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Up to [Development] / xfs-linux / linux-2.4

cleanup delayed allocate write path a little and fix some
small bugs in there.
Improve documentation, fix the handling of buffer heads on
the dirty list, and the vnode modified state when converting
delalloc space to real space. 

/*
 * Copyright (c) 2000-2002 Silicon Graphics, Inc.  All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * Further, this software is distributed without any warranty that it is
 * free of the rightful claim of any third person regarding infringement
 * or the like.	 Any license provided herein, whether implied or
 * otherwise, applies only to this software file.  Patent licenses, if
 * any, provided herein do not apply to combinations of this program with
 * other software, or any other product whatsoever.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write the Free Software Foundation, Inc., 59
 * Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * Contact information: Silicon Graphics, Inc., 1600 Amphitheatre Pkwy,
 * Mountain View, CA  94043, or:
 *
 * http://www.sgi.com
 *
 * For further information regarding this notice, see:
 *
 * http://oss.sgi.com/projects/GenInfo/SGIGPLNoticeExplan/
 */

#include <xfs.h>
#include <linux/mm.h>
#include <linux/iobuf.h>
#include <linux/locks.h>
#include <linux/pagemap.h>


#if LINUX_VERSION_CODE < KERNEL_VERSION(2,5,9)
#define page_buffers(page)	((page)->buffers)
#define page_has_buffers(page)	((page)->buffers)
#endif


STATIC int
map_blocks(
	struct inode		*inode,
	loff_t			offset,
	ssize_t			count,
	page_buf_bmap_t		*pbmapp,
	int			flags)
{
	vnode_t			*vp = LINVFS_GET_VP(inode);
	int			error, nmaps = 1;

	if (((flags & (PBF_DIRECT|PBF_SYNC)) == PBF_DIRECT) &&
	    (offset >= inode->i_size))
		count = max(count, XFS_WRITE_IO_LOG);
retry:
	VOP_BMAP(vp, offset, count, flags, pbmapp, &nmaps, error);
	if (error == EAGAIN)
		return -error;
	if (unlikely((flags & (PBF_WRITE|PBF_DIRECT)) ==
					(PBF_WRITE|PBF_DIRECT) && nmaps &&
					(pbmapp->pbm_flags & PBMF_DELAY))) {
		flags = PBF_FILE_ALLOCATE;
		goto retry;
	}
	if (flags & (PBF_WRITE|PBF_FILE_ALLOCATE)) {
		VMODIFY(vp);
	}
	return -error;
}

/*
 * match_offset_to_mapping
 * Finds the corresponding mapping in block @map array of the
 * given @offset within a @page.
 */
STATIC page_buf_bmap_t *
match_offset_to_mapping(
	struct page		*page,
	page_buf_bmap_t		*map,
	unsigned long		offset)
{
	loff_t			full_offset;	/* offset from start of file */

	ASSERT(offset < PAGE_CACHE_SIZE);

	full_offset = page->index;		/* NB: using 64bit number */
	full_offset <<= PAGE_CACHE_SHIFT;	/* offset from file start */
	full_offset += offset;			/* offset from page start */

	if (full_offset < map->pbm_offset)
		return NULL;
	if (map->pbm_offset + map->pbm_bsize > full_offset)
		return map;
	return NULL;
}

STATIC void
map_buffer_at_offset(
	struct page		*page,
	struct buffer_head	*bh,
	unsigned long		offset,
	int			block_bits,
	page_buf_bmap_t		*mp)
{
	page_buf_daddr_t	bn;
	loff_t			delta;
	int			sector_shift;

