// SPDX-License-Identifier: GPL-2.0-only

  /*
   * linux/fs/nfs/pagelist.c
   *
   * A set of helper functions for managing NFS read and write requests.
   * The main purpose of these routines is to provide support for the
   * coalescing of several requests into a single RPC call.
   *
   * Copyright 2000, 2001 (c) Trond Myklebust <trond.myklebust@fys.uio.no>
   *
   */

  #include <linux/slab.h>
  #include <linux/file.h>

  #include <linux/sched.h>

  #include <linux/sunrpc/clnt.h>

  #include <linux/nfs.h>

  #include <linux/nfs3.h>
  #include <linux/nfs4.h>

  #include <linux/nfs_fs.h>

  #include <linux/nfs_page.h>

  #include <linux/nfs_mount.h>

  #include <linux/export.h>

  #include "internal.h"

  #include "pnfs.h"

  #include "nfstrace.h"

  #define NFSDBG_FACILITY		NFSDBG_PAGECACHE

  static struct kmem_cache *nfs_page_cachep;

  static const struct rpc_call_ops nfs_pgio_common_ops;

  static struct nfs_pgio_mirror *
  nfs_pgio_get_mirror(struct nfs_pageio_descriptor *desc, u32 idx)
  {
  	if (desc->pg_ops->pg_get_mirror)
  		return desc->pg_ops->pg_get_mirror(desc, idx);
  	return &desc->pg_mirrors[0];
  }

  struct nfs_pgio_mirror *
  nfs_pgio_current_mirror(struct nfs_pageio_descriptor *desc)
  {

  	return nfs_pgio_get_mirror(desc, desc->pg_mirror_idx);

  }
  EXPORT_SYMBOL_GPL(nfs_pgio_current_mirror);

  static u32
  nfs_pgio_set_current_mirror(struct nfs_pageio_descriptor *desc, u32 idx)
  {
  	if (desc->pg_ops->pg_set_mirror)
  		return desc->pg_ops->pg_set_mirror(desc, idx);
  	return desc->pg_mirror_idx;
  }

  void nfs_pgheader_init(struct nfs_pageio_descriptor *desc,
  		       struct nfs_pgio_header *hdr,
  		       void (*release)(struct nfs_pgio_header *hdr))
  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  
  
  	hdr->req = nfs_list_entry(mirror->pg_list.next);

  	hdr->inode = desc->pg_inode;

  	hdr->cred = nfs_req_openctx(hdr->req)->cred;

  	hdr->io_start = req_offset(hdr->req);

  	hdr->good_bytes = mirror->pg_count;

  	hdr->io_completion = desc->pg_io_completion;

  	hdr->dreq = desc->pg_dreq;

  	hdr->release = release;

  	hdr->completion_ops = desc->pg_completion_ops;

  	if (hdr->completion_ops->init_hdr)
  		hdr->completion_ops->init_hdr(hdr);

  
  	hdr->pgio_mirror_idx = desc->pg_mirror_idx;

  }

  EXPORT_SYMBOL_GPL(nfs_pgheader_init);

  
  void nfs_set_pgio_error(struct nfs_pgio_header *hdr, int error, loff_t pos)
  {

  	unsigned int new = pos - hdr->io_start;

  	trace_nfs_pgio_error(hdr, error, pos);

  	if (hdr->good_bytes > new) {
  		hdr->good_bytes = new;

  		clear_bit(NFS_IOHDR_EOF, &hdr->flags);

  		if (!test_and_set_bit(NFS_IOHDR_ERROR, &hdr->flags))
  			hdr->error = error;

  	}

  }

  static inline struct nfs_page *
  nfs_page_alloc(void)
  {

  	struct nfs_page	*p = kmem_cache_zalloc(nfs_page_cachep, GFP_KERNEL);

  	if (p)

  		INIT_LIST_HEAD(&p->wb_list);

  	return p;
  }
  
  static inline void
  nfs_page_free(struct nfs_page *p)
  {
  	kmem_cache_free(nfs_page_cachep, p);
  }

  /**
   * nfs_iocounter_wait - wait for i/o to complete

   * @l_ctx: nfs_lock_context with io_counter to use

   *
   * returns -ERESTARTSYS if interrupted by a fatal signal.
   * Otherwise returns 0 once the io_count hits 0.
   */
  int

  nfs_iocounter_wait(struct nfs_lock_context *l_ctx)

  {

  	return wait_var_event_killable(&l_ctx->io_count,
  				       !atomic_read(&l_ctx->io_count));

  }

  /**
   * nfs_async_iocounter_wait - wait on a rpc_waitqueue for I/O
   * to complete
   * @task: the rpc_task that should wait
   * @l_ctx: nfs_lock_context with io_counter to check
   *
   * Returns true if there is outstanding I/O to wait on and the
   * task has been put to sleep.
   */
  bool
  nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
  {
  	struct inode *inode = d_inode(l_ctx->open_context->dentry);
  	bool ret = false;
  
  	if (atomic_read(&l_ctx->io_count) > 0) {
  		rpc_sleep_on(&NFS_SERVER(inode)->uoc_rpcwaitq, task, NULL);
  		ret = true;
  	}
  
  	if (atomic_read(&l_ctx->io_count) == 0) {
  		rpc_wake_up_queued_task(&NFS_SERVER(inode)->uoc_rpcwaitq, task);
  		ret = false;
  	}
  
  	return ret;
  }
  EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);

  /*

   * nfs_page_lock_head_request - page lock the head of the page group
   * @req: any member of the page group
   */
  struct nfs_page *
  nfs_page_group_lock_head(struct nfs_page *req)
  {
  	struct nfs_page *head = req->wb_head;
  
  	while (!nfs_lock_request(head)) {
  		int ret = nfs_wait_on_request(head);
  		if (ret < 0)
  			return ERR_PTR(ret);
  	}
  	if (head != req)
  		kref_get(&head->wb_kref);
  	return head;
  }
  
  /*

   * nfs_unroll_locks -  unlock all newly locked reqs and wait on @req
   * @head: head request of page group, must be holding head lock
   * @req: request that couldn't lock and needs to wait on the req bit lock
   *
   * This is a helper function for nfs_lock_and_join_requests
   * returns 0 on success, < 0 on error.
   */
  static void
  nfs_unroll_locks(struct nfs_page *head, struct nfs_page *req)
  {
  	struct nfs_page *tmp;
  
