NTFS: The big ntfs write(2) rewrite has arrived. We now implement our own

      file operations ->write(), ->aio_write(), and ->writev() for regular
      files.  This replaces the old use of generic_file_write(), et al and
      the address space operations ->prepare_write and ->commit_write.
      This means that both sparse and non-sparse (unencrypted and
      uncompressed) files can now be extended using the normal write(2)
      code path.  There are two limitations at present and these are that
      we never create sparse files and that we only have limited support
      for highly fragmented files, i.e. ones whose data attribute is split
      across multiple extents.   When such a case is encountered,
      EOPNOTSUPP is returned.
Signed-off-by: Anton Altaparmakov <aia21@cantab.net>

Documentation/filesystems/ntfs.txt

@@ -50,9 +50,14 @@ userspace utilities, etc.
 Features
 ========
 
-- This is a complete rewrite of the NTFS driver that used to be in the kernel.
-  This new driver implements NTFS read support and is functionally equivalent
-  to the old ntfs driver.
+- 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
@@ -78,7 +83,20 @@ Features
 - 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
 =======================
@@ -439,6 +457,22 @@ ChangeLog
 
 Note, a technical ChangeLog aimed at kernel hackers is in fs/ntfs/ChangeLog.
 
+2.1.25:
+	- Write support is now extended with write(2) being able to both
+	  overwrite existing file data and to extend files.  Also, if a write
+	  to a sparse region occurs, write(2) will fill in the hole.  Note,
+	  mmap(2) based writes still do not support writing into holes or
+	  writing beyond the initialized size.
+	- Write support has a new feature and that is that truncate(2) and
+	  open(2) with O_TRUNC are now implemented thus files can be both made
+	  smaller and larger.
+	- Note: Both write(2) and truncate(2)/open(2) with O_TRUNC still have
+	  limitations in that they
+	  - only provide limited support for highly fragmented files.
+	  - only work on regular, i.e. uncompressed and unencrypted files.
+	  - never create sparse files although this will change once directory
+	    operations are implemented.
+	- Lots of bug fixes and enhancements across the board.
 2.1.24:
 	- Support journals ($LogFile) which have been modified by chkdsk.  This
 	  means users can boot into Windows after we marked the volume dirty.

fs/ntfs/ChangeLog

 ToDo/Notes:
 	- Find and fix bugs.
-	- In between ntfs_prepare/commit_write, need exclusion between
-	  simultaneous file extensions.  This is given to us by holding i_sem
-	  on the inode.  The only places in the kernel when a file is resized
-	  are prepare/commit write and ntfs_truncate() for both of which i_sem
-	  is held.  Just have to be careful in read-/writepage and other helpers
+	- The only places in the kernel where a file is resized are
+	  ntfs_file_write*() and ntfs_truncate() for both of which i_sem is
+	  held.  Just have to be careful in read-/writepage and other helpers
 	  not running under i_sem that we play nice...  Also need to be careful
-	  with initialized_size extention in ntfs_prepare_write and writepage.
-	  UPDATE: The only things that need to be checked are
-	  prepare/commit_write as well as the compressed write and the other
-	  attribute resize/write cases like index attributes, etc.  For now
-	  none of these are implemented so are safe.
+	  with initialized_size extension in ntfs_file_write*() and writepage.
+	  UPDATE: The only things that need to be checked are the compressed
+	  write and the other attribute resize/write cases like index
+	  attributes, etc.  For now none of these are implemented so are safe.
+	- Implement filling in of holes in aops.c::ntfs_writepage() and its
+	  helpers.
 	- Implement mft.c::sync_mft_mirror_umount().  We currently will just
 	  leave the volume dirty on umount if the final iput(vol->mft_ino)
 	  causes a write of any mirrored mft records due to the mft mirror
@@ -20,7 +19,7 @@ ToDo/Notes:
 	- Enable the code for setting the NT4 compatibility flag when we start
 	  making NTFS 1.2 specific modifications.
 
-2.1.25-WIP
+2.1.25 - (Almost) fully implement write(2) and truncate(2).
 
 	- Change ntfs_map_runlist_nolock(), ntfs_attr_find_vcn_nolock() and
 	  {__,}ntfs_cluster_free() to also take an optional attribute search
@@ -49,7 +48,12 @@ ToDo/Notes:
 	  extend the allocation of an attributes.  Optionally, the data size,
 	  but not the initialized size can be extended, too.
 	- Implement fs/ntfs/inode.[hc]::ntfs_truncate().  It only supports
-	  uncompressed and unencrypted files.
+	  uncompressed and unencrypted files and it never creates sparse files
+	  at least for the moment (making a file sparse requires us to modify
+	  its directory entries and we do not support directory operations at
+	  the moment).  Also, support for highly fragmented files, i.e. ones
+	  whose data attribute is split across multiple extents, is severly
+	  limited.  When such a case is encountered, EOPNOTSUPP is returned.
 	- Enable ATTR_SIZE attribute changes in ntfs_setattr().  This completes
 	  the initial implementation of file truncation.  Now both open(2)ing
 	  a file with the O_TRUNC flag and the {,f}truncate(2) system calls
@@ -61,6 +65,16 @@ ToDo/Notes:
 	  and cond_resched() in the main loop as we could be dirtying a lot of
 	  pages and this ensures we play nice with the VM and the system as a
 	  whole.
+	- Implement file operations ->write, ->aio_write, ->writev for regular
+	  files.  This replaces the old use of generic_file_write(), et al and
+	  the address space operations ->prepare_write and ->commit_write.
+	  This means that both sparse and non-sparse (unencrypted and
+	  uncompressed) files can now be extended using the normal write(2)
+	  code path.  There are two limitations at present and these are that
+	  we never create sparse files and that we only have limited support
+	  for highly fragmented files, i.e. ones whose data attribute is split
+	  across multiple extents.   When such a case is encountered,
+	  EOPNOTSUPP is returned.
 
 2.1.24 - Lots of bug fixes and support more clean journal states.
 

fs/ntfs/Makefile

@@ -6,7 +6,7 @@ ntfs-objs := aops.o attrib.o collate.o compress.o debug.o dir.o file.o \
 	     index.o inode.o mft.o mst.o namei.o runlist.o super.o sysctl.o \
 	     unistr.o upcase.o
 
-EXTRA_CFLAGS = -DNTFS_VERSION=\"2.1.25-WIP\"
+EXTRA_CFLAGS = -DNTFS_VERSION=\"2.1.25\"
 
 ifeq ($(CONFIG_NTFS_DEBUG),y)
 EXTRA_CFLAGS += -DDEBUG