Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 950 insertions, 0 deletions

diff --git a/fs/ntfs/compress.c b/fs/ntfs/compress.c
new file mode 100644
index 000000000..d2f9d6a0e
--- /dev/null
+++ b/fs/ntfs/compress.c
@@ -0,0 +1,950 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/**
+ * compress.c - NTFS kernel compressed attributes handling.
+ *		Part of the Linux-NTFS project.
+ *
+ * Copyright (c) 2001-2004 Anton Altaparmakov
+ * Copyright (c) 2002 Richard Russon
+ */
+
+#include <linux/fs.h>
+#include <linux/buffer_head.h>
+#include <linux/blkdev.h>
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
+
+#include "attrib.h"
+#include "inode.h"
+#include "debug.h"
+#include "ntfs.h"
+
+/**
+ * ntfs_compression_constants - enum of constants used in the compression code
+ */
+typedef enum {
+	/* Token types and access mask. */
+	NTFS_SYMBOL_TOKEN	=	0,
+	NTFS_PHRASE_TOKEN	=	1,
+	NTFS_TOKEN_MASK		=	1,
+
+	/* Compression sub-block constants. */
+	NTFS_SB_SIZE_MASK	=	0x0fff,
+	NTFS_SB_SIZE		=	0x1000,
+	NTFS_SB_IS_COMPRESSED	=	0x8000,
+
+	/*
+	 * The maximum compression block size is by definition 16 * the cluster
+	 * size, with the maximum supported cluster size being 4kiB. Thus the
+	 * maximum compression buffer size is 64kiB, so we use this when
+	 * initializing the compression buffer.
+	 */
+	NTFS_MAX_CB_SIZE	= 64 * 1024,
+} ntfs_compression_constants;
+
+/**
+ * ntfs_compression_buffer - one buffer for the decompression engine
+ */
+static u8 *ntfs_compression_buffer;
+
+/**
+ * ntfs_cb_lock - spinlock which protects ntfs_compression_buffer
+ */
+static DEFINE_SPINLOCK(ntfs_cb_lock);
+
+/**
+ * allocate_compression_buffers - allocate the decompression buffers
+ *
+ * Caller has to hold the ntfs_lock mutex.
+ *
+ * Return 0 on success or -ENOMEM if the allocations failed.
+ */
+int allocate_compression_buffers(void)
+{
+	BUG_ON(ntfs_compression_buffer);
+
+	ntfs_compression_buffer = vmalloc(NTFS_MAX_CB_SIZE);
+	if (!ntfs_compression_buffer)
+		return -ENOMEM;
+	return 0;
+}
+
+/**
+ * free_compression_buffers - free the decompression buffers
+ *
+ * Caller has to hold the ntfs_lock mutex.
+ */
+void free_compression_buffers(void)
+{
+	BUG_ON(!ntfs_compression_buffer);
+	vfree(ntfs_compression_buffer);
+	ntfs_compression_buffer = NULL;
+}
+
+/**
+ * zero_partial_compressed_page - zero out of bounds compressed page region
+ */
+static void zero_partial_compressed_page(struct page *page,
+		const s64 initialized_size)
+{
+	u8 *kp = page_address(page);
+	unsigned int kp_ofs;
+
+	ntfs_debug("Zeroing page region outside initialized size.");
+	if (((s64)page->index << PAGE_SHIFT) >= initialized_size) {
+		clear_page(kp);
+		return;
+	}
+	kp_ofs = initialized_size & ~PAGE_MASK;
+	memset(kp + kp_ofs, 0, PAGE_SIZE - kp_ofs);
+	return;
+}
+
+/**
+ * handle_bounds_compressed_page - test for&handle out of bounds compressed page
+ */
+static inline void handle_bounds_compressed_page(struct page *page,
+		const loff_t i_size, const s64 initialized_size)
+{
+	if ((page->index >= (initialized_size >> PAGE_SHIFT)) &&
+			(initialized_size < i_size))
+		zero_partial_compressed_page(page, initialized_size);
+	return;
+}
+
+/**
+ * ntfs_decompress - decompress a compression block into an array of pages
+ * @dest_pages:		destination array of pages
+ * @completed_pages:	scratch space to track completed pages
+ * @dest_index:		current index into @dest_pages (IN/OUT)
+ * @dest_ofs:		current offset within @dest_pages[@dest_index] (IN/OUT)
+ * @dest_max_index:	maximum index into @dest_pages (IN)
+ * @dest_max_ofs:	maximum offset within @dest_pages[@dest_max_index] (IN)
+ * @xpage:		the target page (-1 if none) (IN)
+ * @xpage_done:		set to 1 if xpage was completed successfully (IN/OUT)
+ * @cb_start:		compression block to decompress (IN)
+ * @cb_size:		size of compression block @cb_start in bytes (IN)
+ * @i_size:		file size when we started the read (IN)
+ * @initialized_size:	initialized file size when we started the read (IN)
+ *
+ * The caller must have disabled preemption. ntfs_decompress() reenables it when
+ * the critical section is finished.