	ASSERT(!(mp->pbm_flags & PBMF_HOLE));
	ASSERT(!(mp->pbm_flags & PBMF_DELAY));
	ASSERT(mp->pbm_bn != PAGE_BUF_DADDR_NULL);

	delta = page->index;
	delta <<= PAGE_CACHE_SHIFT;
	delta += offset;
	delta -= mp->pbm_offset;
	delta >>= block_bits;

	sector_shift = block_bits - 9;
	bn = mp->pbm_bn >> sector_shift;
	bn += delta;
	ASSERT((bn << sector_shift) >= mp->pbm_bn);

	lock_buffer(bh);
	bh->b_blocknr = bn;
	bh->b_dev = mp->pbm_target->pbr_kdev;
	set_bit(BH_Mapped, &bh->b_state);
	clear_bit(BH_Delay, &bh->b_state);
}

/*
 * Look for a page at index which is unlocked and not mapped
 * yet - clustering for mmap write case.
 */
STATIC unsigned int
probe_unmapped_page(
	struct address_space	*mapping,
	unsigned long		index,
	unsigned int		pg_offset)
{
	struct page		*page;
	int			ret = 0;

	page = find_trylock_page(mapping, index);
	if (!page)
		return 0;

	if (page->mapping && PageDirty(page)) {
		if (page_has_buffers(page)) {
			struct buffer_head	*bh, *head;
			bh = head = page_buffers(page);
			do {
				if (buffer_mapped(bh) || !buffer_uptodate(bh))
					break;
				ret += bh->b_size;
				if (ret >= pg_offset)
					break;
			} while ((bh = bh->b_this_page) != head);
		} else
			ret = PAGE_CACHE_SIZE;
	}

	unlock_page(page);
	return ret;
}

STATIC unsigned int
probe_unmapped_cluster(
	struct inode		*inode,
	struct page		*startpage,
	struct buffer_head	*bh,
	struct buffer_head	*head)
{
	unsigned long		tindex, tlast;
	unsigned int		len, total = 0;
	struct address_space	*mapping = inode->i_mapping;

	/* First sum forwards in this page */
	do {
		if (buffer_mapped(bh))
			break;
		total += bh->b_size;
	} while ((bh = bh->b_this_page) != head);

	/* if we reached the end of the page, sum forwards in
	 * following pages.
	 */
	if (bh == head) {
		tlast = inode->i_size >> PAGE_CACHE_SHIFT;
		for (tindex = startpage->index + 1; tindex < tlast; tindex++) {
			len = probe_unmapped_page(mapping, tindex,
							PAGE_CACHE_SIZE);
			if (!len)
				break;
			total += len;
		}
		if ((tindex == tlast) && (inode->i_size & ~PAGE_CACHE_MASK)) {
			len = probe_unmapped_page(mapping, tindex,
					inode->i_size & ~PAGE_CACHE_MASK);
			total += len;
		}
	}
	return total;
}

/*
 * Probe for a given page (index) in the inode & test if it is delayed.
 * Returns page locked and with an extra reference count.
 */
STATIC struct page *
probe_page(
	struct inode		*inode,
	unsigned long		index)
{
	struct page		*page;

	page = find_trylock_page(inode->i_mapping, index);
	if (!page)
		return NULL;

	if (page->mapping && page_has_buffers(page)) {
		struct buffer_head	*bh, *head;

		bh = head = page_buffers(page);
		do {
			if (buffer_delay(bh))
				return page;
		} while ((bh = bh->b_this_page) != head);
	}

	unlock_page(page);
	return NULL;
}

STATIC void
submit_page(
	struct page		*page,
	struct buffer_head	*bh_arr[],
	int			cnt)
{
	struct buffer_head	*bh;
	int			i;

	if (cnt) {
		for (i = 0; i < cnt; i++) {
			bh = bh_arr[i];
			set_buffer_async_io(bh);
			set_bit(BH_Uptodate, &bh->b_state);
			mark_buffer_clean(bh);
		}

		for (i = 0; i < cnt; i++)
			submit_bh(WRITE, bh_arr[i]);
	} else
		unlock_page(page);
}

