// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * NTFS kernel compressed attributes handling.
 *
 * Copyright (c) 2001-2004 Anton Altaparmakov
 * Copyright (c) 2002 Richard Russon
 * Copyright (c) 2025 LG Electronics Co., Ltd.
 *
 * Part of this file is based on code from the NTFS-3G.
 * and is copyrighted by the respective authors below:
 * 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
 */

#include <linux/fs.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"
#include "lcnalloc.h"
#include "mft.h"

/*
 * Constants used in the compression code
 */
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_buffer - one buffer for the decompression engine
 */
static u8 *ntfs_compression_buffer;

/*
 * ntfs_cb_lock - mutex lock which protects ntfs_compression_buffer
 */
static DEFINE_MUTEX(ntfs_cb_lock);

/*
 * allocate_compression_buffers - allocate the decompression buffers
 *
 * Caller has to hold the ntfs_lock mutex.
 *
 * Return 0 on success or -ENOMEM if the allocations failed.
 */
int allocate_compression_buffers(void)
{
        if (ntfs_compression_buffer)
                return 0;

        ntfs_compression_buffer = vmalloc(NTFS_MAX_CB_SIZE);
        if (!ntfs_compression_buffer)
                return -ENOMEM;
        return 0;
}

/*
 * free_compression_buffers - free the decompression buffers
 *
 * Caller has to hold the ntfs_lock mutex.
 */
void free_compression_buffers(void)
{
        mutex_lock(&ntfs_cb_lock);
        if (!ntfs_compression_buffer) {
                mutex_unlock(&ntfs_cb_lock);
                return;
        }

        vfree(ntfs_compression_buffer);
        ntfs_compression_buffer = NULL;
        mutex_unlock(&ntfs_cb_lock);
}

/*
 * zero_partial_compressed_page - zero out of bounds compressed page region
 * @page: page to zero
 * @initialized_size: initialized size of the attribute
 */
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->__folio_index << PAGE_SHIFT) >= initialized_size) {
                clear_page(kp);
                return;
        }
        kp_ofs = initialized_size & ~PAGE_MASK;
        memset(kp + kp_ofs, 0, PAGE_SIZE - kp_ofs);
}

/*
 * handle_bounds_compressed_page - test for&handle out of bounds compressed page
 * @page: page to check and handle
 * @i_size: file size
 * @initialized_size: initialized size of the attribute
 */
static inline void handle_bounds_compressed_page(struct page *page,
                const loff_t i_size, const s64 initialized_size)
{
        if ((page->__folio_index >= (initialized_size >> PAGE_SHIFT)) &&
                        (initialized_size < i_size))
                zero_partial_compressed_page(page, initialized_size);
}

/*
 * ntfs_decompress - decompress a compression block into an array of pages
 * @dest_pages:         destination array of pages
 * @completed_pages:    scratch space to track completed pages
 * @dest_index:         current index into @dest_pages (IN/OUT)
 * @dest_ofs:           current offset within @dest_pages[@dest_index] (IN/OUT)
 * @dest_max_index:     maximum index into @dest_pages (IN)
 * @dest_max_ofs:       maximum offset within @dest_pages[@dest_max_index] (IN)
 * @xpage:              the target page (-1 if none) (IN)
 * @xpage_done:         set to 1 if xpage was completed successfully (IN/OUT)
 * @cb_start:           compression block to decompress (IN)
 * @cb_size:            size of compression block @cb_start in bytes (IN)
 * @i_size:             file size when we started the read (IN)
 * @initialized_size:   initialized file size when we started the read (IN)
 *
 * The caller must have disabled preemption. ntfs_decompress() reenables it when
 * the critical section is finished.
 *
 * This decompresses the compression block @cb_start into the array of
 * destination pages @dest_pages starting at index @dest_index into @dest_pages
 * and at offset @dest_pos into the page @dest_pages[@dest_index].
 *
 * When the page @dest_pages[@xpage] is completed, @xpage_done is set to 1.
 * If xpage is -1 or @xpage has not been completed, @xpage_done is not modified.
 *
 * @cb_start is a pointer to the compression block which needs decompressing
 * and @cb_size is the size of @cb_start in bytes (8-64kiB).
 *
 * Return 0 if success or -EOVERFLOW on error in the compressed stream.
 * @xpage_done indicates whether the target page (@dest_pages[@xpage]) was
 * completed during the decompression of the compression block (@cb_start).
 *
 * Warning: This function *REQUIRES* PAGE_SIZE >= 4096 or it will blow up
 * unpredicatbly! You have been warned!
 *
 * Note to hackers: This function may not sleep until it has finished accessing
 * the compression block @cb_start as it is a per-CPU buffer.
 */
static int ntfs_decompress(struct page *dest_pages[], int completed_pages[],
                int *dest_index, int *dest_ofs, const int dest_max_index,
                const int dest_max_ofs, const int xpage, char *xpage_done,
                u8 *const cb_start, const u32 cb_size, const loff_t i_size,
                const s64 initialized_size)
{
        /*
         * Pointers into the compressed data, i.e. the compression block (cb),
         * and the therein contained sub-blocks (sb).
         */
        u8 *cb_end = cb_start + cb_size; /* End of cb. */
        u8 *cb = cb_start;      /* Current position in cb. */
        u8 *cb_sb_start = cb;   /* Beginning of the current sb in the cb. */
        u8 *cb_sb_end;          /* End of current sb / beginning of next sb. */