+ *
+ * This decompresses the compression block @cb_start into the array of
+ * destination pages @dest_pages starting at index @dest_index into @dest_pages
+ * and at offset @dest_pos into the page @dest_pages[@dest_index].
+ *
+ * When the page @dest_pages[@xpage] is completed, @xpage_done is set to 1.
+ * If xpage is -1 or @xpage has not been completed, @xpage_done is not modified.
+ *
+ * @cb_start is a pointer to the compression block which needs decompressing
+ * and @cb_size is the size of @cb_start in bytes (8-64kiB).
+ *
+ * Return 0 if success or -EOVERFLOW on error in the compressed stream.
+ * @xpage_done indicates whether the target page (@dest_pages[@xpage]) was
+ * completed during the decompression of the compression block (@cb_start).
+ *
+ * Warning: This function *REQUIRES* PAGE_SIZE >= 4096 or it will blow up
+ * unpredicatbly! You have been warned!
+ *
+ * Note to hackers: This function may not sleep until it has finished accessing
+ * the compression block @cb_start as it is a per-CPU buffer.
+ */
+static int ntfs_decompress(struct page *dest_pages[], int completed_pages[],
+		int *dest_index, int *dest_ofs, const int dest_max_index,
+		const int dest_max_ofs, const int xpage, char *xpage_done,
+		u8 *const cb_start, const u32 cb_size, const loff_t i_size,
+		const s64 initialized_size)
+{
+	/*
+	 * Pointers into the compressed data, i.e. the compression block (cb),
+	 * and the therein contained sub-blocks (sb).
+	 */
+	u8 *cb_end = cb_start + cb_size; /* End of cb. */
+	u8 *cb = cb_start;	/* Current position in cb. */
+	u8 *cb_sb_start = cb;	/* Beginning of the current sb in the cb. */
+	u8 *cb_sb_end;		/* End of current sb / beginning of next sb. */
+
+	/* Variables for uncompressed data / destination. */
+	struct page *dp;	/* Current destination page being worked on. */
+	u8 *dp_addr;		/* Current pointer into dp. */
+	u8 *dp_sb_start;	/* Start of current sub-block in dp. */
+	u8 *dp_sb_end;		/* End of current sb in dp (dp_sb_start +
+				   NTFS_SB_SIZE). */
+	u16 do_sb_start;	/* @dest_ofs when starting this sub-block. */
+	u16 do_sb_end;		/* @dest_ofs of end of this sb (do_sb_start +
+				   NTFS_SB_SIZE). */
+
+	/* Variables for tag and token parsing. */
+	u8 tag;			/* Current tag. */
+	int token;		/* Loop counter for the eight tokens in tag. */
+	int nr_completed_pages = 0;
+
+	/* Default error code. */
+	int err = -EOVERFLOW;
+
+	ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
+do_next_sb:
+	ntfs_debug("Beginning sub-block at offset = 0x%zx in the cb.",
+			cb - cb_start);
+	/*
+	 * Have we reached the end of the compression block or the end of the
+	 * decompressed data?  The latter can happen for example if the current
+	 * position in the compression block is one byte before its end so the
+	 * first two checks do not detect it.
+	 */
+	if (cb == cb_end || !le16_to_cpup((le16*)cb) ||
+			(*dest_index == dest_max_index &&
+			*dest_ofs == dest_max_ofs)) {
+		int i;
+
+		ntfs_debug("Completed. Returning success (0).");
+		err = 0;
+return_error:
+		/* We can sleep from now on, so we drop lock. */
+		spin_unlock(&ntfs_cb_lock);
+		/* Second stage: finalize completed pages. */
+		if (nr_completed_pages > 0) {
+			for (i = 0; i < nr_completed_pages; i++) {
+				int di = completed_pages[i];
+
+				dp = dest_pages[di];
+				/*
+				 * If we are outside the initialized size, zero
+				 * the out of bounds page range.