/*
 * Allocate & map buffers for page given the extent map. Write it out.
 * except for the original page of a writepage, this is called on
 * delalloc pages only, for the original page it is possible that
 * the page has no mapping at all.
 */
STATIC void
convert_page(
	struct inode		*inode,
	struct page		*page,
	page_buf_bmap_t		*maps,
	int			startio,
	int			all_bh)
{
	struct buffer_head	*bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
	page_buf_bmap_t		*mp = maps, *tmp;
	unsigned long		end, offset, end_index;
	int			i = 0, index = 0;
	int			bbits = inode->i_blkbits;

	end_index = inode->i_size >> PAGE_CACHE_SHIFT;
	if (page->index < end_index) {
		end = PAGE_CACHE_SIZE;
	} else {
		end = inode->i_size & (PAGE_CACHE_SIZE-1);
	}
	bh = head = page_buffers(page);
	do {
		offset = i << bbits;
		if (!(Page_Uptodate(page) || buffer_uptodate(bh)))
			continue;
		if (buffer_mapped(bh) && !buffer_delay(bh) && all_bh) {
			if (startio && (offset < end)) {
				lock_buffer(bh);
				bh_arr[index++] = bh;
			}
			continue;
		}
		tmp = match_offset_to_mapping(page, mp, offset);
		if (!tmp)
			continue;
		ASSERT(!(tmp->pbm_flags & PBMF_HOLE));
		ASSERT(!(tmp->pbm_flags & PBMF_DELAY));
		map_buffer_at_offset(page, bh, offset, bbits, tmp);
		if (startio && (offset < end)) {
			bh_arr[index++] = bh;
		} else {
			__mark_buffer_dirty(bh);
			unlock_buffer(bh);
		}
	} while (i++, (bh = bh->b_this_page) != head);

	submit_page(page, bh_arr, index);
}

/*
 * Convert & write out a cluster of pages in the same extent as defined
 * by mp and following the start page.
 */
STATIC void
cluster_write(
	struct inode		*inode,
	unsigned long		tindex,
	page_buf_bmap_t		*mp,
	int			startio,
	int			all_bh)
{
	unsigned long		tlast;
	struct page		*page;

	tlast = (mp->pbm_offset + mp->pbm_bsize) >> PAGE_CACHE_SHIFT;
	for (; tindex < tlast; tindex++) {
		page = probe_page(inode, tindex);
		if (!page)
			break;
		convert_page(inode, page, mp, startio, all_bh);
	}
}

/*
 * Calling this without startio set means we are being asked to make a dirty
 * page ready for freeing it's buffers.  When called with startio set then
 * we are coming from writepage. 
 *
 * When called with startio set it is important that we write the WHOLE
 * page if possible.
 * The bh->b_state's cannot know if any of the blocks or which block for
 * that matter are dirty due to mmap writes, and therefore bh uptodate is
 * only vaild if the page itself isn't completely uptodate.  Some layers
 * may clear the page dirty flag prior to calling write page, under the
 * assumption the entire page will be written out; by not writing out the
 * whole page the page can be reused before all valid dirty data is
 * written out.  Note: in the case of a page that has been dirty'd by
 * mapwrite and but partially setup by block_prepare_write the
 * bh->b_states's will not agree and only ones setup by BPW/BCW will have
 * valid state, thus the whole page must be written out thing.
 */

STATIC int
delalloc_convert(
	struct page	*page,
	int		startio,
	int		unmapped) /* also implies page uptodate */
{
	struct inode		*inode = page->mapping->host;
	struct buffer_head	*bh_arr[MAX_BUF_PER_PAGE], *bh, *head;
	page_buf_bmap_t		*mp, map;
	unsigned long		p_offset = 0, end_index;
	loff_t			offset, end_offset;
	int			len, err, i, cnt = 0;
	int			flags = startio ? 0 : PBF_TRYLOCK;
	int			page_dirty = 1;