        /* Variables for uncompressed data / destination. */
        struct page *dp;        /* Current destination page being worked on. */
        u8 *dp_addr;            /* Current pointer into dp. */
        u8 *dp_sb_start;        /* Start of current sub-block in dp. */
        u8 *dp_sb_end;          /* End of current sb in dp (dp_sb_start + NTFS_SB_SIZE). */
        u16 do_sb_start;        /* @dest_ofs when starting this sub-block. */
        u16 do_sb_end;          /* @dest_ofs of end of this sb (do_sb_start + NTFS_SB_SIZE). */

        /* Variables for tag and token parsing. */
        u8 tag;                 /* Current tag. */
        int token;              /* Loop counter for the eight tokens in tag. */
        int nr_completed_pages = 0;

        /* Default error code. */
        int err = -EOVERFLOW;

        ntfs_debug("Entering, cb_size = 0x%x.", cb_size);
do_next_sb:
        ntfs_debug("Beginning sub-block at offset = 0x%zx in the cb.",
                        cb - cb_start);
        /*
         * Have we reached the end of the compression block or the end of the
         * decompressed data?  The latter can happen for example if the current
         * position in the compression block is one byte before its end so the
         * first two checks do not detect it.
         */
        if (cb == cb_end || !le16_to_cpup((__le16 *)cb) ||
                        (*dest_index == dest_max_index &&
                        *dest_ofs == dest_max_ofs)) {
                int i;

                ntfs_debug("Completed. Returning success (0).");
                err = 0;
return_error:
                /* We can sleep from now on, so we drop lock. */
                mutex_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_local(page_address(dp));
                                SetPageUptodate(dp);
                                unlock_page(dp);
                                if (di == xpage)
                                        *xpage_done = 1;
                                else
                                        put_page(dp);
                                dest_pages[di] = NULL;
                        }
                }
                return err;
        }

        /* Setup offsets for the current sub-block destination. */
        do_sb_start = *dest_ofs;
        do_sb_end = do_sb_start + NTFS_SB_SIZE;

        /* Check that we are still within allowed boundaries. */
        if (*dest_index == dest_max_index && do_sb_end > dest_max_ofs)
                goto return_overflow;

        /* Does the minimum size of a compressed sb overflow valid range? */
        if (cb + 6 > cb_end)
                goto return_overflow;

        /* Setup the current sub-block source pointers and validate range. */
        cb_sb_start = cb;
        cb_sb_end = cb_sb_start + (le16_to_cpup((__le16 *)cb) & NTFS_SB_SIZE_MASK)
                        + 3;
        if (cb_sb_end > cb_end)
                goto return_overflow;

        /* Get the current destination page. */
        dp = dest_pages[*dest_index];
        if (!dp) {
                /* No page present. Skip decompression of this sub-block. */
                cb = cb_sb_end;

