1/**
  2 * compress.c - NTFS kernel compressed attributes handling.
  3 *		Part of the Linux-NTFS project.
  4 *
  5 * Copyright (c) 2001-2004 Anton Altaparmakov
  6 * Copyright (c) 2002 Richard Russon
  7 *
  8 * This program/include file is free software; you can redistribute it and/or
  9 * modify it under the terms of the GNU General Public License as published
 10 * by the Free Software Foundation; either version 2 of the License, or
 11 * (at your option) any later version.
 12 *
 13 * This program/include file is distributed in the hope that it will be
 14 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 15 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 16 * GNU General Public License for more details.
 17 *
 18 * You should have received a copy of the GNU General Public License
 19 * along with this program (in the main directory of the Linux-NTFS
 20 * distribution in the file COPYING); if not, write to the Free Software
 21 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 22 */
 23
 24#include <linux/fs.h>
 25#include <linux/buffer_head.h>
 26#include <linux/blkdev.h>
 27#include <linux/vmalloc.h>
 28#include <linux/slab.h>
 29
 30#include "attrib.h"
 31#include "inode.h"
 32#include "debug.h"
 33#include "ntfs.h"
 34
 35/**
 36 * ntfs_compression_constants - enum of constants used in the compression code
 37 */
 38typedef enum {
 39	/* Token types and access mask. */
 40	NTFS_SYMBOL_TOKEN	=	0,
 41	NTFS_PHRASE_TOKEN	=	1,
 42	NTFS_TOKEN_MASK		=	1,
 43
 44	/* Compression sub-block constants. */
 45	NTFS_SB_SIZE_MASK	=	0x0fff,
 46	NTFS_SB_SIZE		=	0x1000,
 47	NTFS_SB_IS_COMPRESSED	=	0x8000,
 48
 49	/*
 50	 * The maximum compression block size is by definition 16 * the cluster
 51	 * size, with the maximum supported cluster size being 4kiB. Thus the
 52	 * maximum compression buffer size is 64kiB, so we use this when
 53	 * initializing the compression buffer.
 54	 */
 55	NTFS_MAX_CB_SIZE	= 64 * 1024,
 56} ntfs_compression_constants;
 57
 58/**
 59 * ntfs_compression_buffer - one buffer for the decompression engine
 60 */
 61static u8 *ntfs_compression_buffer = NULL;
 62
 63/**
 64 * ntfs_cb_lock - spinlock which protects ntfs_compression_buffer
 65 */
 66static DEFINE_SPINLOCK(ntfs_cb_lock);
 67
 68/**
 69 * allocate_compression_buffers - allocate the decompression buffers
 70 *
 71 * Caller has to hold the ntfs_lock mutex.
 72 *
 73 * Return 0 on success or -ENOMEM if the allocations failed.
 74 */
 75int allocate_compression_buffers(void)
 76{
 77	BUG_ON(ntfs_compression_buffer);
 78
 79	ntfs_compression_buffer = vmalloc(NTFS_MAX_CB_SIZE);
 80	if (!ntfs_compression_buffer)
 81		return -ENOMEM;
 82	return 0;
 83}
 84
 85/**
 86 * free_compression_buffers - free the decompression buffers
 87 *
 88 * Caller has to hold the ntfs_lock mutex.
 89 */
 90void free_compression_buffers(void)
 91{
 92	BUG_ON(!ntfs_compression_buffer);
 93	vfree(ntfs_compression_buffer);
 94	ntfs_compression_buffer = NULL;
 95}
 96
 97/**
 98 * zero_partial_compressed_page - zero out of bounds compressed page region
 99 */
100static void zero_partial_compressed_page(struct page *page,
101		const s64 initialized_size)
102{
103	u8 *kp = page_address(page);
104	unsigned int kp_ofs;
105
106	ntfs_debug("Zeroing page region outside initialized size.");
107	if (((s64)page->index << PAGE_CACHE_SHIFT) >= initialized_size) {
108		/*
109		 * FIXME: Using clear_page() will become wrong when we get
110		 * PAGE_CACHE_SIZE != PAGE_SIZE but for now there is no problem.