+				 */
+				handle_bounds_compressed_page(dp, i_size,
+						initialized_size);
+				flush_dcache_page(dp);
+				kunmap(dp);
+				SetPageUptodate(dp);
+				unlock_page(dp);
+				if (di == xpage)
+					*xpage_done = 1;
+				else
+					put_page(dp);
+				dest_pages[di] = NULL;
+			}
+		}
+		return err;
+	}
+
+	/* Setup offsets for the current sub-block destination. */
+	do_sb_start = *dest_ofs;
+	do_sb_end = do_sb_start + NTFS_SB_SIZE;
+
+	/* Check that we are still within allowed boundaries. */
+	if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
+		goto return_overflow;
+
+	/* Does the minimum size of a compressed sb overflow valid range? */
+	if (cb + 6 > cb_end)
+		goto return_overflow;
+
+	/* Setup the current sub-block source pointers and validate range. */
+	cb_sb_start = cb;
+	cb_sb_end = cb_sb_start + (le16_to_cpup((le16*)cb) & NTFS_SB_SIZE_MASK)
+			+ 3;
+	if (cb_sb_end > cb_end)
+		goto return_overflow;
+
+	/* Get the current destination page. */
+	dp = dest_pages[*dest_index];
+	if (!dp) {
+		/* No page present. Skip decompression of this sub-block. */
+		cb = cb_sb_end;
+
+		/* Advance destination position to next sub-block. */
+		*dest_ofs = (*dest_ofs + NTFS_SB_SIZE) & ~PAGE_MASK;
+		if (!*dest_ofs && (++*dest_index > dest_max_index))
+			goto return_overflow;
+		goto do_next_sb;
+	}
+
+	/* We have a valid destination page. Setup the destination pointers. */
+	dp_addr = (u8*)page_address(dp) + do_sb_start;
+
+	/* Now, we are ready to process the current sub-block (sb). */
+	if (!(le16_to_cpup((le16*)cb) & NTFS_SB_IS_COMPRESSED)) {
+		ntfs_debug("Found uncompressed sub-block.");
+		/* This sb is not compressed, just copy it into destination. */
+
+		/* Advance source position to first data byte. */
+		cb += 2;
+
+		/* An uncompressed sb must be full size. */
+		if (cb_sb_end - cb != NTFS_SB_SIZE)
+			goto return_overflow;
+
+		/* Copy the block and advance the source position. */
+		memcpy(dp_addr, cb, NTFS_SB_SIZE);
+		cb += NTFS_SB_SIZE;
+
+		/* Advance destination position to next sub-block. */
+		*dest_ofs += NTFS_SB_SIZE;
+		if (!(*dest_ofs &= ~PAGE_MASK)) {
+finalize_page:
+			/*
+			 * First stage: add current page index to array of
+			 * completed pages.
+			 */
+			completed_pages[nr_completed_pages++] = *dest_index;
+			if (++*dest_index > dest_max_index)
+				goto return_overflow;
+		}
+		goto do_next_sb;
+	}
+	ntfs_debug("Found compressed sub-block.");
+	/* This sb is compressed, decompress it into destination. */
+
+	/* Setup destination pointers. */
+	dp_sb_start = dp_addr;
+	dp_sb_end = dp_sb_start + NTFS_SB_SIZE;
+
+	/* Forward to the first tag in the sub-block. */
+	cb += 2;
+do_next_tag:
+	if (cb == cb_sb_end) {
+		/* Check if the decompressed sub-block was not full-length. */
+		if (dp_addr < dp_sb_end) {
+			int nr_bytes = do_sb_end - *dest_ofs;
+
+			ntfs_debug("Filling incomplete sub-block with "
+					"zeroes.");
+			/* Zero remainder and update destination position. */
+			memset(dp_addr, 0, nr_bytes);
+			*dest_ofs += nr_bytes;
+		}
+		/* We have finished the current sub-block. */
+		if (!(*dest_ofs &= ~PAGE_MASK))
+			goto finalize_page;
+		goto do_next_sb;
+	}
+
+	/* Check we are still in range. */
+	if (cb > cb_sb_end || dp_addr > dp_sb_end)
+		goto return_overflow;
+
+	/* Get the next tag and advance to first token. */
+	tag = *cb++;
+
+	/* Parse the eight tokens described by the tag. */
+	for (token = 0; token < 8; token++, tag >>= 1) {
+		u16 lg, pt, length, max_non_overlap;
+		register u16 i;
+		u8 *dp_back_addr;
+
+		/* Check if we are done / still in range. */
+		if (cb >= cb_sb_end || dp_addr > dp_sb_end)
+			break;
+
+		/* Determine token type and parse appropriately.*/
+		if ((tag & NTFS_TOKEN_MASK) == NTFS_SYMBOL_TOKEN) {
+			/*
+			 * We have a symbol token, copy the symbol across, and
+			 * advance the source and destination positions.