                /* Advance destination position to next sub-block. */
                *dest_ofs = (*dest_ofs + NTFS_SB_SIZE) & ~PAGE_MASK;
                if (!*dest_ofs && (++*dest_index > dest_max_index))
                        goto return_overflow;
                goto do_next_sb;
        }

        /* We have a valid destination page. Setup the destination pointers. */
        dp_addr = (u8 *)page_address(dp) + do_sb_start;

        /* Now, we are ready to process the current sub-block (sb). */
        if (!(le16_to_cpup((__le16 *)cb) & NTFS_SB_IS_COMPRESSED)) {
                ntfs_debug("Found uncompressed sub-block.");
                /* This sb is not compressed, just copy it into destination. */

                /* Advance source position to first data byte. */
                cb += 2;

                /* An uncompressed sb must be full size. */
                if (cb_sb_end - cb != NTFS_SB_SIZE)
                        goto return_overflow;

                /* Copy the block and advance the source position. */
                memcpy(dp_addr, cb, NTFS_SB_SIZE);
                cb += NTFS_SB_SIZE;

                /* Advance destination position to next sub-block. */
                *dest_ofs += NTFS_SB_SIZE;
                *dest_ofs &= ~PAGE_MASK;
                if (!(*dest_ofs)) {
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. */
                *dest_ofs &= ~PAGE_MASK;
                if (!(*dest_ofs))
                        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) {
                register u16 i;
                u16 lg, pt, length, max_non_overlap;
                u8 *dp_back_addr;

                /* Check if we are done / still in range. */
                if (cb >= cb_sb_end || dp_addr > dp_sb_end)
                        break;

                /* Determine token type and parse appropriately.*/
                if ((tag & NTFS_TOKEN_MASK) == NTFS_SYMBOL_TOKEN) {
                        /*
                         * We have a symbol token, copy the symbol across, and
                         * advance the source and destination positions.
                         */
                        *dp_addr++ = *cb++;
                        ++*dest_ofs;

                        /* Continue with the next token. */
                        continue;
                }

                /*
                 * We have a phrase token. Make sure it is not the first tag in
                 * the sb as this is illegal and would confuse the code below.
                 */
                if (dp_addr == dp_sb_start)
                        goto return_overflow;

                /*
                 * Determine the number of bytes to go back (p) and the number
                 * of bytes to copy (l). We use an optimized algorithm in which
                 * we first calculate log2(current destination position in sb),
                 * which allows determination of l and p in O(1) rather than
                 * O(n). We just need an arch-optimized log2() function now.
                 */
                lg = 0;
                for (i = *dest_ofs - do_sb_start - 1; i >= 0x10; i >>= 1)
                        lg++;

                /* Get the phrase token into i. */
                pt = le16_to_cpup((__le16 *)cb);

                /*
                 * Calculate starting position of the byte sequence in
                 * the destination using the fact that p = (pt >> (12 - lg)) + 1
                 * and make sure we don't go too far back.
                 */
                dp_back_addr = dp_addr - (pt >> (12 - lg)) - 1;
                if (dp_back_addr < dp_sb_start)
                        goto return_overflow;

                /* Now calculate the length of the byte sequence. */
                length = (pt & (0xfff >> lg)) + 3;

                /* Advance destination position and verify it is in range. */
                *dest_ofs += length;
                if (*dest_ofs > do_sb_end)
                        goto return_overflow;

                /* The number of non-overlapping bytes. */
                max_non_overlap = dp_addr - dp_back_addr;

                if (length <= max_non_overlap) {
                        /* The byte sequence doesn't overlap, just copy it. */
                        memcpy(dp_addr, dp_back_addr, length);

                        /* Advance destination pointer. */
                        dp_addr += length;
                } else {
                        /*
                         * The byte sequence does overlap, copy non-overlapping
                         * part and then do a slow byte by byte copy for the
                         * overlapping part. Also, advance the destination
                         * pointer.
                         */
                        memcpy(dp_addr, dp_back_addr, max_non_overlap);
                        dp_addr += max_non_overlap;
                        dp_back_addr += max_non_overlap;
                        length -= max_non_overlap;
                        while (length--)
                                *dp_addr++ = *dp_back_addr++;
                }

                /* Advance source position and continue with the next token. */
                cb += 2;
        }

