patch-2_6_7-vs1_9_1_12

[linux-2.6.git] / fs / ntfs / mft.c

/**
 * mft.c - NTFS kernel mft record operations. Part of the Linux-NTFS project.
 *
 * Copyright (c) 2001-2004 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/swap.h>

#include "ntfs.h"

/**
 * __format_mft_record - initialize an empty mft record
 * @m:          mapped, pinned and locked for writing mft record
 * @size:       size of the mft record
 * @rec_no:     mft record number / inode number
 *
 * Private function to initialize an empty mft record. Use one of the two
 * provided format_mft_record() functions instead.
 */
static void __format_mft_record(MFT_RECORD *m, const int size,
                const unsigned long rec_no)
{
        ATTR_RECORD *a;

        memset(m, 0, size);
        m->magic = magic_FILE;
        /* Aligned to 2-byte boundary. */
        m->usa_ofs = cpu_to_le16((sizeof(MFT_RECORD) + 1) & ~1);
        m->usa_count = cpu_to_le16(size / NTFS_BLOCK_SIZE + 1);
        /* Set the update sequence number to 1. */
        *(u16*)((char*)m + ((sizeof(MFT_RECORD) + 1) & ~1)) = cpu_to_le16(1);
        m->lsn = cpu_to_le64(0LL);
        m->sequence_number = cpu_to_le16(1);
        m->link_count = cpu_to_le16(0);
        /* Aligned to 8-byte boundary. */
        m->attrs_offset = cpu_to_le16((le16_to_cpu(m->usa_ofs) +
                        (le16_to_cpu(m->usa_count) << 1) + 7) & ~7);
        m->flags = cpu_to_le16(0);
        /*
         * Using attrs_offset plus eight bytes (for the termination attribute),
         * aligned to 8-byte boundary.
         */
        m->bytes_in_use = cpu_to_le32((le16_to_cpu(m->attrs_offset) + 8 + 7) &
                        ~7);
        m->bytes_allocated = cpu_to_le32(size);
        m->base_mft_record = cpu_to_le64((MFT_REF)0);
        m->next_attr_instance = cpu_to_le16(0);
        a = (ATTR_RECORD*)((char*)m + le16_to_cpu(m->attrs_offset));
        a->type = AT_END;
        a->length = cpu_to_le32(0);
}

/**
 * format_mft_record - initialize an empty mft record
 * @ni:         ntfs inode of mft record
 * @mft_rec:    mapped, pinned and locked mft record (optional)
 *
 * Initialize an empty mft record. This is used when extending the MFT.
 *
 * If @mft_rec is NULL, we call map_mft_record() to obtain the
 * record and we unmap it again when finished.
 *
 * We return 0 on success or -errno on error.
 */
int format_mft_record(ntfs_inode *ni, MFT_RECORD *mft_rec)
{
        MFT_RECORD *m;

        if (mft_rec)
                m = mft_rec;
        else {
                m = map_mft_record(ni);
                if (IS_ERR(m))
                        return PTR_ERR(m);
        }
        __format_mft_record(m, ni->vol->mft_record_size, ni->mft_no);
        if (!mft_rec) {
                // FIXME: Need to set the mft record dirty!
                unmap_mft_record(ni);
        }
        return 0;
}

/**
 * ntfs_readpage - external declaration, function is in fs/ntfs/aops.c
 */
extern int ntfs_readpage(struct file *, struct page *);

#ifdef NTFS_RW
/**
 * ntfs_mft_writepage - forward declaration, function is further below
 */
static int ntfs_mft_writepage(struct page *page, struct writeback_control *wbc);
#endif /* NTFS_RW */

/**
 * ntfs_mft_aops - address space operations for access to $MFT
 *
 * Address space operations for access to $MFT. This allows us to simply use
 * ntfs_map_page() in map_mft_record_page().
 */
struct address_space_operations ntfs_mft_aops = {
        .readpage       = ntfs_readpage,        /* Fill page with data. */
        .sync_page      = block_sync_page,      /* Currently, just unplugs the
                                                   disk request queue. */
#ifdef NTFS_RW
        .writepage      = ntfs_mft_writepage,   /* Write out the dirty mft
                                                   records in a page. */
#endif /* NTFS_RW */
};

/**
 * map_mft_record_page - map the page in which a specific mft record resides
 * @ni:         ntfs inode whose mft record page to map
 *
 * This maps the page in which the mft record of the ntfs inode @ni is situated
 * and returns a pointer to the mft record within the mapped page.
 *
 * Return value needs to be checked with IS_ERR() and if that is true PTR_ERR()
 * contains the negative error code returned.
 */
static inline MFT_RECORD *map_mft_record_page(ntfs_inode *ni)
{
        ntfs_volume *vol = ni->vol;
        struct inode *mft_vi = vol->mft_ino;
        struct page *page;
        unsigned long index, ofs, end_index;

        BUG_ON(ni->page);
        /*
         * The index into the page cache and the offset within the page cache
         * page of the wanted mft record. FIXME: We need to check for
         * overflowing the unsigned long, but I don't think we would ever get
         * here if the volume was that big...
         */
        index = ni->mft_no << vol->mft_record_size_bits >> PAGE_CACHE_SHIFT;
        ofs = (ni->mft_no << vol->mft_record_size_bits) & ~PAGE_CACHE_MASK;

        /* The maximum valid index into the page cache for $MFT's data. */
        end_index = mft_vi->i_size >> PAGE_CACHE_SHIFT;