+			 */
+			*dp_addr++ = *cb++;
+			++*dest_ofs;
+
+			/* Continue with the next token. */
+			continue;
+		}
+
+		/*
+		 * We have a phrase token. Make sure it is not the first tag in
+		 * the sb as this is illegal and would confuse the code below.
+		 */
+		if (dp_addr == dp_sb_start)
+			goto return_overflow;
+
+		/*
+		 * Determine the number of bytes to go back (p) and the number
+		 * of bytes to copy (l). We use an optimized algorithm in which
+		 * we first calculate log2(current destination position in sb),
+		 * which allows determination of l and p in O(1) rather than
+		 * O(n). We just need an arch-optimized log2() function now.
+		 */
+		lg = 0;
+		for (i = *dest_ofs - do_sb_start - 1; i >= 0x10; i >>= 1)
+			lg++;
+
+		/* Get the phrase token into i. */
+		pt = le16_to_cpup((le16*)cb);
+
+		/*
+		 * Calculate starting position of the byte sequence in
+		 * the destination using the fact that p = (pt >> (12 - lg)) + 1
+		 * and make sure we don't go too far back.
+		 */
+		dp_back_addr = dp_addr - (pt >> (12 - lg)) - 1;
+		if (dp_back_addr < dp_sb_start)
+			goto return_overflow;
+
+		/* Now calculate the length of the byte sequence. */
+		length = (pt & (0xfff >> lg)) + 3;
+
+		/* Advance destination position and verify it is in range. */
+		*dest_ofs += length;
+		if (*dest_ofs > do_sb_end)
+			goto return_overflow;
+
+		/* The number of non-overlapping bytes. */
+		max_non_overlap = dp_addr - dp_back_addr;
+
+		if (length <= max_non_overlap) {
+			/* The byte sequence doesn't overlap, just copy it. */
+			memcpy(dp_addr, dp_back_addr, length);
+
+			/* Advance destination pointer. */
+			dp_addr += length;
+		} else {
+			/*
+			 * The byte sequence does overlap, copy non-overlapping
+			 * part and then do a slow byte by byte copy for the
+			 * overlapping part. Also, advance the destination
+			 * pointer.
+			 */
+			memcpy(dp_addr, dp_back_addr, max_non_overlap);
+			dp_addr += max_non_overlap;
+			dp_back_addr += max_non_overlap;
+			length -= max_non_overlap;
+			while (length--)
+				*dp_addr++ = *dp_back_addr++;
+		}
+
+		/* Advance source position and continue with the next token. */
+		cb += 2;
+	}
+
+	/* No tokens left in the current tag. Continue with the next tag. */
+	goto do_next_tag;
+
+return_overflow:
+	ntfs_error(NULL, "Failed. Returning -EOVERFLOW.");
+	goto return_error;
+}
+
+/**
+ * ntfs_read_compressed_block - read a compressed block into the page cache
+ * @page:	locked page in the compression block(s) we need to read
+ *
+ * When we are called the page has already been verified to be locked and the
+ * attribute is known to be non-resident, not encrypted, but compressed.
+ *
+ * 1. Determine which compression block(s) @page is in.
+ * 2. Get hold of all pages corresponding to this/these compression block(s).
+ * 3. Read the (first) compression block.
+ * 4. Decompress it into the corresponding pages.
+ * 5. Throw the compressed data away and proceed to 3. for the next compression
+ *    block or return success if no more compression blocks left.
+ *
+ * Warning: We have to be careful what we do about existing pages. They might
+ * have been written to so that we would lose data if we were to just overwrite
+ * them with the out-of-date uncompressed data.