        /* No tokens left in the current tag. Continue with the next tag. */
        goto do_next_tag;

return_overflow:
        ntfs_error(NULL, "Failed. Returning -EOVERFLOW.");
        goto return_error;
}

/*
 * ntfs_read_compressed_block - read a compressed block into the page cache
 * @folio:      locked folio in the compression block(s) we need to read
 *
 * When we are called the page has already been verified to be locked and the
 * attribute is known to be non-resident, not encrypted, but compressed.
 *
 * 1. Determine which compression block(s) @page is in.
 * 2. Get hold of all pages corresponding to this/these compression block(s).
 * 3. Read the (first) compression block.
 * 4. Decompress it into the corresponding pages.
 * 5. Throw the compressed data away and proceed to 3. for the next compression
 *    block or return success if no more compression blocks left.
 *
 * Warning: We have to be careful what we do about existing pages. They might
 * have been written to so that we would lose data if we were to just overwrite
 * them with the out-of-date uncompressed data.
 */
int ntfs_read_compressed_block(struct folio *folio)
{
        struct page *page = &folio->page;
        loff_t i_size;
        s64 initialized_size;
        struct address_space *mapping = page->mapping;
        struct ntfs_inode *ni = NTFS_I(mapping->host);
        struct ntfs_volume *vol = ni->vol;
        struct super_block *sb = vol->sb;
        struct runlist_element *rl;
        unsigned long flags;
        u8 *cb, *cb_pos, *cb_end;
        unsigned long offset, index = page->__folio_index;
        u32 cb_size = ni->itype.compressed.block_size;
        u64 cb_size_mask = cb_size - 1UL;
        s64 vcn;
        s64 lcn;
        /* The first wanted vcn (minimum alignment is PAGE_SIZE). */
        s64 start_vcn = (((s64)index << PAGE_SHIFT) & ~cb_size_mask) >>
                        vol->cluster_size_bits;
        /*
         * The first vcn after the last wanted vcn (minimum alignment is again
         * PAGE_SIZE.
         */
        s64 end_vcn = ((((s64)(index + 1UL) << PAGE_SHIFT) + cb_size - 1)
                        & ~cb_size_mask) >> vol->cluster_size_bits;
        /* Number of compression blocks (cbs) in the wanted vcn range. */
        unsigned int nr_cbs = ntfs_cluster_to_bytes(vol, end_vcn - start_vcn) >>
                        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 = ntfs_cluster_to_pidx(vol, end_vcn - start_vcn);
        unsigned int xpage, max_page, cur_page, cur_ofs, i, page_ofs, page_index;
        unsigned int cb_clusters, cb_max_ofs;
        int cb_max_page, err = 0;
        struct page **pages;
        int *completed_pages;
        unsigned char xpage_done = 0;
        struct page *lpage;

        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.
         */
        if (ni->type != AT_DATA || ni->name_len) {
                unlock_page(page);
                return -EIO;
        }

        pages = kmalloc_array(nr_pages, sizeof(struct page *), GFP_NOFS);
        completed_pages = kmalloc_array(nr_pages + 1, sizeof(int), GFP_NOFS);

        if (unlikely(!pages || !completed_pages)) {
                kfree(pages);
                kfree(completed_pages);
                unlock_page(page);
                ntfs_error(vol->sb, "Failed to allocate internal buffers.");
                return -ENOMEM;
        }

        /*
         * We have already been given one page, this is the one we must do.
         * Once again, the alignment guarantees keep it simple.
         */
        offset = ntfs_cluster_to_pidx(vol, start_vcn);
        xpage = index - offset;
        pages[xpage] = page;
        /*
         * The remaining pages need to be allocated and inserted into the page
         * cache, alignment guarantees keep all the below much simpler. (-8
         */
        read_lock_irqsave(&ni->size_lock, flags);
        i_size = i_size_read(VFS_I(ni));
        initialized_size = ni->initialized_size;
        read_unlock_irqrestore(&ni->size_lock, flags);
        max_page = ((i_size + PAGE_SIZE - 1) >> PAGE_SHIFT) -
                        offset;
        /* Is the page fully outside i_size? (truncate in progress) */
        if (xpage >= max_page) {
                kfree(pages);
                kfree(completed_pages);
                zero_user_segments(page, 0, PAGE_SIZE, 0, 0);
                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))) {
                                kmap_local_page(page);
                                continue;
                        }
                        unlock_page(page);
                        put_page(page);
                        pages[i] = NULL;
                }
        }