  	/* relinquish all the locks successfully grabbed this run */
  	for (tmp = head->wb_this_page ; tmp != req; tmp = tmp->wb_this_page) {
  		if (!kref_read(&tmp->wb_kref))
  			continue;
  		nfs_unlock_and_release_request(tmp);
  	}
  }
  
  /*
   * nfs_page_group_lock_subreq -  try to lock a subrequest
   * @head: head request of page group
   * @subreq: request to lock
   *
   * This is a helper function for nfs_lock_and_join_requests which
   * must be called with the head request and page group both locked.
   * On error, it returns with the page group unlocked.
   */
  static int
  nfs_page_group_lock_subreq(struct nfs_page *head, struct nfs_page *subreq)
  {
  	int ret;
  
  	if (!kref_get_unless_zero(&subreq->wb_kref))
  		return 0;
  	while (!nfs_lock_request(subreq)) {
  		nfs_page_group_unlock(head);
  		ret = nfs_wait_on_request(subreq);
  		if (!ret)
  			ret = nfs_page_group_lock(head);
  		if (ret < 0) {
  			nfs_unroll_locks(head, subreq);
  			nfs_release_request(subreq);
  			return ret;
  		}
  	}
  	return 0;
  }
  
  /*
   * nfs_page_group_lock_subrequests -  try to lock the subrequests
   * @head: head request of page group
   *
   * This is a helper function for nfs_lock_and_join_requests which

   * must be called with the head request locked.

   */
  int nfs_page_group_lock_subrequests(struct nfs_page *head)
  {
  	struct nfs_page *subreq;
  	int ret;

  	ret = nfs_page_group_lock(head);
  	if (ret < 0)
  		return ret;

  	/* lock each request in the page group */
  	for (subreq = head->wb_this_page; subreq != head;
  			subreq = subreq->wb_this_page) {
  		ret = nfs_page_group_lock_subreq(head, subreq);
  		if (ret < 0)
  			return ret;
  	}

  	nfs_page_group_unlock(head);

  	return 0;
  }
  
  /*

   * nfs_page_set_headlock - set the request PG_HEADLOCK
   * @req: request that is to be locked

   *

   * this lock must be held when modifying req->wb_head

   *

   * return 0 on success, < 0 on error

   */

  int

  nfs_page_set_headlock(struct nfs_page *req)

  {

  	if (!test_and_set_bit(PG_HEADLOCK, &req->wb_flags))

  		return 0;

  	set_bit(PG_CONTENDED1, &req->wb_flags);

  	smp_mb__after_atomic();

  	return wait_on_bit_lock(&req->wb_flags, PG_HEADLOCK,

  				TASK_UNINTERRUPTIBLE);

  }
  
  /*

   * nfs_page_clear_headlock - clear the request PG_HEADLOCK
   * @req: request that is to be locked

   */
  void

  nfs_page_clear_headlock(struct nfs_page *req)

  {

  	smp_mb__before_atomic();

  	clear_bit(PG_HEADLOCK, &req->wb_flags);

  	smp_mb__after_atomic();

  	if (!test_bit(PG_CONTENDED1, &req->wb_flags))

  		return;

  	wake_up_bit(&req->wb_flags, PG_HEADLOCK);
  }
  
  /*
   * nfs_page_group_lock - lock the head of the page group
   * @req: request in group that is to be locked
   *
   * this lock must be held when traversing or modifying the page
   * group list
   *
   * return 0 on success, < 0 on error
   */
  int
  nfs_page_group_lock(struct nfs_page *req)
  {
  	int ret;
  
  	ret = nfs_page_set_headlock(req);
  	if (ret || req->wb_head == req)
  		return ret;
  	return nfs_page_set_headlock(req->wb_head);
  }
  
  /*
   * nfs_page_group_unlock - unlock the head of the page group
   * @req: request in group that is to be unlocked
   */
  void
  nfs_page_group_unlock(struct nfs_page *req)
  {
  	if (req != req->wb_head)
  		nfs_page_clear_headlock(req->wb_head);
  	nfs_page_clear_headlock(req);

  }
  
  /*
   * nfs_page_group_sync_on_bit_locked
   *
   * must be called with page group lock held
   */
  static bool
  nfs_page_group_sync_on_bit_locked(struct nfs_page *req, unsigned int bit)
  {
  	struct nfs_page *head = req->wb_head;
  	struct nfs_page *tmp;
  
  	WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &head->wb_flags));
  	WARN_ON_ONCE(test_and_set_bit(bit, &req->wb_flags));
  
  	tmp = req->wb_this_page;
  	while (tmp != req) {
  		if (!test_bit(bit, &tmp->wb_flags))
  			return false;
  		tmp = tmp->wb_this_page;
  	}
  
  	/* true! reset all bits */
  	tmp = req;
  	do {
  		clear_bit(bit, &tmp->wb_flags);
  		tmp = tmp->wb_this_page;
  	} while (tmp != req);
  
  	return true;
  }
  
  /*
   * nfs_page_group_sync_on_bit - set bit on current request, but only
   *   return true if the bit is set for all requests in page group
   * @req - request in page group
   * @bit - PG_* bit that is used to sync page group
   */
  bool nfs_page_group_sync_on_bit(struct nfs_page *req, unsigned int bit)
  {
  	bool ret;

  	nfs_page_group_lock(req);

  	ret = nfs_page_group_sync_on_bit_locked(req, bit);
  	nfs_page_group_unlock(req);
  
  	return ret;
  }
  
  /*
   * nfs_page_group_init - Initialize the page group linkage for @req
   * @req - a new nfs request
   * @prev - the previous request in page group, or NULL if @req is the first
   *         or only request in the group (the head).
   */
  static inline void
  nfs_page_group_init(struct nfs_page *req, struct nfs_page *prev)
  {

  	struct inode *inode;

  	WARN_ON_ONCE(prev == req);
  
  	if (!prev) {

  		/* a head request */

  		req->wb_head = req;
  		req->wb_this_page = req;
  	} else {

  		/* a subrequest */

  		WARN_ON_ONCE(prev->wb_this_page != prev->wb_head);
  		WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &prev->wb_head->wb_flags));
  		req->wb_head = prev->wb_head;
  		req->wb_this_page = prev->wb_this_page;
  		prev->wb_this_page = req;

