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write.c

/*
 * 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/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"

#define NFSDBG_FACILITY       NFSDBG_PAGECACHE

#define MIN_POOL_WRITE        (32)
#define MIN_POOL_COMMIT       (4)

/*
 * Local function declarations
 */
static struct nfs_page * nfs_update_request(struct nfs_open_context*,
                                  struct page *,
                                  unsigned int, unsigned int);
static void nfs_pageio_init_write(struct nfs_pageio_descriptor *desc,
                          struct inode *inode, int ioflags);
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_commit_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);
      }
      return p;
}

static void nfs_commit_rcu_free(struct rcu_head *head)
{
      struct nfs_write_data *p = container_of(head, struct nfs_write_data, task.u.tk_rcu);
      if (p && (p->pagevec != &p->page_array[0]))
            kfree(p->pagevec);
      mempool_free(p, nfs_commit_mempool);
}

void nfs_commit_free(struct nfs_write_data *wdata)
{
      call_rcu_bh(&wdata->task.u.tk_rcu, nfs_commit_rcu_free);
}

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;
            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;
}

static void nfs_writedata_rcu_free(struct rcu_head *head)
{
      struct nfs_write_data *p = container_of(head, struct nfs_write_data, task.u.tk_rcu);
      if (p && (p->pagevec != &p->page_array[0]))
            kfree(p->pagevec);
      mempool_free(p, nfs_wdata_mempool);
}

static void nfs_writedata_free(struct nfs_write_data *wdata)
{
      call_rcu_bh(&wdata->task.u.tk_rcu, nfs_writedata_rcu_free);
}

void nfs_writedata_release(void *wdata)
{
      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 = i_size_read(inode);
      pgoff_t end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;

      if (i_size > 0 && page->index < end_index)
            return;
      end = ((loff_t)page->index << PAGE_CACHE_SHIFT) + ((loff_t)offset+count);
      if (i_size >= end)
            return;
      nfs_inc_stats(inode, NFSIOS_EXTENDWRITE);
      i_size_write(inode, end);
}

/* 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 nfs_writepage_setup(struct nfs_open_context *ctx, struct page *page,
            unsigned int offset, unsigned int count)
{
      struct nfs_page   *req;
      int ret;

      for (;;) {
            req = nfs_update_request(ctx, page, offset, count);
            if (!IS_ERR(req))
                  break;
            ret = PTR_ERR(req);
            if (ret != -EBUSY)
                  return ret;
            ret = nfs_wb_page(page->mapping->host, page);
            if (ret != 0)
                  return ret;
      }
      /* Update file length */
      nfs_grow_file(page, offset, count);
      nfs_unlock_request(req);
      return 0;
}

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, WRITE);
      }
      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, WRITE);
}

/*
 * 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 inode *inode = page->mapping->host;
      struct nfs_inode *nfsi = NFS_I(inode);
      struct nfs_page *req;
      int ret;

      spin_lock(&inode->i_lock);
      for(;;) {
            req = nfs_page_find_request_locked(page);
            if (req == NULL) {
                  spin_unlock(&inode->i_lock);
                  return 0;
            }
            if (nfs_lock_request_dontget(req))
                  break;
            /* Note: If we hold the page lock, as is the case in nfs_writepage,
             *     then the call to nfs_lock_request_dontget() 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 ret;
            spin_lock(&inode->i_lock);
      }
      if (test_bit(PG_NEED_COMMIT, &req->wb_flags)) {
            /* This request is marked for commit */
            spin_unlock(&inode->i_lock);
            nfs_unlock_request(req);
            nfs_pageio_complete(pgio);
            return 0;
      }
      if (nfs_set_page_writeback(page) != 0) {
            spin_unlock(&inode->i_lock);
            BUG();
      }
      radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index,
                  NFS_PAGE_TAG_LOCKED);
      spin_unlock(&inode->i_lock);
      nfs_pageio_add_request(pgio, req);
      return 0;
}