+ *
+ * FIXME: For PAGE_SIZE > cb_size we are not doing the Right Thing(TM) at
+ * the end of the file I think. We need to detect this case and zero the out
+ * of bounds remainder of the page in question and mark it as handled. At the
+ * moment we would just return -EIO on such a page. This bug will only become
+ * apparent if pages are above 8kiB and the NTFS volume only uses 512 byte
+ * clusters so is probably not going to be seen by anyone. Still this should
+ * be fixed. (AIA)
+ *
+ * FIXME: Again for PAGE_SIZE > cb_size we are screwing up both in
+ * handling sparse and compressed cbs. (AIA)
+ *
+ * FIXME: At the moment we don't do any zeroing out in the case that
+ * initialized_size is less than data_size. This should be safe because of the
+ * nature of the compression algorithm used. Just in case we check and output
+ * an error message in read inode if the two sizes are not equal for a
+ * compressed file. (AIA)
+ */
+int ntfs_read_compressed_block(struct page *page)
+{
+	loff_t i_size;
+	s64 initialized_size;
+	struct address_space *mapping = page->mapping;
+	ntfs_inode *ni = NTFS_I(mapping->host);
+	ntfs_volume *vol = ni->vol;
+	struct super_block *sb = vol->sb;
+	runlist_element *rl;
+	unsigned long flags, block_size = sb->s_blocksize;
+	unsigned char block_size_bits = sb->s_blocksize_bits;
+	u8 *cb, *cb_pos, *cb_end;
+	struct buffer_head **bhs;
+	unsigned long offset, index = page->index;
+	u32 cb_size = ni->itype.compressed.block_size;
+	u64 cb_size_mask = cb_size - 1UL;
+	VCN vcn;
+	LCN lcn;
+	/* The first wanted vcn (minimum alignment is PAGE_SIZE). */
+	VCN start_vcn = (((s64)index << PAGE_SHIFT) & ~cb_size_mask) >>
+			vol->cluster_size_bits;
+	/*
+	 * The first vcn after the last wanted vcn (minimum alignment is again
+	 * PAGE_SIZE.
+	 */
+	VCN end_vcn = ((((s64)(index + 1UL) << PAGE_SHIFT) + cb_size - 1)
+			& ~cb_size_mask) >> vol->cluster_size_bits;
+	/* Number of compression blocks (cbs) in the wanted vcn range. */
+	unsigned int nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits
+			>> ni->itype.compressed.block_size_bits;
+	/*
+	 * Number of pages required to store the uncompressed data from all
+	 * compression blocks (cbs) overlapping @page. Due to alignment
+	 * guarantees of start_vcn and end_vcn, no need to round up here.
+	 */
+	unsigned int nr_pages = (end_vcn - start_vcn) <<
+			vol->cluster_size_bits >> PAGE_SHIFT;
+	unsigned int xpage, max_page, cur_page, cur_ofs, i;
+	unsigned int cb_clusters, cb_max_ofs;
+	int block, max_block, cb_max_page, bhs_size, nr_bhs, err = 0;
+	struct page **pages;
+	int *completed_pages;
+	unsigned char xpage_done = 0;
+
+	ntfs_debug("Entering, page->index = 0x%lx, cb_size = 0x%x, nr_pages = "
+			"%i.", index, cb_size, nr_pages);
+	/*
+	 * Bad things happen if we get here for anything that is not an
+	 * unnamed $DATA attribute.
+	 */
+	BUG_ON(ni->type != AT_DATA);
+	BUG_ON(ni->name_len);
+
+	pages = kmalloc_array(nr_pages, sizeof(struct page *), GFP_NOFS);
+	completed_pages = kmalloc_array(nr_pages + 1, sizeof(int), GFP_NOFS);
+
+	/* Allocate memory to store the buffer heads we need. */
+	bhs_size = cb_size / block_size * sizeof(struct buffer_head *);
+	bhs = kmalloc(bhs_size, GFP_NOFS);
+
+	if (unlikely(!pages || !bhs || !completed_pages)) {
+		kfree(bhs);
+		kfree(pages);
+		kfree(completed_pages);
+		unlock_page(page);
+		ntfs_error(vol->sb, "Failed to allocate internal buffers.");
+		return -ENOMEM;
+	}
+
+	/*
+	 * We have already been given one page, this is the one we must do.
+	 * Once again, the alignment guarantees keep it simple.
+	 */
+	offset = start_vcn << vol->cluster_size_bits >> PAGE_SHIFT;
+	xpage = index - offset;
+	pages[xpage] = page;
+	/*
+	 * The remaining pages need to be allocated and inserted into the page
+	 * cache, alignment guarantees keep all the below much simpler. (-8
+	 */
+	read_lock_irqsave(&ni->size_lock, flags);
+	i_size = i_size_read(VFS_I(ni));
+	initialized_size = ni->initialized_size;
+	read_unlock_irqrestore(&ni->size_lock, flags);
+	max_page = ((i_size + PAGE_SIZE - 1) >> PAGE_SHIFT) -
+			offset;
+	/* Is the page fully outside i_size? (truncate in progress) */
+	if (xpage >= max_page) {
+		kfree(bhs);
+		kfree(pages);
+		kfree(completed_pages);
+		zero_user(page, 0, PAGE_SIZE);
+		ntfs_debug("Compressed read outside i_size - truncated?");
+		SetPageUptodate(page);
+		unlock_page(page);
+		return 0;
+	}
+	if (nr_pages < max_page)
+		max_page = nr_pages;
+	for (i = 0; i < max_page; i++, offset++) {
+		if (i != xpage)
+			pages[i] = grab_cache_page_nowait(mapping, offset);
+		page = pages[i];
+		if (page) {
+			/*
+			 * We only (re)read the page if it isn't already read
+			 * in and/or dirty or we would be losing data or at
+			 * least wasting our time.
