NTFS: Change ntfs_attr_make_non_resident to take the attribute value size

[safe/jmp/linux-2.6] / fs / ntfs / attrib.c

/**
 * attrib.c - NTFS attribute operations.  Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2005 Anton Altaparmakov
 * Copyright (c) 2002 Richard Russon
 *
 * 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 Linux-NTFS
 * distribution in the file COPYING); if not, write to the Free Software
 * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/buffer_head.h>
#include <linux/swap.h>

#include "attrib.h"
#include "debug.h"
#include "layout.h"
#include "lcnalloc.h"
#include "malloc.h"
#include "mft.h"
#include "ntfs.h"
#include "types.h"

/**
 * ntfs_map_runlist_nolock - map (a part of) a runlist of an ntfs inode
 * @ni:         ntfs inode for which to map (part of) a runlist
 * @vcn:        map runlist part containing this vcn
 * @ctx:        active attribute search context if present or NULL if not
 *
 * Map the part of a runlist containing the @vcn of the ntfs inode @ni.
 *
 * If @ctx is specified, it is an active search context of @ni and its base mft
 * record.  This is needed when ntfs_map_runlist_nolock() encounters unmapped
 * runlist fragments and allows their mapping.  If you do not have the mft
 * record mapped, you can specify @ctx as NULL and ntfs_map_runlist_nolock()
 * will perform the necessary mapping and unmapping.
 *
 * Note, ntfs_map_runlist_nolock() saves the state of @ctx on entry and
 * restores it before returning.  Thus, @ctx will be left pointing to the same
 * attribute on return as on entry.  However, the actual pointers in @ctx may
 * point to different memory locations on return, so you must remember to reset
 * any cached pointers from the @ctx, i.e. after the call to
 * ntfs_map_runlist_nolock(), you will probably want to do:
 *      m = ctx->mrec;
 *      a = ctx->attr;
 * Assuming you cache ctx->attr in a variable @a of type ATTR_RECORD * and that
 * you cache ctx->mrec in a variable @m of type MFT_RECORD *.
 *
 * Return 0 on success and -errno on error.  There is one special error code
 * which is not an error as such.  This is -ENOENT.  It means that @vcn is out
 * of bounds of the runlist.
 *
 * Note the runlist can be NULL after this function returns if @vcn is zero and
 * the attribute has zero allocated size, i.e. there simply is no runlist.
 *
 * WARNING: If @ctx is supplied, regardless of whether success or failure is
 *          returned, you need to check IS_ERR(@ctx->mrec) and if TRUE the @ctx
 *          is no longer valid, i.e. you need to either call
 *          ntfs_attr_reinit_search_ctx() or ntfs_attr_put_search_ctx() on it.
 *          In that case PTR_ERR(@ctx->mrec) will give you the error code for
 *          why the mapping of the old inode failed.
 *
 * Locking: - The runlist described by @ni must be locked for writing on entry
 *            and is locked on return.  Note the runlist will be modified.
 *          - If @ctx is NULL, the base mft record of @ni must not be mapped on
 *            entry and it will be left unmapped on return.
 *          - If @ctx is not NULL, the base mft record must be mapped on entry
 *            and it will be left mapped on return.
 */
int ntfs_map_runlist_nolock(ntfs_inode *ni, VCN vcn, ntfs_attr_search_ctx *ctx)
{
        VCN end_vcn;
        unsigned long flags;
        ntfs_inode *base_ni;
        MFT_RECORD *m;
        ATTR_RECORD *a;
        runlist_element *rl;
        struct page *put_this_page = NULL;
        int err = 0;
        BOOL ctx_is_temporary, ctx_needs_reset;
        ntfs_attr_search_ctx old_ctx;

        ntfs_debug("Mapping runlist part containing vcn 0x%llx.",
                        (unsigned long long)vcn);
        if (!NInoAttr(ni))
                base_ni = ni;
        else
                base_ni = ni->ext.base_ntfs_ino;
        if (!ctx) {
                ctx_is_temporary = ctx_needs_reset = TRUE;
                m = map_mft_record(base_ni);
                if (IS_ERR(m))
                        return PTR_ERR(m);
                ctx = ntfs_attr_get_search_ctx(base_ni, m);
                if (unlikely(!ctx)) {
                        err = -ENOMEM;
                        goto err_out;
                }
        } else {
                VCN allocated_size_vcn;

                BUG_ON(IS_ERR(ctx->mrec));
                a = ctx->attr;
                BUG_ON(!a->non_resident);
                ctx_is_temporary = FALSE;
                end_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn);
                read_lock_irqsave(&ni->size_lock, flags);
                allocated_size_vcn = ni->allocated_size >>
                                ni->vol->cluster_size_bits;
                read_unlock_irqrestore(&ni->size_lock, flags);
                if (!a->data.non_resident.lowest_vcn && end_vcn <= 0)
                        end_vcn = allocated_size_vcn - 1;
                /*
                 * If we already have the attribute extent containing @vcn in
                 * @ctx, no need to look it up again.  We slightly cheat in
                 * that if vcn exceeds the allocated size, we will refuse to
                 * map the runlist below, so there is definitely no need to get
                 * the right attribute extent.
                 */
                if (vcn >= allocated_size_vcn || (a->type == ni->type &&
                                a->name_length == ni->name_len &&
                                !memcmp((u8*)a + le16_to_cpu(a->name_offset),
                                ni->name, ni->name_len) &&
                                sle64_to_cpu(a->data.non_resident.lowest_vcn)
                                <= vcn && end_vcn >= vcn))
                        ctx_needs_reset = FALSE;
                else {
                        /* Save the old search context. */
                        old_ctx = *ctx;
                        /*
                         * If the currently mapped (extent) inode is not the
                         * base inode we will unmap it when we reinitialize the
                         * search context which means we need to get a
                         * reference to the page containing the mapped mft
                         * record so we do not accidentally drop changes to the
                         * mft record when it has not been marked dirty yet.
                         */
                        if (old_ctx.base_ntfs_ino && old_ctx.ntfs_ino !=
                                        old_ctx.base_ntfs_ino) {
                                put_this_page = old_ctx.ntfs_ino->page;
                                page_cache_get(put_this_page);
                        }
                        /*
                         * Reinitialize the search context so we can lookup the
                         * needed attribute extent.
                         */
                        ntfs_attr_reinit_search_ctx(ctx);
                        ctx_needs_reset = TRUE;
                }
        }
        if (ctx_needs_reset) {
                err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
                                CASE_SENSITIVE, vcn, NULL, 0, ctx);
                if (unlikely(err)) {
                        if (err == -ENOENT)
                                err = -EIO;
                        goto err_out;
                }
                BUG_ON(!ctx->attr->non_resident);
        }
        a = ctx->attr;
        /*
         * Only decompress the mapping pairs if @vcn is inside it.  Otherwise
         * we get into problems when we try to map an out of bounds vcn because
         * we then try to map the already mapped runlist fragment and
         * ntfs_mapping_pairs_decompress() fails.
         */
        end_vcn = sle64_to_cpu(a->data.non_resident.highest_vcn) + 1;
        if (!a->data.non_resident.lowest_vcn && end_vcn == 1)
                end_vcn = sle64_to_cpu(a->data.non_resident.allocated_size) >>
                                ni->vol->cluster_size_bits;
        if (unlikely(vcn >= end_vcn)) {
                err = -ENOENT;
                goto err_out;
        }
        rl = ntfs_mapping_pairs_decompress(ni->vol, a, ni->runlist.rl);
        if (IS_ERR(rl))
                err = PTR_ERR(rl);
        else
                ni->runlist.rl = rl;
err_out:
        if (ctx_is_temporary) {
                if (likely(ctx))
                        ntfs_attr_put_search_ctx(ctx);
                unmap_mft_record(base_ni);
        } else if (ctx_needs_reset) {
                /*
                 * If there is no attribute list, restoring the search context
                 * is acomplished simply by copying the saved context back over
                 * the caller supplied context.  If there is an attribute list,
                 * things are more complicated as we need to deal with mapping
                 * of mft records and resulting potential changes in pointers.
                 */
                if (NInoAttrList(base_ni)) {
                        /*
                         * If the currently mapped (extent) inode is not the
                         * one we had before, we need to unmap it and map the
                         * old one.
                         */
                        if (ctx->ntfs_ino != old_ctx.ntfs_ino) {
                                /*
                                 * If the currently mapped inode is not the
                                 * base inode, unmap it.
                                 */
                                if (ctx->base_ntfs_ino && ctx->ntfs_ino !=
                                                ctx->base_ntfs_ino) {
                                        unmap_extent_mft_record(ctx->ntfs_ino);
                                        ctx->mrec = ctx->base_mrec;
                                        BUG_ON(!ctx->mrec);
                                }
                                /*
                                 * If the old mapped inode is not the base
                                 * inode, map it.
                                 */
                                if (old_ctx.base_ntfs_ino &&
                                                old_ctx.ntfs_ino !=
                                                old_ctx.base_ntfs_ino) {
retry_map:
                                        ctx->mrec = map_mft_record(
                                                        old_ctx.ntfs_ino);
                                        /*
                                         * Something bad has happened.  If out
                                         * of memory retry till it succeeds.
                                         * Any other errors are fatal and we
                                         * return the error code in ctx->mrec.
                                         * Let the caller deal with it...  We
                                         * just need to fudge things so the
                                         * caller can reinit and/or put the
                                         * search context safely.
                                         */
                                        if (IS_ERR(ctx->mrec)) {
                                                if (PTR_ERR(ctx->mrec) ==
                                                                -ENOMEM) {
                                                        schedule();
                                                        goto retry_map;
                                                } else
                                                        old_ctx.ntfs_ino =
                                                                old_ctx.
                                                                base_ntfs_ino;
                                        }
                                }
                        }
                        /* Update the changed pointers in the saved context. */
                        if (ctx->mrec != old_ctx.mrec) {
                                if (!IS_ERR(ctx->mrec))
                                        old_ctx.attr = (ATTR_RECORD*)(
                                                        (u8*)ctx->mrec +
                                                        ((u8*)old_ctx.attr -
                                                        (u8*)old_ctx.mrec));
                                old_ctx.mrec = ctx->mrec;
                        }
                }
                /* Restore the search context to the saved one. */
                *ctx = old_ctx;
                /*
                 * We drop the reference on the page we took earlier.  In the
                 * case that IS_ERR(ctx->mrec) is true this means we might lose
                 * some changes to the mft record that had been made between
                 * the last time it was marked dirty/written out and now.  This
                 * at this stage is not a problem as the mapping error is fatal
                 * enough that the mft record cannot be written out anyway and
                 * the caller is very likely to shutdown the whole inode
                 * immediately and mark the volume dirty for chkdsk to pick up
                 * the pieces anyway.
                 */
                if (put_this_page)
                        page_cache_release(put_this_page);
        }
        return err;
}

