/**
 * compress.c - Compressed attribute handling code.  Originated from the Linux-NTFS
 *              project.
 *
 * Copyright (c) 2004-2005 Anton Altaparmakov
 * Copyright (c) 2004-2006 Szabolcs Szakacsits
 * Copyright (c)      2005 Yura Pakhuchiy
 * Copyright (c) 2009-2014 Jean-Pierre Andre
 * Copyright (c)      2014 Eric Biggers
 *
 * This program/include file is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program/include file is distributed in the hope that it will be
 * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
 * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program (in the main directory of the NTFS-3G
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#ifdef HAVE_STDIO_H
#include <stdio.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif

#include "attrib.h"
#include "debug.h"
#include "volume.h"
#include "types.h"
#include "layout.h"
#include "runlist.h"
#include "compress.h"
#include "lcnalloc.h"
#include "logging.h"
#include "misc.h"

#undef le16_to_cpup 
/* the standard le16_to_cpup() crashes for unaligned data on some processors */ 
#define le16_to_cpup(p) (*(u8*)(p) + (((u8*)(p))[1] << 8))

/**
 * enum ntfs_compression_constants - constants used in the compression code
 */
typedef enum {
        /* Token types and access mask. */
        NTFS_SYMBOL_TOKEN       =       0,
        NTFS_PHRASE_TOKEN       =       1,
        NTFS_TOKEN_MASK         =       1,

        /* Compression sub-block constants. */
        NTFS_SB_SIZE_MASK       =       0x0fff,
        NTFS_SB_SIZE            =       0x1000,
        NTFS_SB_IS_COMPRESSED   =       0x8000,
} ntfs_compression_constants;

/* Match length at or above which ntfs_best_match() will stop searching for
 * longer matches.  */
#define NICE_MATCH_LEN 18

/* Maximum number of potential matches that ntfs_best_match() will consider at
 * each position.  */
#define MAX_SEARCH_DEPTH 24

/* log base 2 of the number of entries in the hash table for match-finding.  */
#define HASH_SHIFT 14

/* Constant for the multiplicative hash function.  */
#define HASH_MULTIPLIER 0x1E35A7BD

struct COMPRESS_CONTEXT {
        const unsigned char *inbuf;
        int bufsize;
        int size;
        int rel;
        int mxsz;
        s16 head[1 << HASH_SHIFT];
        s16 prev[NTFS_SB_SIZE];
} ;

/*
 *              Hash the next 3-byte sequence in the input buffer
 */
static inline unsigned int ntfs_hash(const u8 *p)
{
        u32 str;
        u32 hash;

#if defined(__i386__) || defined(__x86_64__)
        /* Unaligned access allowed, and little endian CPU.
         * Callers ensure that at least 4 (not 3) bytes are remaining.  */
        str = *(const u32 *)p & 0xFFFFFF;
#else
        str = ((u32)p[0] << 0) | ((u32)p[1] << 8) | ((u32)p[2] << 16);
#endif

        hash = str * HASH_MULTIPLIER;

        /* High bits are more random than the low bits.  */
        return hash >> (32 - HASH_SHIFT);
}

/*
 *              Search for the longest sequence matching current position
 *
 *      A hash table, each entry of which points to a chain of sequence
 *      positions sharing the corresponding hash code, is maintained to speed up
 *      searching for matches.  To maintain the hash table, either
 *      ntfs_best_match() or ntfs_skip_position() has to be called for each
 *      consecutive position.
 *
 *      This function is heavily used; it has to be optimized carefully.
 *
 *      This function sets pctx->size and pctx->rel to the length and offset,
 *      respectively, of the longest match found.
 *
 *      The minimum match length is assumed to be 3, and the maximum match
 *      length is assumed to be pctx->mxsz.  If this function produces
 *      pctx->size < 3, then no match was found.
 *
 *      Note: for the following reasons, this function is not guaranteed to find
 *      *the* longest match up to pctx->mxsz:
 *
 *      (1) If this function finds a match of NICE_MATCH_LEN bytes or greater,
 *          it ends early because a match this long is good enough and it's not
 *          worth spending more time searching.
 *
 *      (2) If this function considers MAX_SEARCH_DEPTH matches with a single
 *          position, it ends early and returns the longest match found so far.
 *          This saves a lot of time on degenerate inputs.
 */
static void ntfs_best_match(struct COMPRESS_CONTEXT *pctx, const int i,
                            int best_len)
{
        const u8 * const inbuf = pctx->inbuf;
        const u8 * const strptr = &inbuf[i]; /* String we're matching against */
        s16 * const prev = pctx->prev;
        const int max_len = min(pctx->bufsize - i, pctx->mxsz);
        const int nice_len = min(NICE_MATCH_LEN, max_len);
        int depth_remaining = MAX_SEARCH_DEPTH;
        const u8 *best_matchptr = strptr;
        unsigned int hash;
        s16 cur_match;
        const u8 *matchptr;
        int len;

        if (max_len < 4)
                goto out;

        /* Insert the current sequence into the appropriate hash chain.  */
        hash = ntfs_hash(strptr);
        cur_match = pctx->head[hash];
        prev[i] = cur_match;
        pctx->head[hash] = i;

        if (best_len >= max_len) {
                /* Lazy match is being attempted, but there aren't enough length
                 * bits remaining to code a longer match.  */
                goto out;
        }

        /* Search the appropriate hash chain for matches.  */

        for (; cur_match >= 0 && depth_remaining--;
                cur_match = prev[cur_match])
        {

                matchptr = &inbuf[cur_match];

                /* Considering the potential match at 'matchptr':  is it longer
                 * than 'best_len'?
                 *
                 * The bytes at index 'best_len' are the most likely to differ,
                 * so check them first.
                 *
                 * The bytes at indices 'best_len - 1' and '0' are less
                 * important to check separately.  But doing so still gives a
                 * slight performance improvement, at least on x86_64, probably
                 * because they create separate branches for the CPU to predict
                 * independently of the branches in the main comparison loops.
                 */
                if (matchptr[best_len] != strptr[best_len] ||
                    matchptr[best_len - 1] != strptr[best_len - 1] ||
                    matchptr[0] != strptr[0])
                        goto next_match;

                for (len = 1; len < best_len - 1; len++)
                        if (matchptr[len] != strptr[len])
                                goto next_match;

                /* The match is the longest found so far ---
                 * at least 'best_len' + 1 bytes.  Continue extending it.  */

                best_matchptr = matchptr;

                do {
                        if (++best_len >= nice_len) {
                                /* 'nice_len' reached; don't waste time
                                 * searching for longer matches.  Extend the
                                 * match as far as possible and terminate the
                                 * search.  */
                                while (best_len < max_len &&
                                        (best_matchptr[best_len] ==
                                                strptr[best_len]))
                                {
                                        best_len++;
                                }
                                goto out;
                        }
                } while (best_matchptr[best_len] == strptr[best_len]);

                /* Found a longer match, but 'nice_len' not yet reached.  */

        next_match:
                /* Continue to next match in the chain.  */
                ;
        }

        /* Reached end of chain, or ended early due to reaching the maximum
         * search depth.  */

out:
        /* Return the longest match we were able to find.  */
        pctx->size = best_len;
        pctx->rel = best_matchptr - strptr; /* given as a negative number! */
}

/*
 *              Advance the match-finder, but don't search for matches.
 */
static void ntfs_skip_position(struct COMPRESS_CONTEXT *pctx, const int i)
{
        unsigned int hash;

        if (pctx->bufsize - i < 4)
                return;

        /* Insert the current sequence into the appropriate hash chain.  */
        hash = ntfs_hash(pctx->inbuf + i);
        pctx->prev[i] = pctx->head[hash];
        pctx->head[hash] = i;
}