+			 */
+			if (!PageDirty(page) && (!PageUptodate(page) ||
+					PageError(page))) {
+				ClearPageError(page);
+				kmap(page);
+				continue;
+			}
+			unlock_page(page);
+			put_page(page);
+			pages[i] = NULL;
+		}
+	}
+
+	/*
+	 * We have the runlist, and all the destination pages we need to fill.
+	 * Now read the first compression block.
+	 */
+	cur_page = 0;
+	cur_ofs = 0;
+	cb_clusters = ni->itype.compressed.block_clusters;
+do_next_cb:
+	nr_cbs--;
+	nr_bhs = 0;
+
+	/* Read all cb buffer heads one cluster at a time. */
+	rl = NULL;
+	for (vcn = start_vcn, start_vcn += cb_clusters; vcn < start_vcn;
+			vcn++) {
+		bool is_retry = false;
+
+		if (!rl) {
+lock_retry_remap:
+			down_read(&ni->runlist.lock);
+			rl = ni->runlist.rl;
+		}
+		if (likely(rl != NULL)) {
+			/* Seek to element containing target vcn. */
+			while (rl->length && rl[1].vcn <= vcn)
+				rl++;
+			lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
+		} else
+			lcn = LCN_RL_NOT_MAPPED;
+		ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
+				(unsigned long long)vcn,
+				(unsigned long long)lcn);
+		if (lcn < 0) {
+			/*
+			 * When we reach the first sparse cluster we have
+			 * finished with the cb.
+			 */
+			if (lcn == LCN_HOLE)
+				break;
+			if (is_retry || lcn != LCN_RL_NOT_MAPPED)
+				goto rl_err;
+			is_retry = true;
+			/*
+			 * Attempt to map runlist, dropping lock for the
+			 * duration.
+			 */
+			up_read(&ni->runlist.lock);
+			if (!ntfs_map_runlist(ni, vcn))
+				goto lock_retry_remap;
+			goto map_rl_err;
+		}
+		block = lcn << vol->cluster_size_bits >> block_size_bits;
+		/* Read the lcn from device in chunks of block_size bytes. */
+		max_block = block + (vol->cluster_size >> block_size_bits);
+		do {
+			ntfs_debug("block = 0x%x.", block);
+			if (unlikely(!(bhs[nr_bhs] = sb_getblk(sb, block))))
+				goto getblk_err;
+			nr_bhs++;
+		} while (++block < max_block);
+	}
+
+	/* Release the lock if we took it. */
+	if (rl)
+		up_read(&ni->runlist.lock);
+
+	/* Setup and initiate io on all buffer heads. */
+	for (i = 0; i < nr_bhs; i++) {
+		struct buffer_head *tbh = bhs[i];
+
+		if (!trylock_buffer(tbh))
+			continue;
+		if (unlikely(buffer_uptodate(tbh))) {
+			unlock_buffer(tbh);
+			continue;
+		}
+		get_bh(tbh);
+		tbh->b_end_io = end_buffer_read_sync;
+		submit_bh(REQ_OP_READ, 0, tbh);
+	}
+
+	/* Wait for io completion on all buffer heads. */
+	for (i = 0; i < nr_bhs; i++) {
+		struct buffer_head *tbh = bhs[i];
+
+		if (buffer_uptodate(tbh))
+			continue;
+		wait_on_buffer(tbh);
+		/*
+		 * We need an optimization barrier here, otherwise we start
+		 * hitting the below fixup code when accessing a loopback
+		 * mounted ntfs partition. This indicates either there is a
+		 * race condition in the loop driver or, more likely, gcc
+		 * overoptimises the code without the barrier and it doesn't
+		 * do the Right Thing(TM).
+		 */
+		barrier();
+		if (unlikely(!buffer_uptodate(tbh))) {
+			ntfs_warning(vol->sb, "Buffer is unlocked but not "
+					"uptodate! Unplugging the disk queue "
+					"and rescheduling.");
+			get_bh(tbh);
+			io_schedule();
+			put_bh(tbh);
+			if (unlikely(!buffer_uptodate(tbh)))
+				goto read_err;
+			ntfs_warning(vol->sb, "Buffer is now uptodate. Good.");
+		}
+	}
+
+	/*
+	 * Get the compression buffer. We must not sleep any more
+	 * until we are finished with it.