/**
 * ntfs_map_runlist - map (a part of) a runlist of an ntfs inode
 * @ni:         ntfs inode for which to map (part of) a runlist
 * @vcn:        map runlist part containing this vcn
 *
 * Map the part of a runlist containing the @vcn of the ntfs inode @ni.
 *
 * Return 0 on success and -errno on error.  There is one special error code
 * which is not an error as such.  This is -ENOENT.  It means that @vcn is out
 * of bounds of the runlist.
 *
 * Locking: - The runlist must be unlocked on entry and is unlocked on return.
 *          - This function takes the runlist lock for writing and may modify
 *            the runlist.
 */
int ntfs_map_runlist(ntfs_inode *ni, VCN vcn)
{
        int err = 0;

        down_write(&ni->runlist.lock);
        /* Make sure someone else didn't do the work while we were sleeping. */
        if (likely(ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn) <=
                        LCN_RL_NOT_MAPPED))
                err = ntfs_map_runlist_nolock(ni, vcn, NULL);
        up_write(&ni->runlist.lock);
        return err;
}

/**
 * ntfs_attr_vcn_to_lcn_nolock - convert a vcn into a lcn given an ntfs inode
 * @ni:                 ntfs inode of the attribute whose runlist to search
 * @vcn:                vcn to convert
 * @write_locked:       true if the runlist is locked for writing
 *
 * Find the virtual cluster number @vcn in the runlist of the ntfs attribute
 * described by the ntfs inode @ni and return the corresponding logical cluster
 * number (lcn).
 *
 * If the @vcn is not mapped yet, the attempt is made to map the attribute
 * extent containing the @vcn and the vcn to lcn conversion is retried.
 *
 * If @write_locked is true the caller has locked the runlist for writing and
 * if false for reading.
 *
 * Since lcns must be >= 0, we use negative return codes with special meaning:
 *
 * Return code  Meaning / Description
 * ==========================================
 *  LCN_HOLE    Hole / not allocated on disk.
 *  LCN_ENOENT  There is no such vcn in the runlist, i.e. @vcn is out of bounds.
 *  LCN_ENOMEM  Not enough memory to map runlist.
 *  LCN_EIO     Critical error (runlist/file is corrupt, i/o error, etc).
 *
 * Locking: - The runlist must be locked on entry and is left locked on return.
 *          - If @write_locked is FALSE, i.e. the runlist is locked for reading,
 *            the lock may be dropped inside the function so you cannot rely on
 *            the runlist still being the same when this function returns.
 */
LCN ntfs_attr_vcn_to_lcn_nolock(ntfs_inode *ni, const VCN vcn,
                const BOOL write_locked)
{
        LCN lcn;
        unsigned long flags;
        BOOL is_retry = FALSE;

        ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, %s_locked.",
                        ni->mft_no, (unsigned long long)vcn,
                        write_locked ? "write" : "read");
        BUG_ON(!ni);
        BUG_ON(!NInoNonResident(ni));
        BUG_ON(vcn < 0);
        if (!ni->runlist.rl) {
                read_lock_irqsave(&ni->size_lock, flags);
                if (!ni->allocated_size) {
                        read_unlock_irqrestore(&ni->size_lock, flags);
                        return LCN_ENOENT;
                }
                read_unlock_irqrestore(&ni->size_lock, flags);
        }
retry_remap:
        /* Convert vcn to lcn.  If that fails map the runlist and retry once. */
        lcn = ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn);
        if (likely(lcn >= LCN_HOLE)) {
                ntfs_debug("Done, lcn 0x%llx.", (long long)lcn);
                return lcn;
        }
        if (lcn != LCN_RL_NOT_MAPPED) {
                if (lcn != LCN_ENOENT)
                        lcn = LCN_EIO;
        } else if (!is_retry) {
                int err;

                if (!write_locked) {
                        up_read(&ni->runlist.lock);
                        down_write(&ni->runlist.lock);
                        if (unlikely(ntfs_rl_vcn_to_lcn(ni->runlist.rl, vcn) !=
                                        LCN_RL_NOT_MAPPED)) {
                                up_write(&ni->runlist.lock);
                                down_read(&ni->runlist.lock);
                                goto retry_remap;
                        }
                }
                err = ntfs_map_runlist_nolock(ni, vcn, NULL);
                if (!write_locked) {
                        up_write(&ni->runlist.lock);
                        down_read(&ni->runlist.lock);
                }
                if (likely(!err)) {
                        is_retry = TRUE;
                        goto retry_remap;
                }
                if (err == -ENOENT)
                        lcn = LCN_ENOENT;
                else if (err == -ENOMEM)
                        lcn = LCN_ENOMEM;
                else
                        lcn = LCN_EIO;
        }
        if (lcn != LCN_ENOENT)
                ntfs_error(ni->vol->sb, "Failed with error code %lli.",
                                (long long)lcn);
        return lcn;
}

/**
 * ntfs_attr_find_vcn_nolock - find a vcn in the runlist of an ntfs inode
 * @ni:         ntfs inode describing the runlist to search
 * @vcn:        vcn to find
 * @ctx:        active attribute search context if present or NULL if not
 *
 * Find the virtual cluster number @vcn in the runlist described by the ntfs
 * inode @ni and return the address of the runlist element containing the @vcn.
 *
 * If the @vcn is not mapped yet, the attempt is made to map the attribute
 * extent containing the @vcn and the vcn to lcn conversion is retried.
 *
 * If @ctx is specified, it is an active search context of @ni and its base mft
 * record.  This is needed when ntfs_attr_find_vcn_nolock() encounters unmapped
 * runlist fragments and allows their mapping.  If you do not have the mft
 * record mapped, you can specify @ctx as NULL and ntfs_attr_find_vcn_nolock()
 * will perform the necessary mapping and unmapping.
 *
 * Note, ntfs_attr_find_vcn_nolock() saves the state of @ctx on entry and
 * restores it before returning.  Thus, @ctx will be left pointing to the same
 * attribute on return as on entry.  However, the actual pointers in @ctx may
 * point to different memory locations on return, so you must remember to reset
 * any cached pointers from the @ctx, i.e. after the call to
 * ntfs_attr_find_vcn_nolock(), you will probably want to do:
 *      m = ctx->mrec;
 *      a = ctx->attr;
 * Assuming you cache ctx->attr in a variable @a of type ATTR_RECORD * and that
 * you cache ctx->mrec in a variable @m of type MFT_RECORD *.
 * Note you need to distinguish between the lcn of the returned runlist element
 * being >= 0 and LCN_HOLE.  In the later case you have to return zeroes on
 * read and allocate clusters on write.
 *
 * Return the runlist element containing the @vcn on success and
 * ERR_PTR(-errno) on error.  You need to test the return value with IS_ERR()
 * to decide if the return is success or failure and PTR_ERR() to get to the
 * error code if IS_ERR() is true.
 *
 * The possible error return codes are:
 *      -ENOENT - No such vcn in the runlist, i.e. @vcn is out of bounds.
 *      -ENOMEM - Not enough memory to map runlist.
 *      -EIO    - Critical error (runlist/file is corrupt, i/o error, etc).
 *
 * WARNING: If @ctx is supplied, regardless of whether success or failure is
 *          returned, you need to check IS_ERR(@ctx->mrec) and if TRUE the @ctx
 *          is no longer valid, i.e. you need to either call
 *          ntfs_attr_reinit_search_ctx() or ntfs_attr_put_search_ctx() on it.
 *          In that case PTR_ERR(@ctx->mrec) will give you the error code for
 *          why the mapping of the old inode failed.
 *
 * Locking: - The runlist described by @ni must be locked for writing on entry
 *            and is locked on return.  Note the runlist may be modified when
 *            needed runlist fragments need to be mapped.
 *          - If @ctx is NULL, the base mft record of @ni must not be mapped on
 *            entry and it will be left unmapped on return.
 *          - If @ctx is not NULL, the base mft record must be mapped on entry
 *            and it will be left mapped on return.
 */
runlist_element *ntfs_attr_find_vcn_nolock(ntfs_inode *ni, const VCN vcn,
                ntfs_attr_search_ctx *ctx)
{
        unsigned long flags;
        runlist_element *rl;
        int err = 0;
        BOOL is_retry = FALSE;

        ntfs_debug("Entering for i_ino 0x%lx, vcn 0x%llx, with%s ctx.",
                        ni->mft_no, (unsigned long long)vcn, ctx ? "" : "out");
        BUG_ON(!ni);
        BUG_ON(!NInoNonResident(ni));
        BUG_ON(vcn < 0);
        if (!ni->runlist.rl) {
                read_lock_irqsave(&ni->size_lock, flags);
                if (!ni->allocated_size) {
                        read_unlock_irqrestore(&ni->size_lock, flags);
                        return ERR_PTR(-ENOENT);
                }
                read_unlock_irqrestore(&ni->size_lock, flags);
        }
retry_remap:
        rl = ni->runlist.rl;
        if (likely(rl && vcn >= rl[0].vcn)) {
                while (likely(rl->length)) {
                        if (unlikely(vcn < rl[1].vcn)) {
                                if (likely(rl->lcn >= LCN_HOLE)) {
                                        ntfs_debug("Done.");
                                        return rl;
                                }
                                break;
                        }
                        rl++;
                }
                if (likely(rl->lcn != LCN_RL_NOT_MAPPED)) {
                        if (likely(rl->lcn == LCN_ENOENT))
                                err = -ENOENT;
                        else
                                err = -EIO;
                }
        }
        if (!err && !is_retry) {
                /*
                 * If the search context is invalid we cannot map the unmapped
                 * region.
                 */
                if (IS_ERR(ctx->mrec))
                        err = PTR_ERR(ctx->mrec);
                else {
                        /*
                         * The @vcn is in an unmapped region, map the runlist
                         * and retry.
                         */
                        err = ntfs_map_runlist_nolock(ni, vcn, ctx);
                        if (likely(!err)) {
                                is_retry = TRUE;
                                goto retry_remap;
                        }
                }
                if (err == -EINVAL)
                        err = -EIO;
        } else if (!err)
                err = -EIO;
        if (err != -ENOENT)
                ntfs_error(ni->vol->sb, "Failed with error code %i.", err);
        return ERR_PTR(err);
}