  		/* All subrequests take a ref on the head request until
  		 * nfs_page_group_destroy is called */
  		kref_get(&req->wb_head->wb_kref);

  		/* grab extra ref and bump the request count if head request
  		 * has extra ref from the write/commit path to handle handoff
  		 * between write and commit lists. */

  		if (test_bit(PG_INODE_REF, &prev->wb_head->wb_flags)) {

  			inode = page_file_mapping(req->wb_page)->host;

  			set_bit(PG_INODE_REF, &req->wb_flags);

  			kref_get(&req->wb_kref);

  			atomic_long_inc(&NFS_I(inode)->nrequests);

  		}

  	}
  }
  
  /*
   * nfs_page_group_destroy - sync the destruction of page groups
   * @req - request that no longer needs the page group
   *
   * releases the page group reference from each member once all
   * members have called this function.
   */
  static void
  nfs_page_group_destroy(struct kref *kref)
  {
  	struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref);

  	struct nfs_page *head = req->wb_head;

  	struct nfs_page *tmp, *next;
  
  	if (!nfs_page_group_sync_on_bit(req, PG_TEARDOWN))

  		goto out;

  
  	tmp = req;
  	do {
  		next = tmp->wb_this_page;
  		/* unlink and free */
  		tmp->wb_this_page = tmp;
  		tmp->wb_head = tmp;
  		nfs_free_request(tmp);
  		tmp = next;
  	} while (tmp != req);

  out:
  	/* subrequests must release the ref on the head request */
  	if (head != req)
  		nfs_release_request(head);

  }

  static struct nfs_page *
  __nfs_create_request(struct nfs_lock_context *l_ctx, struct page *page,

  		   unsigned int pgbase, unsigned int offset,
  		   unsigned int count)

  {

  	struct nfs_page		*req;

  	struct nfs_open_context *ctx = l_ctx->open_context;

  	if (test_bit(NFS_CONTEXT_BAD, &ctx->flags))
  		return ERR_PTR(-EBADF);

  	/* try to allocate the request struct */
  	req = nfs_page_alloc();
  	if (req == NULL)
  		return ERR_PTR(-ENOMEM);

  	req->wb_lock_context = l_ctx;

  	refcount_inc(&l_ctx->count);

  	atomic_inc(&l_ctx->io_count);

  	/* Initialize the request struct. Initially, we assume a
  	 * long write-back delay. This will be adjusted in
  	 * update_nfs_request below if the region is not locked. */
  	req->wb_page    = page;

  	if (page) {

  		req->wb_index = page_index(page);

  		get_page(page);
  	}

  	req->wb_offset  = offset;

  	req->wb_pgbase	= pgbase;

  	req->wb_bytes   = count;

  	kref_init(&req->wb_kref);

  	req->wb_nio = 0;

  	return req;
  }
  
  /**

   * nfs_create_request - Create an NFS read/write request.
   * @ctx: open context to use
   * @page: page to write

   * @offset: starting offset within the page for the write
   * @count: number of bytes to read/write
   *
   * The page must be locked by the caller. This makes sure we never
   * create two different requests for the same page.
   * User should ensure it is safe to sleep in this function.
   */
  struct nfs_page *
  nfs_create_request(struct nfs_open_context *ctx, struct page *page,

  		   unsigned int offset, unsigned int count)

  {
  	struct nfs_lock_context *l_ctx = nfs_get_lock_context(ctx);
  	struct nfs_page *ret;
  
  	if (IS_ERR(l_ctx))
  		return ERR_CAST(l_ctx);

  	ret = __nfs_create_request(l_ctx, page, offset, offset, count);
  	if (!IS_ERR(ret))
  		nfs_page_group_init(ret, NULL);

  	nfs_put_lock_context(l_ctx);
  	return ret;
  }
  
  static struct nfs_page *

  nfs_create_subreq(struct nfs_page *req,
  		  unsigned int pgbase,
  		  unsigned int offset,

  		  unsigned int count)
  {

  	struct nfs_page *last;

  	struct nfs_page *ret;

  	ret = __nfs_create_request(req->wb_lock_context, req->wb_page,

  			pgbase, offset, count);
  	if (!IS_ERR(ret)) {

  		/* find the last request */
  		for (last = req->wb_head;
  		     last->wb_this_page != req->wb_head;
  		     last = last->wb_this_page)
  			;

  		nfs_lock_request(ret);
  		ret->wb_index = req->wb_index;

  		nfs_page_group_init(ret, last);

  		ret->wb_nio = req->wb_nio;

  	}
  	return ret;
  }
  
  /**

   * nfs_unlock_request - Unlock request and wake up sleepers.

   * @req: pointer to request

   */

  void nfs_unlock_request(struct nfs_page *req)

  {
  	if (!NFS_WBACK_BUSY(req)) {
  		printk(KERN_ERR "NFS: Invalid unlock attempted
  ");
  		BUG();
  	}

  	smp_mb__before_atomic();

  	clear_bit(PG_BUSY, &req->wb_flags);

  	smp_mb__after_atomic();

  	if (!test_bit(PG_CONTENDED2, &req->wb_flags))
  		return;

  	wake_up_bit(&req->wb_flags, PG_BUSY);

  }
  
  /**

   * nfs_unlock_and_release_request - Unlock request and release the nfs_page

   * @req: pointer to request

   */

  void nfs_unlock_and_release_request(struct nfs_page *req)

  {

  	nfs_unlock_request(req);

  	nfs_release_request(req);
  }

  /*

   * nfs_clear_request - Free up all resources allocated to the request
   * @req:
   *

   * Release page and open context resources associated with a read/write
   * request after it has completed.

