/*
   * linux/fs/nfs/write.c
   *

   * Write file data over NFS.

   *
   * Copyright (C) 1996, 1997, Olaf Kirch <okir@monad.swb.de>
   */

  #include <linux/types.h>
  #include <linux/slab.h>
  #include <linux/mm.h>
  #include <linux/pagemap.h>
  #include <linux/file.h>

  #include <linux/writeback.h>

  #include <linux/swap.h>

  #include <linux/migrate.h>

  
  #include <linux/sunrpc/clnt.h>
  #include <linux/nfs_fs.h>
  #include <linux/nfs_mount.h>
  #include <linux/nfs_page.h>

  #include <linux/backing-dev.h>

  #include <asm/uaccess.h>

  
  #include "delegation.h"

  #include "internal.h"

  #include "iostat.h"

  #include "nfs4_fs.h"

  #include "fscache.h"

  
  #define NFSDBG_FACILITY		NFSDBG_PAGECACHE
  
  #define MIN_POOL_WRITE		(32)
  #define MIN_POOL_COMMIT		(4)
  
  /*
   * Local function declarations
   */

  static void nfs_pageio_init_write(struct nfs_pageio_descriptor *desc,
  				  struct inode *inode, int ioflags);

  static void nfs_redirty_request(struct nfs_page *req);

  static const struct rpc_call_ops nfs_write_partial_ops;
  static const struct rpc_call_ops nfs_write_full_ops;
  static const struct rpc_call_ops nfs_commit_ops;

  static struct kmem_cache *nfs_wdata_cachep;

  static mempool_t *nfs_wdata_mempool;

  static mempool_t *nfs_commit_mempool;

  struct nfs_write_data *nfs_commitdata_alloc(void)

  {

  	struct nfs_write_data *p = mempool_alloc(nfs_commit_mempool, GFP_NOFS);

  	if (p) {
  		memset(p, 0, sizeof(*p));
  		INIT_LIST_HEAD(&p->pages);

  		p->res.seq_res.sr_slotid = NFS4_MAX_SLOT_TABLE;

  	}
  	return p;
  }

  void nfs_commit_free(struct nfs_write_data *p)

  {

  	if (p && (p->pagevec != &p->page_array[0]))
  		kfree(p->pagevec);

  	mempool_free(p, nfs_commit_mempool);
  }

  struct nfs_write_data *nfs_writedata_alloc(unsigned int pagecount)

  {

  	struct nfs_write_data *p = mempool_alloc(nfs_wdata_mempool, GFP_NOFS);

  
  	if (p) {
  		memset(p, 0, sizeof(*p));
  		INIT_LIST_HEAD(&p->pages);

  		p->npages = pagecount;

  		p->res.seq_res.sr_slotid = NFS4_MAX_SLOT_TABLE;

  		if (pagecount <= ARRAY_SIZE(p->page_array))
  			p->pagevec = p->page_array;

  		else {

  			p->pagevec = kcalloc(pagecount, sizeof(struct page *), GFP_NOFS);
  			if (!p->pagevec) {

  				mempool_free(p, nfs_wdata_mempool);
  				p = NULL;
  			}
  		}
  	}
  	return p;
  }

  void nfs_writedata_free(struct nfs_write_data *p)

  {
  	if (p && (p->pagevec != &p->page_array[0]))
  		kfree(p->pagevec);
  	mempool_free(p, nfs_wdata_mempool);
  }

  static void nfs_writedata_release(struct nfs_write_data *wdata)

  {

  	put_nfs_open_context(wdata->args.context);

  	nfs_writedata_free(wdata);
  }

  static void nfs_context_set_write_error(struct nfs_open_context *ctx, int error)
  {
  	ctx->error = error;
  	smp_wmb();
  	set_bit(NFS_CONTEXT_ERROR_WRITE, &ctx->flags);
  }

  static struct nfs_page *nfs_page_find_request_locked(struct page *page)
  {
  	struct nfs_page *req = NULL;
  
  	if (PagePrivate(page)) {
  		req = (struct nfs_page *)page_private(page);
  		if (req != NULL)

  			kref_get(&req->wb_kref);

  	}
  	return req;
  }
  
  static struct nfs_page *nfs_page_find_request(struct page *page)
  {

  	struct inode *inode = page->mapping->host;

  	struct nfs_page *req = NULL;

  	spin_lock(&inode->i_lock);

  	req = nfs_page_find_request_locked(page);

  	spin_unlock(&inode->i_lock);

  	return req;
  }

  /* Adjust the file length if we're writing beyond the end */
  static void nfs_grow_file(struct page *page, unsigned int offset, unsigned int count)
  {
  	struct inode *inode = page->mapping->host;

  	loff_t end, i_size;
  	pgoff_t end_index;

  	spin_lock(&inode->i_lock);
  	i_size = i_size_read(inode);
  	end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;

  	if (i_size > 0 && page->index < end_index)

  		goto out;

  	end = ((loff_t)page->index << PAGE_CACHE_SHIFT) + ((loff_t)offset+count);
  	if (i_size >= end)

  		goto out;

  	i_size_write(inode, end);

  	nfs_inc_stats(inode, NFSIOS_EXTENDWRITE);
  out:
  	spin_unlock(&inode->i_lock);

  }

  /* A writeback failed: mark the page as bad, and invalidate the page cache */
  static void nfs_set_pageerror(struct page *page)
  {
  	SetPageError(page);
  	nfs_zap_mapping(page->mapping->host, page->mapping);
  }

  /* We can set the PG_uptodate flag if we see that a write request
   * covers the full page.
   */
  static void nfs_mark_uptodate(struct page *page, unsigned int base, unsigned int count)
  {

  	if (PageUptodate(page))
  		return;
  	if (base != 0)
  		return;

  	if (count != nfs_page_length(page))

  		return;

  	SetPageUptodate(page);

  }

  static int wb_priority(struct writeback_control *wbc)
  {
  	if (wbc->for_reclaim)

  		return FLUSH_HIGHPRI | FLUSH_STABLE;

  	if (wbc->for_kupdate)
  		return FLUSH_LOWPRI;
  	return 0;
  }
  
  /*

   * NFS congestion control
   */
  
  int nfs_congestion_kb;
  
  #define NFS_CONGESTION_ON_THRESH 	(nfs_congestion_kb >> (PAGE_SHIFT-10))
  #define NFS_CONGESTION_OFF_THRESH	\
  	(NFS_CONGESTION_ON_THRESH - (NFS_CONGESTION_ON_THRESH >> 2))

  static int nfs_set_page_writeback(struct page *page)