/**
 * ntfs_attr_find - find (next) attribute in mft record
 * @type:       attribute type to find
 * @name:       attribute name to find (optional, i.e. NULL means don't care)
 * @name_len:   attribute name length (only needed if @name present)
 * @ic:         IGNORE_CASE or CASE_SENSITIVE (ignored if @name not present)
 * @val:        attribute value to find (optional, resident attributes only)
 * @val_len:    attribute value length
 * @ctx:        search context with mft record and attribute to search from
 *
 * You should not need to call this function directly.  Use ntfs_attr_lookup()
 * instead.
 *
 * ntfs_attr_find() takes a search context @ctx as parameter and searches the
 * mft record specified by @ctx->mrec, beginning at @ctx->attr, for an
 * attribute of @type, optionally @name and @val.
 *
 * If the attribute is found, ntfs_attr_find() returns 0 and @ctx->attr will
 * point to the found attribute.
 *
 * If the attribute is not found, ntfs_attr_find() returns -ENOENT and
 * @ctx->attr will point to the attribute before which the attribute being
 * searched for would need to be inserted if such an action were to be desired.
 *
 * On actual error, ntfs_attr_find() returns -EIO.  In this case @ctx->attr is
 * undefined and in particular do not rely on it not changing.
 *
 * If @ctx->is_first is TRUE, the search begins with @ctx->attr itself.  If it
 * is FALSE, the search begins after @ctx->attr.
 *
 * If @ic is IGNORE_CASE, the @name comparisson is not case sensitive and
 * @ctx->ntfs_ino must be set to the ntfs inode to which the mft record
 * @ctx->mrec belongs.  This is so we can get at the ntfs volume and hence at
 * the upcase table.  If @ic is CASE_SENSITIVE, the comparison is case
 * sensitive.  When @name is present, @name_len is the @name length in Unicode
 * characters.
 *
 * If @name is not present (NULL), we assume that the unnamed attribute is
 * being searched for.
 *
 * Finally, the resident attribute value @val is looked for, if present.  If
 * @val is not present (NULL), @val_len is ignored.
 *
 * ntfs_attr_find() only searches the specified mft record and it ignores the
 * presence of an attribute list attribute (unless it is the one being searched
 * for, obviously).  If you need to take attribute lists into consideration,
 * use ntfs_attr_lookup() instead (see below).  This also means that you cannot
 * use ntfs_attr_find() to search for extent records of non-resident
 * attributes, as extents with lowest_vcn != 0 are usually described by the
 * attribute list attribute only. - Note that it is possible that the first
 * extent is only in the attribute list while the last extent is in the base
 * mft record, so do not rely on being able to find the first extent in the
 * base mft record.
 *
 * Warning: Never use @val when looking for attribute types which can be
 *          non-resident as this most likely will result in a crash!
 */
static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
                const u32 name_len, const IGNORE_CASE_BOOL ic,
                const u8 *val, const u32 val_len, ntfs_attr_search_ctx *ctx)
{
        ATTR_RECORD *a;
        ntfs_volume *vol = ctx->ntfs_ino->vol;
        ntfschar *upcase = vol->upcase;
        u32 upcase_len = vol->upcase_len;

        /*
         * Iterate over attributes in mft record starting at @ctx->attr, or the
         * attribute following that, if @ctx->is_first is TRUE.
         */
        if (ctx->is_first) {
                a = ctx->attr;
                ctx->is_first = FALSE;
        } else
                a = (ATTR_RECORD*)((u8*)ctx->attr +
                                le32_to_cpu(ctx->attr->length));
        for (;; a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
                if ((u8*)a < (u8*)ctx->mrec || (u8*)a > (u8*)ctx->mrec +
                                le32_to_cpu(ctx->mrec->bytes_allocated))
                        break;
                ctx->attr = a;
                if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
                                a->type == AT_END))
                        return -ENOENT;
                if (unlikely(!a->length))
                        break;
                if (a->type != type)
                        continue;
                /*
                 * If @name is present, compare the two names.  If @name is
                 * missing, assume we want an unnamed attribute.
                 */
                if (!name) {
                        /* The search failed if the found attribute is named. */
                        if (a->name_length)
                                return -ENOENT;
                } else if (!ntfs_are_names_equal(name, name_len,
                            (ntfschar*)((u8*)a + le16_to_cpu(a->name_offset)),
                            a->name_length, ic, upcase, upcase_len)) {
                        register int rc;

                        rc = ntfs_collate_names(name, name_len,
                                        (ntfschar*)((u8*)a +
                                        le16_to_cpu(a->name_offset)),
                                        a->name_length, 1, IGNORE_CASE,
                                        upcase, upcase_len);
                        /*
                         * If @name collates before a->name, there is no
                         * matching attribute.
                         */
                        if (rc == -1)
                                return -ENOENT;
                        /* If the strings are not equal, continue search. */
                        if (rc)
                                continue;
                        rc = ntfs_collate_names(name, name_len,
                                        (ntfschar*)((u8*)a +
                                        le16_to_cpu(a->name_offset)),
                                        a->name_length, 1, CASE_SENSITIVE,
                                        upcase, upcase_len);
                        if (rc == -1)
                                return -ENOENT;
                        if (rc)
                                continue;
                }
                /*
                 * The names match or @name not present and attribute is
                 * unnamed.  If no @val specified, we have found the attribute
                 * and are done.
                 */
                if (!val)
                        return 0;
                /* @val is present; compare values. */
                else {
                        register int rc;

                        rc = memcmp(val, (u8*)a + le16_to_cpu(
                                        a->data.resident.value_offset),
                                        min_t(u32, val_len, le32_to_cpu(
                                        a->data.resident.value_length)));
                        /*
                         * If @val collates before the current attribute's
                         * value, there is no matching attribute.
                         */
                        if (!rc) {
                                register u32 avl;

                                avl = le32_to_cpu(
                                                a->data.resident.value_length);
                                if (val_len == avl)
                                        return 0;
                                if (val_len < avl)
                                        return -ENOENT;
                        } else if (rc < 0)
                                return -ENOENT;
                }
        }
        ntfs_error(vol->sb, "Inode is corrupt.  Run chkdsk.");
        NVolSetErrors(vol);
        return -EIO;
}

/**
 * load_attribute_list - load an attribute list into memory
 * @vol:                ntfs volume from which to read
 * @runlist:            runlist of the attribute list
 * @al_start:           destination buffer
 * @size:               size of the destination buffer in bytes
 * @initialized_size:   initialized size of the attribute list
 *
 * Walk the runlist @runlist and load all clusters from it copying them into
 * the linear buffer @al. The maximum number of bytes copied to @al is @size
 * bytes. Note, @size does not need to be a multiple of the cluster size. If
 * @initialized_size is less than @size, the region in @al between
 * @initialized_size and @size will be zeroed and not read from disk.
 *
 * Return 0 on success or -errno on error.
 */
int load_attribute_list(ntfs_volume *vol, runlist *runlist, u8 *al_start,
                const s64 size, const s64 initialized_size)
{
        LCN lcn;
        u8 *al = al_start;
        u8 *al_end = al + initialized_size;
        runlist_element *rl;
        struct buffer_head *bh;
        struct super_block *sb;
        unsigned long block_size;
        unsigned long block, max_block;
        int err = 0;
        unsigned char block_size_bits;

        ntfs_debug("Entering.");
        if (!vol || !runlist || !al || size <= 0 || initialized_size < 0 ||
                        initialized_size > size)
                return -EINVAL;
        if (!initialized_size) {
                memset(al, 0, size);
                return 0;
        }
        sb = vol->sb;
        block_size = sb->s_blocksize;
        block_size_bits = sb->s_blocksize_bits;
        down_read(&runlist->lock);
        rl = runlist->rl;
        if (!rl) {
                ntfs_error(sb, "Cannot read attribute list since runlist is "
                                "missing.");
                goto err_out;   
        }
        /* Read all clusters specified by the runlist one run at a time. */
        while (rl->length) {
                lcn = ntfs_rl_vcn_to_lcn(rl, rl->vcn);
                ntfs_debug("Reading vcn = 0x%llx, lcn = 0x%llx.",
                                (unsigned long long)rl->vcn,
                                (unsigned long long)lcn);
                /* The attribute list cannot be sparse. */
                if (lcn < 0) {
                        ntfs_error(sb, "ntfs_rl_vcn_to_lcn() failed.  Cannot "
                                        "read attribute list.");
                        goto err_out;
                }
                block = lcn << vol->cluster_size_bits >> block_size_bits;
                /* Read the run from device in chunks of block_size bytes. */
                max_block = block + (rl->length << vol->cluster_size_bits >>
                                block_size_bits);
                ntfs_debug("max_block = 0x%lx.", max_block);
                do {
                        ntfs_debug("Reading block = 0x%lx.", block);
                        bh = sb_bread(sb, block);
                        if (!bh) {
                                ntfs_error(sb, "sb_bread() failed. Cannot "
                                                "read attribute list.");
                                goto err_out;
                        }
                        if (al + block_size >= al_end)
                                goto do_final;
                        memcpy(al, bh->b_data, block_size);
                        brelse(bh);
                        al += block_size;
                } while (++block < max_block);
                rl++;
        }
        if (initialized_size < size) {
initialize:
                memset(al_start + initialized_size, 0, size - initialized_size);
        }
done:
        up_read(&runlist->lock);
        return err;
do_final:
        if (al < al_end) {
                /*
                 * Partial block.
                 *
                 * Note: The attribute list can be smaller than its allocation
                 * by multiple clusters.  This has been encountered by at least
                 * two people running Windows XP, thus we cannot do any
                 * truncation sanity checking here. (AIA)
                 */
                memcpy(al, bh->b_data, al_end - al);
                brelse(bh);
                if (initialized_size < size)
                        goto initialize;
                goto done;
        }
        brelse(bh);
        /* Real overflow! */
        ntfs_error(sb, "Attribute list buffer overflow. Read attribute list "
                        "is truncated.");
err_out:
        err = -EIO;
        goto done;
}