   */

  static void nfs_clear_request(struct nfs_page *req)

  {

  	struct page *page = req->wb_page;

  	struct nfs_lock_context *l_ctx = req->wb_lock_context;

  	struct nfs_open_context *ctx;

  	if (page != NULL) {

  		put_page(page);

  		req->wb_page = NULL;
  	}

  	if (l_ctx != NULL) {

  		if (atomic_dec_and_test(&l_ctx->io_count)) {

  			wake_up_var(&l_ctx->io_count);

  			ctx = l_ctx->open_context;

  			if (test_bit(NFS_CONTEXT_UNLOCK, &ctx->flags))
  				rpc_wake_up(&NFS_SERVER(d_inode(ctx->dentry))->uoc_rpcwaitq);
  		}

  		nfs_put_lock_context(l_ctx);
  		req->wb_lock_context = NULL;
  	}

  }

  /**
   * nfs_release_request - Release the count on an NFS read/write request
   * @req: request to release
   *
   * Note: Should never be called with the spinlock held!
   */

  void nfs_free_request(struct nfs_page *req)

  {

  	WARN_ON_ONCE(req->wb_this_page != req);
  
  	/* extra debug: make sure no sync bits are still set */
  	WARN_ON_ONCE(test_bit(PG_TEARDOWN, &req->wb_flags));

  	WARN_ON_ONCE(test_bit(PG_UNLOCKPAGE, &req->wb_flags));
  	WARN_ON_ONCE(test_bit(PG_UPTODATE, &req->wb_flags));

  	WARN_ON_ONCE(test_bit(PG_WB_END, &req->wb_flags));
  	WARN_ON_ONCE(test_bit(PG_REMOVE, &req->wb_flags));

  	/* Release struct file and open context */

  	nfs_clear_request(req);

  	nfs_page_free(req);
  }

  void nfs_release_request(struct nfs_page *req)
  {

  	kref_put(&req->wb_kref, nfs_page_group_destroy);

  }

  EXPORT_SYMBOL_GPL(nfs_release_request);

  /**
   * nfs_wait_on_request - Wait for a request to complete.
   * @req: request to wait upon.
   *

   * Interruptible by fatal signals only.

   * The user is responsible for holding a count on the request.
   */
  int
  nfs_wait_on_request(struct nfs_page *req)
  {

  	if (!test_bit(PG_BUSY, &req->wb_flags))
  		return 0;
  	set_bit(PG_CONTENDED2, &req->wb_flags);
  	smp_mb__after_atomic();

  	return wait_on_bit_io(&req->wb_flags, PG_BUSY,
  			      TASK_UNINTERRUPTIBLE);

  }

  EXPORT_SYMBOL_GPL(nfs_wait_on_request);

  /*
   * nfs_generic_pg_test - determine if requests can be coalesced
   * @desc: pointer to descriptor
   * @prev: previous request in desc, or NULL
   * @req: this request
   *

   * Returns zero if @req cannot be coalesced into @desc, otherwise it returns

   * the size of the request.
   */
  size_t nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
  			   struct nfs_page *prev, struct nfs_page *req)

  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  
  
  	if (mirror->pg_count > mirror->pg_bsize) {

  		/* should never happen */
  		WARN_ON_ONCE(1);

  		return 0;

  	}

  	/*
  	 * Limit the request size so that we can still allocate a page array
  	 * for it without upsetting the slab allocator.
  	 */

  	if (((mirror->pg_count + req->wb_bytes) >> PAGE_SHIFT) *

  			sizeof(struct page *) > PAGE_SIZE)

  		return 0;

  	return min(mirror->pg_bsize - mirror->pg_count, (size_t)req->wb_bytes);

  }

  EXPORT_SYMBOL_GPL(nfs_generic_pg_test);

  struct nfs_pgio_header *nfs_pgio_header_alloc(const struct nfs_rw_ops *ops)

  {

  	struct nfs_pgio_header *hdr = ops->rw_alloc_header();

  	if (hdr) {

  		INIT_LIST_HEAD(&hdr->pages);

  		hdr->rw_ops = ops;
  	}

  	return hdr;

  }

  EXPORT_SYMBOL_GPL(nfs_pgio_header_alloc);

  /**

   * nfs_pgio_data_destroy - make @hdr suitable for reuse
   *
   * Frees memory and releases refs from nfs_generic_pgio, so that it may
   * be called again.
   *
   * @hdr: A header that has had nfs_generic_pgio called

   */

  static void nfs_pgio_data_destroy(struct nfs_pgio_header *hdr)

  {

  	if (hdr->args.context)
  		put_nfs_open_context(hdr->args.context);

  	if (hdr->page_array.pagevec != hdr->page_array.page_array)
  		kfree(hdr->page_array.pagevec);

  }

  
  /*
   * nfs_pgio_header_free - Free a read or write header
   * @hdr: The header to free
   */
  void nfs_pgio_header_free(struct nfs_pgio_header *hdr)
  {
  	nfs_pgio_data_destroy(hdr);
  	hdr->rw_ops->rw_free_header(hdr);
  }
  EXPORT_SYMBOL_GPL(nfs_pgio_header_free);

  /**

   * nfs_pgio_rpcsetup - Set up arguments for a pageio call

   * @hdr: The pageio hdr

   * @count: Number of bytes to read

   * @how: How to commit data (writes only)
   * @cinfo: Commit information for the call (writes only)
   */

  static void nfs_pgio_rpcsetup(struct nfs_pgio_header *hdr,

  			      unsigned int count,

  			      int how, struct nfs_commit_info *cinfo)
  {

  	struct nfs_page *req = hdr->req;

  
  	/* Set up the RPC argument and reply structs

  	 * NB: take care not to mess about with hdr->commit et al. */

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

  	hdr->args.offset = req_offset(req);

  	/* pnfs_set_layoutcommit needs this */

  	hdr->mds_offset = hdr->args.offset;

  	hdr->args.pgbase = req->wb_pgbase;

  	hdr->args.pages  = hdr->page_array.pagevec;
  	hdr->args.count  = count;

  	hdr->args.context = get_nfs_open_context(nfs_req_openctx(req));

  	hdr->args.lock_context = req->wb_lock_context;
  	hdr->args.stable  = NFS_UNSTABLE;

  	switch (how & (FLUSH_STABLE | FLUSH_COND_STABLE)) {
  	case 0:
  		break;
  	case FLUSH_COND_STABLE:
  		if (nfs_reqs_to_commit(cinfo))
  			break;

  		fallthrough;

  	default:

  		hdr->args.stable = NFS_FILE_SYNC;

  	}

  	hdr->res.fattr   = &hdr->fattr;

  	hdr->res.count   = 0;

  	hdr->res.eof     = 0;

  	hdr->res.verf    = &hdr->verf;

  	nfs_fattr_init(&hdr->fattr);