111		 */
112		clear_page(kp);
113		return;
114	}
115	kp_ofs = initialized_size & ~PAGE_CACHE_MASK;
116	memset(kp + kp_ofs, 0, PAGE_CACHE_SIZE - kp_ofs);
117	return;
118}
119
120/**
121 * handle_bounds_compressed_page - test for&handle out of bounds compressed page
122 */
123static inline void handle_bounds_compressed_page(struct page *page,
124		const loff_t i_size, const s64 initialized_size)
125{
126	if ((page->index >= (initialized_size >> PAGE_CACHE_SHIFT)) &&
127			(initialized_size < i_size))
128		zero_partial_compressed_page(page, initialized_size);
129	return;
130}
131
132/**
133 * ntfs_decompress - decompress a compression block into an array of pages
134 * @dest_pages:		destination array of pages
135 * @dest_index:		current index into @dest_pages (IN/OUT)
136 * @dest_ofs:		current offset within @dest_pages[@dest_index] (IN/OUT)
137 * @dest_max_index:	maximum index into @dest_pages (IN)
138 * @dest_max_ofs:	maximum offset within @dest_pages[@dest_max_index] (IN)
139 * @xpage:		the target page (-1 if none) (IN)
140 * @xpage_done:		set to 1 if xpage was completed successfully (IN/OUT)
141 * @cb_start:		compression block to decompress (IN)
142 * @cb_size:		size of compression block @cb_start in bytes (IN)
143 * @i_size:		file size when we started the read (IN)
144 * @initialized_size:	initialized file size when we started the read (IN)
145 *
146 * The caller must have disabled preemption. ntfs_decompress() reenables it when
147 * the critical section is finished.
148 *
149 * This decompresses the compression block @cb_start into the array of
150 * destination pages @dest_pages starting at index @dest_index into @dest_pages
151 * and at offset @dest_pos into the page @dest_pages[@dest_index].
152 *
153 * When the page @dest_pages[@xpage] is completed, @xpage_done is set to 1.
154 * If xpage is -1 or @xpage has not been completed, @xpage_done is not modified.
155 *
156 * @cb_start is a pointer to the compression block which needs decompressing
157 * and @cb_size is the size of @cb_start in bytes (8-64kiB).
158 *
159 * Return 0 if success or -EOVERFLOW on error in the compressed stream.
160 * @xpage_done indicates whether the target page (@dest_pages[@xpage]) was
161 * completed during the decompression of the compression block (@cb_start).
162 *
163 * Warning: This function *REQUIRES* PAGE_CACHE_SIZE >= 4096 or it will blow up
164 * unpredicatbly! You have been warned!
165 *
166 * Note to hackers: This function may not sleep until it has finished accessing
167 * the compression block @cb_start as it is a per-CPU buffer.
168 */
169static int ntfs_decompress(struct page *dest_pages[], int *dest_index,
170		int *dest_ofs, const int dest_max_index, const int dest_max_ofs,
171		const int xpage, char *xpage_done, u8 *const cb_start,
172		const u32 cb_size, const loff_t i_size,
173		const s64 initialized_size)
174{
175	/*
176	 * Pointers into the compressed data, i.e. the compression block (cb),
177	 * and the therein contained sub-blocks (sb).
178	 */
179	u8 *cb_end = cb_start + cb_size; /* End of cb. */
180	u8 *cb = cb_start;	/* Current position in cb. */
181	u8 *cb_sb_start = cb;	/* Beginning of the current sb in the cb. */
182	u8 *cb_sb_end;		/* End of current sb / beginning of next sb. */
183
184	/* Variables for uncompressed data / destination. */
185	struct page *dp;	/* Current destination page being worked on. */
186	u8 *dp_addr;		/* Current pointer into dp. */
187	u8 *dp_sb_start;	/* Start of current sub-block in dp. */
188	u8 *dp_sb_end;		/* End of current sb in dp (dp_sb_start +
189				   NTFS_SB_SIZE). */
190	u16 do_sb_start;	/* @dest_ofs when starting this sub-block. */
191	u16 do_sb_end;		/* @dest_ofs of end of this sb (do_sb_start +
192				   NTFS_SB_SIZE). */
193
194	/* Variables for tag and token parsing. */
195	u8 tag;			/* Current tag. */
196	int token;		/* Loop counter for the eight tokens in tag. */
197
198	/* Need this because we can't sleep, so need two stages. */
199	int completed_pages[dest_max_index - *dest_index + 1];
200	int nr_completed_pages = 0;
201
202	/* Default error code. */
203	int err = -EOVERFLOW;
204
205	ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
206do_next_sb:
207	ntfs_debug("Beginning sub-block at offset = 0x%zx in the cb.",
208			cb - cb_start);
209	/*
210	 * Have we reached the end of the compression block or the end of the
211	 * decompressed data?  The latter can happen for example if the current
212	 * position in the compression block is one byte before its end so the
213	 * first two checks do not detect it.
214	 */
215	if (cb == cb_end || !le16_to_cpup((le16*)cb) ||
216			(*dest_index == dest_max_index &&
217			*dest_ofs == dest_max_ofs)) {
218		int i;
219
220		ntfs_debug("Completed. Returning success (0).");
221		err = 0;
222return_error:
223		/* We can sleep from now on, so we drop lock. */
224		spin_unlock(&ntfs_cb_lock);
225		/* Second stage: finalize completed pages. */
226		if (nr_completed_pages > 0) {
227			for (i = 0; i < nr_completed_pages; i++) {
228				int di = completed_pages[i];
229
230				dp = dest_pages[di];
231				/*
232				 * If we are outside the initialized size, zero
233				 * the out of bounds page range.