  {

  	int ret = test_set_page_writeback(page);
  
  	if (!ret) {

  		struct inode *inode = page->mapping->host;
  		struct nfs_server *nfss = NFS_SERVER(inode);

  		if (atomic_long_inc_return(&nfss->writeback) >

  				NFS_CONGESTION_ON_THRESH) {
  			set_bdi_congested(&nfss->backing_dev_info,
  						BLK_RW_ASYNC);
  		}

  	}

  	return ret;

  }
  
  static void nfs_end_page_writeback(struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	struct nfs_server *nfss = NFS_SERVER(inode);
  
  	end_page_writeback(page);

  	if (atomic_long_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)

  		clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);

  }

  static struct nfs_page *nfs_find_and_lock_request(struct page *page)

  {

  	struct inode *inode = page->mapping->host;

  	struct nfs_page *req;

  	int ret;

  	spin_lock(&inode->i_lock);

  	for (;;) {

  		req = nfs_page_find_request_locked(page);

  		if (req == NULL)
  			break;

  		if (nfs_set_page_tag_locked(req))

  			break;
  		/* Note: If we hold the page lock, as is the case in nfs_writepage,

  		 *	 then the call to nfs_set_page_tag_locked() will always

  		 *	 succeed provided that someone hasn't already marked the
  		 *	 request as dirty (in which case we don't care).
  		 */

  		spin_unlock(&inode->i_lock);

  		ret = nfs_wait_on_request(req);
  		nfs_release_request(req);
  		if (ret != 0)

  			return ERR_PTR(ret);

  		spin_lock(&inode->i_lock);

  	}

  	spin_unlock(&inode->i_lock);

  	return req;
  }
  
  /*
   * Find an associated nfs write request, and prepare to flush it out
   * May return an error if the user signalled nfs_wait_on_request().
   */
  static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
  				struct page *page)
  {
  	struct nfs_page *req;
  	int ret = 0;
  
  	req = nfs_find_and_lock_request(page);
  	if (!req)
  		goto out;
  	ret = PTR_ERR(req);
  	if (IS_ERR(req))
  		goto out;
  
  	ret = nfs_set_page_writeback(page);
  	BUG_ON(ret != 0);
  	BUG_ON(test_bit(PG_CLEAN, &req->wb_flags));

  	if (!nfs_pageio_add_request(pgio, req)) {
  		nfs_redirty_request(req);

  		ret = pgio->pg_error;

  	}

  out:
  	return ret;

  }

  static int nfs_do_writepage(struct page *page, struct writeback_control *wbc, struct nfs_pageio_descriptor *pgio)

  {

  	struct inode *inode = page->mapping->host;

  	nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGE);
  	nfs_add_stats(inode, NFSIOS_WRITEPAGES, 1);

  	nfs_pageio_cond_complete(pgio, page->index);

  	return nfs_page_async_flush(pgio, page);
  }

  /*
   * Write an mmapped page to the server.
   */
  static int nfs_writepage_locked(struct page *page, struct writeback_control *wbc)
  {
  	struct nfs_pageio_descriptor pgio;
  	int err;

  	nfs_pageio_init_write(&pgio, page->mapping->host, wb_priority(wbc));
  	err = nfs_do_writepage(page, wbc, &pgio);
  	nfs_pageio_complete(&pgio);
  	if (err < 0)
  		return err;
  	if (pgio.pg_error < 0)
  		return pgio.pg_error;
  	return 0;

  }
  
  int nfs_writepage(struct page *page, struct writeback_control *wbc)
  {

  	int ret;

  	ret = nfs_writepage_locked(page, wbc);

  	unlock_page(page);

  	return ret;
  }
  
  static int nfs_writepages_callback(struct page *page, struct writeback_control *wbc, void *data)
  {
  	int ret;
  
  	ret = nfs_do_writepage(page, wbc, data);
  	unlock_page(page);
  	return ret;

  }

  int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
  {

  	struct inode *inode = mapping->host;

  	unsigned long *bitlock = &NFS_I(inode)->flags;

  	struct nfs_pageio_descriptor pgio;

  	int err;

  	/* Stop dirtying of new pages while we sync */
  	err = wait_on_bit_lock(bitlock, NFS_INO_FLUSHING,
  			nfs_wait_bit_killable, TASK_KILLABLE);
  	if (err)
  		goto out_err;

  	nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGES);

  	nfs_pageio_init_write(&pgio, inode, wb_priority(wbc));

  	err = write_cache_pages(mapping, wbc, nfs_writepages_callback, &pgio);

  	nfs_pageio_complete(&pgio);

  
  	clear_bit_unlock(NFS_INO_FLUSHING, bitlock);
  	smp_mb__after_clear_bit();
  	wake_up_bit(bitlock, NFS_INO_FLUSHING);

  	if (err < 0)

  		goto out_err;
  	err = pgio.pg_error;
  	if (err < 0)
  		goto out_err;

  	return 0;

  out_err:
  	return err;

  }
  
  /*
   * Insert a write request into an inode
   */

  static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)

  {
  	struct nfs_inode *nfsi = NFS_I(inode);
  	int error;

  	error = radix_tree_preload(GFP_NOFS);
  	if (error != 0)
  		goto out;
  
  	/* Lock the request! */
  	nfs_lock_request_dontget(req);
  
  	spin_lock(&inode->i_lock);

  	error = radix_tree_insert(&nfsi->nfs_page_tree, req->wb_index, req);

  	BUG_ON(error);

  	if (!nfsi->npages) {
  		igrab(inode);

  		if (nfs_have_delegation(inode, FMODE_WRITE))
  			nfsi->change_attr++;
  	}

  	SetPagePrivate(req->wb_page);

  	set_page_private(req->wb_page, (unsigned long)req);

  	nfsi->npages++;

  	kref_get(&req->wb_kref);

  	radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index,
  				NFS_PAGE_TAG_LOCKED);

  	spin_unlock(&inode->i_lock);
  	radix_tree_preload_end();
  out:
  	return error;

  }
  
  /*

   * Remove a write request from an inode

   */
  static void nfs_inode_remove_request(struct nfs_page *req)
  {

  	struct inode *inode = req->wb_context->path.dentry->d_inode;

  	struct nfs_inode *nfsi = NFS_I(inode);
  
  	BUG_ON (!NFS_WBACK_BUSY(req));

  	spin_lock(&inode->i_lock);

  	set_page_private(req->wb_page, 0);

  	ClearPagePrivate(req->wb_page);

  	radix_tree_delete(&nfsi->nfs_page_tree, req->wb_index);
  	nfsi->npages--;
  	if (!nfsi->npages) {

  		spin_unlock(&inode->i_lock);

  		iput(inode);
  	} else

  		spin_unlock(&inode->i_lock);

  	nfs_clear_request(req);
  	nfs_release_request(req);
  }

  static void

  nfs_mark_request_dirty(struct nfs_page *req)