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;
      struct nfs_pageio_descriptor pgio;
      int 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);
      if (err < 0)
            return err;
      if (pgio.pg_error < 0)
            return pgio.pg_error;
      return 0;
}

/*
 * 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_insert(&nfsi->nfs_page_tree, req->wb_index, req);
      BUG_ON(error == -EEXIST);
      if (error)
            return 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);
      return 0;
}

/*
 * 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_redirty_request(struct nfs_page *req)
{
      __set_page_dirty_nobuffers(req->wb_page);
}

/*
 * Check if a request is dirty
 */
static inline int
nfs_dirty_request(struct nfs_page *req)
{
      struct page *page = req->wb_page;

      if (page == NULL || test_bit(PG_NEED_COMMIT, &req->wb_flags))
            return 0;
      return !PageWriteback(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);
      nfsi->ncommit++;
      set_bit(PG_NEED_COMMIT, &(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 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_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_redirty_request(req);
            return 1;
      }
      return 0;
}
#else
static inline void
nfs_mark_request_commit(struct nfs_page *req)
{
}

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 signals only if mounted with intr flag.
 */
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);
            dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
            dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
                        BDI_RECLAIMABLE);
            nfs_list_remove_request(req);
            clear_bit(PG_NEED_COMMIT, &(req)->wb_flags);
            nfs_inode_remove_request(req);
            nfs_unlock_request(req);
      }
}

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
/*
 * 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);
      int res = 0;

      if (nfsi->ncommit != 0) {
            res = nfs_scan_list(nfsi, dst, idx_start, npages,
                        NFS_PAGE_TAG_COMMIT);
            nfsi->ncommit -= res;
      }
      return res;
}
#else
static inline int nfs_scan_commit(struct inode *inode, struct list_head *dst, pgoff_t idx_start, unsigned int npages)
{
      return 0;
}
#endif

/*
 * Try to update any existing write request, or create one if there is none.
 * In order to match, the request's credentials must match those of
 * the calling process.
 *
 * Note: Should always be called with the Page Lock held!
 */
static struct nfs_page * nfs_update_request(struct nfs_open_context* ctx,
            struct page *page, unsigned int offset, unsigned int bytes)
{
      struct address_space *mapping = page->mapping;
      struct inode *inode = mapping->host;
      struct nfs_page         *req, *new = NULL;
      pgoff_t           rqend, end;

      end = offset + bytes;

      for (;;) {
            /* Loop over all inode entries and see if we find
             * A request for the page we wish to update
             */
            spin_lock(&inode->i_lock);
            req = nfs_page_find_request_locked(page);
            if (req) {
                  if (!nfs_lock_request_dontget(req)) {
                        int error;

                        spin_unlock(&inode->i_lock);
                        error = nfs_wait_on_request(req);
                        nfs_release_request(req);
                        if (error < 0) {
                              if (new)
                                    nfs_release_request(new);
                              return ERR_PTR(error);
                        }
                        continue;
                  }
                  spin_unlock(&inode->i_lock);
                  if (new)
                        nfs_release_request(new);
                  break;
            }

            if (new) {
                  int error;
                  nfs_lock_request_dontget(new);
                  error = nfs_inode_add_request(inode, new);
                  if (error) {
                        spin_unlock(&inode->i_lock);
                        nfs_unlock_request(new);
                        return ERR_PTR(error);
                  }
                  spin_unlock(&inode->i_lock);
                  req = new;
                  goto zero_page;
            }
            spin_unlock(&inode->i_lock);

            new = nfs_create_request(ctx, inode, page, offset, bytes);
            if (IS_ERR(new))
                  return new;
      }

      /* We have a request for our page.
       * If the creds don't match, or the
       * page addresses don't match,
       * tell the caller to wait on the conflicting
       * request.
       */
      rqend = req->wb_offset + req->wb_bytes;
      if (req->wb_context != ctx
          || req->wb_page != page
          || !nfs_dirty_request(req)
          || offset > rqend || end < req->wb_offset) {
            nfs_unlock_request(req);
            return ERR_PTR(-EBUSY);
      }