        /* If the wanted index is out of bounds the mft record doesn't exist. */
        if (unlikely(index >= end_index)) {
                if (index > end_index || (mft_vi->i_size & ~PAGE_CACHE_MASK) <
                                ofs + vol->mft_record_size) {
                        page = ERR_PTR(-ENOENT);
                        goto err_out;
                }
        }
        /* Read, map, and pin the page. */
        page = ntfs_map_page(mft_vi->i_mapping, index);
        if (likely(!IS_ERR(page))) {
                ni->page = page;
                ni->page_ofs = ofs;
                return page_address(page) + ofs;
        }
err_out:
        ni->page = NULL;
        ni->page_ofs = 0;
        ntfs_error(vol->sb, "Failed with error code %lu.", -PTR_ERR(page));
        return (void*)page;
}

/**
 * map_mft_record - map, pin and lock an mft record
 * @ni:         ntfs inode whose MFT record to map
 *
 * First, take the mrec_lock semaphore. We might now be sleeping, while waiting
 * for the semaphore if it was already locked by someone else.
 *
 * The page of the record is mapped using map_mft_record_page() before being
 * returned to the caller.
 *
 * This in turn uses ntfs_map_page() to get the page containing the wanted mft
 * record (it in turn calls read_cache_page() which reads it in from disk if
 * necessary, increments the use count on the page so that it cannot disappear
 * under us and returns a reference to the page cache page).
 *
 * If read_cache_page() invokes ntfs_readpage() to load the page from disk, it
 * sets PG_locked and clears PG_uptodate on the page. Once I/O has completed
 * and the post-read mst fixups on each mft record in the page have been
 * performed, the page gets PG_uptodate set and PG_locked cleared (this is done
 * in our asynchronous I/O completion handler end_buffer_read_mft_async()).
 * ntfs_map_page() waits for PG_locked to become clear and checks if
 * PG_uptodate is set and returns an error code if not. This provides
 * sufficient protection against races when reading/using the page.
 *
 * However there is the write mapping to think about. Doing the above described
 * checking here will be fine, because when initiating the write we will set
 * PG_locked and clear PG_uptodate making sure nobody is touching the page
 * contents. Doing the locking this way means that the commit to disk code in
 * the page cache code paths is automatically sufficiently locked with us as
 * we will not touch a page that has been locked or is not uptodate. The only
 * locking problem then is them locking the page while we are accessing it.
 *
 * So that code will end up having to own the mrec_lock of all mft
 * records/inodes present in the page before I/O can proceed. In that case we
 * wouldn't need to bother with PG_locked and PG_uptodate as nobody will be
 * accessing anything without owning the mrec_lock semaphore. But we do need
 * to use them because of the read_cache_page() invocation and the code becomes
 * so much simpler this way that it is well worth it.
 *
 * The mft record is now ours and we return a pointer to it. You need to check
 * the returned pointer with IS_ERR() and if that is true, PTR_ERR() will return
 * the error code.
 *
 * NOTE: Caller is responsible for setting the mft record dirty before calling
 * unmap_mft_record(). This is obviously only necessary if the caller really
 * modified the mft record...
 * Q: Do we want to recycle one of the VFS inode state bits instead?
 * A: No, the inode ones mean we want to change the mft record, not we want to
 * write it out.
 */
MFT_RECORD *map_mft_record(ntfs_inode *ni)
{
        MFT_RECORD *m;

        ntfs_debug("Entering for mft_no 0x%lx.", ni->mft_no);

        /* Make sure the ntfs inode doesn't go away. */
        atomic_inc(&ni->count);

        /* Serialize access to this mft record. */
        down(&ni->mrec_lock);

        m = map_mft_record_page(ni);
        if (likely(!IS_ERR(m)))
                return m;

        up(&ni->mrec_lock);
        atomic_dec(&ni->count);
        ntfs_error(ni->vol->sb, "Failed with error code %lu.", -PTR_ERR(m));
        return m;
}

/**
 * unmap_mft_record_page - unmap the page in which a specific mft record resides
 * @ni:         ntfs inode whose mft record page to unmap
 *
 * This unmaps the page in which the mft record of the ntfs inode @ni is
 * situated and returns. This is a NOOP if highmem is not configured.
 *
 * The unmap happens via ntfs_unmap_page() which in turn decrements the use
 * count on the page thus releasing it from the pinned state.
 *
 * We do not actually unmap the page from memory of course, as that will be
 * done by the page cache code itself when memory pressure increases or
 * whatever.
 */
static inline void unmap_mft_record_page(ntfs_inode *ni)
{
        BUG_ON(!ni->page);

        // TODO: If dirty, blah...
        ntfs_unmap_page(ni->page);
        ni->page = NULL;
        ni->page_ofs = 0;
        return;
}

/**
 * unmap_mft_record - release a mapped mft record
 * @ni:         ntfs inode whose MFT record to unmap
 *
 * We release the page mapping and the mrec_lock mutex which unmaps the mft
 * record and releases it for others to get hold of. We also release the ntfs
 * inode by decrementing the ntfs inode reference count.
 *
 * NOTE: If caller has modified the mft record, it is imperative to set the mft
 * record dirty BEFORE calling unmap_mft_record().
 */
void unmap_mft_record(ntfs_inode *ni)
{
        struct page *page = ni->page;