/**
 * ntfs_external_attr_find - find an attribute in the attribute list of an inode
 * @type:       attribute type to find
 * @name:       attribute name to find (optional, i.e. NULL means don't care)
 * @name_len:   attribute name length (only needed if @name present)
 * @ic:         IGNORE_CASE or CASE_SENSITIVE (ignored if @name not present)
 * @lowest_vcn: lowest vcn to find (optional, non-resident attributes only)
 * @val:        attribute value to find (optional, resident attributes only)
 * @val_len:    attribute value length
 * @ctx:        search context with mft record and attribute to search from
 *
 * You should not need to call this function directly.  Use ntfs_attr_lookup()
 * instead.
 *
 * Find an attribute by searching the attribute list for the corresponding
 * attribute list entry.  Having found the entry, map the mft record if the
 * attribute is in a different mft record/inode, ntfs_attr_find() the attribute
 * in there and return it.
 *
 * On first search @ctx->ntfs_ino must be the base mft record and @ctx must
 * have been obtained from a call to ntfs_attr_get_search_ctx().  On subsequent
 * calls @ctx->ntfs_ino can be any extent inode, too (@ctx->base_ntfs_ino is
 * then the base inode).
 *
 * After finishing with the attribute/mft record you need to call
 * ntfs_attr_put_search_ctx() to cleanup the search context (unmapping any
 * mapped inodes, etc).
 *
 * If the attribute is found, ntfs_external_attr_find() returns 0 and
 * @ctx->attr will point to the found attribute.  @ctx->mrec will point to the
 * mft record in which @ctx->attr is located and @ctx->al_entry will point to
 * the attribute list entry for the attribute.
 *
 * If the attribute is not found, ntfs_external_attr_find() returns -ENOENT and
 * @ctx->attr will point to the attribute in the base mft record before which
 * the attribute being searched for would need to be inserted if such an action
 * were to be desired.  @ctx->mrec will point to the mft record in which
 * @ctx->attr is located and @ctx->al_entry will point to the attribute list
 * entry of the attribute before which the attribute being searched for would
 * need to be inserted if such an action were to be desired.
 *
 * Thus to insert the not found attribute, one wants to add the attribute to
 * @ctx->mrec (the base mft record) and if there is not enough space, the
 * attribute should be placed in a newly allocated extent mft record.  The
 * attribute list entry for the inserted attribute should be inserted in the
 * attribute list attribute at @ctx->al_entry.
 *
 * On actual error, ntfs_external_attr_find() returns -EIO.  In this case
 * @ctx->attr is undefined and in particular do not rely on it not changing.
 */
static int ntfs_external_attr_find(const ATTR_TYPE type,
                const ntfschar *name, const u32 name_len,
                const IGNORE_CASE_BOOL ic, const VCN lowest_vcn,
                const u8 *val, const u32 val_len, ntfs_attr_search_ctx *ctx)
{
        ntfs_inode *base_ni, *ni;
        ntfs_volume *vol;
        ATTR_LIST_ENTRY *al_entry, *next_al_entry;
        u8 *al_start, *al_end;
        ATTR_RECORD *a;
        ntfschar *al_name;
        u32 al_name_len;
        int err = 0;
        static const char *es = " Unmount and run chkdsk.";

        ni = ctx->ntfs_ino;
        base_ni = ctx->base_ntfs_ino;
        ntfs_debug("Entering for inode 0x%lx, type 0x%x.", ni->mft_no, type);
        if (!base_ni) {
                /* First call happens with the base mft record. */
                base_ni = ctx->base_ntfs_ino = ctx->ntfs_ino;
                ctx->base_mrec = ctx->mrec;
        }
        if (ni == base_ni)
                ctx->base_attr = ctx->attr;
        if (type == AT_END)
                goto not_found;
        vol = base_ni->vol;
        al_start = base_ni->attr_list;
        al_end = al_start + base_ni->attr_list_size;
        if (!ctx->al_entry)
                ctx->al_entry = (ATTR_LIST_ENTRY*)al_start;
        /*
         * Iterate over entries in attribute list starting at @ctx->al_entry,
         * or the entry following that, if @ctx->is_first is TRUE.
         */
        if (ctx->is_first) {
                al_entry = ctx->al_entry;
                ctx->is_first = FALSE;
        } else
                al_entry = (ATTR_LIST_ENTRY*)((u8*)ctx->al_entry +
                                le16_to_cpu(ctx->al_entry->length));
        for (;; al_entry = next_al_entry) {
                /* Out of bounds check. */
                if ((u8*)al_entry < base_ni->attr_list ||
                                (u8*)al_entry > al_end)
                        break;  /* Inode is corrupt. */
                ctx->al_entry = al_entry;
                /* Catch the end of the attribute list. */
                if ((u8*)al_entry == al_end)
                        goto not_found;
                if (!al_entry->length)
                        break;
                if ((u8*)al_entry + 6 > al_end || (u8*)al_entry +
                                le16_to_cpu(al_entry->length) > al_end)
                        break;
                next_al_entry = (ATTR_LIST_ENTRY*)((u8*)al_entry +
                                le16_to_cpu(al_entry->length));
                if (le32_to_cpu(al_entry->type) > le32_to_cpu(type))
                        goto not_found;
                if (type != al_entry->type)
                        continue;
                /*
                 * If @name is present, compare the two names.  If @name is
                 * missing, assume we want an unnamed attribute.
                 */
                al_name_len = al_entry->name_length;
                al_name = (ntfschar*)((u8*)al_entry + al_entry->name_offset);
                if (!name) {
                        if (al_name_len)
                                goto not_found;
                } else if (!ntfs_are_names_equal(al_name, al_name_len, name,
                                name_len, ic, vol->upcase, vol->upcase_len)) {
                        register int rc;