      /* Okay, the request matches. Update the region */
      if (offset < req->wb_offset) {
            req->wb_offset = offset;
            req->wb_pgbase = offset;
            req->wb_bytes = max(end, rqend) - req->wb_offset;
            goto zero_page;
      }

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

      return req;
zero_page:
      /* If this page might potentially be marked as up to date,
       * then we need to zero any uninitalised data. */
      if (req->wb_pgbase == 0 && req->wb_bytes != PAGE_CACHE_SIZE
                  && !PageUptodate(req->wb_page))
            zero_user_page(req->wb_page, req->wb_bytes,
                        PAGE_CACHE_SIZE - req->wb_bytes,
                        KM_USER0);
      return req;
}

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

/*
 * 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@%Ld)\n",
            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 entirely in cache, it may be more efficient to avoid
       * fragmenting write requests.
       */
      if (PageUptodate(page) && inode->i_flock == NULL && !(file->f_mode & O_SYNC)) {
            count = max(count + offset, nfs_page_length(page));
            offset = 0;
      }

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

        dprintk("NFS:      nfs_updatepage returns %d (isize %Ld)\n",
                  status, (long long)i_size_read(inode));
      if (status < 0)
            nfs_set_pageerror(page);
      return status;
}

static void nfs_writepage_release(struct nfs_page *req)
{

      if (PageError(req->wb_page)) {
            nfs_end_page_writeback(req->wb_page);
            nfs_inode_remove_request(req);
      } else if (!nfs_reschedule_unstable_write(req)) {
            /* Set the PG_uptodate flag */
            nfs_mark_uptodate(req->wb_page, req->wb_pgbase, req->wb_bytes);
            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 inline 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 void 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;
      int flags;

      /* 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 = req->wb_context->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 = req->wb_context;

      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.  */
      flags = (how & FLUSH_SYNC) ? 0 : RPC_TASK_ASYNC;
      rpc_init_task(&data->task, NFS_CLIENT(inode), flags, call_ops, data);
      NFS_PROTO(inode)->write_setup(data, how);

      data->task.tk_priority = flush_task_priority(how);
      data->task.tk_cookie = (unsigned long)inode;

      dprintk("NFS: %5u initiated write call "
            "(req %s/%Ld, %u bytes @ offset %Lu)\n",
            data->task.tk_pid,
            inode->i_sb->s_id,
            (long long)NFS_FILEID(inode),
            count,
            (unsigned long long)data->args.offset);
}

static void nfs_execute_write(struct nfs_write_data *data)
{
      struct rpc_clnt *clnt = NFS_CLIENT(data->inode);
      sigset_t oldset;

      rpc_clnt_sigmask(clnt, &oldset);
      rpc_execute(&data->task);
      rpc_clnt_sigunmask(clnt, &oldset);
}

/*
 * 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;
      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 {
            data = list_entry(list.next, struct nfs_write_data, pages);
            list_del_init(&data->pages);

            data->pagevec[0] = page;

            if (nbytes < wsize)
                  wsize = nbytes;
            nfs_write_rpcsetup(req, data, &nfs_write_partial_ops,
                           wsize, offset, how);
            offset += wsize;
            nbytes -= wsize;
            nfs_execute_write(data);
      } while (nbytes != 0);

      return 0;