234				 */
235				handle_bounds_compressed_page(dp, i_size,
236						initialized_size);
237				flush_dcache_page(dp);
238				kunmap(dp);
239				SetPageUptodate(dp);
240				unlock_page(dp);
241				if (di == xpage)
242					*xpage_done = 1;
243				else
244					page_cache_release(dp);
245				dest_pages[di] = NULL;
246			}
247		}
248		return err;
249	}
250
251	/* Setup offsets for the current sub-block destination. */
252	do_sb_start = *dest_ofs;
253	do_sb_end = do_sb_start + NTFS_SB_SIZE;
254
255	/* Check that we are still within allowed boundaries. */
256	if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
257		goto return_overflow;
258
259	/* Does the minimum size of a compressed sb overflow valid range? */
260	if (cb + 6 > cb_end)
261		goto return_overflow;
262
263	/* Setup the current sub-block source pointers and validate range. */
264	cb_sb_start = cb;
265	cb_sb_end = cb_sb_start + (le16_to_cpup((le16*)cb) & NTFS_SB_SIZE_MASK)
266			+ 3;
267	if (cb_sb_end > cb_end)
268		goto return_overflow;
269
270	/* Get the current destination page. */
271	dp = dest_pages[*dest_index];
272	if (!dp) {
273		/* No page present. Skip decompression of this sub-block. */
274		cb = cb_sb_end;
275
276		/* Advance destination position to next sub-block. */
277		*dest_ofs = (*dest_ofs + NTFS_SB_SIZE) & ~PAGE_CACHE_MASK;
278		if (!*dest_ofs && (++*dest_index > dest_max_index))
279			goto return_overflow;
280		goto do_next_sb;
281	}
282
283	/* We have a valid destination page. Setup the destination pointers. */
284	dp_addr = (u8*)page_address(dp) + do_sb_start;
285
286	/* Now, we are ready to process the current sub-block (sb). */
287	if (!(le16_to_cpup((le16*)cb) & NTFS_SB_IS_COMPRESSED)) {
288		ntfs_debug("Found uncompressed sub-block.");
289		/* This sb is not compressed, just copy it into destination. */
290
291		/* Advance source position to first data byte. */
292		cb += 2;
293
294		/* An uncompressed sb must be full size. */
295		if (cb_sb_end - cb != NTFS_SB_SIZE)
296			goto return_overflow;
297
298		/* Copy the block and advance the source position. */
299		memcpy(dp_addr, cb, NTFS_SB_SIZE);
300		cb += NTFS_SB_SIZE;
301
302		/* Advance destination position to next sub-block. */
303		*dest_ofs += NTFS_SB_SIZE;
304		if (!(*dest_ofs &= ~PAGE_CACHE_MASK)) {
305finalize_page:
306			/*
307			 * First stage: add current page index to array of
308			 * completed pages.
309			 */
310			completed_pages[nr_completed_pages++] = *dest_index;
311			if (++*dest_index > dest_max_index)
312				goto return_overflow;
313		}
314		goto do_next_sb;
315	}
316	ntfs_debug("Found compressed sub-block.");
317	/* This sb is compressed, decompress it into destination. */
318
319	/* Setup destination pointers. */
320	dp_sb_start = dp_addr;
321	dp_sb_end = dp_sb_start + NTFS_SB_SIZE;
322
323	/* Forward to the first tag in the sub-block. */
324	cb += 2;
325do_next_tag:
326	if (cb == cb_sb_end) {
327		/* Check if the decompressed sub-block was not full-length. */
328		if (dp_addr < dp_sb_end) {
329			int nr_bytes = do_sb_end - *dest_ofs;
330
331			ntfs_debug("Filling incomplete sub-block with "
332					"zeroes.");
333			/* Zero remainder and update destination position. */
334			memset(dp_addr, 0, nr_bytes);
335			*dest_ofs += nr_bytes;
336		}
337		/* We have finished the current sub-block. */
338		if (!(*dest_ofs &= ~PAGE_CACHE_MASK))
339			goto finalize_page;
340		goto do_next_sb;
341	}
342
343	/* Check we are still in range. */
344	if (cb > cb_sb_end || dp_addr > dp_sb_end)
345		goto return_overflow;
346
347	/* Get the next tag and advance to first token. */
348	tag = *cb++;
349
350	/* Parse the eight tokens described by the tag. */
351	for (token = 0; token < 8; token++, tag >>= 1) {
352		u16 lg, pt, length, max_non_overlap;
353		register u16 i;
354		u8 *dp_back_addr;
355
356		/* Check if we are done / still in range. */
357		if (cb >= cb_sb_end || dp_addr > dp_sb_end)
358			break;
359
360		/* Determine token type and parse appropriately.*/
361		if ((tag & NTFS_TOKEN_MASK) == NTFS_SYMBOL_TOKEN) {
362			/*
363			 * We have a symbol token, copy the symbol across, and
364			 * advance the source and destination positions.