        /*
         * We have the runlist, and all the destination pages we need to fill.
         * Now read the first compression block.
         */
        cur_page = 0;
        cur_ofs = 0;
        cb_clusters = ni->itype.compressed.block_clusters;
do_next_cb:
        nr_cbs--;

        mutex_lock(&ntfs_cb_lock);
        if (!ntfs_compression_buffer)
                if (allocate_compression_buffers()) {
                        mutex_unlock(&ntfs_cb_lock);
                        goto err_out;
                }


        cb = ntfs_compression_buffer;
        cb_pos = cb;
        cb_end = cb + cb_size;

        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) {
                                mutex_unlock(&ntfs_cb_lock);
                                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;
                        mutex_unlock(&ntfs_cb_lock);
                        goto map_rl_err;
                }

                page_ofs = ntfs_cluster_to_poff(vol, lcn);
                page_index = ntfs_cluster_to_pidx(vol, lcn);

                lpage = read_mapping_page(sb->s_bdev->bd_mapping,
                                          page_index, NULL);
                if (IS_ERR(lpage)) {
                        err = PTR_ERR(lpage);
                        mutex_unlock(&ntfs_cb_lock);
                        goto read_err;
                }

                lock_page(lpage);
                memcpy(cb_pos, page_address(lpage) + page_ofs,
                       vol->cluster_size);
                unlock_page(lpage);
                put_page(lpage);
                cb_pos += vol->cluster_size;
        }

        /* Release the lock if we took it. */
        if (rl)
                up_read(&ni->runlist.lock);

        /* Just a precaution. */
        if (cb_pos + 2 <= cb + cb_size)
                *(u16 *)cb_pos = 0;

        /* Reset cb_pos back to the beginning. */
        cb_pos = cb;

        /* We now have both source (if present) and destination. */
        ntfs_debug("Successfully read the compression block.");

        /* The last page and maximum offset within it for the current cb. */
        cb_max_page = (cur_page << PAGE_SHIFT) + cur_ofs + cb_size;
        cb_max_ofs = cb_max_page & ~PAGE_MASK;
        cb_max_page >>= PAGE_SHIFT;

        /* Catch end of file inside a compression block. */
        if (cb_max_page > max_page)
                cb_max_page = max_page;

        if (vcn == start_vcn - cb_clusters) {
                /* Sparse cb, zero out page range overlapping the cb. */
                ntfs_debug("Found sparse compression block.");
                /* We can sleep from now on, so we drop lock. */
                mutex_unlock(&ntfs_cb_lock);
                if (cb_max_ofs)
                        cb_max_page--;
                for (; cur_page < cb_max_page; cur_page++) {
                        page = pages[cur_page];
                        if (page) {
                                if (likely(!cur_ofs))
                                        clear_page(page_address(page));
                                else
                                        memset(page_address(page) + cur_ofs, 0,
                                                        PAGE_SIZE -
                                                        cur_ofs);
                                flush_dcache_page(page);
                                kunmap_local(page_address(page));
                                SetPageUptodate(page);
                                unlock_page(page);
                                if (cur_page == xpage)
                                        xpage_done = 1;
                                else
                                        put_page(page);
                                pages[cur_page] = NULL;
                        }
                        cb_pos += PAGE_SIZE - cur_ofs;
                        cur_ofs = 0;
                        if (cb_pos >= cb_end)
                                break;
                }
                /* If we have a partial final page, deal with it now. */
                if (cb_max_ofs && cb_pos < cb_end) {
                        page = pages[cur_page];
                        if (page)
                                memset(page_address(page) + cur_ofs, 0,
                                                cb_max_ofs - cur_ofs);
                        /*
                         * No need to update cb_pos at this stage:
                         *      cb_pos += cb_max_ofs - cur_ofs;
                         */
                        cur_ofs = cb_max_ofs;
                }
        } else if (vcn == start_vcn) {
                /* We can't sleep so we need two stages. */
                unsigned int cur2_page = cur_page;
                unsigned int cur_ofs2 = cur_ofs;
                u8 *cb_pos2 = cb_pos;