                        rc = ntfs_collate_names(name, name_len, al_name,
                                        al_name_len, 1, IGNORE_CASE,
                                        vol->upcase, vol->upcase_len);
                        /*
                         * If @name collates before al_name, there is no
                         * matching attribute.
                         */
                        if (rc == -1)
                                goto not_found;
                        /* If the strings are not equal, continue search. */
                        if (rc)
                                continue;
                        /*
                         * FIXME: Reverse engineering showed 0, IGNORE_CASE but
                         * that is inconsistent with ntfs_attr_find().  The
                         * subsequent rc checks were also different.  Perhaps I
                         * made a mistake in one of the two.  Need to recheck
                         * which is correct or at least see what is going on...
                         * (AIA)
                         */
                        rc = ntfs_collate_names(name, name_len, al_name,
                                        al_name_len, 1, CASE_SENSITIVE,
                                        vol->upcase, vol->upcase_len);
                        if (rc == -1)
                                goto not_found;
                        if (rc)
                                continue;
                }
                /*
                 * The names match or @name not present and attribute is
                 * unnamed.  Now check @lowest_vcn.  Continue search if the
                 * next attribute list entry still fits @lowest_vcn.  Otherwise
                 * we have reached the right one or the search has failed.
                 */
                if (lowest_vcn && (u8*)next_al_entry >= al_start            &&
                                (u8*)next_al_entry + 6 < al_end             &&
                                (u8*)next_al_entry + le16_to_cpu(
                                        next_al_entry->length) <= al_end    &&
                                sle64_to_cpu(next_al_entry->lowest_vcn) <=
                                        lowest_vcn                          &&
                                next_al_entry->type == al_entry->type       &&
                                next_al_entry->name_length == al_name_len   &&
                                ntfs_are_names_equal((ntfschar*)((u8*)
                                        next_al_entry +
                                        next_al_entry->name_offset),
                                        next_al_entry->name_length,
                                        al_name, al_name_len, CASE_SENSITIVE,
                                        vol->upcase, vol->upcase_len))
                        continue;
                if (MREF_LE(al_entry->mft_reference) == ni->mft_no) {
                        if (MSEQNO_LE(al_entry->mft_reference) != ni->seq_no) {
                                ntfs_error(vol->sb, "Found stale mft "
                                                "reference in attribute list "
                                                "of base inode 0x%lx.%s",
                                                base_ni->mft_no, es);
                                err = -EIO;
                                break;
                        }
                } else { /* Mft references do not match. */
                        /* If there is a mapped record unmap it first. */
                        if (ni != base_ni)
                                unmap_extent_mft_record(ni);
                        /* Do we want the base record back? */
                        if (MREF_LE(al_entry->mft_reference) ==
                                        base_ni->mft_no) {
                                ni = ctx->ntfs_ino = base_ni;
                                ctx->mrec = ctx->base_mrec;
                        } else {
                                /* We want an extent record. */
                                ctx->mrec = map_extent_mft_record(base_ni,
                                                le64_to_cpu(
                                                al_entry->mft_reference), &ni);
                                if (IS_ERR(ctx->mrec)) {
                                        ntfs_error(vol->sb, "Failed to map "
                                                        "extent mft record "
                                                        "0x%lx of base inode "
                                                        "0x%lx.%s",
                                                        MREF_LE(al_entry->
                                                        mft_reference),
                                                        base_ni->mft_no, es);
                                        err = PTR_ERR(ctx->mrec);
                                        if (err == -ENOENT)
                                                err = -EIO;
                                        /* Cause @ctx to be sanitized below. */
                                        ni = NULL;
                                        break;
                                }
                                ctx->ntfs_ino = ni;
                        }
                        ctx->attr = (ATTR_RECORD*)((u8*)ctx->mrec +
                                        le16_to_cpu(ctx->mrec->attrs_offset));
                }
                /*
                 * ctx->vfs_ino, ctx->mrec, and ctx->attr now point to the
                 * mft record containing the attribute represented by the
                 * current al_entry.
                 */
                /*
                 * We could call into ntfs_attr_find() to find the right
                 * attribute in this mft record but this would be less
                 * efficient and not quite accurate as ntfs_attr_find() ignores
                 * the attribute instance numbers for example which become
                 * important when one plays with attribute lists.  Also,
                 * because a proper match has been found in the attribute list
                 * entry above, the comparison can now be optimized.  So it is
                 * worth re-implementing a simplified ntfs_attr_find() here.
                 */
                a = ctx->attr;
                /*
                 * Use a manual loop so we can still use break and continue
                 * with the same meanings as above.
                 */
do_next_attr_loop:
                if ((u8*)a < (u8*)ctx->mrec || (u8*)a > (u8*)ctx->mrec +
                                le32_to_cpu(ctx->mrec->bytes_allocated))
                        break;
                if (a->type == AT_END)
                        continue;
                if (!a->length)
                        break;
                if (al_entry->instance != a->instance)
                        goto do_next_attr;
                /*
                 * If the type and/or the name are mismatched between the
                 * attribute list entry and the attribute record, there is
                 * corruption so we break and return error EIO.
                 */
                if (al_entry->type != a->type)
                        break;
                if (!ntfs_are_names_equal((ntfschar*)((u8*)a +
                                le16_to_cpu(a->name_offset)), a->name_length,
                                al_name, al_name_len, CASE_SENSITIVE,
                                vol->upcase, vol->upcase_len))
                        break;
                ctx->attr = a;
                /*
                 * If no @val specified or @val specified and it matches, we
                 * have found it!
                 */
                if (!val || (!a->non_resident && le32_to_cpu(
                                a->data.resident.value_length) == val_len &&
                                !memcmp((u8*)a +
                                le16_to_cpu(a->data.resident.value_offset),
                                val, val_len))) {
                        ntfs_debug("Done, found.");
                        return 0;
                }
do_next_attr:
                /* Proceed to the next attribute in the current mft record. */
                a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length));
                goto do_next_attr_loop;
        }
        if (!err) {
                ntfs_error(vol->sb, "Base inode 0x%lx contains corrupt "
                                "attribute list attribute.%s", base_ni->mft_no,
                                es);
                err = -EIO;
        }
        if (ni != base_ni) {
                if (ni)
                        unmap_extent_mft_record(ni);
                ctx->ntfs_ino = base_ni;
                ctx->mrec = ctx->base_mrec;
                ctx->attr = ctx->base_attr;
        }
        if (err != -ENOMEM)
                NVolSetErrors(vol);
        return err;
not_found:
        /*
         * If we were looking for AT_END, we reset the search context @ctx and
         * use ntfs_attr_find() to seek to the end of the base mft record.
         */
        if (type == AT_END) {
                ntfs_attr_reinit_search_ctx(ctx);
                return ntfs_attr_find(AT_END, name, name_len, ic, val, val_len,
                                ctx);
        }
        /*
         * The attribute was not found.  Before we return, we want to ensure
         * @ctx->mrec and @ctx->attr indicate the position at which the
         * attribute should be inserted in the base mft record.  Since we also
         * want to preserve @ctx->al_entry we cannot reinitialize the search
         * context using ntfs_attr_reinit_search_ctx() as this would set
         * @ctx->al_entry to NULL.  Thus we do the necessary bits manually (see
         * ntfs_attr_init_search_ctx() below).  Note, we _only_ preserve
         * @ctx->al_entry as the remaining fields (base_*) are identical to
         * their non base_ counterparts and we cannot set @ctx->base_attr
         * correctly yet as we do not know what @ctx->attr will be set to by
         * the call to ntfs_attr_find() below.
         */
        if (ni != base_ni)
                unmap_extent_mft_record(ni);
        ctx->mrec = ctx->base_mrec;
        ctx->attr = (ATTR_RECORD*)((u8*)ctx->mrec +
                        le16_to_cpu(ctx->mrec->attrs_offset));
        ctx->is_first = TRUE;
        ctx->ntfs_ino = base_ni;
        ctx->base_ntfs_ino = NULL;
        ctx->base_mrec = NULL;
        ctx->base_attr = NULL;
        /*
         * In case there are multiple matches in the base mft record, need to
         * keep enumerating until we get an attribute not found response (or
         * another error), otherwise we would keep returning the same attribute
         * over and over again and all programs using us for enumeration would
         * lock up in a tight loop.
         */
        do {
                err = ntfs_attr_find(type, name, name_len, ic, val, val_len,
                                ctx);
        } while (!err);
        ntfs_debug("Done, not found.");
        return err;
}

/**
 * ntfs_attr_lookup - find an attribute in an ntfs inode
 * @type:       attribute type to find
 * @name:       attribute name to find (optional, i.e. NULL means don't care)
 * @name_len:   attribute name length (only needed if @name present)
 * @ic:         IGNORE_CASE or CASE_SENSITIVE (ignored if @name not present)
 * @lowest_vcn: lowest vcn to find (optional, non-resident attributes only)
 * @val:        attribute value to find (optional, resident attributes only)
 * @val_len:    attribute value length
 * @ctx:        search context with mft record and attribute to search from
 *
 * Find an attribute in an ntfs inode.  On first search @ctx->ntfs_ino must
 * be the base mft record and @ctx must have been obtained from a call to
 * ntfs_attr_get_search_ctx().
 *
 * This function transparently handles attribute lists and @ctx is used to
 * continue searches where they were left off at.
 *
 * After finishing with the attribute/mft record you need to call
 * ntfs_attr_put_search_ctx() to cleanup the search context (unmapping any
 * mapped inodes, etc).
 *
 * Return 0 if the search was successful and -errno if not.
 *
 * When 0, @ctx->attr is the found attribute and it is in mft record
 * @ctx->mrec.  If an attribute list attribute is present, @ctx->al_entry is
 * the attribute list entry of the found attribute.
 *
 * When -ENOENT, @ctx->attr is the attribute which collates just after the
 * attribute being searched for, i.e. if one wants to add the attribute to the
 * mft record this is the correct place to insert it into.  If an attribute
 * list attribute is present, @ctx->al_entry is the attribute list entry which
 * collates just after the attribute list entry of the attribute being searched
 * for, i.e. if one wants to add the attribute to the mft record this is the
 * correct place to insert its attribute list entry into.
 *
 * When -errno != -ENOENT, an error occured during the lookup.  @ctx->attr is
 * then undefined and in particular you should not rely on it not changing.
 */
int ntfs_attr_lookup(const ATTR_TYPE type, const ntfschar *name,
                const u32 name_len, const IGNORE_CASE_BOOL ic,
                const VCN lowest_vcn, const u8 *val, const u32 val_len,
                ntfs_attr_search_ctx *ctx)
{
        ntfs_inode *base_ni;

        ntfs_debug("Entering.");
        BUG_ON(IS_ERR(ctx->mrec));
        if (ctx->base_ntfs_ino)
                base_ni = ctx->base_ntfs_ino;
        else
                base_ni = ctx->ntfs_ino;
        /* Sanity check, just for debugging really. */
        BUG_ON(!base_ni);
        if (!NInoAttrList(base_ni) || type == AT_ATTRIBUTE_LIST)
                return ntfs_attr_find(type, name, name_len, ic, val, val_len,
                                ctx);
        return ntfs_external_attr_find(type, name, name_len, ic, lowest_vcn,
                        val, val_len, ctx);
}

/**
 * ntfs_attr_init_search_ctx - initialize an attribute search context
 * @ctx:        attribute search context to initialize
 * @ni:         ntfs inode with which to initialize the search context
 * @mrec:       mft record with which to initialize the search context
 *
 * Initialize the attribute search context @ctx with @ni and @mrec.
 */
static inline void ntfs_attr_init_search_ctx(ntfs_attr_search_ctx *ctx,
                ntfs_inode *ni, MFT_RECORD *mrec)
{
        *ctx = (ntfs_attr_search_ctx) {
                .mrec = mrec,
                /* Sanity checks are performed elsewhere. */
                .attr = (ATTR_RECORD*)((u8*)mrec +
                                le16_to_cpu(mrec->attrs_offset)),
                .is_first = TRUE,
                .ntfs_ino = ni,
        };
}

/**
 * ntfs_attr_reinit_search_ctx - reinitialize an attribute search context
 * @ctx:        attribute search context to reinitialize
 *
 * Reinitialize the attribute search context @ctx, unmapping an associated
 * extent mft record if present, and initialize the search context again.
 *
 * This is used when a search for a new attribute is being started to reset
 * the search context to the beginning.
 */
void ntfs_attr_reinit_search_ctx(ntfs_attr_search_ctx *ctx)
{
        if (likely(!ctx->base_ntfs_ino)) {
                /* No attribute list. */
                ctx->is_first = TRUE;
                /* Sanity checks are performed elsewhere. */
                ctx->attr = (ATTR_RECORD*)((u8*)ctx->mrec +
                                le16_to_cpu(ctx->mrec->attrs_offset));
                /*
                 * This needs resetting due to ntfs_external_attr_find() which
                 * can leave it set despite having zeroed ctx->base_ntfs_ino.
                 */
                ctx->al_entry = NULL;
                return;
        } /* Attribute list. */
        if (ctx->ntfs_ino != ctx->base_ntfs_ino)
                unmap_extent_mft_record(ctx->ntfs_ino);
        ntfs_attr_init_search_ctx(ctx, ctx->base_ntfs_ino, ctx->base_mrec);
        return;
}