  {

  	__set_page_dirty_nobuffers(req->wb_page);
  }

  #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
  /*
   * Add a request to the inode's commit list.
   */
  static void
  nfs_mark_request_commit(struct nfs_page *req)
  {

  	struct inode *inode = req->wb_context->path.dentry->d_inode;

  	struct nfs_inode *nfsi = NFS_I(inode);

  	spin_lock(&inode->i_lock);

  	set_bit(PG_CLEAN, &(req)->wb_flags);

  	radix_tree_tag_set(&nfsi->nfs_page_tree,
  			req->wb_index,
  			NFS_PAGE_TAG_COMMIT);

  	spin_unlock(&inode->i_lock);

  	inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);

  	inc_bdi_stat(req->wb_page->mapping->backing_dev_info, BDI_RECLAIMABLE);

  	__mark_inode_dirty(inode, I_DIRTY_DATASYNC);

  }

  static int
  nfs_clear_request_commit(struct nfs_page *req)
  {
  	struct page *page = req->wb_page;
  
  	if (test_and_clear_bit(PG_CLEAN, &(req)->wb_flags)) {
  		dec_zone_page_state(page, NR_UNSTABLE_NFS);
  		dec_bdi_stat(page->mapping->backing_dev_info, BDI_RECLAIMABLE);
  		return 1;
  	}
  	return 0;
  }

  static inline
  int nfs_write_need_commit(struct nfs_write_data *data)
  {
  	return data->verf.committed != NFS_FILE_SYNC;
  }
  
  static inline
  int nfs_reschedule_unstable_write(struct nfs_page *req)
  {

  	if (test_and_clear_bit(PG_NEED_COMMIT, &req->wb_flags)) {

  		nfs_mark_request_commit(req);
  		return 1;
  	}
  	if (test_and_clear_bit(PG_NEED_RESCHED, &req->wb_flags)) {

  		nfs_mark_request_dirty(req);

  		return 1;
  	}
  	return 0;
  }
  #else
  static inline void
  nfs_mark_request_commit(struct nfs_page *req)
  {
  }

  static inline int
  nfs_clear_request_commit(struct nfs_page *req)
  {
  	return 0;
  }

  static inline
  int nfs_write_need_commit(struct nfs_write_data *data)
  {
  	return 0;
  }
  
  static inline
  int nfs_reschedule_unstable_write(struct nfs_page *req)
  {
  	return 0;
  }

  #endif
  
  /*
   * Wait for a request to complete.
   *

   * Interruptible by fatal signals only.

   */

  static int nfs_wait_on_requests_locked(struct inode *inode, pgoff_t idx_start, unsigned int npages)

  {
  	struct nfs_inode *nfsi = NFS_I(inode);
  	struct nfs_page *req;

  	pgoff_t idx_end, next;

  	unsigned int		res = 0;
  	int			error;
  
  	if (npages == 0)
  		idx_end = ~0;
  	else
  		idx_end = idx_start + npages - 1;

  	next = idx_start;

  	while (radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree, (void **)&req, next, 1, NFS_PAGE_TAG_LOCKED)) {

  		if (req->wb_index > idx_end)
  			break;
  
  		next = req->wb_index + 1;

  		BUG_ON(!NFS_WBACK_BUSY(req));

  		kref_get(&req->wb_kref);

  		spin_unlock(&inode->i_lock);

  		error = nfs_wait_on_request(req);
  		nfs_release_request(req);

  		spin_lock(&inode->i_lock);

  		if (error < 0)
  			return error;

  		res++;
  	}

  	return res;
  }

  static void nfs_cancel_commit_list(struct list_head *head)
  {
  	struct nfs_page *req;
  
  	while(!list_empty(head)) {
  		req = nfs_list_entry(head->next);
  		nfs_list_remove_request(req);

  		nfs_clear_request_commit(req);

  		nfs_inode_remove_request(req);

  		nfs_unlock_request(req);

  	}
  }

  #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)

  static int
  nfs_need_commit(struct nfs_inode *nfsi)
  {
  	return radix_tree_tagged(&nfsi->nfs_page_tree, NFS_PAGE_TAG_COMMIT);
  }

  /*
   * nfs_scan_commit - Scan an inode for commit requests
   * @inode: NFS inode to scan
   * @dst: destination list
   * @idx_start: lower bound of page->index to scan.
   * @npages: idx_start + npages sets the upper bound to scan.
   *
   * Moves requests from the inode's 'commit' request list.
   * The requests are *not* checked to ensure that they form a contiguous set.
   */
  static int

  nfs_scan_commit(struct inode *inode, struct list_head *dst, pgoff_t idx_start, unsigned int npages)

  {
  	struct nfs_inode *nfsi = NFS_I(inode);

  	if (!nfs_need_commit(nfsi))
  		return 0;
  
  	return nfs_scan_list(nfsi, dst, idx_start, npages, NFS_PAGE_TAG_COMMIT);

  }

  #else

  static inline int nfs_need_commit(struct nfs_inode *nfsi)
  {
  	return 0;
  }

  static inline int nfs_scan_commit(struct inode *inode, struct list_head *dst, pgoff_t idx_start, unsigned int npages)

  {
  	return 0;
  }

  #endif

  /*

   * Search for an existing write request, and attempt to update
   * it to reflect a new dirty region on a given page.

   *

   * If the attempt fails, then the existing request is flushed out
   * to disk.

   */

  static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
  		struct page *page,
  		unsigned int offset,
  		unsigned int bytes)

  {

  	struct nfs_page *req;
  	unsigned int rqend;
  	unsigned int end;
  	int error;
  
  	if (!PagePrivate(page))
  		return NULL;

  
  	end = offset + bytes;

  	spin_lock(&inode->i_lock);

  	for (;;) {

  		req = nfs_page_find_request_locked(page);

  		if (req == NULL)
  			goto out_unlock;
  
  		rqend = req->wb_offset + req->wb_bytes;
  		/*
  		 * Tell the caller to flush out the request if
  		 * the offsets are non-contiguous.
  		 * Note: nfs_flush_incompatible() will already
  		 * have flushed out requests having wrong owners.
  		 */

  		if (offset > rqend

  		    || end < req->wb_offset)
  			goto out_flushme;
  
  		if (nfs_set_page_tag_locked(req))

  			break;

  		/* The request is locked, so wait and then retry */

  		spin_unlock(&inode->i_lock);

  		error = nfs_wait_on_request(req);
  		nfs_release_request(req);
  		if (error != 0)
  			goto out_err;
  		spin_lock(&inode->i_lock);

  	}

  	if (nfs_clear_request_commit(req))
  		radix_tree_tag_clear(&NFS_I(inode)->nfs_page_tree,
  				req->wb_index, NFS_PAGE_TAG_COMMIT);