                ntfs_debug("Found uncompressed compression block.");
                /* Uncompressed cb, copy it to the destination pages. */
                if (cb_max_ofs)
                        cb_max_page--;
                /* First stage: copy data into destination pages. */
                for (; cur_page < cb_max_page; cur_page++) {
                        page = pages[cur_page];
                        if (page)
                                memcpy(page_address(page) + cur_ofs, cb_pos,
                                                PAGE_SIZE - cur_ofs);
                        cb_pos += PAGE_SIZE - cur_ofs;
                        cur_ofs = 0;
                        if (cb_pos >= cb_end)
                                break;
                }
                /* If we have a partial final page, deal with it now. */
                if (cb_max_ofs && cb_pos < cb_end) {
                        page = pages[cur_page];
                        if (page)
                                memcpy(page_address(page) + cur_ofs, cb_pos,
                                                cb_max_ofs - cur_ofs);
                        cb_pos += cb_max_ofs - cur_ofs;
                        cur_ofs = cb_max_ofs;
                }
                /* We can sleep from now on, so drop lock. */
                mutex_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_local(page_address(page));
                                SetPageUptodate(page);
                                unlock_page(page);
                                if (cur2_page == xpage)
                                        xpage_done = 1;
                                else
                                        put_page(page);
                                pages[cur2_page] = NULL;
                        }
                        cb_pos2 += PAGE_SIZE - cur_ofs2;
                        cur_ofs2 = 0;
                        if (cb_pos2 >= cb_end)
                                break;
                }
        } else {
                /* Compressed cb, decompress it into the destination page(s). */
                unsigned int prev_cur_page = cur_page;

                ntfs_debug("Found compressed compression block.");
                err = ntfs_decompress(pages, completed_pages, &cur_page,
                                &cur_ofs, cb_max_page, cb_max_ofs, xpage,
                                &xpage_done, cb_pos, cb_size - (cb_pos - cb),
                                i_size, initialized_size);
                /*
                 * We can sleep from now on, lock already dropped by
                 * ntfs_decompress().
                 */
                if (err) {
                        ntfs_error(vol->sb,
                                "ntfs_decompress() failed in inode 0x%llx 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_local(page_address(page));
                                        unlock_page(page);
                                        if (prev_cur_page != xpage)
                                                put_page(page);
                                        pages[prev_cur_page] = NULL;
                                }
                        }
                }
        }

        /* Do we have more work to do? */
        if (nr_cbs)
                goto do_next_cb;

        /* 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%llx, page index 0x%lx.",
                                ni->mft_no, page->__folio_index);
                        flush_dcache_page(page);
                        kunmap_local(page_address(page));
                        unlock_page(page);
                        if (cur_page != xpage)
                                put_page(page);
                        pages[cur_page] = NULL;
                }
        }

        /* We no longer need the list of pages. */
        kfree(pages);
        kfree(completed_pages);

        /* If we have completed the requested page, we return success. */
        if (likely(xpage_done))
                return 0;

        ntfs_debug("Failed. Returning error code %s.", err == -EOVERFLOW ?
                        "EOVERFLOW" : (!err ? "EIO" : "unknown error"));
        return err < 0 ? err : -EIO;

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;

read_err:
        up_read(&ni->runlist.lock);
        ntfs_error(vol->sb, "IO error while reading compressed data.");

err_out:
        for (i = cur_page; i < max_page; i++) {
                page = pages[i];
                if (page) {
                        flush_dcache_page(page);
                        kunmap_local(page_address(page));
                        unlock_page(page);
                        if (i != xpage)
                                put_page(page);
                }
        }
        kfree(pages);
        kfree(completed_pages);
        return -EIO;
}

/*
 * 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. These hashing constants
 * are used solely for the match-finding algorithm during compression.
 * They are NOT part of the on-disk format. The decompressor does not
 * utilize this hash.
 */
#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;

        /*
         * Unaligned access allowed, and little endian CPU.
         * Callers ensure that at least 4 (not 3) bytes are remaining.
         */
        str = *(const u32 *)p & 0xFFFFFF;
        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 = kvzalloc(sizeof(struct compress_context), GFP_NOFS);
        if (!pctx)
                return -ENOMEM;

