NTFS: Fixup handling of sparse, compressed, and encrypted attributes in

	  fs/ntfs/inode.c::ntfs_read_locked_{,attr_,index_}inode().

	- Make ntfs_write_block() not instantiate sparse blocks if they contain

	  only zeroes.

	- Fixup handling of sparse, compressed, and encrypted attributes in

	  fs/ntfs/aops.c::ntfs_writepage().

2.1.23 - Implement extension of resident files and make writing safe as well as

	 many bug fixes, cleanups, and enhancements...

		ntfs_debug("Write outside i_size - truncated?");

		return 0;

	}

	/* NInoNonResident() == NInoIndexAllocPresent() */

	if (NInoNonResident(ni)) {

	/*

		 * Only unnamed $DATA attributes can be compressed, encrypted,

		 * and/or sparse.

	 * Only $DATA attributes can be encrypted and only unnamed $DATA

	 * attributes can be compressed.  Index root can have the flags set but

	 * this means to create compressed/encrypted files, not that the

	 * attribute is compressed/encrypted.

	 */

		if (ni->type == AT_DATA && !ni->name_len) {

	if (ni->type != AT_INDEX_ROOT) {

		/* If file is encrypted, deny access, just like NT4. */

		if (NInoEncrypted(ni)) {

			unlock_page(page);

			BUG_ON(ni->type != AT_DATA);

			ntfs_debug("Denying write access to encrypted "

					"file.");

			return -EACCES;

		}

		/* Compressed data streams are handled in compress.c. */

			if (NInoCompressed(ni)) {

				// TODO: Implement and replace this check with

		if (NInoNonResident(ni) && NInoCompressed(ni)) {

			BUG_ON(ni->type != AT_DATA);

			BUG_ON(ni->name_len);

			// TODO: Implement and replace this with

			// return ntfs_write_compressed_block(page);

			unlock_page(page);

				ntfs_error(vi->i_sb, "Writing to compressed "

						"files is not supported yet. "

						"Sorry.");

			ntfs_error(vi->i_sb, "Writing to compressed files is "

					"not supported yet.  Sorry.");

			return -EOPNOTSUPP;

		}

		// TODO: Implement and remove this check.

			if (NInoSparse(ni)) {

		if (NInoNonResident(ni) && NInoSparse(ni)) {

			unlock_page(page);

				ntfs_error(vi->i_sb, "Writing to sparse files "

						"is not supported yet. Sorry.");

			ntfs_error(vi->i_sb, "Writing to sparse files is not "

					"supported yet.  Sorry.");

			return -EOPNOTSUPP;

		}

	}

	/* NInoNonResident() == NInoIndexAllocPresent() */

	if (NInoNonResident(ni)) {

		/* We have to zero every time due to mmap-at-end-of-file. */

		if (page->index >= (i_size >> PAGE_CACHE_SHIFT)) {

			/* The page straddles i_size. */

		/* Handle mst protected attributes. */

		if (NInoMstProtected(ni))

			return ntfs_write_mst_block(page, wbc);

		/* Normal data stream. */

		/* Normal, non-resident data stream. */

		return ntfs_write_block(page, wbc);

	}

	/*

	 * Attribute is resident, implying it is not compressed, encrypted,

	 * sparse, or mst protected.  This also means the attribute is smaller

	 * than an mft record and hence smaller than a page, so can simply

	 * return error on any pages with index above 0.

	 * Attribute is resident, implying it is not compressed, encrypted, or

	 * mst protected.  This also means the attribute is smaller than an mft

	 * record and hence smaller than a page, so can simply return error on

	 * any pages with index above 0.  Note the attribute can actually be

	 * marked compressed but if it is resident the actual data is not

	 * compressed so we are ok to ignore the compressed flag here.

	 */

	BUG_ON(page_has_buffers(page));

	BUG_ON(!PageUptodate(page));

	BUG_ON(PageWriteback(page));

	set_page_writeback(page);

	unlock_page(page);

	/*

	 * Here, we don't need to zero the out of bounds area everytime because

	 * the below memcpy() already takes care of the mmap-at-end-of-file

	 * requirements. If the file is converted to a non-resident one, then

	 * the code path use is switched to the non-resident one where the

	 * zeroing happens on each ntfs_writepage() invocation.

	 *

	 * The above also applies nicely when i_size is decreased.

	 *

	 * When i_size is increased, the memory between the old and new i_size

	 * _must_ be zeroed (or overwritten with new data). Otherwise we will

	 * expose data to userspace/disk which should never have been exposed.

	 *

	 * FIXME: Ensure that i_size increases do the zeroing/overwriting and

	 * if we cannot guarantee that, then enable the zeroing below.  If the

	 * zeroing below is enabled, we MUST move the unlock_page() from above

	 * to after the kunmap_atomic(), i.e. just before the

	 * end_page_writeback().

	 * UPDATE: ntfs_prepare/commit_write() do the zeroing on i_size

	 * increases for resident attributes so those are ok.

	 * TODO: ntfs_truncate(), others?

	 * Here, we do not need to zero the out of bounds area everytime

	 * because the below memcpy() already takes care of the

	 * mmap-at-end-of-file requirements.  If the file is converted to a

	 * non-resident one, then the code path use is switched to the

	 * non-resident one where the zeroing happens on each ntfs_writepage()

	 * invocation.

	 */

	attr_len = le32_to_cpu(ctx->attr->data.resident.value_length);

	i_size = i_size_read(vi);

	if (unlikely(attr_len > i_size)) {