365			 */
366			*dp_addr++ = *cb++;
367			++*dest_ofs;
368
369			/* Continue with the next token. */
370			continue;
371		}
372
373		/*
374		 * We have a phrase token. Make sure it is not the first tag in
375		 * the sb as this is illegal and would confuse the code below.
376		 */
377		if (dp_addr == dp_sb_start)
378			goto return_overflow;
379
380		/*
381		 * Determine the number of bytes to go back (p) and the number
382		 * of bytes to copy (l). We use an optimized algorithm in which
383		 * we first calculate log2(current destination position in sb),
384		 * which allows determination of l and p in O(1) rather than
385		 * O(n). We just need an arch-optimized log2() function now.
386		 */
387		lg = 0;
388		for (i = *dest_ofs - do_sb_start - 1; i >= 0x10; i >>= 1)
389			lg++;
390
391		/* Get the phrase token into i. */
392		pt = le16_to_cpup((le16*)cb);
393
394		/*
395		 * Calculate starting position of the byte sequence in
396		 * the destination using the fact that p = (pt >> (12 - lg)) + 1
397		 * and make sure we don't go too far back.
398		 */
399		dp_back_addr = dp_addr - (pt >> (12 - lg)) - 1;
400		if (dp_back_addr < dp_sb_start)
401			goto return_overflow;
402
403		/* Now calculate the length of the byte sequence. */
404		length = (pt & (0xfff >> lg)) + 3;
405
406		/* Advance destination position and verify it is in range. */
407		*dest_ofs += length;
408		if (*dest_ofs > do_sb_end)
409			goto return_overflow;
410
411		/* The number of non-overlapping bytes. */
412		max_non_overlap = dp_addr - dp_back_addr;
413
414		if (length <= max_non_overlap) {
415			/* The byte sequence doesn't overlap, just copy it. */
416			memcpy(dp_addr, dp_back_addr, length);
417
418			/* Advance destination pointer. */
419			dp_addr += length;
420		} else {
421			/*
422			 * The byte sequence does overlap, copy non-overlapping
423			 * part and then do a slow byte by byte copy for the
424			 * overlapping part. Also, advance the destination
425			 * pointer.
426			 */
427			memcpy(dp_addr, dp_back_addr, max_non_overlap);
428			dp_addr += max_non_overlap;
429			dp_back_addr += max_non_overlap;
430			length -= max_non_overlap;
431			while (length--)
432				*dp_addr++ = *dp_back_addr++;
433		}
434
435		/* Advance source position and continue with the next token. */
436		cb += 2;
437	}
438
439	/* No tokens left in the current tag. Continue with the next tag. */
440	goto do_next_tag;
441
442return_overflow:
443	ntfs_error(NULL, "Failed. Returning -EOVERFLOW.");
444	goto return_error;
445}
446
447/**
448 * ntfs_read_compressed_block - read a compressed block into the page cache
449 * @page:	locked page in the compression block(s) we need to read
450 *
451 * When we are called the page has already been verified to be locked and the
452 * attribute is known to be non-resident, not encrypted, but compressed.
453 *
454 * 1. Determine which compression block(s) @page is in.
455 * 2. Get hold of all pages corresponding to this/these compression block(s).
456 * 3. Read the (first) compression block.
457 * 4. Decompress it into the corresponding pages.
458 * 5. Throw the compressed data away and proceed to 3. for the next compression
459 *    block or return success if no more compression blocks left.
460 *
461 * Warning: We have to be careful what we do about existing pages. They might
462 * have been written to so that we would lose data if we were to just overwrite
463 * them with the out-of-date uncompressed data.