/*
 *              Compress a 4096-byte block
 *
 *      Returns a header of two bytes followed by the compressed data.
 *      If compression is not effective, the header and an uncompressed
 *      block is returned.
 *
 *      Note : two bytes may be output before output buffer overflow
 *      is detected, so a 4100-bytes output buffer must be reserved.
 *
 *      Returns the size of the compressed block, including the
 *                      header (minimal size is 2, maximum size is 4098)
 *              0 if an error has been met. 
 */

static unsigned int ntfs_compress_block(const char *inbuf, const int bufsize,
                                char *outbuf)
{
        struct COMPRESS_CONTEXT *pctx;
        int i; /* current position */
        int j; /* end of best match from current position */
        int k; /* end of best match from next position */
        int offs; /* offset to best match */
        int bp; /* bits to store offset */
        int bp_cur; /* saved bits to store offset at current position */
        int mxoff; /* max match offset : 1 << bp */
        unsigned int xout;
        unsigned int q; /* aggregated offset and size */
        int have_match; /* do we have a match at the current position? */
        char *ptag; /* location reserved for a tag */
        int tag;    /* current value of tag */
        int ntag;   /* count of bits still undefined in tag */

        pctx = ntfs_malloc(sizeof(struct COMPRESS_CONTEXT));
        if (!pctx) {
                errno = ENOMEM;
                return 0;
        }

        /* All hash chains start as empty.  The special value '-1' indicates the
         * end of each hash chain.  */
        memset(pctx->head, 0xFF, sizeof(pctx->head));

        pctx->inbuf = (const unsigned char*)inbuf;
        pctx->bufsize = bufsize;
        xout = 2;
        i = 0;
        bp = 4;
        mxoff = 1 << bp;
        pctx->mxsz = (1 << (16 - bp)) + 2;
        have_match = 0;
        tag = 0;
        ntag = 8;
        ptag = &outbuf[xout++];

        while ((i < bufsize) && (xout < (NTFS_SB_SIZE + 2))) {

                /* This implementation uses "lazy" parsing: it always chooses
                 * the longest match, unless the match at the next position is
                 * longer.  This is the same strategy used by the high
                 * compression modes of zlib.  */

                if (!have_match) {
                        /* Find the longest match at the current position.  But
                         * first adjust the maximum match length if needed.
                         * (This loop might need to run more than one time in
                         * the case that we just output a long match.)  */
                        while (mxoff < i) {
                                bp++;
                                mxoff <<= 1;
                                pctx->mxsz = (pctx->mxsz + 2) >> 1;
                        }
                        ntfs_best_match(pctx, i, 2);
                }

                if (pctx->size >= 3) {

                        /* Found a match at the current position.  */

                        j = i + pctx->size;
                        bp_cur = bp;
                        offs = pctx->rel;

                        if (pctx->size >= NICE_MATCH_LEN) {

                                /* Choose long matches immediately.  */

                                q = (~offs << (16 - bp_cur)) + (j - i - 3);
                                outbuf[xout++] = q & 255;
                                outbuf[xout++] = (q >> 8) & 255;
                                tag |= (1 << (8 - ntag));

                                if (j == bufsize) {
                                        /* Shortcut if the match extends to the
                                         * end of the buffer.  */
                                        i = j;
                                        --ntag;
                                        break;
                                }
                                i += 1;
                                do {
                                        ntfs_skip_position(pctx, i);
                                } while (++i != j);
                                have_match = 0;
                        } else {
                                /* Check for a longer match at the next
                                 * position.  */

                                /* Doesn't need to be while() since we just
                                 * adjusted the maximum match length at the
                                 * previous position.  */
                                if (mxoff < i + 1) {
                                        bp++;
                                        mxoff <<= 1;
                                        pctx->mxsz = (pctx->mxsz + 2) >> 1;
                                }
                                ntfs_best_match(pctx, i + 1, pctx->size);
                                k = i + 1 + pctx->size;

                                if (k > (j + 1)) {
                                        /* Next match is longer.
                                         * Output a literal.  */
                                        outbuf[xout++] = inbuf[i++];
                                        have_match = 1;
                                } else {
                                        /* Next match isn't longer.
                                         * Output the current match.  */
                                        q = (~offs << (16 - bp_cur)) +
                                                        (j - i - 3);
                                        outbuf[xout++] = q & 255;
                                        outbuf[xout++] = (q >> 8) & 255;
                                        tag |= (1 << (8 - ntag));

                                        /* The minimum match length is 3, and
                                         * we've run two bytes through the
                                         * matchfinder already.  So the minimum
                                         * number of positions we need to skip
                                         * is 1.  */
                                        i += 2;
                                        do {
                                                ntfs_skip_position(pctx, i);
                                        } while (++i != j);
                                        have_match = 0;
                                }
                        }
                } else {
                        /* No match at current position.  Output a literal.  */
                        outbuf[xout++] = inbuf[i++];
                        have_match = 0;
                }

                /* Store the tag if fully used.  */
                if (!--ntag) {
                        *ptag = tag;
                        ntag = 8;
                        ptag = &outbuf[xout++];
                        tag = 0;
                }
        }

        /* Store the last tag if partially used.  */
        if (ntag == 8)
                xout--;
        else
                *ptag = tag;

        /* Determine whether to store the data compressed or uncompressed.  */

        if ((i >= bufsize) && (xout < (NTFS_SB_SIZE + 2))) {
                /* Compressed.  */
                outbuf[0] = (xout - 3) & 255;
                outbuf[1] = 0xb0 + (((xout - 3) >> 8) & 15);
        } else {
                /* Uncompressed.  */
                memcpy(&outbuf[2], inbuf, bufsize);
                if (bufsize < NTFS_SB_SIZE)
                        memset(&outbuf[bufsize + 2], 0, NTFS_SB_SIZE - bufsize);
                outbuf[0] = 0xff;
                outbuf[1] = 0x3f;
                xout = NTFS_SB_SIZE + 2;
        }

        /* Free the compression context and return the total number of bytes
         * written to 'outbuf'.  */
        free(pctx);
        return (xout);
}

/**
 * ntfs_decompress - decompress a compression block into an array of pages
 * @dest:       buffer to which to write the decompressed data
 * @dest_size:  size of buffer @dest in bytes
 * @cb_start:   compression block to decompress
 * @cb_size:    size of compression block @cb_start in bytes
 *
 * This decompresses the compression block @cb_start into the destination
 * buffer @dest.
 *
 * @cb_start is a pointer to the compression block which needs decompressing
 * and @cb_size is the size of @cb_start in bytes (8-64kiB).
 *
 * Return 0 if success or -EOVERFLOW on error in the compressed stream.
 */
static int ntfs_decompress(u8 *dest, const u32 dest_size,
                u8 *const cb_start, const u32 cb_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. */
        u8 *dest_end = dest + dest_size;        /* End of dest buffer. */
        u8 *dest_sb_start;      /* Start of current sub-block in dest. */
        u8 *dest_sb_end;        /* End of current sb in dest. */
        /* Variables for tag and token parsing. */
        u8 tag;                 /* Current tag. */
        int token;              /* Loop counter for the eight tokens in tag. */

        ntfs_log_trace("Entering, cb_size = 0x%x.\n", (unsigned)cb_size);
do_next_sb:
        ntfs_log_debug("Beginning sub-block at offset = %d in the cb.\n",
                        (int)(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 == dest_end) {
                if (dest_end > dest)
                        memset(dest, 0, dest_end - dest);
                ntfs_log_debug("Completed. Returning success (0).\n");
                return 0;
        }
        /* Setup offset for the current sub-block destination. */
        dest_sb_start = dest;
        dest_sb_end = dest + NTFS_SB_SIZE;
        /* Check that we are still within allowed boundaries. */
        if (dest_sb_end > dest_end)
                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;
        /* Now, we are ready to process the current sub-block (sb). */
        if (!(le16_to_cpup((le16*)cb) & NTFS_SB_IS_COMPRESSED)) {
                ntfs_log_debug("Found uncompressed sub-block.\n");
                /* 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(dest, cb, NTFS_SB_SIZE);
                cb += NTFS_SB_SIZE;
                /* Advance destination position to next sub-block. */
                dest += NTFS_SB_SIZE;
                goto do_next_sb;
        }
        ntfs_log_debug("Found compressed sub-block.\n");
        /* This sb is compressed, decompress it into destination. */
        /* 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 (dest < dest_sb_end) {
                        int nr_bytes = dest_sb_end - dest;