  	/* Okay, the request matches. Update the region */
  	if (offset < req->wb_offset) {
  		req->wb_offset = offset;
  		req->wb_pgbase = offset;

  	}

  	if (end > rqend)
  		req->wb_bytes = end - req->wb_offset;

  	else
  		req->wb_bytes = rqend - req->wb_offset;
  out_unlock:
  	spin_unlock(&inode->i_lock);
  	return req;
  out_flushme:
  	spin_unlock(&inode->i_lock);
  	nfs_release_request(req);
  	error = nfs_wb_page(inode, page);
  out_err:
  	return ERR_PTR(error);
  }
  
  /*
   * Try to update an existing write request, or create one if there is none.
   *
   * Note: Should always be called with the Page Lock held to prevent races
   * if we have to add a new request. Also assumes that the caller has
   * already called nfs_flush_incompatible() if necessary.
   */
  static struct nfs_page * nfs_setup_write_request(struct nfs_open_context* ctx,
  		struct page *page, unsigned int offset, unsigned int bytes)
  {
  	struct inode *inode = page->mapping->host;
  	struct nfs_page	*req;
  	int error;

  	req = nfs_try_to_update_request(inode, page, offset, bytes);
  	if (req != NULL)
  		goto out;
  	req = nfs_create_request(ctx, inode, page, offset, bytes);
  	if (IS_ERR(req))
  		goto out;
  	error = nfs_inode_add_request(inode, req);
  	if (error != 0) {
  		nfs_release_request(req);
  		req = ERR_PTR(error);
  	}

  out:

  	return req;

  }

  static int nfs_writepage_setup(struct nfs_open_context *ctx, struct page *page,
  		unsigned int offset, unsigned int count)
  {
  	struct nfs_page	*req;
  
  	req = nfs_setup_write_request(ctx, page, offset, count);
  	if (IS_ERR(req))
  		return PTR_ERR(req);
  	/* Update file length */
  	nfs_grow_file(page, offset, count);
  	nfs_mark_uptodate(page, req->wb_pgbase, req->wb_bytes);
  	nfs_clear_page_tag_locked(req);
  	return 0;
  }

  int nfs_flush_incompatible(struct file *file, struct page *page)
  {

  	struct nfs_open_context *ctx = nfs_file_open_context(file);

  	struct nfs_page	*req;

  	int do_flush, status;

  	/*
  	 * Look for a request corresponding to this page. If there
  	 * is one, and it belongs to another file, we flush it out
  	 * before we try to copy anything into the page. Do this
  	 * due to the lack of an ACCESS-type call in NFSv2.
  	 * Also do the same if we find a request from an existing
  	 * dropped page.
  	 */

  	do {
  		req = nfs_page_find_request(page);
  		if (req == NULL)
  			return 0;

  		do_flush = req->wb_page != page || req->wb_context != ctx;

  		nfs_release_request(req);

  		if (!do_flush)
  			return 0;
  		status = nfs_wb_page(page->mapping->host, page);
  	} while (status == 0);
  	return status;

  }
  
  /*

   * If the page cache is marked as unsafe or invalid, then we can't rely on
   * the PageUptodate() flag. In this case, we will need to turn off
   * write optimisations that depend on the page contents being correct.
   */
  static int nfs_write_pageuptodate(struct page *page, struct inode *inode)
  {
  	return PageUptodate(page) &&
  		!(NFS_I(inode)->cache_validity & (NFS_INO_REVAL_PAGECACHE|NFS_INO_INVALID_DATA));
  }
  
  /*

   * Update and possibly write a cached page of an NFS file.
   *
   * XXX: Keep an eye on generic_file_read to make sure it doesn't do bad
   * things with a page scheduled for an RPC call (e.g. invalidate it).
   */
  int nfs_updatepage(struct file *file, struct page *page,
  		unsigned int offset, unsigned int count)
  {

  	struct nfs_open_context *ctx = nfs_file_open_context(file);

  	struct inode	*inode = page->mapping->host;

  	int		status = 0;

  	nfs_inc_stats(inode, NFSIOS_VFSUPDATEPAGE);

  	dprintk("NFS:       nfs_updatepage(%s/%s %d@%lld)
  ",

  		file->f_path.dentry->d_parent->d_name.name,
  		file->f_path.dentry->d_name.name, count,

  		(long long)(page_offset(page) + offset));

  	/* If we're not using byte range locks, and we know the page

  	 * is up to date, it may be more efficient to extend the write
  	 * to cover the entire page in order to avoid fragmentation
  	 * inefficiencies.

  	 */

  	if (nfs_write_pageuptodate(page, inode) &&
  			inode->i_flock == NULL &&

  			!(file->f_flags & O_SYNC)) {

  		count = max(count + offset, nfs_page_length(page));

  		offset = 0;

  	}

  	status = nfs_writepage_setup(ctx, page, offset, count);

  	if (status < 0)
  		nfs_set_pageerror(page);
  	else
  		__set_page_dirty_nobuffers(page);

  	dprintk("NFS:       nfs_updatepage returns %d (isize %lld)
  ",

  			status, (long long)i_size_read(inode));

  	return status;
  }
  
  static void nfs_writepage_release(struct nfs_page *req)
  {

  	if (PageError(req->wb_page) || !nfs_reschedule_unstable_write(req)) {

  		nfs_end_page_writeback(req->wb_page);
  		nfs_inode_remove_request(req);
  	} else
  		nfs_end_page_writeback(req->wb_page);

  	nfs_clear_page_tag_locked(req);

  }

  static int flush_task_priority(int how)

  {
  	switch (how & (FLUSH_HIGHPRI|FLUSH_LOWPRI)) {
  		case FLUSH_HIGHPRI:
  			return RPC_PRIORITY_HIGH;
  		case FLUSH_LOWPRI:
  			return RPC_PRIORITY_LOW;
  	}
  	return RPC_PRIORITY_NORMAL;
  }
  
  /*
   * Set up the argument/result storage required for the RPC call.
   */

  static int nfs_write_rpcsetup(struct nfs_page *req,

  		struct nfs_write_data *data,

  		const struct rpc_call_ops *call_ops,

  		unsigned int count, unsigned int offset,
  		int how)
  {

  	struct inode *inode = req->wb_context->path.dentry->d_inode;
  	int flags = (how & FLUSH_SYNC) ? 0 : RPC_TASK_ASYNC;

  	int priority = flush_task_priority(how);

  	struct rpc_task *task;

  	struct rpc_message msg = {
  		.rpc_argp = &data->args,
  		.rpc_resp = &data->res,
  		.rpc_cred = req->wb_context->cred,
  	};

  	struct rpc_task_setup task_setup_data = {
  		.rpc_client = NFS_CLIENT(inode),

  		.task = &data->task,

  		.rpc_message = &msg,

  		.callback_ops = call_ops,
  		.callback_data = data,

  		.workqueue = nfsiod_workqueue,

  		.flags = flags,

  		.priority = priority,

  	};