        BUG_ON(!page);

        ntfs_debug("Entering for mft_no 0x%lx.", ni->mft_no);

        unmap_mft_record_page(ni);
        up(&ni->mrec_lock);
        atomic_dec(&ni->count);
        /*
         * If pure ntfs_inode, i.e. no vfs inode attached, we leave it to
         * ntfs_clear_extent_inode() in the extent inode case, and to the
         * caller in the non-extent, yet pure ntfs inode case, to do the actual
         * tear down of all structures and freeing of all allocated memory.
         */
        return;
}

/**
 * map_extent_mft_record - load an extent inode and attach it to its base
 * @base_ni:    base ntfs inode
 * @mref:       mft reference of the extent inode to load (in little endian)
 * @ntfs_ino:   on successful return, pointer to the ntfs_inode structure
 *
 * Load the extent mft record @mref and attach it to its base inode @base_ni.
 * Return the mapped extent mft record if IS_ERR(result) is false. Otherwise
 * PTR_ERR(result) gives the negative error code.
 *
 * On successful return, @ntfs_ino contains a pointer to the ntfs_inode
 * structure of the mapped extent inode.
 */
MFT_RECORD *map_extent_mft_record(ntfs_inode *base_ni, MFT_REF mref,
                ntfs_inode **ntfs_ino)
{
        MFT_RECORD *m;
        ntfs_inode *ni = NULL;
        ntfs_inode **extent_nis = NULL;
        int i;
        unsigned long mft_no = MREF_LE(mref);
        u16 seq_no = MSEQNO_LE(mref);
        BOOL destroy_ni = FALSE;

        ntfs_debug("Mapping extent mft record 0x%lx (base mft record 0x%lx).",
                        mft_no, base_ni->mft_no);
        /* Make sure the base ntfs inode doesn't go away. */
        atomic_inc(&base_ni->count);
        /*
         * Check if this extent inode has already been added to the base inode,
         * in which case just return it. If not found, add it to the base
         * inode before returning it.
         */
        down(&base_ni->extent_lock);
        if (base_ni->nr_extents > 0) {
                extent_nis = base_ni->ext.extent_ntfs_inos;
                for (i = 0; i < base_ni->nr_extents; i++) {
                        if (mft_no != extent_nis[i]->mft_no)
                                continue;
                        ni = extent_nis[i];
                        /* Make sure the ntfs inode doesn't go away. */
                        atomic_inc(&ni->count);
                        break;
                }
        }
        if (likely(ni != NULL)) {
                up(&base_ni->extent_lock);
                atomic_dec(&base_ni->count);
                /* We found the record; just have to map and return it. */
                m = map_mft_record(ni);
                /* map_mft_record() has incremented this on success. */
                atomic_dec(&ni->count);
                if (likely(!IS_ERR(m))) {
                        /* Verify the sequence number. */
                        if (likely(le16_to_cpu(m->sequence_number) == seq_no)) {
                                ntfs_debug("Done 1.");
                                *ntfs_ino = ni;
                                return m;
                        }
                        unmap_mft_record(ni);
                        ntfs_error(base_ni->vol->sb, "Found stale extent mft "
                                        "reference! Corrupt file system. "
                                        "Run chkdsk.");
                        return ERR_PTR(-EIO);
                }
map_err_out:
                ntfs_error(base_ni->vol->sb, "Failed to map extent "
                                "mft record, error code %ld.", -PTR_ERR(m));
                return m;
        }
        /* Record wasn't there. Get a new ntfs inode and initialize it. */
        ni = ntfs_new_extent_inode(base_ni->vol->sb, mft_no);
        if (unlikely(!ni)) {
                up(&base_ni->extent_lock);
                atomic_dec(&base_ni->count);
                return ERR_PTR(-ENOMEM);
        }
        ni->vol = base_ni->vol;
        ni->seq_no = seq_no;
        ni->nr_extents = -1;
        ni->ext.base_ntfs_ino = base_ni;
        /* Now map the record. */
        m = map_mft_record(ni);
        if (unlikely(IS_ERR(m))) {
                up(&base_ni->extent_lock);
                atomic_dec(&base_ni->count);
                ntfs_clear_extent_inode(ni);
                goto map_err_out;
        }
        /* Verify the sequence number. */
        if (unlikely(le16_to_cpu(m->sequence_number) != seq_no)) {
                ntfs_error(base_ni->vol->sb, "Found stale extent mft "
                                "reference! Corrupt file system. Run chkdsk.");
                destroy_ni = TRUE;
                m = ERR_PTR(-EIO);
                goto unm_err_out;
        }
        /* Attach extent inode to base inode, reallocating memory if needed. */
        if (!(base_ni->nr_extents & 3)) {
                ntfs_inode **tmp;
                int new_size = (base_ni->nr_extents + 4) * sizeof(ntfs_inode *);

                tmp = (ntfs_inode **)kmalloc(new_size, GFP_NOFS);
                if (unlikely(!tmp)) {
                        ntfs_error(base_ni->vol->sb, "Failed to allocate "
                                        "internal buffer.");
                        destroy_ni = TRUE;
                        m = ERR_PTR(-ENOMEM);
                        goto unm_err_out;
                }
                if (base_ni->ext.extent_ntfs_inos) {
                        memcpy(tmp, base_ni->ext.extent_ntfs_inos, new_size -
                                        4 * sizeof(ntfs_inode *));
                        kfree(base_ni->ext.extent_ntfs_inos);
                }
                base_ni->ext.extent_ntfs_inos = tmp;
        }
        base_ni->ext.extent_ntfs_inos[base_ni->nr_extents++] = ni;
        up(&base_ni->extent_lock);
        atomic_dec(&base_ni->count);
        ntfs_debug("Done 2.");
        *ntfs_ino = ni;
        return m;
unm_err_out:
        unmap_mft_record(ni);
        up(&base_ni->extent_lock);
        atomic_dec(&base_ni->count);
        /*
         * If the extent inode was not attached to the base inode we need to
         * release it or we will leak memory.
         */
        if (destroy_ni)
                ntfs_clear_extent_inode(ni);
        return m;
}