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);
      nfs_end_page_writeback(req->wb_page);
      nfs_clear_page_tag_locked(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 */
      nfs_write_rpcsetup(req, data, &nfs_write_full_ops, count, 0, how);

      nfs_execute_write(data);
      return 0;
 out_bad:
      while (!list_empty(head)) {
            req = nfs_list_entry(head->next);
            nfs_list_remove_request(req);
            nfs_redirty_request(req);
            nfs_end_page_writeback(req->wb_page);
            nfs_clear_page_tag_locked(req);
      }
      return -ENOMEM;
}

static void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
                          struct inode *inode, int ioflags)
{
      int 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;
      struct nfs_page         *req = data->req;
      struct page       *page = req->wb_page;

      dprintk("NFS: write (%s/%Ld %d@%Ld)",
            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 (nfs_writeback_done(task, data) != 0)
            return;

      if (task->tk_status < 0) {
            nfs_set_pageerror(page);
            nfs_context_set_write_error(req->wb_context, task->tk_status);
            dprintk(", error = %d\n", task->tk_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\n");
            } 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\n");
            }
            spin_unlock(&inode->i_lock);
      } else
            dprintk(" OK\n");

out:
      if (atomic_dec_and_test(&req->wb_complete))
            nfs_writepage_release(req);
}

static const struct rpc_call_ops nfs_write_partial_ops = {
      .rpc_call_done = nfs_writeback_done_partial,
      .rpc_release = nfs_writedata_release,
};

/*
 * 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;
      struct nfs_page         *req;
      struct page       *page;

      if (nfs_writeback_done(task, data) != 0)
            return;

      /* Update attributes as result of writeback. */
      while (!list_empty(&data->pages)) {
            req = nfs_list_entry(data->pages.next);
            nfs_list_remove_request(req);
            page = req->wb_page;

            dprintk("NFS: write (%s/%Ld %d@%Ld)",
                  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 (task->tk_status < 0) {
                  nfs_set_pageerror(page);
                  nfs_context_set_write_error(req->wb_context, task->tk_status);
                  dprintk(", error = %d\n", task->tk_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\n");
                  goto next;
            }
            /* Set the PG_uptodate flag? */
            nfs_mark_uptodate(page, req->wb_pgbase, req->wb_bytes);
            dprintk(" OK\n");
remove_request:
            nfs_end_page_writeback(page);
            nfs_inode_remove_request(req);
      next:
            nfs_clear_page_tag_locked(req);
      }
}

static const struct rpc_call_ops nfs_write_full_ops = {
      .rpc_call_done = nfs_writeback_done_full,
      .rpc_release = nfs_writedata_release,
};


/*
 * 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;
      int status;

      dprintk("NFS: %5u nfs_writeback_done (status %d)\n",
            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)\n",
                        NFS_SERVER(data->inode)->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;
                  }
                  rpc_restart_call(task);
                  return -EAGAIN;
            }
            if (time_before(complain, jiffies)) {
                  printk(KERN_WARNING
                         "NFS: Server wrote zero bytes, expected %u.\n",
                              argp->count);
                  complain = jiffies + 300 * HZ;
            }
            /* Can't do anything about it except throw an error. */
            task->tk_status = -EIO;
      }
      return 0;
}


#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
void nfs_commit_release(void *wdata)
{
      nfs_commit_free(wdata);
}

/*
 * Set up the argument/result storage required for the RPC call.
 */
static void nfs_commit_rpcsetup(struct list_head *head,
            struct nfs_write_data *data,
            int how)
{
      struct nfs_page         *first;
      struct inode            *inode;
      int flags;

      /* 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);
      first = nfs_list_entry(data->pages.next);
      inode = first->wb_context->path.dentry->d_inode;

      data->inode   = inode;
      data->cred    = first->wb_context->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->res.count   = 0;
      data->res.fattr   = &data->fattr;
      data->res.verf    = &data->verf;
      nfs_fattr_init(&data->fattr);

      /* Set up the initial task struct.  */
      flags = (how & FLUSH_SYNC) ? 0 : RPC_TASK_ASYNC;
      rpc_init_task(&data->task, NFS_CLIENT(inode), flags, &nfs_commit_ops, data);
      NFS_PROTO(inode)->commit_setup(data, how);

      data->task.tk_priority = flush_task_priority(how);
      data->task.tk_cookie = (unsigned long)inode;
      
      dprintk("NFS: %5u initiated commit call\n", data->task.tk_pid);
}

/*
 * 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_commit_alloc();

      if (!data)
            goto out_bad;