/**
 * ntfs_attr_get_search_ctx - allocate/initialize a new attribute search context
 * @ni:         ntfs inode with which to initialize the search context
 * @mrec:       mft record with which to initialize the search context
 *
 * Allocate a new attribute search context, initialize it with @ni and @mrec,
 * and return it. Return NULL if allocation failed.
 */
ntfs_attr_search_ctx *ntfs_attr_get_search_ctx(ntfs_inode *ni, MFT_RECORD *mrec)
{
        ntfs_attr_search_ctx *ctx;

        ctx = kmem_cache_alloc(ntfs_attr_ctx_cache, SLAB_NOFS);
        if (ctx)
                ntfs_attr_init_search_ctx(ctx, ni, mrec);
        return ctx;
}

/**
 * ntfs_attr_put_search_ctx - release an attribute search context
 * @ctx:        attribute search context to free
 *
 * Release the attribute search context @ctx, unmapping an associated extent
 * mft record if present.
 */
void ntfs_attr_put_search_ctx(ntfs_attr_search_ctx *ctx)
{
        if (ctx->base_ntfs_ino && ctx->ntfs_ino != ctx->base_ntfs_ino)
                unmap_extent_mft_record(ctx->ntfs_ino);
        kmem_cache_free(ntfs_attr_ctx_cache, ctx);
        return;
}

#ifdef NTFS_RW

/**
 * ntfs_attr_find_in_attrdef - find an attribute in the $AttrDef system file
 * @vol:        ntfs volume to which the attribute belongs
 * @type:       attribute type which to find
 *
 * Search for the attribute definition record corresponding to the attribute
 * @type in the $AttrDef system file.
 *
 * Return the attribute type definition record if found and NULL if not found.
 */
static ATTR_DEF *ntfs_attr_find_in_attrdef(const ntfs_volume *vol,
                const ATTR_TYPE type)
{
        ATTR_DEF *ad;

        BUG_ON(!vol->attrdef);
        BUG_ON(!type);
        for (ad = vol->attrdef; (u8*)ad - (u8*)vol->attrdef <
                        vol->attrdef_size && ad->type; ++ad) {
                /* We have not found it yet, carry on searching. */
                if (likely(le32_to_cpu(ad->type) < le32_to_cpu(type)))
                        continue;
                /* We found the attribute; return it. */
                if (likely(ad->type == type))
                        return ad;
                /* We have gone too far already.  No point in continuing. */
                break;
        }
        /* Attribute not found. */
        ntfs_debug("Attribute type 0x%x not found in $AttrDef.",
                        le32_to_cpu(type));
        return NULL;
}

/**
 * ntfs_attr_size_bounds_check - check a size of an attribute type for validity
 * @vol:        ntfs volume to which the attribute belongs
 * @type:       attribute type which to check
 * @size:       size which to check
 *
 * Check whether the @size in bytes is valid for an attribute of @type on the
 * ntfs volume @vol.  This information is obtained from $AttrDef system file.
 *
 * Return 0 if valid, -ERANGE if not valid, or -ENOENT if the attribute is not
 * listed in $AttrDef.
 */
int ntfs_attr_size_bounds_check(const ntfs_volume *vol, const ATTR_TYPE type,
                const s64 size)
{
        ATTR_DEF *ad;

        BUG_ON(size < 0);
        /*
         * $ATTRIBUTE_LIST has a maximum size of 256kiB, but this is not
         * listed in $AttrDef.
         */
        if (unlikely(type == AT_ATTRIBUTE_LIST && size > 256 * 1024))
                return -ERANGE;
        /* Get the $AttrDef entry for the attribute @type. */
        ad = ntfs_attr_find_in_attrdef(vol, type);
        if (unlikely(!ad))
                return -ENOENT;
        /* Do the bounds check. */
        if (((sle64_to_cpu(ad->min_size) > 0) &&
                        size < sle64_to_cpu(ad->min_size)) ||
                        ((sle64_to_cpu(ad->max_size) > 0) && size >
                        sle64_to_cpu(ad->max_size)))
                return -ERANGE;
        return 0;
}

/**
 * ntfs_attr_can_be_non_resident - check if an attribute can be non-resident
 * @vol:        ntfs volume to which the attribute belongs
 * @type:       attribute type which to check
 *
 * Check whether the attribute of @type on the ntfs volume @vol is allowed to
 * be non-resident.  This information is obtained from $AttrDef system file.
 *
 * Return 0 if the attribute is allowed to be non-resident, -EPERM if not, and
 * -ENOENT if the attribute is not listed in $AttrDef.
 */
int ntfs_attr_can_be_non_resident(const ntfs_volume *vol, const ATTR_TYPE type)
{
        ATTR_DEF *ad;

        /* Find the attribute definition record in $AttrDef. */
        ad = ntfs_attr_find_in_attrdef(vol, type);
        if (unlikely(!ad))
                return -ENOENT;
        /* Check the flags and return the result. */
        if (ad->flags & ATTR_DEF_RESIDENT)
                return -EPERM;
        return 0;
}

/**
 * ntfs_attr_can_be_resident - check if an attribute can be resident
 * @vol:        ntfs volume to which the attribute belongs
 * @type:       attribute type which to check
 *
 * Check whether the attribute of @type on the ntfs volume @vol is allowed to
 * be resident.  This information is derived from our ntfs knowledge and may
 * not be completely accurate, especially when user defined attributes are
 * present.  Basically we allow everything to be resident except for index
 * allocation and $EA attributes.
 *
 * Return 0 if the attribute is allowed to be non-resident and -EPERM if not.
 *
 * Warning: In the system file $MFT the attribute $Bitmap must be non-resident
 *          otherwise windows will not boot (blue screen of death)!  We cannot
 *          check for this here as we do not know which inode's $Bitmap is
 *          being asked about so the caller needs to special case this.
 */
int ntfs_attr_can_be_resident(const ntfs_volume *vol, const ATTR_TYPE type)
{
        if (type == AT_INDEX_ALLOCATION || type == AT_EA)
                return -EPERM;
        return 0;
}

/**
 * ntfs_attr_record_resize - resize an attribute record
 * @m:          mft record containing attribute record
 * @a:          attribute record to resize
 * @new_size:   new size in bytes to which to resize the attribute record @a
 *
 * Resize the attribute record @a, i.e. the resident part of the attribute, in
 * the mft record @m to @new_size bytes.
 *
 * Return 0 on success and -errno on error.  The following error codes are
 * defined:
 *      -ENOSPC - Not enough space in the mft record @m to perform the resize.
 *
 * Note: On error, no modifications have been performed whatsoever.
 *
 * Warning: If you make a record smaller without having copied all the data you
 *          are interested in the data may be overwritten.
 */
int ntfs_attr_record_resize(MFT_RECORD *m, ATTR_RECORD *a, u32 new_size)
{
        ntfs_debug("Entering for new_size %u.", new_size);
        /* Align to 8 bytes if it is not already done. */
        if (new_size & 7)
                new_size = (new_size + 7) & ~7;
        /* If the actual attribute length has changed, move things around. */
        if (new_size != le32_to_cpu(a->length)) {
                u32 new_muse = le32_to_cpu(m->bytes_in_use) -
                                le32_to_cpu(a->length) + new_size;
                /* Not enough space in this mft record. */
                if (new_muse > le32_to_cpu(m->bytes_allocated))
                        return -ENOSPC;
                /* Move attributes following @a to their new location. */
                memmove((u8*)a + new_size, (u8*)a + le32_to_cpu(a->length),
                                le32_to_cpu(m->bytes_in_use) - ((u8*)a -
                                (u8*)m) - le32_to_cpu(a->length));
                /* Adjust @m to reflect the change in used space. */
                m->bytes_in_use = cpu_to_le32(new_muse);
                /* Adjust @a to reflect the new size. */
                if (new_size >= offsetof(ATTR_REC, length) + sizeof(a->length))
                        a->length = cpu_to_le32(new_size);
        }
        return 0;
}

/**
 * ntfs_resident_attr_value_resize - resize the value of a resident attribute
 * @m:          mft record containing attribute record
 * @a:          attribute record whose value to resize
 * @new_size:   new size in bytes to which to resize the attribute value of @a
 *
 * Resize the value of the attribute @a in the mft record @m to @new_size bytes.
 * If the value is made bigger, the newly allocated space is cleared.
 *
 * Return 0 on success and -errno on error.  The following error codes are
 * defined:
 *      -ENOSPC - Not enough space in the mft record @m to perform the resize.
 *
 * Note: On error, no modifications have been performed whatsoever.
 *
 * Warning: If you make a record smaller without having copied all the data you
 *          are interested in the data may be overwritten.
 */
int ntfs_resident_attr_value_resize(MFT_RECORD *m, ATTR_RECORD *a,
                const u32 new_size)
{
        u32 old_size;

        /* Resize the resident part of the attribute record. */
        if (ntfs_attr_record_resize(m, a,
                        le16_to_cpu(a->data.resident.value_offset) + new_size))
                return -ENOSPC;
        /*
         * The resize succeeded!  If we made the attribute value bigger, clear
         * the area between the old size and @new_size.
         */
        old_size = le32_to_cpu(a->data.resident.value_length);
        if (new_size > old_size)
                memset((u8*)a + le16_to_cpu(a->data.resident.value_offset) +
                                old_size, 0, new_size - old_size);
        /* Finally update the length of the attribute value. */
        a->data.resident.value_length = cpu_to_le32(new_size);
        return 0;
}