#ifdef NTFS_RW

/**
 * __mark_mft_record_dirty - set the mft record and the page containing it dirty
 * @ni:         ntfs inode describing the mapped mft record
 *
 * Internal function.  Users should call mark_mft_record_dirty() instead.
 *
 * Set the mapped (extent) mft record of the (base or extent) ntfs inode @ni,
 * as well as the page containing the mft record, dirty.  Also, mark the base
 * vfs inode dirty.  This ensures that any changes to the mft record are
 * written out to disk.
 *
 * NOTE:  We only set I_DIRTY_SYNC and I_DIRTY_DATASYNC (and not I_DIRTY_PAGES)
 * on the base vfs inode, because even though file data may have been modified,
 * it is dirty in the inode meta data rather than the data page cache of the
 * inode, and thus there are no data pages that need writing out.  Therefore, a
 * full mark_inode_dirty() is overkill.  A mark_inode_dirty_sync(), on the
 * other hand, is not sufficient, because I_DIRTY_DATASYNC needs to be set to
 * ensure ->write_inode is called from generic_osync_inode() and this needs to
 * happen or the file data would not necessarily hit the device synchronously,
 * even though the vfs inode has the O_SYNC flag set.  Also, I_DIRTY_DATASYNC
 * simply "feels" better than just I_DIRTY_SYNC, since the file data has not
 * actually hit the block device yet, which is not what I_DIRTY_SYNC on its own
 * would suggest.
 */
void __mark_mft_record_dirty(ntfs_inode *ni)
{
        struct page *page = ni->page;
        ntfs_inode *base_ni;

        ntfs_debug("Entering for inode 0x%lx.", ni->mft_no);
        BUG_ON(!page);
        BUG_ON(NInoAttr(ni));

        /*
         * Set the page containing the mft record dirty.  This also marks the
         * $MFT inode dirty (I_DIRTY_PAGES).
         */
        __set_page_dirty_nobuffers(page);

        /* Determine the base vfs inode and mark it dirty, too. */
        down(&ni->extent_lock);
        if (likely(ni->nr_extents >= 0))
                base_ni = ni;
        else
                base_ni = ni->ext.base_ntfs_ino;
        up(&ni->extent_lock);
        __mark_inode_dirty(VFS_I(base_ni), I_DIRTY_SYNC | I_DIRTY_DATASYNC);
}

static const char *ntfs_please_email = "Please email "
                "linux-ntfs-dev@lists.sourceforge.net and say that you saw "
                "this message.  Thank you.";

/**
 * sync_mft_mirror_umount - synchronise an mft record to the mft mirror
 * @ni:         ntfs inode whose mft record to synchronize
 * @m:          mapped, mst protected (extent) mft record to synchronize
 *
 * Write the mapped, mst protected (extent) mft record @m described by the
 * (regular or extent) ntfs inode @ni to the mft mirror ($MFTMirr) bypassing
 * the page cache and the $MFTMirr inode itself.
 *
 * This function is only for use at umount time when the mft mirror inode has
 * already been disposed off.  We BUG() if we are called while the mft mirror
 * inode is still attached to the volume.
 *
 * On success return 0.  On error return -errno.
 *
 * NOTE:  This function is not implemented yet as I am not convinced it can
 * actually be triggered considering the sequence of commits we do in super.c::
 * ntfs_put_super().  But just in case we provide this place holder as the
 * alternative would be either to BUG() or to get a NULL pointer dereference
 * and Oops.
 */
static int sync_mft_mirror_umount(ntfs_inode *ni, MFT_RECORD *m)
{
        ntfs_volume *vol = ni->vol;

        BUG_ON(vol->mftmirr_ino);
        ntfs_error(vol->sb, "Umount time mft mirror syncing is not "
                        "implemented yet.  %s", ntfs_please_email);
        return -EOPNOTSUPP;
}

/**
 * sync_mft_mirror - synchronize an mft record to the mft mirror
 * @ni:         ntfs inode whose mft record to synchronize
 * @m:          mapped, mst protected (extent) mft record to synchronize
 * @sync:       if true, wait for i/o completion
 *
 * Write the mapped, mst protected (extent) mft record @m described by the
 * (regular or extent) ntfs inode @ni to the mft mirror ($MFTMirr).
 *
 * On success return 0.  On error return -errno and set the volume errors flag
 * in the ntfs_volume to which @ni belongs.
 *
 * NOTE:  We always perform synchronous i/o and ignore the @sync parameter.
 *
 * TODO:  If @sync is false, want to do truly asynchronous i/o, i.e. just
 * schedule i/o via ->writepage or do it via kntfsd or whatever.
 */
static int sync_mft_mirror(ntfs_inode *ni, MFT_RECORD *m, int sync)
{
        ntfs_volume *vol = ni->vol;
        struct page *page;
        unsigned int blocksize = vol->sb->s_blocksize;
        int max_bhs = vol->mft_record_size / blocksize;
        struct buffer_head *bhs[max_bhs];
        struct buffer_head *bh, *head;
        u8 *kmirr;
        unsigned int block_start, block_end, m_start, m_end;
        int i_bhs, nr_bhs, err = 0;