  
  	/* Set up the RPC argument and reply structs
  	 * NB: take care not to mess about with data->commit et al. */
  
  	data->req = req;

  	data->inode = inode = req->wb_context->path.dentry->d_inode;

  	data->cred = msg.rpc_cred;

  
  	data->args.fh     = NFS_FH(inode);
  	data->args.offset = req_offset(req) + offset;
  	data->args.pgbase = req->wb_pgbase + offset;
  	data->args.pages  = data->pagevec;
  	data->args.count  = count;

  	data->args.context = get_nfs_open_context(req->wb_context);

  	data->args.stable  = NFS_UNSTABLE;
  	if (how & FLUSH_STABLE) {
  		data->args.stable = NFS_DATA_SYNC;

  		if (!nfs_need_commit(NFS_I(inode)))

  			data->args.stable = NFS_FILE_SYNC;
  	}

  
  	data->res.fattr   = &data->fattr;
  	data->res.count   = count;
  	data->res.verf    = &data->verf;

  	nfs_fattr_init(&data->fattr);

  	/* Set up the initial task struct.  */

  	NFS_PROTO(inode)->write_setup(data, &msg);

  	dprintk("NFS: %5u initiated write call "

  		"(req %s/%lld, %u bytes @ offset %llu)
  ",

  		data->task.tk_pid,

  		inode->i_sb->s_id,
  		(long long)NFS_FILEID(inode),
  		count,
  		(unsigned long long)data->args.offset);

  	task = rpc_run_task(&task_setup_data);

  	if (IS_ERR(task))
  		return PTR_ERR(task);
  	rpc_put_task(task);
  	return 0;

  }

  /* If a nfs_flush_* function fails, it should remove reqs from @head and
   * call this on each, which will prepare them to be retried on next
   * writeback using standard nfs.
   */
  static void nfs_redirty_request(struct nfs_page *req)
  {
  	nfs_mark_request_dirty(req);
  	nfs_end_page_writeback(req->wb_page);
  	nfs_clear_page_tag_locked(req);
  }

  /*
   * Generate multiple small requests to write out a single
   * contiguous dirty area on one page.
   */

  static int nfs_flush_multi(struct inode *inode, struct list_head *head, unsigned int npages, size_t count, int how)

  {
  	struct nfs_page *req = nfs_list_entry(head->next);
  	struct page *page = req->wb_page;
  	struct nfs_write_data *data;

  	size_t wsize = NFS_SERVER(inode)->wsize, nbytes;
  	unsigned int offset;

  	int requests = 0;

  	int ret = 0;

  	LIST_HEAD(list);
  
  	nfs_list_remove_request(req);

  	nbytes = count;

  	do {
  		size_t len = min(nbytes, wsize);

  		data = nfs_writedata_alloc(1);

  		if (!data)
  			goto out_bad;
  		list_add(&data->pages, &list);
  		requests++;

  		nbytes -= len;
  	} while (nbytes != 0);

  	atomic_set(&req->wb_complete, requests);
  
  	ClearPageError(page);

  	offset = 0;

  	nbytes = count;

  	do {

  		int ret2;

  		data = list_entry(list.next, struct nfs_write_data, pages);
  		list_del_init(&data->pages);
  
  		data->pagevec[0] = page;

  		if (nbytes < wsize)
  			wsize = nbytes;

  		ret2 = nfs_write_rpcsetup(req, data, &nfs_write_partial_ops,

  				   wsize, offset, how);

  		if (ret == 0)
  			ret = ret2;

  		offset += wsize;
  		nbytes -= wsize;

  	} while (nbytes != 0);

  	return ret;

  
  out_bad:
  	while (!list_empty(&list)) {
  		data = list_entry(list.next, struct nfs_write_data, pages);
  		list_del(&data->pages);

  		nfs_writedata_release(data);

  	}

  	nfs_redirty_request(req);

  	return -ENOMEM;
  }
  
  /*
   * Create an RPC task for the given write request and kick it.
   * The page must have been locked by the caller.
   *
   * It may happen that the page we're passed is not marked dirty.
   * This is the case if nfs_updatepage detects a conflicting request
   * that has been written but not committed.
   */

  static int nfs_flush_one(struct inode *inode, struct list_head *head, unsigned int npages, size_t count, int how)

  {
  	struct nfs_page		*req;
  	struct page		**pages;
  	struct nfs_write_data	*data;

  	data = nfs_writedata_alloc(npages);

  	if (!data)
  		goto out_bad;
  
  	pages = data->pagevec;

  	while (!list_empty(head)) {
  		req = nfs_list_entry(head->next);
  		nfs_list_remove_request(req);
  		nfs_list_add_request(req, &data->pages);
  		ClearPageError(req->wb_page);

  		*pages++ = req->wb_page;

  	}
  	req = nfs_list_entry(data->pages.next);

  	/* Set up the argument struct */

  	return nfs_write_rpcsetup(req, data, &nfs_write_full_ops, count, 0, how);

   out_bad:
  	while (!list_empty(head)) {

  		req = nfs_list_entry(head->next);

  		nfs_list_remove_request(req);

  		nfs_redirty_request(req);

  	}
  	return -ENOMEM;
  }

  static void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
  				  struct inode *inode, int ioflags)

  {

  	size_t wsize = NFS_SERVER(inode)->wsize;

  	if (wsize < PAGE_CACHE_SIZE)

  		nfs_pageio_init(pgio, inode, nfs_flush_multi, wsize, ioflags);

  	else

  		nfs_pageio_init(pgio, inode, nfs_flush_one, wsize, ioflags);

  }
  
  /*
   * Handle a write reply that flushed part of a page.
   */

  static void nfs_writeback_done_partial(struct rpc_task *task, void *calldata)

  {

  	struct nfs_write_data	*data = calldata;

  	dprintk("NFS: %5u write(%s/%lld %d@%lld)",
  		task->tk_pid,
  		data->req->wb_context->path.dentry->d_inode->i_sb->s_id,
  		(long long)
  		  NFS_FILEID(data->req->wb_context->path.dentry->d_inode),
  		data->req->wb_bytes, (long long)req_offset(data->req));

  	nfs_writeback_done(task, data);
  }

  static void nfs_writeback_release_partial(void *calldata)
  {
  	struct nfs_write_data	*data = calldata;
  	struct nfs_page		*req = data->req;
  	struct page		*page = req->wb_page;
  	int status = data->task.tk_status;
  
  	if (status < 0) {

  		nfs_set_pageerror(page);

  		nfs_context_set_write_error(req->wb_context, status);
  		dprintk(", error = %d
  ", status);

  		goto out;