                        ntfs_log_debug("Filling incomplete sub-block with zeroes.\n");
                        /* Zero remainder and update destination position. */
                        memset(dest, 0, nr_bytes);
                        dest += nr_bytes;
                }
                /* We have finished the current sub-block. */
                goto do_next_sb;
        }
        /* Check we are still in range. */
        if (cb > cb_sb_end || dest > dest_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 *dest_back_addr;

                /* Check if we are done / still in range. */
                if (cb >= cb_sb_end || dest > dest_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.
                         */
                        *dest++ = *cb++;
                        /* 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 (dest == dest_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 - dest_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.
                 */
                dest_back_addr = dest - (pt >> (12 - lg)) - 1;
                if (dest_back_addr < dest_sb_start)
                        goto return_overflow;
                /* Now calculate the length of the byte sequence. */
                length = (pt & (0xfff >> lg)) + 3;
                /* Verify destination is in range. */
                if (dest + length > dest_sb_end)
                        goto return_overflow;
                /* The number of non-overlapping bytes. */
                max_non_overlap = dest - dest_back_addr;
                if (length <= max_non_overlap) {
                        /* The byte sequence doesn't overlap, just copy it. */
                        memcpy(dest, dest_back_addr, length);
                        /* Advance destination pointer. */
                        dest += 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(dest, dest_back_addr, max_non_overlap);
                        dest += max_non_overlap;
                        dest_back_addr += max_non_overlap;
                        length -= max_non_overlap;
                        while (length--)
                                *dest++ = *dest_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:
        errno = EOVERFLOW;
        ntfs_log_perror("Failed to decompress file");
        return -1;
}

/**
 * ntfs_is_cb_compressed - internal function, do not use
 *
 * This is a very specialised function determining if a cb is compressed or
 * uncompressed.  It is assumed that checking for a sparse cb has already been
 * performed and that the cb is not sparse.  It makes all sorts of other
 * assumptions as well and hence it is not useful anywhere other than where it
 * is used at the moment.  Please, do not make this function available for use
 * outside of compress.c as it is bound to confuse people and not do what they
 * want.
 *
 * Return TRUE on errors so that the error will be detected later on in the
 * code.  Might be a bit confusing to debug but there really should never be
 * errors coming from here.
 */
static BOOL ntfs_is_cb_compressed(ntfs_attr *na, runlist_element *rl, 
                                  VCN cb_start_vcn, int cb_clusters)
{
        /*
         * The simplest case: the run starting at @cb_start_vcn contains
         * @cb_clusters clusters which are all not sparse, thus the cb is not
         * compressed.
         */
restart:
        cb_clusters -= rl->length - (cb_start_vcn - rl->vcn);
        while (cb_clusters > 0) {
                /* Go to the next run. */
                rl++;
                /* Map the next runlist fragment if it is not mapped. */
                if (rl->lcn < LCN_HOLE || !rl->length) {
                        cb_start_vcn = rl->vcn;
                        rl = ntfs_attr_find_vcn(na, rl->vcn);
                        if (!rl || rl->lcn < LCN_HOLE || !rl->length)
                                return TRUE;
                        /*
                         * If the runs were merged need to deal with the
                         * resulting partial run so simply restart.
                         */
                        if (rl->vcn < cb_start_vcn)
                                goto restart;
                }
                /* If the current run is sparse, the cb is compressed. */
                if (rl->lcn == LCN_HOLE)
                        return TRUE;
                /* If the whole cb is not sparse, it is not compressed. */
                if (rl->length >= cb_clusters)
                        return FALSE;
                cb_clusters -= rl->length;
        };
        /* All cb_clusters were not sparse thus the cb is not compressed. */
        return FALSE;
}

/**
 * ntfs_compressed_attr_pread - read from a compressed attribute
 * @na:         ntfs attribute to read from
 * @pos:        byte position in the attribute to begin reading from
 * @count:      number of bytes to read
 * @b:          output data buffer
 *
 * NOTE:  You probably want to be using attrib.c::ntfs_attr_pread() instead.
 *
 * This function will read @count bytes starting at offset @pos from the
 * compressed ntfs attribute @na into the data buffer @b.
 *
 * On success, return the number of successfully read bytes.  If this number
 * is lower than @count this means that the read reached end of file or that
 * an error was encountered during the read so that the read is partial.
 * 0 means end of file or nothing was read (also return 0 when @count is 0).
 *
 * On error and nothing has been read, return -1 with errno set appropriately
 * to the return code of ntfs_pread(), or to EINVAL in case of invalid
 * arguments.
 */
s64 ntfs_compressed_attr_pread(ntfs_attr *na, s64 pos, s64 count, void *b)
{
        s64 br, to_read, ofs, total, total2;
        u64 cb_size_mask;
        VCN start_vcn, vcn, end_vcn;
        ntfs_volume *vol;
        runlist_element *rl;
        u8 *dest, *cb, *cb_pos, *cb_end;
        u32 cb_size;
        int err;
        ATTR_FLAGS data_flags;
        FILE_ATTR_FLAGS compression;
        unsigned int nr_cbs, cb_clusters;

        ntfs_log_trace("Entering for inode 0x%llx, attr 0x%x, pos 0x%llx, count 0x%llx.\n",
                        (unsigned long long)na->ni->mft_no, le32_to_cpu(na->type),
                        (long long)pos, (long long)count);
        data_flags = na->data_flags;
        compression = na->ni->flags & FILE_ATTR_COMPRESSED;
        if (!na || !na->ni || !na->ni->vol || !b
                        || ((data_flags & ATTR_COMPRESSION_MASK)
                                != ATTR_IS_COMPRESSED)
                        || pos < 0 || count < 0) {
                errno = EINVAL;
                return -1;
        }
        /*
         * Encrypted attributes are not supported.  We return access denied,
         * which is what Windows NT4 does, too.
         */
        if (NAttrEncrypted(na)) {
                errno = EACCES;
                return -1;
        }
        if (!count)
                return 0;
        /* Truncate reads beyond end of attribute. */
        if (pos + count > na->data_size) {
                if (pos >= na->data_size) {
                        return 0;
                }
                count = na->data_size - pos;
        }
        /* If it is a resident attribute, simply use ntfs_attr_pread(). */
        if (!NAttrNonResident(na))
                return ntfs_attr_pread(na, pos, count, b);
        if (na->compression_block_size < NTFS_SB_SIZE) {
                ntfs_log_error("Unsupported compression block size %ld\n",
                                (long)na->compression_block_size);
                errno = EOVERFLOW;
                return (-1);
        }
        total = total2 = 0;
        /* Zero out reads beyond initialized size. */
        if (pos + count > na->initialized_size) {
                if (pos >= na->initialized_size) {
                        memset(b, 0, count);
                        return count;
                }
                total2 = pos + count - na->initialized_size;
                count -= total2;
                memset((u8*)b + count, 0, total2);
        }
        vol = na->ni->vol;
        cb_size = na->compression_block_size;
        cb_size_mask = cb_size - 1UL;
        cb_clusters = na->compression_block_clusters;
        