        ntfs_debug("Entering for inode 0x%lx.", ni->mft_no);
        BUG_ON(!max_bhs);
        if (unlikely(!vol->mftmirr_ino)) {
                /* This could happen during umount... */
                err = sync_mft_mirror_umount(ni, m);
                if (likely(!err))
                        return err;
                goto err_out;
        }
        /* Get the page containing the mirror copy of the mft record @m. */
        page = ntfs_map_page(vol->mftmirr_ino->i_mapping, ni->mft_no >>
                        (PAGE_CACHE_SHIFT - vol->mft_record_size_bits));
        if (unlikely(IS_ERR(page))) {
                ntfs_error(vol->sb, "Failed to map mft mirror page.");
                err = PTR_ERR(page);
                goto err_out;
        }
        /*
         * Exclusion against other writers.   This should never be a problem
         * since the page in which the mft record @m resides is also locked and
         * hence any other writers would be held up there but it is better to
         * make sure no one is writing from elsewhere.
         */
        lock_page(page);
        /* The address in the page of the mirror copy of the mft record @m. */
        kmirr = page_address(page) + ((ni->mft_no << vol->mft_record_size_bits)
                        & ~PAGE_CACHE_MASK);
        /* Copy the mst protected mft record to the mirror. */
        memcpy(kmirr, m, vol->mft_record_size);
        /* Make sure we have mapped buffers. */
        if (!page_has_buffers(page)) {
no_buffers_err_out:
                ntfs_error(vol->sb, "Writing mft mirror records without "
                                "existing buffers is not implemented yet.  %s",
                                ntfs_please_email);
                err = -EOPNOTSUPP;
                goto unlock_err_out;
        }
        bh = head = page_buffers(page);
        if (!bh)
                goto no_buffers_err_out;
        nr_bhs = 0;
        block_start = 0;
        m_start = kmirr - (u8*)page_address(page);
        m_end = m_start + vol->mft_record_size;
        do {
                block_end = block_start + blocksize;
                /*
                 * If the buffer is outside the mft record, just skip it,
                 * clearing it if it is dirty to make sure it is not written
                 * out.  It should never be marked dirty but better be safe.
                 */
                if ((block_end <= m_start) || (block_start >= m_end)) {
                        if (buffer_dirty(bh)) {
                                ntfs_warning(vol->sb, "Clearing dirty mft "
                                                "record page buffer.  %s",
                                                ntfs_please_email);
                                clear_buffer_dirty(bh);
                        }
                        continue;
                }
                if (!buffer_mapped(bh)) {
                        ntfs_error(vol->sb, "Writing mft mirror records "
                                        "without existing mapped buffers is "
                                        "not implemented yet.  %s",
                                        ntfs_please_email);
                        err = -EOPNOTSUPP;
                        continue;
                }
                if (!buffer_uptodate(bh)) {
                        ntfs_error(vol->sb, "Writing mft mirror records "
                                        "without existing uptodate buffers is "
                                        "not implemented yet.  %s",
                                        ntfs_please_email);
                        err = -EOPNOTSUPP;
                        continue;
                }
                BUG_ON(!nr_bhs && (m_start != block_start));
                BUG_ON(nr_bhs >= max_bhs);
                bhs[nr_bhs++] = bh;
                BUG_ON((nr_bhs >= max_bhs) && (m_end != block_end));
        } while (block_start = block_end, (bh = bh->b_this_page) != head);
        if (likely(!err)) {
                /* Lock buffers and start synchronous write i/o on them. */
                for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++) {
                        struct buffer_head *tbh = bhs[i_bhs];

                        if (unlikely(test_set_buffer_locked(tbh)))
                                BUG();
                        BUG_ON(!buffer_uptodate(tbh));
                        if (buffer_dirty(tbh))
                                clear_buffer_dirty(tbh);
                        get_bh(tbh);
                        tbh->b_end_io = end_buffer_write_sync;
                        submit_bh(WRITE, tbh);
                }
                /* Wait on i/o completion of buffers. */
                for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++) {
                        struct buffer_head *tbh = bhs[i_bhs];

                        wait_on_buffer(tbh);
                        if (unlikely(!buffer_uptodate(tbh))) {
                                err = -EIO;
                                /*
                                 * Set the buffer uptodate so the page & buffer
                                 * states don't become out of sync.
                                 */
                                if (PageUptodate(page))
                                        set_buffer_uptodate(tbh);
                        }
                }
        } else /* if (unlikely(err)) */ {
                /* Clean the buffers. */
                for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++)
                        clear_buffer_dirty(bhs[i_bhs]);
        }
unlock_err_out:
        /* Current state: all buffers are clean, unlocked, and uptodate. */
        /* Remove the mst protection fixups again. */
        post_write_mst_fixup((NTFS_RECORD*)kmirr);
        flush_dcache_page(page);
        unlock_page(page);
        ntfs_unmap_page(page);
        if (unlikely(err)) {
                /* I/O error during writing.  This is really bad! */
                ntfs_error(vol->sb, "I/O error while writing mft mirror "
                                "record 0x%lx!  You should unmount the volume "
                                "and run chkdsk or ntfsfix.", ni->mft_no);
                goto err_out;
        }
        ntfs_debug("Done.");
        return 0;
err_out:
        ntfs_error(vol->sb, "Failed to synchronize $MFTMirr (error code %i).  "
                        "Volume will be left marked dirty on umount.  Run "
                        "ntfsfix on the partition after umounting to correct "
                        "this.", -err);
        /* We don't want to clear the dirty bit on umount. */
        NVolSetErrors(vol);
        return err;
}