  }
  
  /**

   * nfs_pgio_prepare - Prepare pageio hdr to go over the wire

   * @task: The current task

   * @calldata: pageio header to prepare

   */

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

  {

  	struct nfs_pgio_header *hdr = calldata;

  	int err;

  	err = NFS_PROTO(hdr->inode)->pgio_rpc_prepare(task, hdr);

  	if (err)
  		rpc_exit(task, err);
  }

  int nfs_initiate_pgio(struct rpc_clnt *clnt, struct nfs_pgio_header *hdr,

  		      const struct cred *cred, const struct nfs_rpc_ops *rpc_ops,

  		      const struct rpc_call_ops *call_ops, int how, int flags)
  {
  	struct rpc_task *task;
  	struct rpc_message msg = {

  		.rpc_argp = &hdr->args,
  		.rpc_resp = &hdr->res,

  		.rpc_cred = cred,

  	};
  	struct rpc_task_setup task_setup_data = {
  		.rpc_client = clnt,

  		.task = &hdr->task,

  		.rpc_message = &msg,
  		.callback_ops = call_ops,

  		.callback_data = hdr,

  		.workqueue = nfsiod_workqueue,

  		.flags = RPC_TASK_ASYNC | flags,

  	};

  	hdr->rw_ops->rw_initiate(hdr, &msg, rpc_ops, &task_setup_data, how);

  	dprintk("NFS: initiated pgio call "

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

  		hdr->inode->i_sb->s_id,
  		(unsigned long long)NFS_FILEID(hdr->inode),

  		hdr->args.count,
  		(unsigned long long)hdr->args.offset);

  
  	task = rpc_run_task(&task_setup_data);

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

  	rpc_put_task(task);

  	return 0;

  }
  EXPORT_SYMBOL_GPL(nfs_initiate_pgio);

  /**

   * nfs_pgio_error - Clean up from a pageio error

   * @hdr: pageio header
   */

  static void nfs_pgio_error(struct nfs_pgio_header *hdr)

  {

  	set_bit(NFS_IOHDR_REDO, &hdr->flags);

  	hdr->completion_ops->completion(hdr);

  }
  
  /**

   * nfs_pgio_release - Release pageio data

   * @calldata: The pageio header to release

   */

  static void nfs_pgio_release(void *calldata)

  {

  	struct nfs_pgio_header *hdr = calldata;

  	hdr->completion_ops->completion(hdr);

  }

  static void nfs_pageio_mirror_init(struct nfs_pgio_mirror *mirror,
  				   unsigned int bsize)
  {
  	INIT_LIST_HEAD(&mirror->pg_list);
  	mirror->pg_bytes_written = 0;
  	mirror->pg_count = 0;
  	mirror->pg_bsize = bsize;
  	mirror->pg_base = 0;
  	mirror->pg_recoalesce = 0;
  }

  /**

   * nfs_pageio_init - initialise a page io descriptor
   * @desc: pointer to descriptor

   * @inode: pointer to inode

   * @pg_ops: pointer to pageio operations
   * @compl_ops: pointer to pageio completion operations
   * @rw_ops: pointer to nfs read/write operations

   * @bsize: io block size
   * @io_flags: extra parameters for the io function

   */

  void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
  		     struct inode *inode,

  		     const struct nfs_pageio_ops *pg_ops,

  		     const struct nfs_pgio_completion_ops *compl_ops,

  		     const struct nfs_rw_ops *rw_ops,

  		     size_t bsize,

  		     int io_flags)

  {

  	desc->pg_moreio = 0;

  	desc->pg_inode = inode;

  	desc->pg_ops = pg_ops;

  	desc->pg_completion_ops = compl_ops;

  	desc->pg_rw_ops = rw_ops;

  	desc->pg_ioflags = io_flags;
  	desc->pg_error = 0;

  	desc->pg_lseg = NULL;

  	desc->pg_io_completion = NULL;

  	desc->pg_dreq = NULL;

  	desc->pg_bsize = bsize;
  
  	desc->pg_mirror_count = 1;
  	desc->pg_mirror_idx = 0;

  	desc->pg_mirrors_dynamic = NULL;
  	desc->pg_mirrors = desc->pg_mirrors_static;
  	nfs_pageio_mirror_init(&desc->pg_mirrors[0], bsize);

  	desc->pg_maxretrans = 0;

  }

  /**
   * nfs_pgio_result - Basic pageio error handling
   * @task: The task that ran

   * @calldata: Pageio header to check

   */

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

  {

  	struct nfs_pgio_header *hdr = calldata;
  	struct inode *inode = hdr->inode;

  
  	dprintk("NFS: %s: %5u, (status %d)
  ", __func__,
  		task->tk_pid, task->tk_status);

  	if (hdr->rw_ops->rw_done(task, hdr, inode) != 0)

  		return;
  	if (task->tk_status < 0)

  		nfs_set_pgio_error(hdr, task->tk_status, hdr->args.offset);

  	else

  		hdr->rw_ops->rw_result(task, hdr);

  }

  /*

   * Create an RPC task for the given read or 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.
   */

  int nfs_generic_pgio(struct nfs_pageio_descriptor *desc,
  		     struct nfs_pgio_header *hdr)

  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  	struct nfs_page		*req;

  	struct page		**pages,
  				*last_page;

  	struct list_head *head = &mirror->pg_list;

  	struct nfs_commit_info cinfo;

  	struct nfs_page_array *pg_array = &hdr->page_array;

  	unsigned int pagecount, pageused;

  	gfp_t gfp_flags = GFP_KERNEL;

  	pagecount = nfs_page_array_len(mirror->pg_base, mirror->pg_count);

  	pg_array->npages = pagecount;

  
  	if (pagecount <= ARRAY_SIZE(pg_array->page_array))
  		pg_array->pagevec = pg_array->page_array;
  	else {

  		pg_array->pagevec = kcalloc(pagecount, sizeof(struct page *), gfp_flags);
  		if (!pg_array->pagevec) {
  			pg_array->npages = 0;
  			nfs_pgio_error(hdr);
  			desc->pg_error = -ENOMEM;
  			return desc->pg_error;
  		}

