Root/fs/ntfs/compress.c

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}
970

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