/**
 * write_mft_record_nolock - write out a mapped (extent) mft record
 * @ni:         ntfs inode describing the mapped (extent) mft record
 * @m:          mapped (extent) mft record to write
 * @sync:       if true, wait for i/o completion
 *
 * Write the mapped (extent) mft record @m described by the (regular or extent)
 * ntfs inode @ni to backing store.  If the mft record @m has a counterpart in
 * the mft mirror, that is also updated.
 *
 * On success, clean the mft record and return 0.  On error, leave the mft
 * record dirty and return -errno.  The caller should call make_bad_inode() on
 * the base inode to ensure no more access happens to this inode.  We do not do
 * it here as the caller may want to finish writing other extent mft records
 * first to minimize on-disk metadata inconsistencies.
 *
 * NOTE:  We always perform synchronous i/o and ignore the @sync parameter.
 * However, if the mft record has a counterpart in the mft mirror and @sync is
 * true, we write the mft record, wait for i/o completion, and only then write
 * the mft mirror copy.  This ensures that if the system crashes either the mft
 * or the mft mirror will contain a self-consistent mft record @m.  If @sync is
 * false on the other hand, we start i/o on both and then wait for completion
 * on them.  This provides a speedup but no longer guarantees that you will end
 * up with a self-consistent mft record in the case of a crash but if you asked
 * for asynchronous writing you probably do not care about that anyway.
 *
 * TODO:  If @sync is false, want to do truly asynchronous i/o, i.e. just
 * schedule i/o via ->writepage or do it via kntfsd or whatever.
 */
int write_mft_record_nolock(ntfs_inode *ni, MFT_RECORD *m, int sync)
{
        ntfs_volume *vol = ni->vol;
        struct page *page = ni->page;
        unsigned int blocksize = vol->sb->s_blocksize;
        int max_bhs = vol->mft_record_size / blocksize;
        struct buffer_head *bhs[max_bhs];
        struct buffer_head *bh, *head;
        unsigned int block_start, block_end, m_start, m_end;
        int i_bhs, nr_bhs, err = 0;

        ntfs_debug("Entering for inode 0x%lx.", ni->mft_no);
        BUG_ON(NInoAttr(ni));
        BUG_ON(!max_bhs);
        BUG_ON(!page);
        BUG_ON(!PageLocked(page));
        /*
         * If the ntfs_inode is clean no need to do anything.  If it is dirty,
         * mark it as clean now so that it can be redirtied later on if needed.
         * There is no danger of races as as long as the caller is holding the
         * locks for the mft record @m and the page it is in.
         */
        if (!NInoTestClearDirty(ni))
                goto done;
        /* Make sure we have mapped buffers. */
        if (!page_has_buffers(page)) {
no_buffers_err_out:
                ntfs_error(vol->sb, "Writing mft records without existing "
                                "buffers is not implemented yet.  %s",
                                ntfs_please_email);
                err = -EOPNOTSUPP;
                goto err_out;
        }
        bh = head = page_buffers(page);
        if (!bh)
                goto no_buffers_err_out;
        nr_bhs = 0;
        block_start = 0;
        m_start = ni->page_ofs;
        m_end = m_start + vol->mft_record_size;
        do {
                block_end = block_start + blocksize;
                /*
                 * If the buffer is outside the mft record, just skip it,
                 * clearing it if it is dirty to make sure it is not written
                 * out.  It should never be marked dirty but better be safe.
                 */
                if ((block_end <= m_start) || (block_start >= m_end)) {
                        if (buffer_dirty(bh)) {
                                ntfs_warning(vol->sb, "Clearing dirty mft "
                                                "record page buffer.  %s",
                                                ntfs_please_email);
                                clear_buffer_dirty(bh);
                        }
                        continue;
                }
                if (!buffer_mapped(bh)) {
                        ntfs_error(vol->sb, "Writing mft records without "
                                        "existing mapped buffers is not "
                                        "implemented yet.  %s",
                                        ntfs_please_email);
                        err = -EOPNOTSUPP;
                        continue;
                }
                if (!buffer_uptodate(bh)) {
                        ntfs_error(vol->sb, "Writing mft records without "
                                        "existing uptodate buffers is not "
                                        "implemented yet.  %s",
                                        ntfs_please_email);
                        err = -EOPNOTSUPP;
                        continue;
                }
                BUG_ON(!nr_bhs && (m_start != block_start));
                BUG_ON(nr_bhs >= max_bhs);
                bhs[nr_bhs++] = bh;
                BUG_ON((nr_bhs >= max_bhs) && (m_end != block_end));
        } while (block_start = block_end, (bh = bh->b_this_page) != head);
        if (unlikely(err))
                goto cleanup_out;
        /* Apply the mst protection fixups. */
        err = pre_write_mst_fixup((NTFS_RECORD*)m, vol->mft_record_size);
        if (err) {
                ntfs_error(vol->sb, "Failed to apply mst fixups!");
                goto cleanup_out;
        }
        flush_dcache_mft_record_page(ni);
        /* Lock buffers and start synchronous write i/o on them. */
        for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++) {
                struct buffer_head *tbh = bhs[i_bhs];