        /* Need a temporary buffer for each loaded compression block. */
        cb = (u8*)ntfs_malloc(cb_size);
        if (!cb)
                return -1;
        
        /* Need a temporary buffer for each uncompressed block. */
        dest = (u8*)ntfs_malloc(cb_size);
        if (!dest) {
                free(cb);
                return -1;
        }
        /*
         * The first vcn in the first compression block (cb) which we need to
         * decompress.
         */
        start_vcn = (pos & ~cb_size_mask) >> vol->cluster_size_bits;
        /* Offset in the uncompressed cb at which to start reading data. */
        ofs = pos & cb_size_mask;
        /*
         * The first vcn in the cb after the last cb which we need to
         * decompress.
         */
        end_vcn = ((pos + count + cb_size - 1) & ~cb_size_mask) >>
                        vol->cluster_size_bits;
        /* Number of compression blocks (cbs) in the wanted vcn range. */
        nr_cbs = (end_vcn - start_vcn) << vol->cluster_size_bits >>
                        na->compression_block_size_bits;
        cb_end = cb + cb_size;
do_next_cb:
        nr_cbs--;
        cb_pos = cb;
        vcn = start_vcn;
        start_vcn += cb_clusters;

        /* Check whether the compression block is sparse. */
        rl = ntfs_attr_find_vcn(na, vcn);
        if (!rl || rl->lcn < LCN_HOLE) {
                free(cb);
                free(dest);
                if (total)
                        return total;
                /* FIXME: Do we want EIO or the error code? (AIA) */
                errno = EIO;
                return -1;
        }
        if (rl->lcn == LCN_HOLE) {
                /* Sparse cb, zero out destination range overlapping the cb. */
                ntfs_log_debug("Found sparse compression block.\n");
                to_read = min(count, cb_size - ofs);
                memset(b, 0, to_read);
                ofs = 0;
                total += to_read;
                count -= to_read;
                b = (u8*)b + to_read;
        } else if (!ntfs_is_cb_compressed(na, rl, vcn, cb_clusters)) {
                s64 tdata_size, tinitialized_size;
                /*
                 * Uncompressed cb, read it straight into the destination range
                 * overlapping the cb.
                 */
                ntfs_log_debug("Found uncompressed compression block.\n");
                /*
                 * Read the uncompressed data into the destination buffer.
                 * NOTE: We cheat a little bit here by marking the attribute as
                 * not compressed in the ntfs_attr structure so that we can
                 * read the data by simply using ntfs_attr_pread().  (-8
                 * NOTE: we have to modify data_size and initialized_size
                 * temporarily as well...
                 */
                to_read = min(count, cb_size - ofs);
                ofs += vcn << vol->cluster_size_bits;
                NAttrClearCompressed(na);
                na->data_flags &= ~ATTR_COMPRESSION_MASK;
                tdata_size = na->data_size;
                tinitialized_size = na->initialized_size;
                na->data_size = na->initialized_size = na->allocated_size;
                do {
                        br = ntfs_attr_pread(na, ofs, to_read, b);
                        if (br <= 0) {
                                if (!br) {
                                        ntfs_log_error("Failed to read an"
                                                " uncompressed cluster,"
                                                " inode %lld offs 0x%llx\n",
                                                (long long)na->ni->mft_no,
                                                (long long)ofs);
                                        errno = EIO;
                                }
                                err = errno;
                                na->data_size = tdata_size;
                                na->initialized_size = tinitialized_size;
                                na->ni->flags |= compression;
                                na->data_flags = data_flags;
                                free(cb);
                                free(dest);
                                if (total)
                                        return total;
                                errno = err;
                                return br;
                        }
                        total += br;
                        count -= br;
                        b = (u8*)b + br;
                        to_read -= br;
                        ofs += br;
                } while (to_read > 0);
                na->data_size = tdata_size;
                na->initialized_size = tinitialized_size;
                na->ni->flags |= compression;
                na->data_flags = data_flags;
                ofs = 0;
        } else {
                s64 tdata_size, tinitialized_size;
                u32 decompsz;

                /*
                 * Compressed cb, decompress it into the temporary buffer, then
                 * copy the data to the destination range overlapping the cb.
                 */
                ntfs_log_debug("Found compressed compression block.\n");
                /*
                 * Read the compressed data into the temporary buffer.
                 * NOTE: We cheat a little bit here by marking the attribute as
                 * not compressed in the ntfs_attr structure so that we can
                 * read the raw, compressed data by simply using
                 * ntfs_attr_pread().  (-8
                 * NOTE: We have to modify data_size and initialized_size
                 * temporarily as well...
                 */
                to_read = cb_size;
                NAttrClearCompressed(na);
                na->data_flags &= ~ATTR_COMPRESSION_MASK;
                tdata_size = na->data_size;
                tinitialized_size = na->initialized_size;
                na->data_size = na->initialized_size = na->allocated_size;
                do {
                        br = ntfs_attr_pread(na,
                                        (vcn << vol->cluster_size_bits) +
                                        (cb_pos - cb), to_read, cb_pos);
                        if (br <= 0) {
                                if (!br) {
                                        ntfs_log_error("Failed to read a"
                                                " compressed cluster, "
                                                " inode %lld offs 0x%llx\n",
                                                (long long)na->ni->mft_no,
                                                (long long)(vcn << vol->cluster_size_bits));
                                        errno = EIO;
                                }
                                err = errno;
                                na->data_size = tdata_size;
                                na->initialized_size = tinitialized_size;
                                na->ni->flags |= compression;
                                na->data_flags = data_flags;
                                free(cb);
                                free(dest);
                                if (total)
                                        return total;
                                errno = err;
                                return br;
                        }
                        cb_pos += br;
                        to_read -= br;
                } while (to_read > 0);
                na->data_size = tdata_size;
                na->initialized_size = tinitialized_size;
                na->ni->flags |= compression;
                na->data_flags = data_flags;
                /* Just a precaution. */
                if (cb_pos + 2 <= cb_end)
                        *(u16*)cb_pos = 0;
                ntfs_log_debug("Successfully read the compression block.\n");
                /* Do not decompress beyond the requested block */
                to_read = min(count, cb_size - ofs);
                decompsz = ((ofs + to_read - 1) | (NTFS_SB_SIZE - 1)) + 1;
                if (ntfs_decompress(dest, decompsz, cb, cb_size) < 0) {
                        err = errno;
                        free(cb);
                        free(dest);
                        if (total)
                                return total;
                        errno = err;
                        return -1;
                }
                memcpy(b, dest + ofs, to_read);
                total += to_read;
                count -= to_read;
                b = (u8*)b + to_read;
                ofs = 0;
        }
        /* Do we have more work to do? */
        if (nr_cbs)
                goto do_next_cb;
        /* We no longer need the buffers. */
        free(cb);
        free(dest);
        /* Return number of bytes read. */
        return total + total2;
}

/*
 *              Read data from a set of clusters
 *
 *      Returns the amount of data read
 */

static u32 read_clusters(ntfs_volume *vol, const runlist_element *rl,
                        s64 offs, u32 to_read, char *inbuf)
{
        u32 count;
        int xgot;
        u32 got;
        s64 xpos;
        BOOL first;
        char *xinbuf;
        const runlist_element *xrl;

        got = 0;
        xrl = rl;
        xinbuf = inbuf;
        first = TRUE;
        do {
                count = xrl->length << vol->cluster_size_bits;
                xpos = xrl->lcn << vol->cluster_size_bits;
                if (first) {
                        count -= offs;
                        xpos += offs;
                }
                if ((to_read - got) < count)
                        count = to_read - got;
                xgot = ntfs_pread(vol->dev, xpos, count, xinbuf);
                if (xgot == (int)count) {
                        got += count;
                        xpos += count;
                        xinbuf += count;
                        xrl++;
                }
                first = FALSE;
        } while ((xgot == (int)count) && (got < to_read));
        return (got);
}