  	}

  
  	nfs_init_cinfo(&cinfo, desc->pg_inode, desc->pg_dreq);

  	pages = hdr->page_array.pagevec;

  	last_page = NULL;
  	pageused = 0;

  	while (!list_empty(head)) {
  		req = nfs_list_entry(head->next);

  		nfs_list_move_request(req, &hdr->pages);

  		if (!last_page || last_page != req->wb_page) {

  			pageused++;

  			if (pageused > pagecount)
  				break;
  			*pages++ = last_page = req->wb_page;

  		}

  	}

  	if (WARN_ON_ONCE(pageused != pagecount)) {
  		nfs_pgio_error(hdr);
  		desc->pg_error = -EINVAL;
  		return desc->pg_error;
  	}

  
  	if ((desc->pg_ioflags & FLUSH_COND_STABLE) &&
  	    (desc->pg_moreio || nfs_reqs_to_commit(&cinfo)))
  		desc->pg_ioflags &= ~FLUSH_COND_STABLE;
  
  	/* Set up the argument struct */

  	nfs_pgio_rpcsetup(hdr, mirror->pg_count, desc->pg_ioflags, &cinfo);

  	desc->pg_rpc_callops = &nfs_pgio_common_ops;
  	return 0;
  }

  EXPORT_SYMBOL_GPL(nfs_generic_pgio);

  static int nfs_generic_pg_pgios(struct nfs_pageio_descriptor *desc)

  {

  	struct nfs_pgio_header *hdr;
  	int ret;

  	hdr = nfs_pgio_header_alloc(desc->pg_rw_ops);
  	if (!hdr) {

  		desc->pg_error = -ENOMEM;
  		return desc->pg_error;

  	}

  	nfs_pgheader_init(desc, hdr, nfs_pgio_header_free);

  	ret = nfs_generic_pgio(desc, hdr);
  	if (ret == 0)

  		ret = nfs_initiate_pgio(NFS_CLIENT(hdr->inode),

  					hdr,
  					hdr->cred,
  					NFS_PROTO(hdr->inode),

  					desc->pg_rpc_callops,

  					desc->pg_ioflags,
  					RPC_TASK_CRED_NOREF);

  	return ret;
  }

  static struct nfs_pgio_mirror *
  nfs_pageio_alloc_mirrors(struct nfs_pageio_descriptor *desc,
  		unsigned int mirror_count)
  {
  	struct nfs_pgio_mirror *ret;
  	unsigned int i;
  
  	kfree(desc->pg_mirrors_dynamic);
  	desc->pg_mirrors_dynamic = NULL;
  	if (mirror_count == 1)
  		return desc->pg_mirrors_static;

  	ret = kmalloc_array(mirror_count, sizeof(*ret), GFP_KERNEL);

  	if (ret != NULL) {
  		for (i = 0; i < mirror_count; i++)
  			nfs_pageio_mirror_init(&ret[i], desc->pg_bsize);
  		desc->pg_mirrors_dynamic = ret;
  	}
  	return ret;
  }

  /*
   * nfs_pageio_setup_mirroring - determine if mirroring is to be used
   *				by calling the pg_get_mirror_count op
   */

  static void nfs_pageio_setup_mirroring(struct nfs_pageio_descriptor *pgio,

  				       struct nfs_page *req)
  {

  	unsigned int mirror_count = 1;

  	if (pgio->pg_ops->pg_get_mirror_count)
  		mirror_count = pgio->pg_ops->pg_get_mirror_count(pgio, req);
  	if (mirror_count == pgio->pg_mirror_count || pgio->pg_error < 0)
  		return;

  	if (!mirror_count || mirror_count > NFS_PAGEIO_DESCRIPTOR_MIRROR_MAX) {
  		pgio->pg_error = -EINVAL;
  		return;
  	}

  	pgio->pg_mirrors = nfs_pageio_alloc_mirrors(pgio, mirror_count);
  	if (pgio->pg_mirrors == NULL) {
  		pgio->pg_error = -ENOMEM;
  		pgio->pg_mirrors = pgio->pg_mirrors_static;
  		mirror_count = 1;
  	}

  	pgio->pg_mirror_count = mirror_count;

  }

  static void nfs_pageio_cleanup_mirroring(struct nfs_pageio_descriptor *pgio)
  {
  	pgio->pg_mirror_count = 1;
  	pgio->pg_mirror_idx = 0;
  	pgio->pg_mirrors = pgio->pg_mirrors_static;
  	kfree(pgio->pg_mirrors_dynamic);
  	pgio->pg_mirrors_dynamic = NULL;
  }

  static bool nfs_match_lock_context(const struct nfs_lock_context *l1,
  		const struct nfs_lock_context *l2)
  {

  	return l1->lockowner == l2->lockowner;

  }

  /**

   * nfs_coalesce_size - test two requests for compatibility

   * @prev: pointer to nfs_page
   * @req: pointer to nfs_page

   * @pgio: pointer to nfs_pagio_descriptor

   *
   * The nfs_page structures 'prev' and 'req' are compared to ensure that the
   * page data area they describe is contiguous, and that their RPC
   * credentials, NFSv4 open state, and lockowners are the same.
   *

   * Returns size of the request that can be coalesced

   */

  static unsigned int nfs_coalesce_size(struct nfs_page *prev,

  				      struct nfs_page *req,
  				      struct nfs_pageio_descriptor *pgio)

  {

  	struct file_lock_context *flctx;

  	if (prev) {

  		if (!nfs_match_open_context(nfs_req_openctx(req), nfs_req_openctx(prev)))

  			return 0;

  		flctx = d_inode(nfs_req_openctx(req)->dentry)->i_flctx;

  		if (flctx != NULL &&
  		    !(list_empty_careful(&flctx->flc_posix) &&
  		      list_empty_careful(&flctx->flc_flock)) &&

  		    !nfs_match_lock_context(req->wb_lock_context,
  					    prev->wb_lock_context))

  			return 0;

  		if (req_offset(req) != req_offset(prev) + prev->wb_bytes)

  			return 0;

  		if (req->wb_page == prev->wb_page) {
  			if (req->wb_pgbase != prev->wb_pgbase + prev->wb_bytes)

  				return 0;

  		} else {
  			if (req->wb_pgbase != 0 ||

  			    prev->wb_pgbase + prev->wb_bytes != PAGE_SIZE)

  				return 0;

  		}

  	}

  	return pgio->pg_ops->pg_test(pgio, prev, req);

  }
  
  /**

   * nfs_pageio_do_add_request - Attempt to coalesce a request into a page list.