464 *
465 * FIXME: For PAGE_CACHE_SIZE > cb_size we are not doing the Right Thing(TM) at
466 * the end of the file I think. We need to detect this case and zero the out
467 * of bounds remainder of the page in question and mark it as handled. At the
468 * moment we would just return -EIO on such a page. This bug will only become
469 * apparent if pages are above 8kiB and the NTFS volume only uses 512 byte
470 * clusters so is probably not going to be seen by anyone. Still this should
471 * be fixed. (AIA)
472 *
473 * FIXME: Again for PAGE_CACHE_SIZE > cb_size we are screwing up both in
474 * handling sparse and compressed cbs. (AIA)
475 *
476 * FIXME: At the moment we don't do any zeroing out in the case that
477 * initialized_size is less than data_size. This should be safe because of the
478 * nature of the compression algorithm used. Just in case we check and output
479 * an error message in read inode if the two sizes are not equal for a
480 * compressed file. (AIA)
481 */
482int ntfs_read_compressed_block(struct page *page)
483{
484	loff_t i_size;
485	s64 initialized_size;
486	struct address_space *mapping = page->mapping;
487	ntfs_inode *ni = NTFS_I(mapping->host);
488	ntfs_volume *vol = ni->vol;
489	struct super_block *sb = vol->sb;
490	runlist_element *rl;
491	unsigned long flags, block_size = sb->s_blocksize;
492	unsigned char block_size_bits = sb->s_blocksize_bits;
493	u8 *cb, *cb_pos, *cb_end;
494	struct buffer_head **bhs;
495	unsigned long offset, index = page->index;
496	u32 cb_size = ni->itype.compressed.block_size;
497	u64 cb_size_mask = cb_size - 1UL;
498	VCN vcn;
499	LCN lcn;
500	/* The first wanted vcn (minimum alignment is PAGE_CACHE_SIZE). */
501	VCN start_vcn = (((s64)index << PAGE_CACHE_SHIFT) & ~cb_size_mask) >>
502			vol->cluster_size_bits;
503	/*
504	 * The first vcn after the last wanted vcn (minimum alignment is again
505	 * PAGE_CACHE_SIZE.
506	 */
507	VCN end_vcn = ((((s64)(index + 1UL) << PAGE_CACHE_SHIFT) + cb_size - 1)
508			& ~cb_size_mask) >> vol->cluster_size_bits;
509	/* Number of compression blocks (cbs) in the wanted vcn range. */
510	unsigned int nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits
511			>> ni->itype.compressed.block_size_bits;
512	/*
513	 * Number of pages required to store the uncompressed data from all
514	 * compression blocks (cbs) overlapping @page. Due to alignment
515	 * guarantees of start_vcn and end_vcn, no need to round up here.
516	 */
517	unsigned int nr_pages = (end_vcn - start_vcn) <<
518			vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
519	unsigned int xpage, max_page, cur_page, cur_ofs, i;
520	unsigned int cb_clusters, cb_max_ofs;
521	int block, max_block, cb_max_page, bhs_size, nr_bhs, err = 0;
522	struct page **pages;
523	unsigned char xpage_done = 0;
524
525	ntfs_debug("Entering, page->index = 0x%lx, cb_size = 0x%x, nr_pages = "
526			"%i.", index, cb_size, nr_pages);
527	/*
528	 * Bad things happen if we get here for anything that is not an
529	 * unnamed $DATA attribute.
530	 */
531	BUG_ON(ni->type != AT_DATA);
532	BUG_ON(ni->name_len);
533
534	pages = kmalloc(nr_pages * sizeof(struct page *), GFP_NOFS);
535
536	/* Allocate memory to store the buffer heads we need. */
537	bhs_size = cb_size / block_size * sizeof(struct buffer_head *);
538	bhs = kmalloc(bhs_size, GFP_NOFS);
539
540	if (unlikely(!pages || !bhs)) {
541		kfree(bhs);
542		kfree(pages);
543		unlock_page(page);
544		ntfs_error(vol->sb, "Failed to allocate internal buffers.");
545		return -ENOMEM;
546	}
547
548	/*
549	 * We have already been given one page, this is the one we must do.
550	 * Once again, the alignment guarantees keep it simple.
551	 */
552	offset = start_vcn << vol->cluster_size_bits >> PAGE_CACHE_SHIFT;
553	xpage = index - offset;
554	pages[xpage] = page;
555	/*
556	 * The remaining pages need to be allocated and inserted into the page
557	 * cache, alignment guarantees keep all the below much simpler. (-8
558	 */
559	read_lock_irqsave(&ni->size_lock, flags);
560	i_size = i_size_read(VFS_I(ni));
561	initialized_size = ni->initialized_size;
562	read_unlock_irqrestore(&ni->size_lock, flags);
563	max_page = ((i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
564			offset;
565	/* Is the page fully outside i_size? (truncate in progress) */
566	if (xpage >= max_page) {
567		kfree(bhs);
568		kfree(pages);
569		zero_user(page, 0, PAGE_CACHE_SIZE);
570		ntfs_debug("Compressed read outside i_size - truncated?");
571		SetPageUptodate(page);
572		unlock_page(page);
573		return 0;
574	}
575	if (nr_pages < max_page)
576		max_page = nr_pages;
577	for (i = 0; i < max_page; i++, offset++) {
578		if (i != xpage)
579			pages[i] = grab_cache_page_nowait(mapping, offset);
580		page = pages[i];
581		if (page) {
582			/*
583			 * We only (re)read the page if it isn't already read
584			 * in and/or dirty or we would be losing data or at
585			 * least wasting our time.