/*
 *              Write data to a set of clusters
 *
 *      Returns the amount of data written
 */

static s32 write_clusters(ntfs_volume *vol, const runlist_element *rl,
                        s64 offs, s32 to_write, const char *outbuf)
{
        s32 count;
        s32 put, xput;
        s64 xpos;
        BOOL first;
        const char *xoutbuf;
        const runlist_element *xrl;

        put = 0;
        xrl = rl;
        xoutbuf = outbuf;
        first = TRUE;
        do {
                count = xrl->length << vol->cluster_size_bits;
                xpos = xrl->lcn << vol->cluster_size_bits;
                if (first) {
                        count -= offs;
                        xpos += offs;
                }
                if ((to_write - put) < count)
                        count = to_write - put;
                xput = ntfs_pwrite(vol->dev, xpos, count, xoutbuf);
                if (xput == count) {
                        put += count;
                        xpos += count;
                        xoutbuf += count;
                        xrl++;
                }
                first = FALSE;
        } while ((xput == count) && (put < to_write));
        return (put);
}


/*
 *              Compress and write a set of blocks
 *
 *      returns the size actually written (rounded to a full cluster)
 *              or 0 if all zeroes (nothing is written)
 *              or -1 if could not compress (nothing is written)
 *              or -2 if there were an irrecoverable error (errno set)
 */

static s32 ntfs_comp_set(ntfs_attr *na, runlist_element *rl,
                        s64 offs, u32 insz, const char *inbuf)
{
        ntfs_volume *vol;
        char *outbuf;
        char *pbuf;
        u32 compsz;
        s32 written;
        s32 rounded;
        unsigned int clsz;
        u32 p;
        unsigned int sz;
        unsigned int bsz;
        BOOL fail;
        BOOL allzeroes;
                /* a single compressed zero */
        static char onezero[] = { 0x01, 0xb0, 0x00, 0x00 } ;
                /* a couple of compressed zeroes */
        static char twozeroes[] = { 0x02, 0xb0, 0x00, 0x00, 0x00 } ;
                /* more compressed zeroes, to be followed by some count */
        static char morezeroes[] = { 0x03, 0xb0, 0x02, 0x00 } ;

        vol = na->ni->vol;
        written = -1; /* default return */
        clsz = 1 << vol->cluster_size_bits;
                /* may need 2 extra bytes per block and 2 more bytes */
        outbuf = (char*)ntfs_malloc(na->compression_block_size
                        + 2*(na->compression_block_size/NTFS_SB_SIZE)
                        + 2);
        if (outbuf) {
                fail = FALSE;
                compsz = 0;
                allzeroes = TRUE;
                for (p=0; (p<insz) && !fail; p+=NTFS_SB_SIZE) {
                        if ((p + NTFS_SB_SIZE) < insz)
                                bsz = NTFS_SB_SIZE;
                        else
                                bsz = insz - p;
                        pbuf = &outbuf[compsz];
                        sz = ntfs_compress_block(&inbuf[p],bsz,pbuf);
                        /* fail if all the clusters (or more) are needed */
                        if (!sz || ((compsz + sz + clsz + 2)
                                         > na->compression_block_size))
                                fail = TRUE;
                        else {
                                if (allzeroes) {
                                /* check whether this is all zeroes */
                                        switch (sz) {
                                        case 4 :
                                                allzeroes = !memcmp(
                                                        pbuf,onezero,4);
                                                break;
                                        case 5 :
                                                allzeroes = !memcmp(
                                                        pbuf,twozeroes,5);
                                                break;
                                        case 6 :
                                                allzeroes = !memcmp(
                                                        pbuf,morezeroes,4);
                                                break;
                                        default :
                                                allzeroes = FALSE;
                                                break;
                                        }
                                }
                        compsz += sz;
                        }
                }
                if (!fail && !allzeroes) {
                        /* add a couple of null bytes, space has been checked */
                        outbuf[compsz++] = 0;
                        outbuf[compsz++] = 0;
                        /* write a full cluster, to avoid partial reading */
                        rounded = ((compsz - 1) | (clsz - 1)) + 1;
                        memset(&outbuf[compsz], 0, rounded - compsz);
                        written = write_clusters(vol, rl, offs, rounded, outbuf);
                        if (written != rounded) {
                                /*
                                 * TODO : previously written text has been
                                 * spoilt, should return a specific error
                                 */
                                ntfs_log_error("error writing compressed data\n");
                                errno = EIO;
                                written = -2;
                        }
                } else
                        if (!fail)
                                written = 0;
                free(outbuf);
        }
        return (written);
}

/*
 *              Check the validity of a compressed runlist
 *      The check starts at the beginning of current run and ends
 *      at the end of runlist
 *      errno is set if the runlist is not valid
 */

static BOOL valid_compressed_run(ntfs_attr *na, runlist_element *rl,
                        BOOL fullcheck, const char *text)
{
        runlist_element *xrl;
        const char *err;
        BOOL ok = TRUE;

        xrl = rl;
        while (xrl->vcn & (na->compression_block_clusters - 1))
                xrl--;
        err = (const char*)NULL;
        while (xrl->length) {
                if ((xrl->vcn + xrl->length) != xrl[1].vcn)
                        err = "Runs not adjacent";
                if (xrl->lcn == LCN_HOLE) {
                        if ((xrl->vcn + xrl->length)
                            & (na->compression_block_clusters - 1)) {
                                err = "Invalid hole";
                        }
                        if (fullcheck && (xrl[1].lcn == LCN_HOLE)) {
                                err = "Adjacent holes";
                        }
                }
                if (err) {
                        ntfs_log_error("%s at %s index %ld inode %lld\n",
                                err, text, (long)(xrl - na->rl),
                                (long long)na->ni->mft_no);
                        errno = EIO;
                        ok = FALSE;
                        err = (const char*)NULL;
                }
                xrl++;
        }
        return (ok);
}

/*
 *              Free unneeded clusters after overwriting compressed data
 *
 *      This generally requires one or two empty slots at the end of runlist,
 *      but we do not want to reallocate the runlist here because
 *      there are many pointers to it.
 *      So the empty slots have to be reserved beforehand
 *
 *      Returns zero unless some error occurred (described by errno)
 *
 *         +======= start of block =====+
 *      0  |A     chunk may overflow    | <-- rl         usedcnt : A + B
 *         |A     on previous block     |                        then B
 *         |A                           |
 *         +-- end of allocated chunk --+                freelength : C
 *         |B                           |                      (incl overflow)
 *         +== end of compressed data ==+
 *         |C                           | <-- freerl     freecnt : C + D
 *         |C     chunk may overflow    |
 *         |C     on next block         |
 *         +-- end of allocated chunk --+
 *         |D                           |
 *         |D     chunk may overflow    |
 *     15  |D     on next block         |
 *         +======== end of block ======+
 *
 */

static int ntfs_compress_overwr_free(ntfs_attr *na, runlist_element *rl,
                        s32 usedcnt, s32 freecnt, VCN *update_from)
{
        BOOL beginhole;
        BOOL mergeholes;
        s32 oldlength;
        s32 freelength;
        s64 freelcn;
        s64 freevcn;
        runlist_element *freerl;
        ntfs_volume *vol;
        s32 carry;
        int res;

        vol = na->ni->vol;
        res = 0;
        freelcn = rl->lcn + usedcnt;
        freevcn = rl->vcn + usedcnt;
        freelength = rl->length - usedcnt;
        beginhole = !usedcnt && !rl->vcn;
                /* can merge with hole before ? */
        mergeholes = !usedcnt
                        && rl[0].vcn
                        && (rl[-1].lcn == LCN_HOLE);
                /* truncate current run, carry to subsequent hole */
        carry = freelength;
        oldlength = rl->length;
        if (mergeholes) {
                        /* merging with a hole before */
                freerl = rl;
        } else {
                rl->length -= freelength; /* warning : can be zero */
                freerl = ++rl;
        }
        if (!mergeholes && (usedcnt || beginhole)) {
                s32 freed;
                runlist_element *frl;
                runlist_element *erl;
                int holes = 0;
                BOOL threeparts;