   * @desc: destination io descriptor
   * @req: request
   *

   * If the request 'req' was successfully coalesced into the existing list
   * of pages 'desc', it returns the size of req.

   */

  static unsigned int
  nfs_pageio_do_add_request(struct nfs_pageio_descriptor *desc,
  		struct nfs_page *req)

  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  	struct nfs_page *prev = NULL;

  	unsigned int size;

  
  	if (mirror->pg_count != 0) {
  		prev = nfs_list_entry(mirror->pg_list.prev);

  	} else {

  		if (desc->pg_ops->pg_init)
  			desc->pg_ops->pg_init(desc, req);

  		if (desc->pg_error < 0)
  			return 0;

  		mirror->pg_base = req->wb_pgbase;

  	}

  
  	if (desc->pg_maxretrans && req->wb_nio > desc->pg_maxretrans) {
  		if (NFS_SERVER(desc->pg_inode)->flags & NFS_MOUNT_SOFTERR)
  			desc->pg_error = -ETIMEDOUT;
  		else
  			desc->pg_error = -EIO;
  		return 0;
  	}

  	size = nfs_coalesce_size(prev, req, desc);
  	if (size < req->wb_bytes)
  		return size;

  	nfs_list_move_request(req, &mirror->pg_list);

  	mirror->pg_count += req->wb_bytes;

  	return req->wb_bytes;

  }

  /*
   * Helper for nfs_pageio_add_request and nfs_pageio_complete
   */
  static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc)
  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  
  
  	if (!list_empty(&mirror->pg_list)) {

  		int error = desc->pg_ops->pg_doio(desc);

  		if (error < 0)
  			desc->pg_error = error;
  		else

  			mirror->pg_bytes_written += mirror->pg_count;

  	}

  	if (list_empty(&mirror->pg_list)) {
  		mirror->pg_count = 0;
  		mirror->pg_base = 0;

  	}
  }

  static void
  nfs_pageio_cleanup_request(struct nfs_pageio_descriptor *desc,
  		struct nfs_page *req)
  {
  	LIST_HEAD(head);

  	nfs_list_move_request(req, &head);

  	desc->pg_completion_ops->error_cleanup(&head, desc->pg_error);

  }

  /**
   * nfs_pageio_add_request - Attempt to coalesce a request into a page list.
   * @desc: destination io descriptor
   * @req: request
   *

   * This may split a request into subrequests which are all part of the

   * same page group. If so, it will submit @req as the last one, to ensure
   * the pointer to @req is still valid in case of failure.

   *

   * Returns true if the request 'req' was successfully coalesced into the
   * existing list of pages 'desc'.
   */

  static int __nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,

  			   struct nfs_page *req)

  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  	struct nfs_page *subreq;

  	unsigned int size, subreq_size;

  	nfs_page_group_lock(req);

  
  	subreq = req;

  	subreq_size = subreq->wb_bytes;
  	for(;;) {
  		size = nfs_pageio_do_add_request(desc, subreq);
  		if (size == subreq_size) {
  			/* We successfully submitted a request */
  			if (subreq == req)
  				break;
  			req->wb_pgbase += size;
  			req->wb_bytes -= size;
  			req->wb_offset += size;
  			subreq_size = req->wb_bytes;
  			subreq = req;
  			continue;
  		}
  		if (WARN_ON_ONCE(subreq != req)) {
  			nfs_page_group_unlock(req);
  			nfs_pageio_cleanup_request(desc, subreq);
  			subreq = req;
  			subreq_size = req->wb_bytes;
  			nfs_page_group_lock(req);
  		}
  		if (!size) {
  			/* Can't coalesce any more, so do I/O */

  			nfs_page_group_unlock(req);
  			desc->pg_moreio = 1;
  			nfs_pageio_doio(desc);

  			if (desc->pg_error < 0 || mirror->pg_recoalesce)

  				return 0;

  			/* retry add_request for this subreq */

  			nfs_page_group_lock(req);

  			continue;
  		}

  		subreq = nfs_create_subreq(req, req->wb_pgbase,
  				req->wb_offset, size);
  		if (IS_ERR(subreq))
  			goto err_ptr;
  		subreq_size = size;
  	}

  
  	nfs_page_group_unlock(req);

  	return 1;

  err_ptr:
  	desc->pg_error = PTR_ERR(subreq);
  	nfs_page_group_unlock(req);
  	return 0;

  }

  static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
  {

  	struct nfs_pgio_mirror *mirror = nfs_pgio_current_mirror(desc);

  	LIST_HEAD(head);
  
  	do {

  		list_splice_init(&mirror->pg_list, &head);
  		mirror->pg_bytes_written -= mirror->pg_count;
  		mirror->pg_count = 0;
  		mirror->pg_base = 0;
  		mirror->pg_recoalesce = 0;

  		while (!list_empty(&head)) {
  			struct nfs_page *req;
  
  			req = list_first_entry(&head, struct nfs_page, wb_list);

  			if (__nfs_pageio_add_request(desc, req))
  				continue;

  			if (desc->pg_error < 0) {
  				list_splice_tail(&head, &mirror->pg_list);
  				mirror->pg_recoalesce = 1;

  				return 0;

  			}

  			break;
  		}

  	} while (mirror->pg_recoalesce);

  	return 1;
  }

  static int nfs_pageio_add_request_mirror(struct nfs_pageio_descriptor *desc,

  		struct nfs_page *req)
  {
  	int ret;
  
  	do {
  		ret = __nfs_pageio_add_request(desc, req);
  		if (ret)
  			break;
  		if (desc->pg_error < 0)
  			break;
  		ret = nfs_do_recoalesce(desc);
  	} while (ret);

  	return ret;
  }

  static void nfs_pageio_error_cleanup(struct nfs_pageio_descriptor *desc)
  {
  	u32 midx;
  	struct nfs_pgio_mirror *mirror;
  
  	if (!desc->pg_error)
  		return;
  
  	for (midx = 0; midx < desc->pg_mirror_count; midx++) {

  		mirror = nfs_pgio_get_mirror(desc, midx);

  		desc->pg_completion_ops->error_cleanup(&mirror->pg_list,
  				desc->pg_error);