+	 */
+	spin_lock(&ntfs_cb_lock);
+	cb = ntfs_compression_buffer;
+
+	BUG_ON(!cb);
+
+	cb_pos = cb;
+	cb_end = cb + cb_size;
+
+	/* Copy the buffer heads into the contiguous buffer. */
+	for (i = 0; i < nr_bhs; i++) {
+		memcpy(cb_pos, bhs[i]->b_data, block_size);
+		cb_pos += block_size;
+	}
+
+	/* Just a precaution. */
+	if (cb_pos + 2 <= cb + cb_size)
+		*(u16*)cb_pos = 0;
+
+	/* Reset cb_pos back to the beginning. */
+	cb_pos = cb;
+
+	/* We now have both source (if present) and destination. */
+	ntfs_debug("Successfully read the compression block.");
+
+	/* The last page and maximum offset within it for the current cb. */
+	cb_max_page = (cur_page << PAGE_SHIFT) + cur_ofs + cb_size;
+	cb_max_ofs = cb_max_page & ~PAGE_MASK;
+	cb_max_page >>= PAGE_SHIFT;
+
+	/* Catch end of file inside a compression block. */
+	if (cb_max_page > max_page)
+		cb_max_page = max_page;
+
+	if (vcn == start_vcn - cb_clusters) {
+		/* Sparse cb, zero out page range overlapping the cb. */
+		ntfs_debug("Found sparse compression block.");
+		/* We can sleep from now on, so we drop lock. */
+		spin_unlock(&ntfs_cb_lock);
+		if (cb_max_ofs)
+			cb_max_page--;
+		for (; cur_page < cb_max_page; cur_page++) {
+			page = pages[cur_page];
+			if (page) {
+				if (likely(!cur_ofs))
+					clear_page(page_address(page));
+				else
+					memset(page_address(page) + cur_ofs, 0,
+							PAGE_SIZE -
+							cur_ofs);
+				flush_dcache_page(page);
+				kunmap(page);
+				SetPageUptodate(page);
+				unlock_page(page);
+				if (cur_page == xpage)
+					xpage_done = 1;
+				else
+					put_page(page);
+				pages[cur_page] = NULL;
+			}
+			cb_pos += PAGE_SIZE - cur_ofs;
+			cur_ofs = 0;
+			if (cb_pos >= cb_end)
+				break;
+		}
+		/* If we have a partial final page, deal with it now. */
+		if (cb_max_ofs && cb_pos < cb_end) {
+			page = pages[cur_page];
+			if (page)
+				memset(page_address(page) + cur_ofs, 0,
+						cb_max_ofs - cur_ofs);
+			/*
+			 * No need to update cb_pos at this stage:
+			 *	cb_pos += cb_max_ofs - cur_ofs;
+			 */
+			cur_ofs = cb_max_ofs;
+		}
+	} else if (vcn == start_vcn) {
+		/* We can't sleep so we need two stages. */
+		unsigned int cur2_page = cur_page;
+		unsigned int cur_ofs2 = cur_ofs;
+		u8 *cb_pos2 = cb_pos;
+
+		ntfs_debug("Found uncompressed compression block.");
+		/* Uncompressed cb, copy it to the destination pages. */
+		/*
+		 * TODO: As a big optimization, we could detect this case
+		 * before we read all the pages and use block_read_full_page()
+		 * on all full pages instead (we still have to treat partial
+		 * pages especially but at least we are getting rid of the
+		 * synchronous io for the majority of pages.
+		 * Or if we choose not to do the read-ahead/-behind stuff, we
+		 * could just return block_read_full_page(pages[xpage]) as long
+		 * as PAGE_SIZE <= cb_size.
+		 */
+		if (cb_max_ofs)
+			cb_max_page--;
+		/* First stage: copy data into destination pages. */
+		for (; cur_page < cb_max_page; cur_page++) {
+			page = pages[cur_page];
+			if (page)
+				memcpy(page_address(page) + cur_ofs, cb_pos,
+						PAGE_SIZE - cur_ofs);
+			cb_pos += PAGE_SIZE - cur_ofs;
+			cur_ofs = 0;
+			if (cb_pos >= cb_end)
+				break;
+		}
+		/* If we have a partial final page, deal with it now. */
+		if (cb_max_ofs && cb_pos < cb_end) {
+			page = pages[cur_page];
+			if (page)
+				memcpy(page_address(page) + cur_ofs, cb_pos,
+						cb_max_ofs - cur_ofs);
+			cb_pos += cb_max_ofs - cur_ofs;
+			cur_ofs = cb_max_ofs;
+		}
+		/* We can sleep from now on, so drop lock. */
+		spin_unlock(&ntfs_cb_lock);
+		/* Second stage: finalize pages. */
+		for (; cur2_page < cb_max_page; cur2_page++) {
+			page = pages[cur2_page];
+			if (page) {
+				/*
+				 * If we are outside the initialized size, zero
+				 * the out of bounds page range.