  	}

  	if (nfs_write_need_commit(data)) {

  		struct inode *inode = page->mapping->host;

  		spin_lock(&inode->i_lock);

  		if (test_bit(PG_NEED_RESCHED, &req->wb_flags)) {
  			/* Do nothing we need to resend the writes */
  		} else if (!test_and_set_bit(PG_NEED_COMMIT, &req->wb_flags)) {
  			memcpy(&req->wb_verf, &data->verf, sizeof(req->wb_verf));
  			dprintk(" defer commit
  ");
  		} else if (memcmp(&req->wb_verf, &data->verf, sizeof(req->wb_verf))) {
  			set_bit(PG_NEED_RESCHED, &req->wb_flags);
  			clear_bit(PG_NEED_COMMIT, &req->wb_flags);
  			dprintk(" server reboot detected
  ");
  		}

  		spin_unlock(&inode->i_lock);

  	} else
  		dprintk(" OK
  ");
  
  out:

  	if (atomic_dec_and_test(&req->wb_complete))
  		nfs_writepage_release(req);

  	nfs_writedata_release(calldata);

  }

  #if defined(CONFIG_NFS_V4_1)
  void nfs_write_prepare(struct rpc_task *task, void *calldata)
  {
  	struct nfs_write_data *data = calldata;
  	struct nfs_client *clp = (NFS_SERVER(data->inode))->nfs_client;
  
  	if (nfs4_setup_sequence(clp, &data->args.seq_args,
  				&data->res.seq_res, 1, task))
  		return;
  	rpc_call_start(task);
  }
  #endif /* CONFIG_NFS_V4_1 */

  static const struct rpc_call_ops nfs_write_partial_ops = {

  #if defined(CONFIG_NFS_V4_1)
  	.rpc_call_prepare = nfs_write_prepare,
  #endif /* CONFIG_NFS_V4_1 */

  	.rpc_call_done = nfs_writeback_done_partial,

  	.rpc_release = nfs_writeback_release_partial,

  };

  /*
   * Handle a write reply that flushes a whole page.
   *
   * FIXME: There is an inherent race with invalidate_inode_pages and
   *	  writebacks since the page->count is kept > 1 for as long
   *	  as the page has a write request pending.
   */

  static void nfs_writeback_done_full(struct rpc_task *task, void *calldata)

  {

  	struct nfs_write_data	*data = calldata;

  	nfs_writeback_done(task, data);
  }
  
  static void nfs_writeback_release_full(void *calldata)
  {
  	struct nfs_write_data	*data = calldata;
  	int status = data->task.tk_status;

  	/* Update attributes as result of writeback. */
  	while (!list_empty(&data->pages)) {

  		struct nfs_page *req = nfs_list_entry(data->pages.next);
  		struct page *page = req->wb_page;

  		nfs_list_remove_request(req);

  		dprintk("NFS: %5u write (%s/%lld %d@%lld)",
  			data->task.tk_pid,

  			req->wb_context->path.dentry->d_inode->i_sb->s_id,
  			(long long)NFS_FILEID(req->wb_context->path.dentry->d_inode),

  			req->wb_bytes,
  			(long long)req_offset(req));

  		if (status < 0) {

  			nfs_set_pageerror(page);

  			nfs_context_set_write_error(req->wb_context, status);
  			dprintk(", error = %d
  ", status);

  			goto remove_request;

  		}

  		if (nfs_write_need_commit(data)) {
  			memcpy(&req->wb_verf, &data->verf, sizeof(req->wb_verf));
  			nfs_mark_request_commit(req);
  			nfs_end_page_writeback(page);
  			dprintk(" marked for commit
  ");

  			goto next;
  		}

  		dprintk(" OK
  ");
  remove_request:
  		nfs_end_page_writeback(page);

  		nfs_inode_remove_request(req);

  	next:

  		nfs_clear_page_tag_locked(req);

  	}

  	nfs_writedata_release(calldata);

  }

  static const struct rpc_call_ops nfs_write_full_ops = {

  #if defined(CONFIG_NFS_V4_1)
  	.rpc_call_prepare = nfs_write_prepare,
  #endif /* CONFIG_NFS_V4_1 */

  	.rpc_call_done = nfs_writeback_done_full,

  	.rpc_release = nfs_writeback_release_full,

  };

  /*
   * This function is called when the WRITE call is complete.
   */

  int nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data)

  {

  	struct nfs_writeargs	*argp = &data->args;
  	struct nfs_writeres	*resp = &data->res;

  	struct nfs_server	*server = NFS_SERVER(data->inode);

  	int status;

  	dprintk("NFS: %5u nfs_writeback_done (status %d)
  ",

  		task->tk_pid, task->tk_status);

  	/*
  	 * ->write_done will attempt to use post-op attributes to detect
  	 * conflicting writes by other clients.  A strict interpretation
  	 * of close-to-open would allow us to continue caching even if
  	 * another writer had changed the file, but some applications
  	 * depend on tighter cache coherency when writing.
  	 */

  	status = NFS_PROTO(data->inode)->write_done(task, data);
  	if (status != 0)
  		return status;

  	nfs_add_stats(data->inode, NFSIOS_SERVERWRITTENBYTES, resp->count);

  #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
  	if (resp->verf->committed < argp->stable && task->tk_status >= 0) {
  		/* We tried a write call, but the server did not
  		 * commit data to stable storage even though we
  		 * requested it.
  		 * Note: There is a known bug in Tru64 < 5.0 in which
  		 *	 the server reports NFS_DATA_SYNC, but performs
  		 *	 NFS_FILE_SYNC. We therefore implement this checking
  		 *	 as a dprintk() in order to avoid filling syslog.
  		 */
  		static unsigned long    complain;
  
  		if (time_before(complain, jiffies)) {

  			dprintk("NFS:       faulty NFS server %s:"

  				" (committed = %d) != (stable = %d)
  ",

  				server->nfs_client->cl_hostname,

  				resp->verf->committed, argp->stable);
  			complain = jiffies + 300 * HZ;
  		}
  	}
  #endif
  	/* Is this a short write? */
  	if (task->tk_status >= 0 && resp->count < argp->count) {
  		static unsigned long    complain;

  		nfs_inc_stats(data->inode, NFSIOS_SHORTWRITE);

  		/* Has the server at least made some progress? */
  		if (resp->count != 0) {
  			/* Was this an NFSv2 write or an NFSv3 stable write? */
  			if (resp->verf->committed != NFS_UNSTABLE) {
  				/* Resend from where the server left off */
  				argp->offset += resp->count;
  				argp->pgbase += resp->count;
  				argp->count -= resp->count;
  			} else {
  				/* Resend as a stable write in order to avoid
  				 * headaches in the case of a server crash.
  				 */
  				argp->stable = NFS_FILE_SYNC;
  			}

  			nfs4_restart_rpc(task, server->nfs_client);

  			return -EAGAIN;