586			 */
587			if (!PageDirty(page) && (!PageUptodate(page) ||
588					PageError(page))) {
589				ClearPageError(page);
590				kmap(page);
591				continue;
592			}
593			unlock_page(page);
594			page_cache_release(page);
595			pages[i] = NULL;
596		}
597	}
598
599	/*
600	 * We have the runlist, and all the destination pages we need to fill.
601	 * Now read the first compression block.
602	 */
603	cur_page = 0;
604	cur_ofs = 0;
605	cb_clusters = ni->itype.compressed.block_clusters;
606do_next_cb:
607	nr_cbs--;
608	nr_bhs = 0;
609
610	/* Read all cb buffer heads one cluster at a time. */
611	rl = NULL;
612	for (vcn = start_vcn, start_vcn += cb_clusters; vcn < start_vcn;
613			vcn++) {
614		bool is_retry = false;
615
616		if (!rl) {
617lock_retry_remap:
618			down_read(&ni->runlist.lock);
619			rl = ni->runlist.rl;
620		}
621		if (likely(rl != NULL)) {
622			/* Seek to element containing target vcn. */
623			while (rl->length && rl[1].vcn <= vcn)
624				rl++;
625			lcn = ntfs_rl_vcn_to_lcn(rl, vcn);
626		} else
627			lcn = LCN_RL_NOT_MAPPED;
628		ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
629				(unsigned long long)vcn,
630				(unsigned long long)lcn);
631		if (lcn < 0) {
632			/*
633			 * When we reach the first sparse cluster we have
634			 * finished with the cb.
635			 */
636			if (lcn == LCN_HOLE)
637				break;
638			if (is_retry || lcn != LCN_RL_NOT_MAPPED)
639				goto rl_err;
640			is_retry = true;
641			/*
642			 * Attempt to map runlist, dropping lock for the
643			 * duration.
644			 */
645			up_read(&ni->runlist.lock);
646			if (!ntfs_map_runlist(ni, vcn))
647				goto lock_retry_remap;
648			goto map_rl_err;
649		}
650		block = lcn << vol->cluster_size_bits >> block_size_bits;
651		/* Read the lcn from device in chunks of block_size bytes. */
652		max_block = block + (vol->cluster_size >> block_size_bits);
653		do {
654			ntfs_debug("block = 0x%x.", block);
655			if (unlikely(!(bhs[nr_bhs] = sb_getblk(sb, block))))
656				goto getblk_err;
657			nr_bhs++;
658		} while (++block < max_block);
659	}
660
661	/* Release the lock if we took it. */
662	if (rl)
663		up_read(&ni->runlist.lock);
664
665	/* Setup and initiate io on all buffer heads. */
666	for (i = 0; i < nr_bhs; i++) {
667		struct buffer_head *tbh = bhs[i];
668
669		if (!trylock_buffer(tbh))
670			continue;
671		if (unlikely(buffer_uptodate(tbh))) {
672			unlock_buffer(tbh);
673			continue;
674		}
675		get_bh(tbh);
676		tbh->b_end_io = end_buffer_read_sync;
677		submit_bh(READ, tbh);
678	}
679
680	/* Wait for io completion on all buffer heads. */
681	for (i = 0; i < nr_bhs; i++) {
682		struct buffer_head *tbh = bhs[i];
683
684		if (buffer_uptodate(tbh))
685			continue;
686		wait_on_buffer(tbh);
687		/*
688		 * We need an optimization barrier here, otherwise we start
689		 * hitting the below fixup code when accessing a loopback
690		 * mounted ntfs partition. This indicates either there is a
691		 * race condition in the loop driver or, more likely, gcc
692		 * overoptimises the code without the barrier and it doesn't
693		 * do the Right Thing(TM).
694		 */
695		barrier();
696		if (unlikely(!buffer_uptodate(tbh))) {
697			ntfs_warning(vol->sb, "Buffer is unlocked but not "
698					"uptodate! Unplugging the disk queue "
699					"and rescheduling.");
700			get_bh(tbh);
701			io_schedule();
702			put_bh(tbh);
703			if (unlikely(!buffer_uptodate(tbh)))
704				goto read_err;
705			ntfs_warning(vol->sb, "Buffer is now uptodate. Good.");
706		}
707	}
708
709	/*
710	 * Get the compression buffer. We must not sleep any more
711	 * until we are finished with it.