	/* Are we off the end of the file ? */
	end_index = inode->i_size >> PAGE_CACHE_SHIFT;
	if (page->index >= end_index) {
		unsigned remaining = inode->i_size & (PAGE_CACHE_SIZE-1);
		if ((page->index >= end_index+1) || !remaining) {
			return -EIO;
		}
	}

	offset = (loff_t)page->index << PAGE_CACHE_SHIFT;
	end_offset = offset + PAGE_CACHE_SIZE;
	if (end_offset > inode->i_size)
		end_offset = inode->i_size;

	bh = head = page_buffers(page);
	mp = NULL;

	len = bh->b_size;
	do {
		if (!(Page_Uptodate(page) || buffer_uptodate(bh)) && !startio) {
			goto next_bh;
		}

		if (mp) {
			mp = match_offset_to_mapping(page, &map, p_offset);
		}

		/*
		 * First case, allocate space for delalloc buffer head
		 * we can return EAGAIN here in the release page case.
		 */
		if (buffer_delay(bh)) {
			if (!mp) {
				err = map_blocks(inode, offset, len, &map,
					PBF_FILE_ALLOCATE | flags);
				if (err) {
					goto error;
				}
				mp = match_offset_to_mapping(page, &map,
								p_offset);
			}
			if (mp) {
				map_buffer_at_offset(page, bh, p_offset,
					inode->i_blkbits, mp);
				if (startio) {
					bh_arr[cnt++] = bh;
				} else {
					__mark_buffer_dirty(bh);
					unlock_buffer(bh);
				}
				page_dirty = 0;
			}
		} else if ((buffer_uptodate(bh) || Page_Uptodate(page)) &&
			   (unmapped || startio)) {

			if (!buffer_mapped(bh)){
				int	size;

				/* Getting here implies an unmapped buffer
				 * was found, and we are in a path where we
				 * need to write the whole page out.
				 */
				if (!mp) {
					size = probe_unmapped_cluster(
							inode, page, bh, head);
					err = map_blocks(inode, offset,
							size, &map,
							PBF_WRITE | PBF_DIRECT);
					if (err) {
						goto error;
					}
					mp = match_offset_to_mapping(page, &map,
								     p_offset);
				}
				if (mp) {
					map_buffer_at_offset(page,
							bh, p_offset,
							inode->i_blkbits, mp);
					if (startio) {
						bh_arr[cnt++] = bh;
					} else {
						__mark_buffer_dirty(bh);
						unlock_buffer(bh);
					}
					page_dirty = 0;
				}
			} else if (startio) {
				if (buffer_uptodate(bh)) {
					lock_buffer(bh);
					bh_arr[cnt++] = bh;
					page_dirty = 0;
				}
			}
		}

next_bh:
		offset += len;
		p_offset += len;
		bh = bh->b_this_page;
	} while (offset < end_offset);

	if (startio) {
		submit_page(page, bh_arr, cnt);
	}

	if (mp) {
		cluster_write(inode, page->index + 1, mp,
				startio, unmapped);
	}

	return page_dirty;

error:
	for (i = 0; i < cnt; i++) {
		unlock_buffer(bh_arr[i]);
	}
	
	/*
	 * If it's delalloc and we have nowhere to put it,
	 * throw it away, unless the lower layers told
	 * us to try again.
	 */
	if (err != -EAGAIN) {
		if (!unmapped) {
			block_flushpage(page, 0);
		}
		ClearPageUptodate(page);
	}
	return err;
}

STATIC int
linvfs_get_block_core(
	struct inode		*inode,
	long			iblock,
	struct buffer_head	*bh_result,
	int			create,
	int			direct,
	page_buf_flags_t	flags)
{
	vnode_t			*vp = LINVFS_GET_VP(inode);
	page_buf_bmap_t		pbmap;
	int			retpbbm = 1;
	int			error;
	ssize_t			size;
	loff_t			offset = (loff_t)iblock << inode->i_blkbits;