  		}
  		if (time_before(complain, jiffies)) {
  			printk(KERN_WARNING
  			       "NFS: Server wrote zero bytes, expected %u.
  ",
  					argp->count);
  			complain = jiffies + 300 * HZ;
  		}
  		/* Can't do anything about it except throw an error. */
  		task->tk_status = -EIO;
  	}

  	nfs4_sequence_free_slot(server->nfs_client, &data->res.seq_res);

  	return 0;

  }
  
  
  #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)

  void nfs_commitdata_release(void *data)

  {

  	struct nfs_write_data *wdata = data;
  
  	put_nfs_open_context(wdata->args.context);

  	nfs_commit_free(wdata);
  }
  
  /*
   * Set up the argument/result storage required for the RPC call.
   */

  static int nfs_commit_rpcsetup(struct list_head *head,

  		struct nfs_write_data *data,
  		int how)

  {

  	struct nfs_page *first = nfs_list_entry(head->next);
  	struct inode *inode = first->wb_context->path.dentry->d_inode;
  	int flags = (how & FLUSH_SYNC) ? 0 : RPC_TASK_ASYNC;

  	int priority = flush_task_priority(how);

  	struct rpc_task *task;

  	struct rpc_message msg = {
  		.rpc_argp = &data->args,
  		.rpc_resp = &data->res,
  		.rpc_cred = first->wb_context->cred,
  	};

  	struct rpc_task_setup task_setup_data = {

  		.task = &data->task,

  		.rpc_client = NFS_CLIENT(inode),

  		.rpc_message = &msg,

  		.callback_ops = &nfs_commit_ops,
  		.callback_data = data,

  		.workqueue = nfsiod_workqueue,

  		.flags = flags,

  		.priority = priority,

  	};

  
  	/* Set up the RPC argument and reply structs
  	 * NB: take care not to mess about with data->commit et al. */
  
  	list_splice_init(head, &data->pages);

  	data->inode	  = inode;

  	data->cred	  = msg.rpc_cred;

  
  	data->args.fh     = NFS_FH(data->inode);

  	/* Note: we always request a commit of the entire inode */
  	data->args.offset = 0;
  	data->args.count  = 0;

  	data->args.context = get_nfs_open_context(first->wb_context);

  	data->res.count   = 0;

  	data->res.fattr   = &data->fattr;
  	data->res.verf    = &data->verf;

  	nfs_fattr_init(&data->fattr);

  
  	/* Set up the initial task struct.  */

  	NFS_PROTO(inode)->commit_setup(data, &msg);

  	dprintk("NFS: %5u initiated commit call
  ", data->task.tk_pid);

  	task = rpc_run_task(&task_setup_data);

  	if (IS_ERR(task))
  		return PTR_ERR(task);
  	rpc_put_task(task);
  	return 0;

  }
  
  /*
   * Commit dirty pages
   */
  static int

  nfs_commit_list(struct inode *inode, struct list_head *head, int how)

  {
  	struct nfs_write_data	*data;
  	struct nfs_page         *req;

  	data = nfs_commitdata_alloc();

  
  	if (!data)
  		goto out_bad;
  
  	/* Set up the argument struct */

  	return nfs_commit_rpcsetup(head, data, how);

   out_bad:
  	while (!list_empty(head)) {
  		req = nfs_list_entry(head->next);
  		nfs_list_remove_request(req);
  		nfs_mark_request_commit(req);

  		dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);

  		dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
  				BDI_RECLAIMABLE);

  		nfs_clear_page_tag_locked(req);

  	}
  	return -ENOMEM;
  }
  
  /*
   * COMMIT call returned
   */

  static void nfs_commit_done(struct rpc_task *task, void *calldata)

  {

  	struct nfs_write_data	*data = calldata;

          dprintk("NFS: %5u nfs_commit_done (status %d)
  ",

                                  task->tk_pid, task->tk_status);

  	/* Call the NFS version-specific code */
  	if (NFS_PROTO(data->inode)->commit_done(task, data) != 0)
  		return;

  }
  
  static void nfs_commit_release(void *calldata)
  {
  	struct nfs_write_data	*data = calldata;
  	struct nfs_page		*req;
  	int status = data->task.tk_status;

  	while (!list_empty(&data->pages)) {
  		req = nfs_list_entry(data->pages.next);
  		nfs_list_remove_request(req);

  		nfs_clear_request_commit(req);

  		dprintk("NFS:       commit (%s/%lld %d@%lld)",

  			req->wb_context->path.dentry->d_inode->i_sb->s_id,
  			(long long)NFS_FILEID(req->wb_context->path.dentry->d_inode),

  			req->wb_bytes,
  			(long long)req_offset(req));

  		if (status < 0) {
  			nfs_context_set_write_error(req->wb_context, status);

  			nfs_inode_remove_request(req);

  			dprintk(", error = %d
  ", status);

  			goto next;
  		}
  
  		/* Okay, COMMIT succeeded, apparently. Check the verifier
  		 * returned by the server against all stored verfs. */
  		if (!memcmp(req->wb_verf.verifier, data->verf.verifier, sizeof(data->verf.verifier))) {
  			/* We have a match */
  			nfs_inode_remove_request(req);
  			dprintk(" OK
  ");
  			goto next;
  		}
  		/* We have a mismatch. Write the page again */
  		dprintk(" mismatch
  ");

  		nfs_mark_request_dirty(req);

  	next:

  		nfs_clear_page_tag_locked(req);

  	}

  	nfs_commitdata_release(calldata);

  }

  
  static const struct rpc_call_ops nfs_commit_ops = {

  #if defined(CONFIG_NFS_V4_1)
  	.rpc_call_prepare = nfs_write_prepare,
  #endif /* CONFIG_NFS_V4_1 */

  	.rpc_call_done = nfs_commit_done,
  	.rpc_release = nfs_commit_release,
  };

  int nfs_commit_inode(struct inode *inode, int how)

  {

  	LIST_HEAD(head);

  	int res;

  	spin_lock(&inode->i_lock);

  	res = nfs_scan_commit(inode, &head, 0, 0);

  	spin_unlock(&inode->i_lock);

  	if (res) {

  		int error = nfs_commit_list(inode, &head, how);

  		if (error < 0)
  			return error;
  	}

  	return res;
  }

  #else
  static inline int nfs_commit_list(struct inode *inode, struct list_head *head, int how)
  {
  	return 0;
  }

  #endif

  long nfs_sync_mapping_wait(struct address_space *mapping, struct writeback_control *wbc, int how)