+				 */
+				handle_bounds_compressed_page(page, i_size,
+						initialized_size);
+				flush_dcache_page(page);
+				kunmap(page);
+				SetPageUptodate(page);
+				unlock_page(page);
+				if (cur2_page == xpage)
+					xpage_done = 1;
+				else
+					put_page(page);
+				pages[cur2_page] = NULL;
+			}
+			cb_pos2 += PAGE_SIZE - cur_ofs2;
+			cur_ofs2 = 0;
+			if (cb_pos2 >= cb_end)
+				break;
+		}
+	} else {
+		/* Compressed cb, decompress it into the destination page(s). */
+		unsigned int prev_cur_page = cur_page;
+
+		ntfs_debug("Found compressed compression block.");
+		err = ntfs_decompress(pages, completed_pages, &cur_page,
+				&cur_ofs, cb_max_page, cb_max_ofs, xpage,
+				&xpage_done, cb_pos, cb_size - (cb_pos - cb),
+				i_size, initialized_size);
+		/*
+		 * We can sleep from now on, lock already dropped by
+		 * ntfs_decompress().
+		 */
+		if (err) {
+			ntfs_error(vol->sb, "ntfs_decompress() failed in inode "
+					"0x%lx with error code %i. Skipping "
+					"this compression block.",
+					ni->mft_no, -err);
+			/* Release the unfinished pages. */
+			for (; prev_cur_page < cur_page; prev_cur_page++) {
+				page = pages[prev_cur_page];
+				if (page) {
+					flush_dcache_page(page);
+					kunmap(page);
+					unlock_page(page);
+					if (prev_cur_page != xpage)
+						put_page(page);
+					pages[prev_cur_page] = NULL;
+				}
+			}
+		}
+	}
+
+	/* Release the buffer heads. */
+	for (i = 0; i < nr_bhs; i++)
+		brelse(bhs[i]);
+
+	/* Do we have more work to do? */
+	if (nr_cbs)
+		goto do_next_cb;
+
+	/* We no longer need the list of buffer heads. */
+	kfree(bhs);
+
+	/* Clean up if we have any pages left. Should never happen. */
+	for (cur_page = 0; cur_page < max_page; cur_page++) {
+		page = pages[cur_page];
+		if (page) {
+			ntfs_error(vol->sb, "Still have pages left! "
+					"Terminating them with extreme "
+					"prejudice.  Inode 0x%lx, page index "
+					"0x%lx.", ni->mft_no, page->index);
+			flush_dcache_page(page);
+			kunmap(page);
+			unlock_page(page);
+			if (cur_page != xpage)
+				put_page(page);
+			pages[cur_page] = NULL;
+		}
+	}
+
+	/* We no longer need the list of pages. */
+	kfree(pages);
+	kfree(completed_pages);
+
+	/* If we have completed the requested page, we return success. */
+	if (likely(xpage_done))
+		return 0;
+
+	ntfs_debug("Failed. Returning error code %s.", err == -EOVERFLOW ?
+			"EOVERFLOW" : (!err ? "EIO" : "unknown error"));
+	return err < 0 ? err : -EIO;
+
+read_err:
+	ntfs_error(vol->sb, "IO error while reading compressed data.");
+	/* Release the buffer heads. */
+	for (i = 0; i < nr_bhs; i++)
+		brelse(bhs[i]);
+	goto err_out;
+
+map_rl_err:
+	ntfs_error(vol->sb, "ntfs_map_runlist() failed. Cannot read "
+			"compression block.");
+	goto err_out;
+
+rl_err:
+	up_read(&ni->runlist.lock);
+	ntfs_error(vol->sb, "ntfs_rl_vcn_to_lcn() failed. Cannot read "
+			"compression block.");
+	goto err_out;
+
+getblk_err:
+	up_read(&ni->runlist.lock);
+	ntfs_error(vol->sb, "getblk() failed. Cannot read compression block.");
+
+err_out:
+	kfree(bhs);
+	for (i = cur_page; i < max_page; i++) {
+		page = pages[i];
+		if (page) {
+			flush_dcache_page(page);
+			kunmap(page);
+			unlock_page(page);
+			if (i != xpage)
+				put_page(page);
+		}
+	}
+	kfree(pages);
+	kfree(completed_pages);
+	return -EIO;
+}