        /*
         * 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'.
         */
        kvfree(pctx);
        return xout;
}

static int ntfs_write_cb(struct ntfs_inode *ni, loff_t pos, struct page **pages,
                int pages_per_cb)
{
        struct ntfs_volume *vol = ni->vol;
        char *outbuf = NULL, *pbuf, *inbuf;
        u32 compsz, p, insz = pages_per_cb << PAGE_SHIFT;
        s32 rounded, bio_size;
        unsigned int sz, bsz;
        bool fail = false, 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};
        struct page **pages_disk = NULL, *pg;
        s64 bio_lcn;
        struct runlist_element *rlc, *rl;
        int i, err;
        int pages_count = (round_up(ni->itype.compressed.block_size + 2 *
                (ni->itype.compressed.block_size / NTFS_SB_SIZE) + 2, PAGE_SIZE)) / PAGE_SIZE;
        size_t new_rl_count;
        struct bio *bio = NULL;
        loff_t new_length;
        s64 new_vcn;

        inbuf = vmap(pages, pages_per_cb, VM_MAP, PAGE_KERNEL_RO);
        if (!inbuf)
                return -ENOMEM;

        /* may need 2 extra bytes per block and 2 more bytes */
        pages_disk = kcalloc(pages_count, sizeof(struct page *), GFP_NOFS);
        if (!pages_disk) {
                vunmap(inbuf);
                return -ENOMEM;
        }

        for (i = 0; i < pages_count; i++) {
                pg = alloc_page(GFP_KERNEL);
                if (!pg) {
                        err = -ENOMEM;
                        goto out;
                }
                pages_disk[i] = pg;
                lock_page(pg);
                kmap_local_page(pg);
        }

        outbuf = vmap(pages_disk, pages_count, VM_MAP, PAGE_KERNEL);
        if (!outbuf) {
                err = -ENOMEM;
                goto out;
        }

        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 + vol->cluster_size + 2) >
                            ni->itype.compressed.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) {
                outbuf[compsz++] = 0;
                outbuf[compsz++] = 0;
                rounded = ((compsz - 1) | (vol->cluster_size - 1)) + 1;
                memset(&outbuf[compsz], 0, rounded - compsz);
                bio_size = rounded;
                pages = pages_disk;
        } else if (allzeroes) {
                err = 0;
                goto out;
        } else {
                bio_size = insz;
        }

        new_vcn = ntfs_bytes_to_cluster(vol,
                        pos & ~((loff_t)ni->itype.compressed.block_size - 1));
        new_length = ntfs_bytes_to_cluster(vol, round_up(bio_size, vol->cluster_size));

        err = ntfs_non_resident_attr_punch_hole(ni, new_vcn, ni->itype.compressed.block_clusters);
        if (err < 0)
                goto out;

        rlc = ntfs_cluster_alloc(vol, new_vcn, new_length, -1, DATA_ZONE,
                        false, true, true);
        if (IS_ERR(rlc)) {
                err = PTR_ERR(rlc);
                goto out;
        }

        bio_lcn = rlc->lcn;
        down_write(&ni->runlist.lock);
        rl = ntfs_runlists_merge(&ni->runlist, rlc, 0, &new_rl_count);
        if (IS_ERR(rl)) {
                up_write(&ni->runlist.lock);
                ntfs_error(vol->sb, "Failed to merge runlists");
                err = PTR_ERR(rl);
                if (ntfs_cluster_free_from_rl(vol, rlc))
                        ntfs_error(vol->sb, "Failed to free hot clusters.");
                kvfree(rlc);
                goto out;
        }

        ni->runlist.count = new_rl_count;
        ni->runlist.rl = rl;

        err = ntfs_attr_update_mapping_pairs(ni, 0);
        up_write(&ni->runlist.lock);
        if (err) {
                err = -EIO;
                goto out;
        }

        i = 0;
        while (bio_size > 0) {
                int page_size;

                if (bio_size >= PAGE_SIZE) {
                        page_size = PAGE_SIZE;
                        bio_size -= PAGE_SIZE;
                } else {
                        page_size = bio_size;
                        bio_size = 0;
                }