712	 */
713	spin_lock(&ntfs_cb_lock);
714	cb = ntfs_compression_buffer;
715
716	BUG_ON(!cb);
717
718	cb_pos = cb;
719	cb_end = cb + cb_size;
720
721	/* Copy the buffer heads into the contiguous buffer. */
722	for (i = 0; i < nr_bhs; i++) {
723		memcpy(cb_pos, bhs[i]->b_data, block_size);
724		cb_pos += block_size;
725	}
726
727	/* Just a precaution. */
728	if (cb_pos + 2 <= cb + cb_size)
729		*(u16*)cb_pos = 0;
730
731	/* Reset cb_pos back to the beginning. */
732	cb_pos = cb;
733
734	/* We now have both source (if present) and destination. */
735	ntfs_debug("Successfully read the compression block.");
736
737	/* The last page and maximum offset within it for the current cb. */
738	cb_max_page = (cur_page << PAGE_CACHE_SHIFT) + cur_ofs + cb_size;
739	cb_max_ofs = cb_max_page & ~PAGE_CACHE_MASK;
740	cb_max_page >>= PAGE_CACHE_SHIFT;
741
742	/* Catch end of file inside a compression block. */
743	if (cb_max_page > max_page)
744		cb_max_page = max_page;
745
746	if (vcn == start_vcn - cb_clusters) {
747		/* Sparse cb, zero out page range overlapping the cb. */
748		ntfs_debug("Found sparse compression block.");
749		/* We can sleep from now on, so we drop lock. */
750		spin_unlock(&ntfs_cb_lock);
751		if (cb_max_ofs)
752			cb_max_page--;
753		for (; cur_page < cb_max_page; cur_page++) {
754			page = pages[cur_page];
755			if (page) {
756				/*
757				 * FIXME: Using clear_page() will become wrong
758				 * when we get PAGE_CACHE_SIZE != PAGE_SIZE but
759				 * for now there is no problem.
760				 */
761				if (likely(!cur_ofs))
762					clear_page(page_address(page));
763				else
764					memset(page_address(page) + cur_ofs, 0,
765							PAGE_CACHE_SIZE -
766							cur_ofs);
767				flush_dcache_page(page);
768				kunmap(page);
769				SetPageUptodate(page);
770				unlock_page(page);
771				if (cur_page == xpage)
772					xpage_done = 1;
773				else
774					page_cache_release(page);
775				pages[cur_page] = NULL;
776			}
777			cb_pos += PAGE_CACHE_SIZE - cur_ofs;
778			cur_ofs = 0;
779			if (cb_pos >= cb_end)
780				break;
781		}
782		/* If we have a partial final page, deal with it now. */
783		if (cb_max_ofs && cb_pos < cb_end) {
784			page = pages[cur_page];
785			if (page)
786				memset(page_address(page) + cur_ofs, 0,
787						cb_max_ofs - cur_ofs);
788			/*
789			 * No need to update cb_pos at this stage:
790			 *	cb_pos += cb_max_ofs - cur_ofs;
791			 */
792			cur_ofs = cb_max_ofs;
793		}
794	} else if (vcn == start_vcn) {
795		/* We can't sleep so we need two stages. */
796		unsigned int cur2_page = cur_page;
797		unsigned int cur_ofs2 = cur_ofs;
798		u8 *cb_pos2 = cb_pos;
799
800		ntfs_debug("Found uncompressed compression block.");
801		/* Uncompressed cb, copy it to the destination pages. */
802		/*
803		 * TODO: As a big optimization, we could detect this case
804		 * before we read all the pages and use block_read_full_page()
805		 * on all full pages instead (we still have to treat partial
806		 * pages especially but at least we are getting rid of the
807		 * synchronous io for the majority of pages.
808		 * Or if we choose not to do the read-ahead/-behind stuff, we
809		 * could just return block_read_full_page(pages[xpage]) as long
810		 * as PAGE_CACHE_SIZE <= cb_size.
811		 */
812		if (cb_max_ofs)
813			cb_max_page--;
814		/* First stage: copy data into destination pages. */
815		for (; cur_page < cb_max_page; cur_page++) {
816			page = pages[cur_page];
817			if (page)
818				memcpy(page_address(page) + cur_ofs, cb_pos,
819						PAGE_CACHE_SIZE - cur_ofs);
820			cb_pos += PAGE_CACHE_SIZE - cur_ofs;
821			cur_ofs = 0;
822			if (cb_pos >= cb_end)
823				break;
824		}
825		/* If we have a partial final page, deal with it now. */
826		if (cb_max_ofs && cb_pos < cb_end) {
827			page = pages[cur_page];
828			if (page)
829				memcpy(page_address(page) + cur_ofs, cb_pos,
830						cb_max_ofs - cur_ofs);
831			cb_pos += cb_max_ofs - cur_ofs;
832			cur_ofs = cb_max_ofs;
833		}
834		/* We can sleep from now on, so drop lock. */
835		spin_unlock(&ntfs_cb_lock);
836		/* Second stage: finalize pages. */
837		for (; cur2_page < cb_max_page; cur2_page++) {
838			page = pages[cur2_page];
839			if (page) {
840				/*
841				 * If we are outside the initialized size, zero
842				 * the out of bounds page range.
