NTFS: Use i_size_read() in fs/ntfs/logfile.c::ntfs_{check,empty}_logfile().

	- Find and fix bugs.

	- Checkpoint or disable the user space journal ($UsnJrnl).

	- In between ntfs_prepare/commit_write, need exclusion between

	  simultaneous file extensions. Need perhaps an NInoResizeUnderway()

	  flag which we can set in ntfs_prepare_write() and clear again in

	  ntfs_commit_write(). Just have to be careful in readpage/writepage,

	  as well as in truncate, that we play nice... We might need to have

	  a data_size field in the ntfs_inode to store the real attribute

	  length. Also need to be careful with initialized_size extention in

	  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 truncate for both of which i_sem is

	  held.  Just have to be careful in readpage/writepage and all other

	  helpers not running under i_sem that we play nice...

	  Also need to be careful with initialized_size extention in

	  ntfs_prepare_write. Basically, just be _very_ careful in this code...

	  OTOH, perhaps i_sem, which is held accross generic_file_write is

	  sufficient for synchronisation here. We then just need to make sure

	  ntfs_readpage/writepage/truncate interoperate properly with us.

	  UPDATE: The above is all ok as it is due to i_sem held.  The only

	  thing that needs to be checked is ntfs_writepage() which does not

	  hold i_sem.  It cannot change i_size but it needs to cope with a

	  concurrent i_size change.

	  UPDATE: The only things that need to be checked are read/writepage

	  which do not hold i_sem.  Note writepage cannot change i_size but it

	  needs to cope with a concurrent i_size change, just like readpage.

	  Also both need to cope with concurrent changes to the other sizes,

	  i.e. initialized/allocated/compressed size, as well.

	- 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

	  attack.  Thanks to Carl-Daniel Hailfinger from SuSE for pointing this

	  out.

	- Use i_size_read() in fs/ntfs/attrib.c::ntfs_attr_set().

	- Use i_size_read() in fs/ntfs/logfile.c::ntfs_{check,empty}_logfile().

2.1.22 - Many bug and race fixes and error handling improvements.

	/* An empty $LogFile must have been clean before it got emptied. */

	if (NVolLogFileEmpty(vol))

		goto is_empty;

	size = log_vi->i_size;

	size = i_size_read(log_vi);

	/* Make sure the file doesn't exceed the maximum allowed size. */

	if (size > MaxLogFileSize)

		size = MaxLogFileSize;

	if (!NVolLogFileEmpty(vol)) {

		int err;

		err = ntfs_attr_set(NTFS_I(log_vi), 0, log_vi->i_size, 0xff);

		err = ntfs_attr_set(NTFS_I(log_vi), 0, i_size_read(log_vi),

				0xff);

		if (unlikely(err)) {

			ntfs_error(vol->sb, "Failed to fill $LogFile with "

					"0xff bytes (error code %i).", err);