setup_bio:
                if (!bio) {
                        bio = bio_alloc(vol->sb->s_bdev, 1, REQ_OP_WRITE,
                                        GFP_NOIO);
                        bio->bi_iter.bi_sector =
                                ntfs_bytes_to_sector(vol,
                                                ntfs_cluster_to_bytes(vol, bio_lcn + i));
                }

                if (!bio_add_page(bio, pages[i], page_size, 0)) {
                        err = submit_bio_wait(bio);
                        bio_put(bio);
                        if (err)
                                goto out;
                        bio = NULL;
                        goto setup_bio;
                }
                i++;
        }

        err = submit_bio_wait(bio);
        bio_put(bio);
out:
        vunmap(outbuf);
        for (i = 0; i < pages_count; i++) {
                pg = pages_disk[i];
                if (pg) {
                        kunmap_local(page_address(pg));
                        unlock_page(pg);
                        put_page(pg);
                }
        }
        kfree(pages_disk);
        vunmap(inbuf);
        NInoSetFileNameDirty(ni);
        mark_mft_record_dirty(ni);

        return err;
}

int ntfs_compress_write(struct ntfs_inode *ni, loff_t pos, size_t count,
                struct iov_iter *from)
{
        struct folio *folio;
        struct page **pages = NULL, *page;
        int pages_per_cb = ni->itype.compressed.block_size >> PAGE_SHIFT;
        int cb_size = ni->itype.compressed.block_size, cb_off, err = 0;
        int i, ip;
        size_t written = 0;
        struct address_space *mapping = VFS_I(ni)->i_mapping;

        if (NInoCompressed(ni) && pos + count > ni->allocated_size) {
                int err;
                loff_t end = pos + count;

                err = ntfs_attr_expand(ni, end,
                                round_up(end, ni->itype.compressed.block_size));
                if (err)
                        return err;
        }

        pages = kmalloc_array(pages_per_cb, sizeof(struct page *), GFP_NOFS);
        if (!pages)
                return -ENOMEM;

        while (count) {
                pgoff_t index;
                size_t copied, bytes;
                int off;

                off = pos & (cb_size - 1);
                bytes = cb_size - off;
                if (bytes > count)
                        bytes = count;

                cb_off = pos & ~(cb_size - 1);
                index = cb_off >> PAGE_SHIFT;

                if (unlikely(fault_in_iov_iter_readable(from, bytes))) {
                        err = -EFAULT;
                        goto out;
                }

                for (i = 0; i < pages_per_cb; i++) {
                        folio = read_mapping_folio(mapping, index + i, NULL);
                        if (IS_ERR(folio)) {
                                for (ip = 0; ip < i; ip++) {
                                        folio_unlock(page_folio(pages[ip]));
                                        folio_put(page_folio(pages[ip]));
                                }
                                err = PTR_ERR(folio);
                                goto out;
                        }

                        folio_lock(folio);
                        pages[i] = folio_page(folio, 0);
                }

                WARN_ON(!bytes);
                copied = 0;
                ip = off >> PAGE_SHIFT;
                off = offset_in_page(pos);

                for (;;) {
                        size_t cp, tail = PAGE_SIZE - off;

                        page = pages[ip];
                        cp = copy_folio_from_iter_atomic(page_folio(page), off,
                                        min(tail, bytes), from);
                        flush_dcache_page(page);

                        copied += cp;
                        bytes -= cp;
                        if (!bytes || !cp)
                                break;

                        if (cp < tail) {
                                off += cp;
                        } else {
                                ip++;
                                off = 0;
                        }
                }

                err = ntfs_write_cb(ni, pos, pages, pages_per_cb);

                for (i = 0; i < pages_per_cb; i++) {
                        folio = page_folio(pages[i]);
                        if (i < ip) {
                                folio_clear_dirty(folio);
                                folio_mark_uptodate(folio);
                        }
                        folio_unlock(folio);
                        folio_put(folio);
                }

                if (err)
                        goto out;

                cond_resched();
                pos += copied;
                written += copied;
                count = iov_iter_count(from);
        }

out:
        kfree(pages);
        if (err < 0)
                written = err;

        return written;
}