                if (unlikely(test_set_buffer_locked(tbh)))
                        BUG();
                BUG_ON(!buffer_uptodate(tbh));
                if (buffer_dirty(tbh))
                        clear_buffer_dirty(tbh);
                get_bh(tbh);
                tbh->b_end_io = end_buffer_write_sync;
                submit_bh(WRITE, tbh);
        }
        /* Synchronize the mft mirror now if not @sync. */
        if (!sync && ni->mft_no < vol->mftmirr_size)
                sync_mft_mirror(ni, m, sync);
        /* Wait on i/o completion of buffers. */
        for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++) {
                struct buffer_head *tbh = bhs[i_bhs];

                wait_on_buffer(tbh);
                if (unlikely(!buffer_uptodate(tbh))) {
                        err = -EIO;
                        /*
                         * Set the buffer uptodate so the page & buffer states
                         * don't become out of sync.
                         */
                        if (PageUptodate(page))
                                set_buffer_uptodate(tbh);
                }
        }
        /* If @sync, now synchronize the mft mirror. */
        if (sync && ni->mft_no < vol->mftmirr_size)
                sync_mft_mirror(ni, m, sync);
        /* Remove the mst protection fixups again. */
        post_write_mst_fixup((NTFS_RECORD*)m);
        flush_dcache_mft_record_page(ni);
        if (unlikely(err)) {
                /* I/O error during writing.  This is really bad! */
                ntfs_error(vol->sb, "I/O error while writing mft record "
                                "0x%lx!  Marking base inode as bad.  You "
                                "should unmount the volume and run chkdsk.",
                                ni->mft_no);
                goto err_out;
        }
done:
        ntfs_debug("Done.");
        return 0;
cleanup_out:
        /* Clean the buffers. */
        for (i_bhs = 0; i_bhs < nr_bhs; i_bhs++)
                clear_buffer_dirty(bhs[i_bhs]);
err_out:
        /*
         * Current state: all buffers are clean, unlocked, and uptodate.
         * The caller should mark the base inode as bad so that no more i/o
         * happens.  ->clear_inode() will still be invoked so all extent inodes
         * and other allocated memory will be freed.
         */
        if (err == -ENOMEM) {
                ntfs_error(vol->sb, "Not enough memory to write mft record.  "
                                "Redirtying so the write is retried later.");
                mark_mft_record_dirty(ni);
                err = 0;
        }
        return err;
}

/**
 * ntfs_mft_writepage - check if a metadata page contains dirty mft records
 * @page:       metadata page possibly containing dirty mft records
 * @wbc:        writeback control structure
 *
 * This is called from the VM when it wants to have a dirty $MFT/$DATA metadata
 * page cache page cleaned.  The VM has already locked the page and marked it
 * clean.  Instead of writing the page as a conventional ->writepage function
 * would do, we check if the page still contains any dirty mft records (it must
 * have done at some point in the past since the page was marked dirty) and if
 * none are found, i.e. all mft records are clean, we unlock the page and
 * return.  The VM is then free to do with the page as it pleases.  If on the
 * other hand we do find any dirty mft records in the page, we redirty the page
 * before unlocking it and returning so the VM knows that the page is still
 * busy and cannot be thrown out.
 *
 * Note, we do not actually write any dirty mft records here because they are
 * dirty inodes and hence will be written by the VFS inode dirty code paths.
 * There is no need to write them from the VM page dirty code paths, too and in
 * fact once we implement journalling it would be a complete nightmare having
 * two code paths leading to mft record writeout.
 */
static int ntfs_mft_writepage(struct page *page, struct writeback_control *wbc)
{
        struct inode *mft_vi = page->mapping->host;
        struct super_block *sb = mft_vi->i_sb;
        ntfs_volume *vol = NTFS_SB(sb);
        u8 *maddr;
        MFT_RECORD *m;
        ntfs_inode **extent_nis;
        unsigned long mft_no;
        int nr, i, j;
        BOOL is_dirty = FALSE;

        BUG_ON(mft_vi != vol->mft_ino);
        /* The first mft record number in the page. */
        mft_no = page->index << (PAGE_CACHE_SHIFT - vol->mft_record_size_bits);
        /* Number of mft records in the page. */
        nr = PAGE_CACHE_SIZE >> vol->mft_record_size_bits;
        BUG_ON(!nr);
        ntfs_debug("Entering for %i inodes starting at 0x%lx.", nr, mft_no);
        /* Iterate over the mft records in the page looking for a dirty one. */
        maddr = (u8*)kmap(page);
        for (i = 0; i < nr; ++i, ++mft_no, maddr += vol->mft_record_size) {
                struct inode *vi;
                ntfs_inode *ni, *eni;
                ntfs_attr na;

