compress.c

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#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"

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;

static u8 *ntfs_compression_buffer = NULL;

static DEFINE_SPINLOCK(ntfs_cb_lock);

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;
}

void free_compression_buffers(void)
{
    BUG_ON(!ntfs_compression_buffer);
    vfree(ntfs_compression_buffer);
    ntfs_compression_buffer = NULL;
}

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_CACHE_SHIFT) >= initialized_size) {
        /*
         * FIXME: Using clear_page() will become wrong when we get
         * PAGE_CACHE_SIZE != PAGE_SIZE but for now there is no problem.
         */
        clear_page(kp);
        return;
    }
    kp_ofs = initialized_size & ~PAGE_CACHE_MASK;
    memset(kp + kp_ofs, 0, PAGE_CACHE_SIZE - kp_ofs);
    return;
}

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_CACHE_SHIFT)) &&
            (initialized_size < i_size))
        zero_partial_compressed_page(page, initialized_size);
    return;
}

static int ntfs_decompress(struct page *dest_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. */

    /* Need this because we can't sleep, so need two stages. */
    int completed_pages[dest_max_index - *dest_index + 1];
    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
                    page_cache_release(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_CACHE_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_CACHE_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_CACHE_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;
}

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_CACHE_SIZE). */
    VCN start_vcn = (((s64)index << PAGE_CACHE_SHIFT) & ~cb_size_mask) >>
            vol->cluster_size_bits;
    /*
     * The first vcn after the last wanted vcn (minimum alignment is again
     * PAGE_CACHE_SIZE.
     */
    VCN end_vcn = ((((s64)(index + 1UL) << PAGE_CACHE_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_CACHE_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;
    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(nr_pages * sizeof(struct page *), 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)) {
        kfree(bhs);
        kfree(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_CACHE_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_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT) -
            offset;
    /* Is the page fully outside i_size? (truncate in progress) */
    if (xpage >= max_page) {
        kfree(bhs);
        kfree(pages);
        zero_user(page, 0, PAGE_CACHE_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);
            page_cache_release(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(READ, 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_CACHE_SHIFT) + cur_ofs + cb_size;
    cb_max_ofs = cb_max_page & ~PAGE_CACHE_MASK;
    cb_max_page >>= PAGE_CACHE_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) {
                /*
                 * FIXME: Using clear_page() will become wrong
                 * when we get PAGE_CACHE_SIZE != PAGE_SIZE but
                 * for now there is no problem.
                 */
                if (likely(!cur_ofs))
                    clear_page(page_address(page));
                else
                    memset(page_address(page) + cur_ofs, 0,
                            PAGE_CACHE_SIZE -
                            cur_ofs);
                flush_dcache_page(page);
                kunmap(page);
                SetPageUptodate(page);
                unlock_page(page);
                if (cur_page == xpage)
                    xpage_done = 1;
                else
                    page_cache_release(page);
                pages[cur_page] = NULL;
            }
            cb_pos += PAGE_CACHE_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_CACHE_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_CACHE_SIZE - cur_ofs);
            cb_pos += PAGE_CACHE_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
                    page_cache_release(page);
                pages[cur2_page] = NULL;
            }
            cb_pos2 += PAGE_CACHE_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, &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)
                        page_cache_release(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)
                page_cache_release(page);
            pages[cur_page] = NULL;
        }
    }

    /* We no longer need the list of pages. */
    kfree(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)
                page_cache_release(page);
        }
    }
    kfree(pages);
    return -EIO;
}