                /* free the unneeded clusters from initial run, then freerl */
                threeparts = (freelength > freecnt);
                freed = 0;
                frl = freerl;
                if (freelength) {
                        res = ntfs_cluster_free_basic(vol,freelcn,
                                (threeparts ? freecnt : freelength));
                        if (!res)
                                freed += (threeparts ? freecnt : freelength);
                        if (!usedcnt) {
                                holes++;
                                freerl--;
                                freerl->length += (threeparts
                                                ? freecnt : freelength);
                                if (freerl->vcn < *update_from)
                                        *update_from = freerl->vcn;
                        }
                }
                while (!res && frl->length && (freed < freecnt)) {
                        if (frl->length <= (freecnt - freed)) {
                                res = ntfs_cluster_free_basic(vol, frl->lcn,
                                                frl->length);
                                if (!res) {
                                        freed += frl->length;
                                        frl->lcn = LCN_HOLE;
                                        frl->length += carry;
                                        carry = 0;
                                        holes++;
                                }
                        } else {
                                res = ntfs_cluster_free_basic(vol, frl->lcn,
                                                freecnt - freed);
                                if (!res) {
                                        frl->lcn += freecnt - freed;
                                        frl->vcn += freecnt - freed;
                                        frl->length -= freecnt - freed;
                                        freed = freecnt;
                                }
                        }
                        frl++;
                }
                na->compressed_size -= freed << vol->cluster_size_bits;
                switch (holes) {
                case 0 :
                        /* there are no hole, must insert one */
                        /* space for hole has been prereserved */
                        if (freerl->lcn == LCN_HOLE) {
                                if (threeparts) {
                                        erl = freerl;
                                        while (erl->length)
                                                erl++;
                                        do {
                                                erl[2] = *erl;
                                        } while (erl-- != freerl);

                                        freerl[1].length = freelength - freecnt;
                                        freerl->length = freecnt;
                                        freerl[1].lcn = freelcn + freecnt;
                                        freerl[1].vcn = freevcn + freecnt;
                                        freerl[2].lcn = LCN_HOLE;
                                        freerl[2].vcn = freerl[1].vcn
                                                        + freerl[1].length;
                                        freerl->vcn = freevcn;
                                } else {
                                        freerl->vcn = freevcn;
                                        freerl->length += freelength;
                                }
                        } else {
                                erl = freerl;
                                while (erl->length)
                                        erl++;
                                if (threeparts) {
                                        do {
                                                erl[2] = *erl;
                                        } while (erl-- != freerl);
                                        freerl[1].lcn = freelcn + freecnt;
                                        freerl[1].vcn = freevcn + freecnt;
                                        freerl[1].length = oldlength - usedcnt - freecnt;
                                } else {
                                        do {
                                                erl[1] = *erl;
                                        } while (erl-- != freerl);
                                }
                                freerl->lcn = LCN_HOLE;
                                freerl->vcn = freevcn;
                                freerl->length = freecnt;
                        }
                        break;
                case 1 :
                        /* there is a single hole, may have to merge */
                        freerl->vcn = freevcn;
                        freerl->length = freecnt;
                        if (freerl[1].lcn == LCN_HOLE) {
                                freerl->length += freerl[1].length;
                                erl = freerl;
                                do {
                                        erl++;
                                        *erl = erl[1];
                                } while (erl->length);
                        }
                        break;
                default :
                        /* there were several holes, must merge them */
                        freerl->lcn = LCN_HOLE;
                        freerl->vcn = freevcn;
                        freerl->length = freecnt;
                        if (freerl[holes].lcn == LCN_HOLE) {
                                freerl->length += freerl[holes].length;
                                holes++;
                        }
                        erl = freerl;
                        do {
                                erl++;
                                *erl = erl[holes - 1];
                        } while (erl->length);
                        break;
                }
        } else {
                s32 freed;
                runlist_element *frl;
                runlist_element *xrl;

                freed = 0;
                frl = freerl--;
                if (freerl->vcn < *update_from)
                        *update_from = freerl->vcn;
                while (!res && frl->length && (freed < freecnt)) {
                        if (frl->length <= (freecnt - freed)) {
                                freerl->length += frl->length;
                                freed += frl->length;
                                res = ntfs_cluster_free_basic(vol, frl->lcn,
                                                frl->length);
                                frl++;
                        } else {
                                freerl->length += freecnt - freed;
                                res = ntfs_cluster_free_basic(vol, frl->lcn,
                                                freecnt - freed);
                                frl->lcn += freecnt - freed;
                                frl->vcn += freecnt - freed;
                                frl->length -= freecnt - freed;
                                freed = freecnt;
                        }
                }
                        /* remove unneded runlist entries */
                xrl = freerl;
                        /* group with next run if also a hole */
                if (frl->length && (frl->lcn == LCN_HOLE)) {
                        xrl->length += frl->length;
                        frl++;
                }
                while (frl->length) {
                        *++xrl = *frl++;
                }
                *++xrl = *frl; /* terminator */
        na->compressed_size -= freed << vol->cluster_size_bits;
        }
        return (res);
}


/*
 *              Free unneeded clusters after compression
 *
 *      This generally requires one or two empty slots at the end of runlist,
 *      but we do not want to reallocate the runlist here because
 *      there are many pointers to it.
 *      So the empty slots have to be reserved beforehand
 *
 *      Returns zero unless some error occurred (described by errno)
 */

static int ntfs_compress_free(ntfs_attr *na, runlist_element *rl,
                                s64 used, s64 reserved, BOOL appending,
                                VCN *update_from)
{
        s32 freecnt;
        s32 usedcnt;
        int res;
        s64 freelcn;
        s64 freevcn;
        s32 freelength;
        BOOL mergeholes;
        BOOL beginhole;
        ntfs_volume *vol;
        runlist_element *freerl;

        res = -1; /* default return */
        vol = na->ni->vol;
        freecnt = (reserved - used) >> vol->cluster_size_bits;
        usedcnt = (reserved >> vol->cluster_size_bits) - freecnt;
        if (rl->vcn < *update_from)
                *update_from = rl->vcn;
                /* skip entries fully used, if any */
        while (rl->length && (rl->length < usedcnt)) {
                usedcnt -= rl->length; /* must be > 0 */
                rl++;
        }
        if (rl->length) {
                /*
                 * Splitting the current allocation block requires
                 * an extra runlist element to create the hole.
                 * The required entry has been prereserved when
                 * mapping the runlist.
                 */
                        /* get the free part in initial run */
                freelcn = rl->lcn + usedcnt;
                freevcn = rl->vcn + usedcnt;
                        /* new count of allocated clusters */
                if (!((freevcn + freecnt)
                            & (na->compression_block_clusters - 1))) {
                        if (!appending)
                                res = ntfs_compress_overwr_free(na,rl,
                                                usedcnt,freecnt,update_from);
                        else {
                                freelength = rl->length - usedcnt;
                                beginhole = !usedcnt && !rl->vcn;
                                mergeholes = !usedcnt
                                                && rl[0].vcn
                                                && (rl[-1].lcn == LCN_HOLE);
                                if (mergeholes) {
                                        s32 carry;