                na.mft_no = mft_no;
                na.name = NULL;
                na.name_len = 0;
                na.type = AT_UNUSED;
                /*
                 * Check if the inode corresponding to this mft record is in
                 * the VFS inode cache and obtain a reference to it if it is.
                 */
                ntfs_debug("Looking for inode 0x%lx in icache.", mft_no);
                /*
                 * For inode 0, i.e. $MFT itself, we cannot use ilookup5() from
                 * here or we deadlock because the inode is already locked by
                 * the kernel (fs/fs-writeback.c::__sync_single_inode()) and
                 * ilookup5() waits until the inode is unlocked before
                 * returning it and it never gets unlocked because
                 * ntfs_mft_writepage() never returns.  )-:  Fortunately, we
                 * have inode 0 pinned in icache for the duration of the mount
                 * so we can access it directly.
                 */
                if (!mft_no) {
                        /* Balance the below iput(). */
                        vi = igrab(mft_vi);
                        BUG_ON(vi != mft_vi);
                } else
                        vi = ilookup5(sb, mft_no, (test_t)ntfs_test_inode, &na);
                if (vi) {
                        ntfs_debug("Inode 0x%lx is in icache.", mft_no);
                        /* The inode is in icache.  Check if it is dirty. */
                        ni = NTFS_I(vi);
                        if (!NInoDirty(ni)) {
                                /* The inode is not dirty, skip this record. */
                                ntfs_debug("Inode 0x%lx is not dirty, "
                                                "continuing search.", mft_no);
                                iput(vi);
                                continue;
                        }
                        ntfs_debug("Inode 0x%lx is dirty, aborting search.",
                                        mft_no);
                        /* The inode is dirty, no need to search further. */
                        iput(vi);
                        is_dirty = TRUE;
                        break;
                }
                ntfs_debug("Inode 0x%lx is not in icache.", mft_no);
                /* The inode is not in icache. */
                /* Skip the record if it is not a mft record (type "FILE"). */
                if (!ntfs_is_mft_recordp(maddr)) {
                        ntfs_debug("Mft record 0x%lx is not a FILE record, "
                                        "continuing search.", mft_no);
                        continue;
                }
                m = (MFT_RECORD*)maddr;
                /*
                 * Skip the mft record if it is not in use.  FIXME:  What about
                 * deleted/deallocated (extent) inodes?  (AIA)
                 */
                if (!(m->flags & MFT_RECORD_IN_USE)) {
                        ntfs_debug("Mft record 0x%lx is not in use, "
                                        "continuing search.", mft_no);
                        continue;
                }
                /* Skip the mft record if it is a base inode. */
                if (!m->base_mft_record) {
                        ntfs_debug("Mft record 0x%lx is a base record, "
                                        "continuing search.", mft_no);
                        continue;
                }
                /*
                 * This is an extent mft record.  Check if the inode
                 * corresponding to its base mft record is in icache.
                 */
                na.mft_no = MREF_LE(m->base_mft_record);
                ntfs_debug("Mft record 0x%lx is an extent record.  Looking "
                                "for base inode 0x%lx in icache.", mft_no,
                                na.mft_no);
                vi = ilookup5(sb, na.mft_no, (test_t)ntfs_test_inode,
                                &na);
                if (!vi) {
                        /*
                         * The base inode is not in icache.  Skip this extent
                         * mft record.
                         */
                        ntfs_debug("Base inode 0x%lx is not in icache, "
                                        "continuing search.", na.mft_no);
                        continue;
                }
                ntfs_debug("Base inode 0x%lx is in icache.", na.mft_no);
                /*
                 * The base inode is in icache.  Check if it has the extent
                 * inode corresponding to this extent mft record attached.
                 */
                ni = NTFS_I(vi);
                down(&ni->extent_lock);
                if (ni->nr_extents <= 0) {
                        /*
                         * The base inode has no attached extent inodes.  Skip
                         * this extent mft record.
                         */
                        up(&ni->extent_lock);
                        iput(vi);
                        continue;
                }
                /* Iterate over the attached extent inodes. */
                extent_nis = ni->ext.extent_ntfs_inos;
                for (eni = NULL, j = 0; j < ni->nr_extents; ++j) {
                        if (mft_no == extent_nis[j]->mft_no) {
                                /*
                                 * Found the extent inode corresponding to this
                                 * extent mft record.
                                 */
                                eni = extent_nis[j];
                                break;
                        }
                }
                /*
                 * If the extent inode was not attached to the base inode, skip
                 * this extent mft record.
                 */
                if (!eni) {
                        up(&ni->extent_lock);
                        iput(vi);
                        continue;
                }
                /*
                 * Found the extent inode corrsponding to this extent mft
                 * record.  If it is dirty, no need to search further.
                 */
                if (NInoDirty(eni)) {
                        up(&ni->extent_lock);
                        iput(vi);
                        is_dirty = TRUE;
                        break;
                }
                /* The extent inode is not dirty, so do the next record. */
                up(&ni->extent_lock);
                iput(vi);
        }
        kunmap(page);
        /* If a dirty mft record was found, redirty the page. */
        if (is_dirty) {
                ntfs_debug("Inode 0x%lx is dirty.  Redirtying the page "
                                "starting at inode 0x%lx.", mft_no,
                                page->index << (PAGE_CACHE_SHIFT -
                                vol->mft_record_size_bits));
                redirty_page_for_writepage(wbc, page);
                unlock_page(page);
        } else {
                /*
                 * Keep the VM happy.  This must be done otherwise the
                 * radix-tree tag PAGECACHE_TAG_DIRTY remains set even though
                 * the page is clean.
                 */
                BUG_ON(PageWriteback(page));
                set_page_writeback(page);
                unlock_page(page);
                end_page_writeback(page);
        }
        ntfs_debug("Done.");
        return 0;
}

#endif /* NTFS_RW */