	/* If we are doing writes at the end of the file,
	 * allocate in chunks
	 */
	if (create && (offset >= inode->i_size) /* && !(flags & PBF_SYNC) */)
		size = 1 << XFS_WRITE_IO_LOG;
	else
		size = 1 << inode->i_blkbits;

	VOP_BMAP(vp, offset, size,
		create ? flags : PBF_READ,
		(struct page_buf_bmap_s *)&pbmap, &retpbbm, error);
	if (error)
		return -error;

	if (retpbbm == 0)
		return 0;

	if (pbmap.pbm_bn != PAGE_BUF_DADDR_NULL) {
		page_buf_daddr_t	bn;
		loff_t			delta;

		/* For unwritten extents do not report a disk address on
		 * the read case.
		 */
		if (create || ((pbmap.pbm_flags & PBMF_UNWRITTEN) == 0)) {
			delta = offset - pbmap.pbm_offset;
			delta >>= inode->i_blkbits;

			bn = pbmap.pbm_bn >> (inode->i_blkbits - 9);
			bn += delta;

			bh_result->b_blocknr = bn;
			set_bit(BH_Mapped, &bh_result->b_state);
		}
	}

	/* If we previously allocated a block out beyond eof and
	 * we are now coming back to use it then we will need to
	 * flag it as new even if it has a disk address.
	 */
	if (create &&
	    ((!buffer_mapped(bh_result) && !buffer_uptodate(bh_result)) ||
	     (offset >= inode->i_size))) {
		set_bit(BH_New, &bh_result->b_state);
	}

	if (pbmap.pbm_flags & PBMF_DELAY) {
		if (unlikely(direct))
			BUG();

		if (create) {
			set_bit(BH_Mapped, &bh_result->b_state);
		}
		set_bit(BH_Delay, &bh_result->b_state);
	}

	return 0;
}

int
linvfs_get_block(
	struct inode		*inode,
	long			iblock,
	struct buffer_head	*bh_result,
	int			create)
{
	return linvfs_get_block_core(inode, iblock, bh_result,
					create, 0, PBF_WRITE);
}

STATIC int
linvfs_get_block_sync(
	struct inode		*inode,
	long			iblock,
	struct buffer_head	*bh_result,
	int			create)
{
	return linvfs_get_block_core(inode, iblock, bh_result,
					create, 0, PBF_SYNC|PBF_WRITE);
}

STATIC int
linvfs_get_block_direct(
	struct inode		*inode,
	long			iblock,
	struct buffer_head	*bh_result,
	int			create)
{
	return linvfs_get_block_core(inode, iblock, bh_result,
					create, 1, PBF_WRITE|PBF_DIRECT);
}

STATIC int
linvfs_bmap(
	struct address_space	*mapping,
	long			block)
{
	struct inode		*inode = (struct inode *)mapping->host;
	vnode_t			*vp = LINVFS_GET_VP(inode);
	int			error;

	/* block	     - Linux disk blocks    512b */
	/* bmap input offset - bytes		      1b */
	/* bmap output bn    - XFS BBs		    512b */
	/* bmap output delta - bytes		      1b */

	vn_trace_entry(vp, "linvfs_bmap", (inst_t *)__return_address);

	VOP_RWLOCK(vp, VRWLOCK_READ);
	VOP_FLUSH_PAGES(vp, (xfs_off_t)0, -1, 0, FI_REMAPF, error);
	VOP_RWUNLOCK(vp, VRWLOCK_READ);
	return generic_block_bmap(mapping, block, linvfs_get_block_direct);
}

STATIC int
linvfs_readpage(
	struct file		*unused,
	struct page		*page)
{
	return block_read_full_page(page, linvfs_get_block);
}

STATIC void
count_page_state(
	struct page		*page,
	int			*delalloc,
	int			*unmapped)
{
	struct buffer_head	*bh, *head;