                                /* shorten the runs which have free space */
                                        carry = freecnt;
                                        freerl = rl;
                                        while (freerl->length < carry) {
                                                carry -= freerl->length;
                                                freerl++;
                                        }
                                        freerl->length = carry;
                                        freerl = rl;
                                } else {
                                        rl->length = usedcnt; /* can be zero ? */
                                        freerl = ++rl;
                                }
                                if ((freelength > 0)
                                    && !mergeholes
                                    && (usedcnt || beginhole)) {
                                /*
                                 * move the unused part to the end. Doing so,
                                 * the vcn will be out of order. This does
                                 * not harm, the vcn are meaningless now, and
                                 * only the lcn are meaningful for freeing.
                                 */
                                        /* locate current end */
                                        while (rl->length)
                                                rl++;
                                        /* new terminator relocated */
                                        rl[1].vcn = rl->vcn;
                                        rl[1].lcn = LCN_ENOENT;
                                        rl[1].length = 0;
                                        /* hole, currently allocated */
                                        rl->vcn = freevcn;
                                        rl->lcn = freelcn;
                                        rl->length = freelength;
                                } else {
        /* why is this different from the begin hole case ? */
                                        if ((freelength > 0)
                                            && !mergeholes
                                            && !usedcnt) {
                                                freerl--;
                                                freerl->length = freelength;
                                                if (freerl->vcn < *update_from)
                                                        *update_from
                                                                = freerl->vcn;
                                        }
                                }
                                /* free the hole */
                                res = ntfs_cluster_free_from_rl(vol,freerl);
                                if (!res) {
                                        na->compressed_size -= freecnt
                                                << vol->cluster_size_bits;
                                        if (mergeholes) {
                                                /* merge with adjacent hole */
                                                freerl--;
                                                freerl->length += freecnt;
                                        } else {
                                                if (beginhole)
                                                        freerl--;
                                                /* mark hole as free */
                                                freerl->lcn = LCN_HOLE;
                                                freerl->vcn = freevcn;
                                                freerl->length = freecnt;
                                        }
                                        if (freerl->vcn < *update_from)
                                                *update_from = freerl->vcn;
                                                /* and set up the new end */
                                        freerl[1].lcn = LCN_ENOENT;
                                        freerl[1].vcn = freevcn + freecnt;
                                        freerl[1].length = 0;
                                }
                        }
                } else {
                        ntfs_log_error("Bad end of a compression block set\n");
                        errno = EIO;
                }
        } else {
                ntfs_log_error("No cluster to free after compression\n");
                errno = EIO;
        }
        NAttrSetRunlistDirty(na);
        return (res);
}

/*
 *              Read existing data, decompress and append buffer
 *      Do nothing if something fails
 */

static int ntfs_read_append(ntfs_attr *na, const runlist_element *rl,
                        s64 offs, u32 compsz, s32 pos, BOOL appending,
                        char *outbuf, s64 to_write, const void *b)
{
        int fail = 1;
        char *compbuf;
        u32 decompsz;
        u32 got;

        if (compsz == na->compression_block_size) {
                        /* if the full block was requested, it was a hole */
                memset(outbuf,0,compsz);
                memcpy(&outbuf[pos],b,to_write);
                fail = 0;
        } else {
                compbuf = (char*)ntfs_malloc(compsz);
                if (compbuf) {
                        /* must align to full block for decompression */
                        if (appending)
                                decompsz = ((pos - 1) | (NTFS_SB_SIZE - 1)) + 1;
                        else
                                decompsz = na->compression_block_size;
                        got = read_clusters(na->ni->vol, rl, offs,
                                        compsz, compbuf);
                        if ((got == compsz)
                            && !ntfs_decompress((u8*)outbuf,decompsz,
                                        (u8*)compbuf,compsz)) {
                                memcpy(&outbuf[pos],b,to_write);
                                fail = 0;
                        }
                        free(compbuf);
                }
        }
        return (fail);
}

/*
 *              Flush a full compression block
 *
 *      returns the size actually written (rounded to a full cluster)
 *              or 0 if could not compress (and written uncompressed)
 *              or -1 if there were an irrecoverable error (errno set)
 */

static s32 ntfs_flush(ntfs_attr *na, runlist_element *rl, s64 offs,
                        char *outbuf, s32 count, BOOL compress,
                        BOOL appending, VCN *update_from)
{
        s32 rounded;
        s32 written;
        int clsz;

        if (compress) {
                written = ntfs_comp_set(na, rl, offs, count, outbuf);
                if (written == -1)
                        compress = FALSE;
                if ((written >= 0)
                   && ntfs_compress_free(na,rl,offs + written,
                                offs + na->compression_block_size, appending,
                                update_from))
                        written = -1;
        } else
                written = 0;
        if (!compress) {
                clsz = 1 << na->ni->vol->cluster_size_bits;
                rounded = ((count - 1) | (clsz - 1)) + 1;
                if (rounded > count)
                        memset(&outbuf[count], 0, rounded - count);
                written = write_clusters(na->ni->vol, rl,
                                offs, rounded, outbuf);
                if (written != rounded)
                        written = -1;
        }
        return (written);
}

/*
 *              Write some data to be compressed.
 *      Compression only occurs when a few clusters (usually 16) are
 *      full. When this occurs an extra runlist slot may be needed, so
 *      it has to be reserved beforehand.
 *
 *      Returns the size of uncompressed data written,
 *              or negative if an error occurred.
 *      When the returned size is less than requested, new clusters have
 *      to be allocated before the function is called again.
 */

s64 ntfs_compressed_pwrite(ntfs_attr *na, runlist_element *wrl, s64 wpos,
                                s64 offs, s64 to_write, s64 rounded,
                                const void *b, int compressed_part,
                                VCN *update_from)
{
        ntfs_volume *vol;
        runlist_element *brl; /* entry containing the beginning of block */
        int compression_length;
        s64 written;
        s64 to_read;
        s64 to_flush;
        s64 roffs;
        s64 got;
        s64 start_vcn;
        s64 nextblock;
        s64 endwrite;
        u32 compsz;
        char *inbuf;
        char *outbuf;
        BOOL fail;
        BOOL done;
        BOOL compress;
        BOOL appending;

