to "raid-level linear", for
+mirrors, change it to "raid-level 1", and for stripe sets with parity, change
+it to "raid-level 5".
+
+Note for stripe sets with parity you will also need to tell the MD driver
+which parity algorithm to use by specifying the option "parity-algorithm
+which", where you need to replace "which" with the name of the algorithm to
+use (see man 5 raidtab for available algorithms) and you will have to try the
+different available algorithms until you find one that works.  Make sure you
+are working read-only when playing with this as you may damage your data
+otherwise.  If you find which algorithm works please let us know (email the
+linux-ntfs developers list linux-ntfs-dev@lists.sourceforge.net or drop in on
+IRC in channel #ntfs on the irc.freenode.net network) so we can update this
+documentation.
+
+Once the raidtab is setup, run for example raid0run -a to start all devices or
+raid0run /dev/md0 to start a particular md device, in this case /dev/md0.
+
+Then just use the mount command as usual to mount the ntfs volume using for
+example::
+
+    mount -t ntfs -o ro /dev/md0 /mnt/myntfsvolume
+
+It is advisable to do the mount read-only to see if the md volume has been
+setup correctly to avoid the possibility of causing damage to the data on the
+ntfs volume.
+
+
+Limitations when using the Software RAID / MD driver
+-----------------------------------------------------
+
+Using the md driver will not work properly if any of your NTFS partitions have
+an odd number of sectors.  This is especially important for linear raid as all
+data after the first partition with an odd number of sectors will be offset by
+one or more sectors so if you mount such a partition with write support you
+will cause massive damage to the data on the volume which will only become
+apparent when you try to use the volume again under Windows.
+
+So when using linear raid, make sure that all your partitions have an even
+number of sectors BEFORE attempting to use it.  You have been warned!
+
+Even better is to simply use the Device-Mapper for linear raid and then you do
+not have this problem with odd numbers of sectors.