	*delalloc = *unmapped = 0;

	bh = head = page_buffers(page);
	do {
		if (buffer_uptodate(bh) && !buffer_mapped(bh))
			(*unmapped) = 1;
		else if (buffer_delay(bh))
			(*delalloc) = 1;
	} while ((bh = bh->b_this_page) != head);
}


/*
 * writepage: Called from one of two places:
 *
 * 1. we are flushing a delalloc buffer head.
 *
 * 2. we are writing out a dirty page. Typically the page dirty
 *    state is cleared before we get here. In this case is it
 *    conceivable we have no buffer heads.
 *
 * For delalloc space on the page we need to allocate space and
 * flush it. For unmapped buffer heads on the page we should
 * allocate space if the page is uptodate. For any other dirty
 * buffer heads on the page we should flush them.
 *
 * If we detect that a transaction would be required to flush
 * the page, we have to check the process flags first, if we
 * are already in a transaction or disk I/O during allocations
 * is off, we need to fail the writepage and redirty the page.
 * We also need to set PF_NOIO ourselves.
 */

STATIC int
linvfs_writepage(
	struct page		*page)
{
	int			error;
	int			need_trans;
	int			delalloc, unmapped;
	struct inode		*inode = page->mapping->host;

	/*
	 * We need a transaction if:
	 *  1. There are delalloc buffers on the page
	 *  2. The page is upto date and we have unmapped buffers
	 *  3. The page is upto date and we have no buffers
	 */

	if (!page_has_buffers(page)) {
		unmapped = 1;
		need_trans = 1;
	} else {
		count_page_state(page, &delalloc, &unmapped);
		if (!Page_Uptodate(page))
			unmapped = 0;
		need_trans = delalloc + unmapped;
	}

	/*
	 * If we need a transaction and the process flags say
	 * we are already in a transaction, or no IO is allowed
	 * then mark the page dirty again and leave the page
	 * as is.
	 */

	if ((current->flags & (PF_FSTRANS|PF_NOIO)) && need_trans)
		goto out_fail;

	/*
	 * Delay hooking up buffer heads until we have
	 * made our go/no-go decision.
	 */
	if (!page_has_buffers(page)) {
		create_empty_buffers(page, inode->i_dev, 1 << inode->i_blkbits);
	}

	/*
	 * Convert delalloc or unmapped space to real space and flush out
	 * to disk.
	 */
	if (need_trans)
		current->flags |= PF_NOIO;
	error = delalloc_convert(page, 1, unmapped);
	if (need_trans)
		current->flags &= ~PF_NOIO;
	if (error == -EAGAIN)
		goto out_fail;

	if (unlikely(error < 0)) {
		unlock_page(page);
		return error;
	}

	return 0;

out_fail:
	SetPageDirty(page);
	unlock_page(page);
	return 0;
}

/*
 * Called to move a page into cleanable state - and from there
 * to be released. Possibly the page is already clean. We always
 * have buffer heads in this call.
 *
 * Returns 0 if the page is ok to release, 1 otherwise.
 *
 * Possible scenarios are:
 *
 * 1. We are being called to release a page which has been written
 *    to via regular I/O. buffer heads will be dirty and possibly
 *    delalloc. If no delalloc buffer heads in this case then we
 *    can just return zero.
 *
 * 2. We are called to release a page which has been written via
 *    mmap, all we need to do is ensure there is no delalloc
 *    state in the buffer heads, if not we can let the caller
 *    free them and we should come back later via writepage.
 */
STATIC int
linvfs_release_page(
	struct page		*page,
	int			gfp_mask)
{
	int			delalloc, unmapped;

	count_page_state(page, &delalloc, &unmapped);
	if (!delalloc)
		return 1;

	if (!(gfp_mask & __GFP_FS))
		return 0;

	/*
	 * Convert delalloc space to real space, do not flush the
	 * data out to disk, that will be done by the caller.
	 * Never need to allocate space here - we will always
	 * come back to writepage in that case.
	 */
	return (delalloc_convert(page, 0, 0) == 0) ? 1 : 0;
}