/**
 * ntfs_attr_make_non_resident - convert a resident to a non-resident attribute
 * @ni:         ntfs inode describing the attribute to convert
 * @data_size:  size of the resident data to copy to the non-resident attribute
 *
 * Convert the resident ntfs attribute described by the ntfs inode @ni to a
 * non-resident one.
 *
 * @data_size must be equal to the attribute value size.  This is needed since
 * we need to know the size before we can map the mft record and our callers
 * always know it.  The reason we cannot simply read the size from the vfs
 * inode i_size is that this is not necessarily uptodate.  This happens when
 * ntfs_attr_make_non_resident() is called in the ->truncate call path(s).
 *
 * Return 0 on success and -errno on error.  The following error return codes
 * are defined:
 *      -EPERM  - The attribute is not allowed to be non-resident.
 *      -ENOMEM - Not enough memory.
 *      -ENOSPC - Not enough disk space.
 *      -EINVAL - Attribute not defined on the volume.
 *      -EIO    - I/o error or other error.
 * Note that -ENOSPC is also returned in the case that there is not enough
 * space in the mft record to do the conversion.  This can happen when the mft
 * record is already very full.  The caller is responsible for trying to make
 * space in the mft record and trying again.  FIXME: Do we need a separate
 * error return code for this kind of -ENOSPC or is it always worth trying
 * again in case the attribute may then fit in a resident state so no need to
 * make it non-resident at all?  Ho-hum...  (AIA)
 *
 * NOTE to self: No changes in the attribute list are required to move from
 *               a resident to a non-resident attribute.
 *
 * Locking: - The caller must hold i_sem on the inode.
 */
int ntfs_attr_make_non_resident(ntfs_inode *ni, const u32 data_size)
{
        s64 new_size;
        struct inode *vi = VFS_I(ni);
        ntfs_volume *vol = ni->vol;
        ntfs_inode *base_ni;
        MFT_RECORD *m;
        ATTR_RECORD *a;
        ntfs_attr_search_ctx *ctx;
        struct page *page;
        runlist_element *rl;
        u8 *kaddr;
        unsigned long flags;
        int mp_size, mp_ofs, name_ofs, arec_size, err, err2;
        u32 attr_size;
        u8 old_res_attr_flags;

        /* Check that the attribute is allowed to be non-resident. */
        err = ntfs_attr_can_be_non_resident(vol, ni->type);
        if (unlikely(err)) {
                if (err == -EPERM)
                        ntfs_debug("Attribute is not allowed to be "
                                        "non-resident.");
                else
                        ntfs_debug("Attribute not defined on the NTFS "
                                        "volume!");
                return err;
        }
        /*
         * FIXME: Compressed and encrypted attributes are not supported when
         * writing and we should never have gotten here for them.
         */
        BUG_ON(NInoCompressed(ni));
        BUG_ON(NInoEncrypted(ni));
        /*
         * The size needs to be aligned to a cluster boundary for allocation
         * purposes.
         */
        new_size = (data_size + vol->cluster_size - 1) &
                        ~(vol->cluster_size - 1);
        if (new_size > 0) {
                /*
                 * Will need the page later and since the page lock nests
                 * outside all ntfs locks, we need to get the page now.
                 */
                page = find_or_create_page(vi->i_mapping, 0,
                                mapping_gfp_mask(vi->i_mapping));
                if (unlikely(!page))
                        return -ENOMEM;
                /* Start by allocating clusters to hold the attribute value. */
                rl = ntfs_cluster_alloc(vol, 0, new_size >>
                                vol->cluster_size_bits, -1, DATA_ZONE, TRUE);
                if (IS_ERR(rl)) {
                        err = PTR_ERR(rl);
                        ntfs_debug("Failed to allocate cluster%s, error code "
                                        "%i.", (new_size >>
                                        vol->cluster_size_bits) > 1 ? "s" : "",
                                        err);
                        goto page_err_out;
                }
        } else {
                rl = NULL;
                page = NULL;
        }
        /* Determine the size of the mapping pairs array. */
        mp_size = ntfs_get_size_for_mapping_pairs(vol, rl, 0, -1);
        if (unlikely(mp_size < 0)) {
                err = mp_size;
                ntfs_debug("Failed to get size for mapping pairs array, error "
                                "code %i.", err);
                goto rl_err_out;
        }
        down_write(&ni->runlist.lock);
        if (!NInoAttr(ni))
                base_ni = ni;
        else
                base_ni = ni->ext.base_ntfs_ino;
        m = map_mft_record(base_ni);
        if (IS_ERR(m)) {
                err = PTR_ERR(m);
                m = NULL;
                ctx = NULL;
                goto err_out;
        }
        ctx = ntfs_attr_get_search_ctx(base_ni, m);
        if (unlikely(!ctx)) {
                err = -ENOMEM;
                goto err_out;
        }
        err = ntfs_attr_lookup(ni->type, ni->name, ni->name_len,
                        CASE_SENSITIVE, 0, NULL, 0, ctx);
        if (unlikely(err)) {
                if (err == -ENOENT)
                        err = -EIO;
                goto err_out;
        }
        m = ctx->mrec;
        a = ctx->attr;
        BUG_ON(NInoNonResident(ni));
        BUG_ON(a->non_resident);
        /*
         * Calculate new offsets for the name and the mapping pairs array.
         */
        if (NInoSparse(ni) || NInoCompressed(ni))
                name_ofs = (offsetof(ATTR_REC,
                                data.non_resident.compressed_size) +
                                sizeof(a->data.non_resident.compressed_size) +
                                7) & ~7;
        else
                name_ofs = (offsetof(ATTR_REC,
                                data.non_resident.compressed_size) + 7) & ~7;
        mp_ofs = (name_ofs + a->name_length * sizeof(ntfschar) + 7) & ~7;
        /*
         * Determine the size of the resident part of the now non-resident
         * attribute record.
         */
        arec_size = (mp_ofs + mp_size + 7) & ~7;
        /*
         * If the page is not uptodate bring it uptodate by copying from the
         * attribute value.
         */
        attr_size = le32_to_cpu(a->data.resident.value_length);
        BUG_ON(attr_size != data_size);
        if (page && !PageUptodate(page)) {
                kaddr = kmap_atomic(page, KM_USER0);
                memcpy(kaddr, (u8*)a +
                                le16_to_cpu(a->data.resident.value_offset),
                                attr_size);
                memset(kaddr + attr_size, 0, PAGE_CACHE_SIZE - attr_size);
                kunmap_atomic(kaddr, KM_USER0);
                flush_dcache_page(page);
                SetPageUptodate(page);
        }
        /* Backup the attribute flag. */
        old_res_attr_flags = a->data.resident.flags;
        /* Resize the resident part of the attribute record. */
        err = ntfs_attr_record_resize(m, a, arec_size);
        if (unlikely(err))
                goto err_out;
        /*
         * Convert the resident part of the attribute record to describe a
         * non-resident attribute.
         */
        a->non_resident = 1;
        /* Move the attribute name if it exists and update the offset. */
        if (a->name_length)
                memmove((u8*)a + name_ofs, (u8*)a + le16_to_cpu(a->name_offset),
                                a->name_length * sizeof(ntfschar));
        a->name_offset = cpu_to_le16(name_ofs);
        /* Setup the fields specific to non-resident attributes. */
        a->data.non_resident.lowest_vcn = 0;
        a->data.non_resident.highest_vcn = cpu_to_sle64((new_size - 1) >>
                        vol->cluster_size_bits);
        a->data.non_resident.mapping_pairs_offset = cpu_to_le16(mp_ofs);
        memset(&a->data.non_resident.reserved, 0,
                        sizeof(a->data.non_resident.reserved));
        a->data.non_resident.allocated_size = cpu_to_sle64(new_size);
        a->data.non_resident.data_size =
                        a->data.non_resident.initialized_size =
                        cpu_to_sle64(attr_size);
        if (NInoSparse(ni) || NInoCompressed(ni)) {
                a->data.non_resident.compression_unit = 4;
                a->data.non_resident.compressed_size =
                                a->data.non_resident.allocated_size;
        } else
                a->data.non_resident.compression_unit = 0;
        /* Generate the mapping pairs array into the attribute record. */
        err = ntfs_mapping_pairs_build(vol, (u8*)a + mp_ofs,
                        arec_size - mp_ofs, rl, 0, -1, NULL);
        if (unlikely(err)) {
                ntfs_debug("Failed to build mapping pairs, error code %i.",
                                err);
                goto undo_err_out;
        }
        /* Setup the in-memory attribute structure to be non-resident. */
        ni->runlist.rl = rl;
        write_lock_irqsave(&ni->size_lock, flags);
        ni->allocated_size = new_size;
        if (NInoSparse(ni) || NInoCompressed(ni)) {
                ni->itype.compressed.size = ni->allocated_size;
                ni->itype.compressed.block_size = 1U <<
                                (a->data.non_resident.compression_unit +
                                vol->cluster_size_bits);
                ni->itype.compressed.block_size_bits =
                                ffs(ni->itype.compressed.block_size) - 1;
                ni->itype.compressed.block_clusters = 1U <<
                                a->data.non_resident.compression_unit;
        }
        write_unlock_irqrestore(&ni->size_lock, flags);
        /*
         * This needs to be last since the address space operations ->readpage
         * and ->writepage can run concurrently with us as they are not
         * serialized on i_sem.  Note, we are not allowed to fail once we flip
         * this switch, which is another reason to do this last.
         */
        NInoSetNonResident(ni);
        /* Mark the mft record dirty, so it gets written back. */
        flush_dcache_mft_record_page(ctx->ntfs_ino);
        mark_mft_record_dirty(ctx->ntfs_ino);
        ntfs_attr_put_search_ctx(ctx);
        unmap_mft_record(base_ni);
        up_write(&ni->runlist.lock);
        if (page) {
                set_page_dirty(page);
                unlock_page(page);
                mark_page_accessed(page);
                page_cache_release(page);
        }
        ntfs_debug("Done.");
        return 0;
undo_err_out:
        /* Convert the attribute back into a resident attribute. */
        a->non_resident = 0;
        /* Move the attribute name if it exists and update the offset. */
        name_ofs = (offsetof(ATTR_RECORD, data.resident.reserved) +
                        sizeof(a->data.resident.reserved) + 7) & ~7;
        if (a->name_length)
                memmove((u8*)a + name_ofs, (u8*)a + le16_to_cpu(a->name_offset),
                                a->name_length * sizeof(ntfschar));
        mp_ofs = (name_ofs + a->name_length * sizeof(ntfschar) + 7) & ~7;
        a->name_offset = cpu_to_le16(name_ofs);
        arec_size = (mp_ofs + attr_size + 7) & ~7;
        /* Resize the resident part of the attribute record. */
        err2 = ntfs_attr_record_resize(m, a, arec_size);
        if (unlikely(err2)) {
                /*
                 * This cannot happen (well if memory corruption is at work it
                 * could happen in theory), but deal with it as well as we can.
                 * If the old size is too small, truncate the attribute,
                 * otherwise simply give it a larger allocated size.
                 * FIXME: Should check whether chkdsk complains when the
                 * allocated size is much bigger than the resident value size.
                 */
                arec_size = le32_to_cpu(a->length);
                if ((mp_ofs + attr_size) > arec_size) {
                        err2 = attr_size;
                        attr_size = arec_size - mp_ofs;
                        ntfs_error(vol->sb, "Failed to undo partial resident "
                                        "to non-resident attribute "
                                        "conversion.  Truncating inode 0x%lx, "
                                        "attribute type 0x%x from %i bytes to "
                                        "%i bytes to maintain metadata "
                                        "consistency.  THIS MEANS YOU ARE "
                                        "LOSING %i BYTES DATA FROM THIS %s.",
                                        vi->i_ino,
                                        (unsigned)le32_to_cpu(ni->type),
                                        err2, attr_size, err2 - attr_size,
                                        ((ni->type == AT_DATA) &&
                                        !ni->name_len) ? "FILE": "ATTRIBUTE");
                        write_lock_irqsave(&ni->size_lock, flags);
                        ni->initialized_size = attr_size;
                        i_size_write(vi, attr_size);
                        write_unlock_irqrestore(&ni->size_lock, flags);
                }
        }
        /* Setup the fields specific to resident attributes. */
        a->data.resident.value_length = cpu_to_le32(attr_size);
        a->data.resident.value_offset = cpu_to_le16(mp_ofs);
        a->data.resident.flags = old_res_attr_flags;
        memset(&a->data.resident.reserved, 0,
                        sizeof(a->data.resident.reserved));
        /* Copy the data from the page back to the attribute value. */
        if (page) {
                kaddr = kmap_atomic(page, KM_USER0);
                memcpy((u8*)a + mp_ofs, kaddr, attr_size);
                kunmap_atomic(kaddr, KM_USER0);
        }
        /* Setup the allocated size in the ntfs inode in case it changed. */
        write_lock_irqsave(&ni->size_lock, flags);
        ni->allocated_size = arec_size - mp_ofs;
        write_unlock_irqrestore(&ni->size_lock, flags);
        /* Mark the mft record dirty, so it gets written back. */
        flush_dcache_mft_record_page(ctx->ntfs_ino);
        mark_mft_record_dirty(ctx->ntfs_ino);
err_out:
        if (ctx)
                ntfs_attr_put_search_ctx(ctx);
        if (m)
                unmap_mft_record(base_ni);
        ni->runlist.rl = NULL;
        up_write(&ni->runlist.lock);
rl_err_out:
        if (rl) {
                if (ntfs_cluster_free_from_rl(vol, rl) < 0) {
                        ntfs_error(vol->sb, "Failed to release allocated "
                                        "cluster(s) in error code path.  Run "
                                        "chkdsk to recover the lost "
                                        "cluster(s).");
                        NVolSetErrors(vol);
                }
                ntfs_free(rl);
page_err_out:
                unlock_page(page);
                page_cache_release(page);
        }
        if (err == -EINVAL)
                err = -EIO;
        return err;
}