843				 */
844				handle_bounds_compressed_page(page, i_size,
845						initialized_size);
846				flush_dcache_page(page);
847				kunmap(page);
848				SetPageUptodate(page);
849				unlock_page(page);
850				if (cur2_page == xpage)
851					xpage_done = 1;
852				else
853					page_cache_release(page);
854				pages[cur2_page] = NULL;
855			}
856			cb_pos2 += PAGE_CACHE_SIZE - cur_ofs2;
857			cur_ofs2 = 0;
858			if (cb_pos2 >= cb_end)
859				break;
860		}
861	} else {
862		/* Compressed cb, decompress it into the destination page(s). */
863		unsigned int prev_cur_page = cur_page;
864
865		ntfs_debug("Found compressed compression block.");
866		err = ntfs_decompress(pages, &cur_page, &cur_ofs,
867				cb_max_page, cb_max_ofs, xpage, &xpage_done,
868				cb_pos,	cb_size - (cb_pos - cb), i_size,
869				initialized_size);
870		/*
871		 * We can sleep from now on, lock already dropped by
872		 * ntfs_decompress().
873		 */
874		if (err) {
875			ntfs_error(vol->sb, "ntfs_decompress() failed in inode "
876					"0x%lx with error code %i. Skipping "
877					"this compression block.",
878					ni->mft_no, -err);
879			/* Release the unfinished pages. */
880			for (; prev_cur_page < cur_page; prev_cur_page++) {
881				page = pages[prev_cur_page];
882				if (page) {
883					flush_dcache_page(page);
884					kunmap(page);
885					unlock_page(page);
886					if (prev_cur_page != xpage)
887						page_cache_release(page);
888					pages[prev_cur_page] = NULL;
889				}
890			}
891		}
892	}
893
894	/* Release the buffer heads. */
895	for (i = 0; i < nr_bhs; i++)
896		brelse(bhs[i]);
897
898	/* Do we have more work to do? */
899	if (nr_cbs)
900		goto do_next_cb;
901
902	/* We no longer need the list of buffer heads. */
903	kfree(bhs);
904
905	/* Clean up if we have any pages left. Should never happen. */
906	for (cur_page = 0; cur_page < max_page; cur_page++) {
907		page = pages[cur_page];
908		if (page) {
909			ntfs_error(vol->sb, "Still have pages left! "
910					"Terminating them with extreme "
911					"prejudice.  Inode 0x%lx, page index "
912					"0x%lx.", ni->mft_no, page->index);
913			flush_dcache_page(page);
914			kunmap(page);
915			unlock_page(page);
916			if (cur_page != xpage)
917				page_cache_release(page);
918			pages[cur_page] = NULL;
919		}
920	}
921
922	/* We no longer need the list of pages. */
923	kfree(pages);
924
925	/* If we have completed the requested page, we return success. */
926	if (likely(xpage_done))
927		return 0;
928
929	ntfs_debug("Failed. Returning error code %s.", err == -EOVERFLOW ?
930			"EOVERFLOW" : (!err ? "EIO" : "unknown error"));
931	return err < 0 ? err : -EIO;
932
933read_err:
934	ntfs_error(vol->sb, "IO error while reading compressed data.");
935	/* Release the buffer heads. */
936	for (i = 0; i < nr_bhs; i++)
937		brelse(bhs[i]);
938	goto err_out;
939
940map_rl_err:
941	ntfs_error(vol->sb, "ntfs_map_runlist() failed. Cannot read "
942			"compression block.");
943	goto err_out;
944
945rl_err:
946	up_read(&ni->runlist.lock);
947	ntfs_error(vol->sb, "ntfs_rl_vcn_to_lcn() failed. Cannot read "
948			"compression block.");
949	goto err_out;
950
951getblk_err:
952	up_read(&ni->runlist.lock);
953	ntfs_error(vol->sb, "getblk() failed. Cannot read compression block.");
954
955err_out:
956	kfree(bhs);
957	for (i = cur_page; i < max_page; i++) {
958		page = pages[i];
959		if (page) {
960			flush_dcache_page(page);
961			kunmap(page);
962			unlock_page(page);
963			if (i != xpage)
964				page_cache_release(page);
965		}
966	}
967	kfree(pages);
968	return -EIO;
969}