STATIC int
linvfs_prepare_write(
	struct file		*file,
	struct page		*page,
	unsigned int		from,
	unsigned int		to)
{
	if (file && (file->f_flags & O_SYNC)) {
		return block_prepare_write(page, from, to,
						linvfs_get_block_sync);
	} else {
		return block_prepare_write(page, from, to,
						linvfs_get_block);
	}
}

/*
 * Initiate I/O on a kiobuf of user memory
 */
STATIC int
linvfs_direct_IO(
	int			rw,
	struct inode		*inode,
	struct kiobuf		*iobuf,
	unsigned long		blocknr,
	int			blocksize)
{
	struct page		**maplist;
	size_t			page_offset;
	page_buf_t		*pb;
	page_buf_bmap_t		map;
	int			error = 0;
	int			pb_flags, map_flags, pg_index = 0;
	size_t			length, total;
	loff_t			offset;
	size_t			map_size, size;

	total = length = iobuf->length;
	offset = blocknr;
	offset <<= inode->i_blkbits;

	maplist = iobuf->maplist;
	page_offset = iobuf->offset;

	map_flags = (rw ? PBF_WRITE : PBF_READ) | PBF_DIRECT;
	pb_flags = (rw ? PBF_WRITE : PBF_READ) | PBF_FORCEIO | _PBF_LOCKABLE;
	while (length) {
		error = map_blocks(inode, offset, length, &map, map_flags);
		if (error)
			break;

		map_size = map.pbm_bsize - map.pbm_delta;
		size = min(map_size, length);
		if (map.pbm_flags & PBMF_HOLE) {
			size_t	zero_len = size;

			if (rw == WRITE)
				break;

			/* Need to zero it all */
			while (zero_len) {
				struct page	*page;
				size_t		pg_len;

				pg_len = min((size_t)
						(PAGE_CACHE_SIZE - page_offset),
						zero_len);

				page = maplist[pg_index];

				memset(kmap(page) + page_offset, 0, pg_len);
				flush_dcache_page(page);
				kunmap(page);

				zero_len -= pg_len;
				if ((pg_len + page_offset) == PAGE_CACHE_SIZE) {
					pg_index++;
					page_offset = 0;
				} else {
					page_offset = (page_offset + pg_len) &
							~PAGE_CACHE_MASK;
				}
			}
		} else {
			int	pg_count;

			pg_count = (size + page_offset + PAGE_CACHE_SIZE - 1)
					>> PAGE_CACHE_SHIFT;
			if ((pb = pagebuf_lookup(map.pbm_target, inode, offset,
						size, pb_flags)) == NULL) {
				error = -ENOMEM;
				break;
			}
			/* Need to hook up pagebuf to kiobuf pages */
			pb->pb_pages = &maplist[pg_index];
			pb->pb_offset = page_offset;
			pb->pb_page_count = pg_count;

			pb->pb_bn = map.pbm_bn + (map.pbm_delta >> 9);
			error = pagebuf_iostart(pb, pb_flags);
			pb->pb_flags &= ~_PBF_LOCKABLE;
			pagebuf_rele(pb);
			if (error != 0) {
				if (error > 0)
					error = -error;
				break;
			}

			page_offset = (page_offset + size) & ~PAGE_CACHE_MASK;
			if (page_offset)
				pg_count--;
			pg_index += pg_count;
		}

		offset += size;
		length -= size;
	}

	return (error ? error : (int)(total - length));
}


struct address_space_operations linvfs_aops = {
	.readpage		= linvfs_readpage,
	.writepage		= linvfs_writepage,
	.sync_page		= block_sync_page,
	.releasepage		= linvfs_release_page,
	.prepare_write		= linvfs_prepare_write,
	.commit_write		= generic_commit_write,
	.bmap			= linvfs_bmap,
	.direct_IO		= linvfs_direct_IO,
};