      /* Set up the argument struct */
      nfs_commit_rpcsetup(head, data, how);

      nfs_execute_write(data);
      return 0;
 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;
      struct nfs_page         *req;

        dprintk("NFS: %5u nfs_commit_done (status %d)\n",
                                task->tk_pid, task->tk_status);

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

      while (!list_empty(&data->pages)) {
            req = nfs_list_entry(data->pages.next);
            nfs_list_remove_request(req);
            clear_bit(PG_NEED_COMMIT, &(req)->wb_flags);
            dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
            dec_bdi_stat(req->wb_page->mapping->backing_dev_info,
                        BDI_RECLAIMABLE);

            dprintk("NFS: commit (%s/%Ld %d@%Ld)",
                  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 (task->tk_status < 0) {
                  nfs_context_set_write_error(req->wb_context, task->tk_status);
                  nfs_inode_remove_request(req);
                  dprintk(", error = %d\n", task->tk_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 */
                  /* Set the PG_uptodate flag */
                  nfs_mark_uptodate(req->wb_page, req->wb_pgbase,
                              req->wb_bytes);
                  nfs_inode_remove_request(req);
                  dprintk(" OK\n");
                  goto next;
            }
            /* We have a mismatch. Write the page again */
            dprintk(" mismatch\n");
            nfs_redirty_request(req);
      next:
            nfs_clear_page_tag_locked(req);
      }
}

static const struct rpc_call_ops nfs_commit_ops = {
      .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_NONE,
            .nr_to_write = LONG_MAX,
            .for_writepages = 1,
            .range_cyclic = 1,
      };
      int ret;

      ret = __nfs_write_mapping(mapping, &wbc, how);
      if (ret < 0)
            return ret;
      wbc.sync_mode = WB_SYNC_ALL;
      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_NEED_COMMIT, &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;

      BUG_ON(!PageLocked(page));
      if (clear_page_dirty_for_io(page)) {
            ret = nfs_writepage_locked(page, &wbc);
            if (ret < 0)
                  goto out;
      }
      if (!PagePrivate(page))
            return 0;
      ret = nfs_sync_mapping_wait(page->mapping, &wbc, how);
      if (ret >= 0)
            return 0;
out:
      __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);
}

int __init nfs_init_writepagecache(void)
{
      nfs_wdata_cachep = kmem_cache_create("nfs_write_data",
                                   sizeof(struct nfs_write_data),
                                   0, SLAB_HWCACHE_ALIGN,
                                   NULL);
      if (nfs_wdata_cachep == NULL)
            return -ENOMEM;

      nfs_wdata_mempool = mempool_create_slab_pool(MIN_POOL_WRITE,
                                         nfs_wdata_cachep);
      if (nfs_wdata_mempool == NULL)
            return -ENOMEM;

      nfs_commit_mempool = mempool_create_slab_pool(MIN_POOL_COMMIT,
                                          nfs_wdata_cachep);
      if (nfs_commit_mempool == NULL)
            return -ENOMEM;

      /*
       * NFS congestion size, scale with available memory.
       *
       *  64MB:    8192k
       * 128MB:   11585k
       * 256MB:   16384k
       * 512MB:   23170k
       *   1GB:   32768k
       *   2GB:   46340k
       *   4GB:   65536k
       *   8GB:   92681k
       *  16GB:  131072k
       *
       * This allows larger machines to have larger/more transfers.
       * Limit the default to 256M
       */
      nfs_congestion_kb = (16*int_sqrt(totalram_pages)) << (PAGE_SHIFT-10);
      if (nfs_congestion_kb > 256*1024)
            nfs_congestion_kb = 256*1024;

      return 0;
}

void nfs_destroy_writepagecache(void)
{
      mempool_destroy(nfs_commit_mempool);
      mempool_destroy(nfs_wdata_mempool);
      kmem_cache_destroy(nfs_wdata_cachep);
}


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