/**
 * ntfs_attr_set - fill (a part of) an attribute with a byte
 * @ni:         ntfs inode describing the attribute to fill
 * @ofs:        offset inside the attribute at which to start to fill
 * @cnt:        number of bytes to fill
 * @val:        the unsigned 8-bit value with which to fill the attribute
 *
 * Fill @cnt bytes of the attribute described by the ntfs inode @ni starting at
 * byte offset @ofs inside the attribute with the constant byte @val.
 *
 * This function is effectively like memset() applied to an ntfs attribute.
 * Note thie function actually only operates on the page cache pages belonging
 * to the ntfs attribute and it marks them dirty after doing the memset().
 * Thus it relies on the vm dirty page write code paths to cause the modified
 * pages to be written to the mft record/disk.
 *
 * Return 0 on success and -errno on error.  An error code of -ESPIPE means
 * that @ofs + @cnt were outside the end of the attribute and no write was
 * performed.
 */
int ntfs_attr_set(ntfs_inode *ni, const s64 ofs, const s64 cnt, const u8 val)
{
        ntfs_volume *vol = ni->vol;
        struct address_space *mapping;
        struct page *page;
        u8 *kaddr;
        pgoff_t idx, end;
        unsigned int start_ofs, end_ofs, size;

        ntfs_debug("Entering for ofs 0x%llx, cnt 0x%llx, val 0x%hx.",
                        (long long)ofs, (long long)cnt, val);
        BUG_ON(ofs < 0);
        BUG_ON(cnt < 0);
        if (!cnt)
                goto done;
        /*
         * FIXME: Compressed and encrypted attributes are not supported when
         * writing and we should never have gotten here for them.
         */
        BUG_ON(NInoCompressed(ni));
        BUG_ON(NInoEncrypted(ni));
        mapping = VFS_I(ni)->i_mapping;
        /* Work out the starting index and page offset. */
        idx = ofs >> PAGE_CACHE_SHIFT;
        start_ofs = ofs & ~PAGE_CACHE_MASK;
        /* Work out the ending index and page offset. */
        end = ofs + cnt;
        end_ofs = end & ~PAGE_CACHE_MASK;
        /* If the end is outside the inode size return -ESPIPE. */
        if (unlikely(end > i_size_read(VFS_I(ni)))) {
                ntfs_error(vol->sb, "Request exceeds end of attribute.");
                return -ESPIPE;
        }
        end >>= PAGE_CACHE_SHIFT;
        /* If there is a first partial page, need to do it the slow way. */
        if (start_ofs) {
                page = read_cache_page(mapping, idx,
                                (filler_t*)mapping->a_ops->readpage, NULL);
                if (IS_ERR(page)) {
                        ntfs_error(vol->sb, "Failed to read first partial "
                                        "page (sync error, index 0x%lx).", idx);
                        return PTR_ERR(page);
                }
                wait_on_page_locked(page);
                if (unlikely(!PageUptodate(page))) {
                        ntfs_error(vol->sb, "Failed to read first partial page "
                                        "(async error, index 0x%lx).", idx);
                        page_cache_release(page);
                        return PTR_ERR(page);
                }
                /*
                 * If the last page is the same as the first page, need to
                 * limit the write to the end offset.
                 */
                size = PAGE_CACHE_SIZE;
                if (idx == end)
                        size = end_ofs;
                kaddr = kmap_atomic(page, KM_USER0);
                memset(kaddr + start_ofs, val, size - start_ofs);
                flush_dcache_page(page);
                kunmap_atomic(kaddr, KM_USER0);
                set_page_dirty(page);
                page_cache_release(page);
                if (idx == end)
                        goto done;
                idx++;
        }
        /* Do the whole pages the fast way. */
        for (; idx < end; idx++) {
                /* Find or create the current page.  (The page is locked.) */
                page = grab_cache_page(mapping, idx);
                if (unlikely(!page)) {
                        ntfs_error(vol->sb, "Insufficient memory to grab "
                                        "page (index 0x%lx).", idx);
                        return -ENOMEM;
                }
                kaddr = kmap_atomic(page, KM_USER0);
                memset(kaddr, val, PAGE_CACHE_SIZE);
                flush_dcache_page(page);
                kunmap_atomic(kaddr, KM_USER0);
                /*
                 * If the page has buffers, mark them uptodate since buffer
                 * state and not page state is definitive in 2.6 kernels.
                 */
                if (page_has_buffers(page)) {
                        struct buffer_head *bh, *head;

                        bh = head = page_buffers(page);
                        do {
                                set_buffer_uptodate(bh);
                        } while ((bh = bh->b_this_page) != head);
                }
                /* Now that buffers are uptodate, set the page uptodate, too. */
                SetPageUptodate(page);
                /*
                 * Set the page and all its buffers dirty and mark the inode
                 * dirty, too.  The VM will write the page later on.
                 */
                set_page_dirty(page);
                /* Finally unlock and release the page. */
                unlock_page(page);
                page_cache_release(page);
        }
        /* If there is a last partial page, need to do it the slow way. */
        if (end_ofs) {
                page = read_cache_page(mapping, idx,
                                (filler_t*)mapping->a_ops->readpage, NULL);
                if (IS_ERR(page)) {
                        ntfs_error(vol->sb, "Failed to read last partial page "
                                        "(sync error, index 0x%lx).", idx);
                        return PTR_ERR(page);
                }
                wait_on_page_locked(page);
                if (unlikely(!PageUptodate(page))) {
                        ntfs_error(vol->sb, "Failed to read last partial page "
                                        "(async error, index 0x%lx).", idx);
                        page_cache_release(page);
                        return PTR_ERR(page);
                }
                kaddr = kmap_atomic(page, KM_USER0);
                memset(kaddr, val, end_ofs);
                flush_dcache_page(page);
                kunmap_atomic(kaddr, KM_USER0);
                set_page_dirty(page);
                page_cache_release(page);
        }
done:
        ntfs_debug("Done.");
        return 0;
}

#endif /* NTFS_RW */