        if (!valid_compressed_run(na,wrl,FALSE,"begin compressed write")) {
                return (-1);
        }
        if ((*update_from < 0)
            || (compressed_part < 0)
            || (compressed_part > (int)na->compression_block_clusters)) {
                ntfs_log_error("Bad update vcn or compressed_part %d for compressed write\n",
                        compressed_part);
                errno = EIO;
                return (-1);
        }
                /* make sure there are two unused entries in runlist */
        if (na->unused_runs < 2) {
                ntfs_log_error("No unused runs for compressed write\n");
                errno = EIO;
                return (-1);
        }
        if (na->compression_block_size < NTFS_SB_SIZE) {
                ntfs_log_error("Unsupported compression block size %ld\n",
                                (long)na->compression_block_size);
                errno = EOVERFLOW;
                return (-1);
        }
        if (wrl->vcn < *update_from)
                *update_from = wrl->vcn;
        written = -1; /* default return */
        vol = na->ni->vol;
        compression_length = na->compression_block_clusters;
        compress = FALSE;
        done = FALSE;
                /*
                 * Cannot accept writing beyond the current compression set
                 * because when compression occurs, clusters are freed
                 * and have to be reallocated.
                 * (cannot happen with standard fuse 4K buffers)
                 * Caller has to avoid this situation, or face consequences.
                 */
        nextblock = ((offs + (wrl->vcn << vol->cluster_size_bits))
                        | (na->compression_block_size - 1)) + 1;
                /* determine whether we are appending to file */
        endwrite = offs + to_write + (wrl->vcn << vol->cluster_size_bits);
        appending = endwrite >= na->initialized_size;
        if (endwrite >= nextblock) {
                        /* it is time to compress */
                compress = TRUE;
                        /* only process what we can */
                to_write = rounded = nextblock
                        - (offs + (wrl->vcn << vol->cluster_size_bits));
        }
        start_vcn = 0;
        fail = FALSE;
        brl = wrl;
        roffs = 0;
                /*
                 * If we are about to compress or we need to decompress
                 * existing data, we have to process a full set of blocks.
                 * So relocate the parameters to the beginning of allocation
                 * containing the first byte of the set of blocks.
                 */
        if (compress || compressed_part) {
                /* find the beginning of block */
                start_vcn = (wrl->vcn + (offs >> vol->cluster_size_bits))
                                & -compression_length;
                if (start_vcn < *update_from)
                        *update_from = start_vcn;
                while (brl->vcn && (brl->vcn > start_vcn)) {
                        /* jumping back a hole means big trouble */
                        if (brl->lcn == (LCN)LCN_HOLE) {
                                ntfs_log_error("jump back over a hole when appending\n");
                                fail = TRUE;
                                errno = EIO;
                        }
                        brl--;
                        offs += brl->length << vol->cluster_size_bits;
                }
                roffs = (start_vcn - brl->vcn) << vol->cluster_size_bits;
        }
        if (compressed_part && !fail) {
                /*
                 * The set of compression blocks contains compressed data
                 * (we are reopening an existing file to append to it)
                 * Decompress the data and append
                 */
                compsz = (s32)compressed_part << vol->cluster_size_bits;
                outbuf = (char*)ntfs_malloc(na->compression_block_size);
                if (outbuf) {
                        if (appending) {
                                to_read = offs - roffs;
                                to_flush = to_read + to_write;
                        } else {
                                to_read = na->data_size
                                        - (brl->vcn << vol->cluster_size_bits);
                                if (to_read > na->compression_block_size)
                                        to_read = na->compression_block_size;
                                to_flush = to_read;
                        }
                        if (!ntfs_read_append(na, brl, roffs, compsz,
                                        (s32)(offs - roffs), appending,
                                        outbuf, to_write, b)) {
                                written = ntfs_flush(na, brl, roffs,
                                        outbuf, to_flush, compress, appending,
                                        update_from);
                                if (written >= 0) {
                                        written = to_write;
                                        done = TRUE;
                                }
                        }
                free(outbuf);
                }
        } else {
                if (compress && !fail) {
                        /*
                         * we are filling up a block, read the full set
                         * of blocks and compress it
                         */
                        inbuf = (char*)ntfs_malloc(na->compression_block_size);
                        if (inbuf) {
                                to_read = offs - roffs;
                                if (to_read)
                                        got = read_clusters(vol, brl, roffs,
                                                        to_read, inbuf);
                                else
                                        got = 0;
                                if (got == to_read) {
                                        memcpy(&inbuf[to_read],b,to_write);
                                        written = ntfs_comp_set(na, brl, roffs,
                                                to_read + to_write, inbuf);
                                /*
                                 * if compression was not successful,
                                 * only write the part which was requested
                                 */
                                        if ((written >= 0)
                                                /* free the unused clusters */
                                          && !ntfs_compress_free(na,brl,
                                                    written + roffs,
                                                    na->compression_block_size
                                                         + roffs,
                                                    appending, update_from)) {
                                                done = TRUE;
                                                written = to_write;
                                        }
                                }
                                free(inbuf);
                        }
                }
                if (!done) {
                        /*
                         * if the compression block is not full, or
                         * if compression failed for whatever reason,
                         * write uncompressed
                         */
                        /* check we are not overflowing current allocation */
                        if ((wpos + rounded)
                            > ((wrl->lcn + wrl->length)
                                 << vol->cluster_size_bits)) {
                                ntfs_log_error("writing on unallocated clusters\n");
                                errno = EIO;
                        } else {
                                written = ntfs_pwrite(vol->dev, wpos,
                                        rounded, b);
                                if (written == rounded)
                                        written = to_write;
                        }
                }
        }
        if ((written >= 0)
            && !valid_compressed_run(na,wrl,TRUE,"end compressed write"))
                written = -1;
        return (written);
}

/*
 *              Close a file written compressed.
 *      This compresses the last partial compression block of the file.
 *      Two empty runlist slots have to be reserved beforehand.
 *
 *      Returns zero if closing is successful.
 */

int ntfs_compressed_close(ntfs_attr *na, runlist_element *wrl, s64 offs,
                        VCN *update_from)
{
        ntfs_volume *vol;
        runlist_element *brl; /* entry containing the beginning of block */
        int compression_length;
        s64 written;
        s64 to_read;
        s64 roffs;
        s64 got;
        s64 start_vcn;
        char *inbuf;
        BOOL fail;
        BOOL done;

        if (na->unused_runs < 2) {
                ntfs_log_error("No unused runs for compressed close\n");
                errno = EIO;
                return (-1);
        }
        if (*update_from < 0) {
                ntfs_log_error("Bad update vcn for compressed close\n");
                errno = EIO;
                return (-1);
        }
        if (na->compression_block_size < NTFS_SB_SIZE) {
                ntfs_log_error("Unsupported compression block size %ld\n",
                                (long)na->compression_block_size);
                errno = EOVERFLOW;
                return (-1);
        }
        if (wrl->vcn < *update_from)
                *update_from = wrl->vcn;
        vol = na->ni->vol;
        compression_length = na->compression_block_clusters;
        done = FALSE;
                /*
                 * There generally is an uncompressed block at end of file,
                 * read the full block and compress it
                 */
        inbuf = (char*)ntfs_malloc(na->compression_block_size);
        if (inbuf) {
                start_vcn = (wrl->vcn + (offs >> vol->cluster_size_bits))
                                & -compression_length;
                if (start_vcn < *update_from)
                        *update_from = start_vcn;
                to_read = offs + ((wrl->vcn - start_vcn)
                                        << vol->cluster_size_bits);
                brl = wrl;
                fail = FALSE;
                while (brl->vcn && (brl->vcn > start_vcn)) {
                        if (brl->lcn == (LCN)LCN_HOLE) {
                                ntfs_log_error("jump back over a hole when closing\n");
                                fail = TRUE;
                                errno = EIO;
                        }
                        brl--;
                }
                if (!fail) {
                        /* roffs can be an offset from another uncomp block */
                        roffs = (start_vcn - brl->vcn)
                                                << vol->cluster_size_bits;
                        if (to_read) {
                                got = read_clusters(vol, brl, roffs, to_read,
                                                 inbuf);
                                if (got == to_read) {
                                        written = ntfs_comp_set(na, brl, roffs,
                                                        to_read, inbuf);
                                        if ((written >= 0)
                                        /* free the unused clusters */
                                            && !ntfs_compress_free(na,brl,
                                                        written + roffs,
                                                        na->compression_block_size + roffs,
                                                        TRUE, update_from)) {
                                                done = TRUE;
                                        } else
                                /* if compression failed, leave uncompressed */
                                                if (written == -1)
                                                        done = TRUE;
                                }
                        } else
                                done = TRUE;
                        free(inbuf);
                }
        }
        if (done && !valid_compressed_run(na,wrl,TRUE,"end compressed close"))
                done = FALSE;
        return (!done);
}