  {

  	struct inode *inode = mapping->host;

  	pgoff_t idx_start, idx_end;

  	unsigned int npages = 0;

  	LIST_HEAD(head);

  	int nocommit = how & FLUSH_NOCOMMIT;

  	long pages, ret;

  	/* FIXME */
  	if (wbc->range_cyclic)
  		idx_start = 0;
  	else {
  		idx_start = wbc->range_start >> PAGE_CACHE_SHIFT;
  		idx_end = wbc->range_end >> PAGE_CACHE_SHIFT;
  		if (idx_end > idx_start) {

  			pgoff_t l_npages = 1 + idx_end - idx_start;

  			npages = l_npages;
  			if (sizeof(npages) != sizeof(l_npages) &&

  					(pgoff_t)npages != l_npages)

  				npages = 0;
  		}
  	}

  	how &= ~FLUSH_NOCOMMIT;

  	spin_lock(&inode->i_lock);

  	do {

  		ret = nfs_wait_on_requests_locked(inode, idx_start, npages);
  		if (ret != 0)

  			continue;

  		if (nocommit)
  			break;

  		pages = nfs_scan_commit(inode, &head, idx_start, npages);

  		if (pages == 0)

  			break;

  		if (how & FLUSH_INVALIDATE) {

  			spin_unlock(&inode->i_lock);

  			nfs_cancel_commit_list(&head);

  			ret = pages;

  			spin_lock(&inode->i_lock);

  			continue;
  		}
  		pages += nfs_scan_commit(inode, &head, 0, 0);

  		spin_unlock(&inode->i_lock);

  		ret = nfs_commit_list(inode, &head, how);

  		spin_lock(&inode->i_lock);

  	} while (ret >= 0);

  	spin_unlock(&inode->i_lock);

  	return ret;

  }

  static int __nfs_write_mapping(struct address_space *mapping, struct writeback_control *wbc, int how)

  {

  	int ret;

  	ret = nfs_writepages(mapping, wbc);

  	if (ret < 0)
  		goto out;

  	ret = nfs_sync_mapping_wait(mapping, wbc, how);

  	if (ret < 0)
  		goto out;
  	return 0;

  out:

  	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);

  	return ret;
  }

  /* Two pass sync: first using WB_SYNC_NONE, then WB_SYNC_ALL */
  static int nfs_write_mapping(struct address_space *mapping, int how)
  {
  	struct writeback_control wbc = {
  		.bdi = mapping->backing_dev_info,

  		.sync_mode = WB_SYNC_ALL,

  		.nr_to_write = LONG_MAX,

  		.range_start = 0,
  		.range_end = LLONG_MAX,

  	};

  	return __nfs_write_mapping(mapping, &wbc, how);
  }

  /*
   * flush the inode to disk.
   */
  int nfs_wb_all(struct inode *inode)

  {

  	return nfs_write_mapping(inode->i_mapping, 0);
  }

  int nfs_wb_nocommit(struct inode *inode)
  {
  	return nfs_write_mapping(inode->i_mapping, FLUSH_NOCOMMIT);

  }

  int nfs_wb_page_cancel(struct inode *inode, struct page *page)
  {
  	struct nfs_page *req;
  	loff_t range_start = page_offset(page);
  	loff_t range_end = range_start + (loff_t)(PAGE_CACHE_SIZE - 1);
  	struct writeback_control wbc = {
  		.bdi = page->mapping->backing_dev_info,
  		.sync_mode = WB_SYNC_ALL,
  		.nr_to_write = LONG_MAX,
  		.range_start = range_start,
  		.range_end = range_end,
  	};
  	int ret = 0;
  
  	BUG_ON(!PageLocked(page));
  	for (;;) {
  		req = nfs_page_find_request(page);
  		if (req == NULL)
  			goto out;

  		if (test_bit(PG_CLEAN, &req->wb_flags)) {

  			nfs_release_request(req);
  			break;
  		}
  		if (nfs_lock_request_dontget(req)) {
  			nfs_inode_remove_request(req);
  			/*
  			 * In case nfs_inode_remove_request has marked the
  			 * page as being dirty
  			 */
  			cancel_dirty_page(page, PAGE_CACHE_SIZE);
  			nfs_unlock_request(req);
  			break;
  		}
  		ret = nfs_wait_on_request(req);
  		if (ret < 0)
  			goto out;
  	}
  	if (!PagePrivate(page))
  		return 0;
  	ret = nfs_sync_mapping_wait(page->mapping, &wbc, FLUSH_INVALIDATE);
  out:
  	return ret;
  }

  static int nfs_wb_page_priority(struct inode *inode, struct page *page,
  				int how)

  {
  	loff_t range_start = page_offset(page);
  	loff_t range_end = range_start + (loff_t)(PAGE_CACHE_SIZE - 1);

  	struct writeback_control wbc = {
  		.bdi = page->mapping->backing_dev_info,
  		.sync_mode = WB_SYNC_ALL,
  		.nr_to_write = LONG_MAX,
  		.range_start = range_start,
  		.range_end = range_end,
  	};
  	int ret;

  	do {
  		if (clear_page_dirty_for_io(page)) {
  			ret = nfs_writepage_locked(page, &wbc);
  			if (ret < 0)
  				goto out_error;
  		} else if (!PagePrivate(page))
  			break;
  		ret = nfs_sync_mapping_wait(page->mapping, &wbc, how);

  		if (ret < 0)

  			goto out_error;
  	} while (PagePrivate(page));
  	return 0;
  out_error:

  	__mark_inode_dirty(inode, I_DIRTY_PAGES);

  	return ret;

  }
  
  /*
   * Write back all requests on one page - we do this before reading it.
   */
  int nfs_wb_page(struct inode *inode, struct page* page)
  {

  	return nfs_wb_page_priority(inode, page, FLUSH_STABLE);

  }

  #ifdef CONFIG_MIGRATION
  int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
  		struct page *page)
  {
  	struct nfs_page *req;
  	int ret;
  
  	if (PageFsCache(page))
  		nfs_fscache_release_page(page, GFP_KERNEL);
  
  	req = nfs_find_and_lock_request(page);
  	ret = PTR_ERR(req);
  	if (IS_ERR(req))
  		goto out;
  
  	ret = migrate_page(mapping, newpage, page);
  	if (!req)
  		goto out;
  	if (ret)
  		goto out_unlock;
  	page_cache_get(newpage);
  	req->wb_page = newpage;
  	SetPagePrivate(newpage);
  	set_page_private(newpage, page_private(page));
  	ClearPagePrivate(page);
  	set_page_private(page, 0);
  	page_cache_release(page);
  out_unlock:
  	nfs_clear_page_tag_locked(req);
  	nfs_release_request(req);
  out:
  	return ret;
  }
  #endif