  	}
  }

  int nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
  			   struct nfs_page *req)
  {
  	u32 midx;
  	unsigned int pgbase, offset, bytes;

  	struct nfs_page *dupreq;

  
  	pgbase = req->wb_pgbase;
  	offset = req->wb_offset;
  	bytes = req->wb_bytes;
  
  	nfs_pageio_setup_mirroring(desc, req);

  	if (desc->pg_error < 0)

  		goto out_failed;

  	/* Create the mirror instances first, and fire them off */
  	for (midx = 1; midx < desc->pg_mirror_count; midx++) {
  		nfs_page_group_lock(req);

  		dupreq = nfs_create_subreq(req,

  				pgbase, offset, bytes);
  
  		nfs_page_group_unlock(req);
  		if (IS_ERR(dupreq)) {
  			desc->pg_error = PTR_ERR(dupreq);
  			goto out_failed;
  		}

  		nfs_pgio_set_current_mirror(desc, midx);

  		if (!nfs_pageio_add_request_mirror(desc, dupreq))

  			goto out_cleanup_subreq;

  	}

  	nfs_pgio_set_current_mirror(desc, 0);

  	if (!nfs_pageio_add_request_mirror(desc, req))
  		goto out_failed;

  	return 1;

  out_cleanup_subreq:

  	nfs_pageio_cleanup_request(desc, dupreq);

  out_failed:

  	nfs_pageio_error_cleanup(desc);

  	return 0;

  }
  
  /*
   * nfs_pageio_complete_mirror - Complete I/O on the current mirror of an
   *				nfs_pageio_descriptor
   * @desc: pointer to io descriptor

   * @mirror_idx: pointer to mirror index

   */
  static void nfs_pageio_complete_mirror(struct nfs_pageio_descriptor *desc,
  				       u32 mirror_idx)
  {

  	struct nfs_pgio_mirror *mirror;
  	u32 restore_idx;
  
  	restore_idx = nfs_pgio_set_current_mirror(desc, mirror_idx);
  	mirror = nfs_pgio_current_mirror(desc);

  	for (;;) {
  		nfs_pageio_doio(desc);

  		if (desc->pg_error < 0 || !mirror->pg_recoalesce)

  			break;
  		if (!nfs_do_recoalesce(desc))
  			break;
  	}

  	nfs_pgio_set_current_mirror(desc, restore_idx);

  }

  /*
   * nfs_pageio_resend - Transfer requests to new descriptor and resend
   * @hdr - the pgio header to move request from
   * @desc - the pageio descriptor to add requests to
   *
   * Try to move each request (nfs_page) from @hdr to @desc then attempt
   * to send them.
   *
   * Returns 0 on success and < 0 on error.
   */
  int nfs_pageio_resend(struct nfs_pageio_descriptor *desc,
  		      struct nfs_pgio_header *hdr)
  {

  	LIST_HEAD(pages);

  	desc->pg_io_completion = hdr->io_completion;

  	desc->pg_dreq = hdr->dreq;

  	list_splice_init(&hdr->pages, &pages);
  	while (!list_empty(&pages)) {
  		struct nfs_page *req = nfs_list_entry(pages.next);

  		if (!nfs_pageio_add_request(desc, req))

  			break;

  	}
  	nfs_pageio_complete(desc);

  	if (!list_empty(&pages)) {
  		int err = desc->pg_error < 0 ? desc->pg_error : -EIO;
  		hdr->completion_ops->error_cleanup(&pages, err);

  		nfs_set_pgio_error(hdr, err, hdr->io_start);

  		return err;

  	}
  	return 0;
  }
  EXPORT_SYMBOL_GPL(nfs_pageio_resend);

  /**

   * nfs_pageio_complete - Complete I/O then cleanup an nfs_pageio_descriptor

   * @desc: pointer to io descriptor
   */
  void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
  {

  	u32 midx;
  
  	for (midx = 0; midx < desc->pg_mirror_count; midx++)
  		nfs_pageio_complete_mirror(desc, midx);

  	if (desc->pg_error < 0)
  		nfs_pageio_error_cleanup(desc);

  	if (desc->pg_ops->pg_cleanup)
  		desc->pg_ops->pg_cleanup(desc);

  	nfs_pageio_cleanup_mirroring(desc);

  }

  /**
   * nfs_pageio_cond_complete - Conditional I/O completion
   * @desc: pointer to io descriptor
   * @index: page index
   *
   * It is important to ensure that processes don't try to take locks
   * on non-contiguous ranges of pages as that might deadlock. This
   * function should be called before attempting to wait on a locked
   * nfs_page. It will complete the I/O if the page index 'index'
   * is not contiguous with the existing list of pages in 'desc'.
   */
  void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
  {

  	struct nfs_pgio_mirror *mirror;
  	struct nfs_page *prev;
  	u32 midx;
  
  	for (midx = 0; midx < desc->pg_mirror_count; midx++) {

  		mirror = nfs_pgio_get_mirror(desc, midx);

  		if (!list_empty(&mirror->pg_list)) {
  			prev = nfs_list_entry(mirror->pg_list.prev);

  			if (index != prev->wb_index + 1) {
  				nfs_pageio_complete(desc);
  				break;
  			}

  		}

  	}
  }

  /*
   * nfs_pageio_stop_mirroring - stop using mirroring (set mirror count to 1)
   */
  void nfs_pageio_stop_mirroring(struct nfs_pageio_descriptor *pgio)
  {
  	nfs_pageio_complete(pgio);
  }

  int __init nfs_init_nfspagecache(void)

  {
  	nfs_page_cachep = kmem_cache_create("nfs_page",
  					    sizeof(struct nfs_page),
  					    0, SLAB_HWCACHE_ALIGN,

  					    NULL);

  	if (nfs_page_cachep == NULL)
  		return -ENOMEM;
  
  	return 0;
  }

  void nfs_destroy_nfspagecache(void)

  {

  	kmem_cache_destroy(nfs_page_cachep);

  }

  static const struct rpc_call_ops nfs_pgio_common_ops = {

  	.rpc_call_prepare = nfs_pgio_prepare,
  	.rpc_call_done = nfs_pgio_result,
  	.rpc_release = nfs_pgio_release,
  };

  
  const struct nfs_pageio_ops nfs_pgio_rw_ops = {
  	.pg_test = nfs_generic_pg_test,
  	.pg_doio = nfs_generic_pg_pgios,
  };