tracing: Keep overwrite in sync between regular and snapshot buffers

[linux/fpc-iii.git] / fs / nfs / 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/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 <linux/export.h>

#include <asm/uaccess.h>

#include "delegation.h"
#include "internal.h"
#include "iostat.h"
#include "nfs4_fs.h"
#include "fscache.h"
#include "pnfs.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);
        }
        return p;
}
EXPORT_SYMBOL_GPL(nfs_commitdata_alloc);

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);
}
EXPORT_SYMBOL_GPL(nfs_commit_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;
}

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);
}

void nfs_writedata_release(struct nfs_write_data *wdata)
{
        put_lseg(wdata->lseg);
        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 || wbc->for_background)
                return FLUSH_LOWPRI | FLUSH_COND_STABLE;
        return FLUSH_COND_STABLE;
}

/*
 * 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);

                page_cache_get(page);
                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);
        page_cache_release(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, bool nonblock)
{
        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);
                if (!nonblock)
                        ret = nfs_wait_on_request(req);
                else
                        ret = -EAGAIN;
                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, bool nonblock)
{
        struct nfs_page *req;
        int ret = 0;

        req = nfs_find_and_lock_request(page, nonblock);
        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;
        int ret;

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

        nfs_pageio_cond_complete(pgio, page->index);
        ret = nfs_page_async_flush(pgio, page, wbc->sync_mode == WB_SYNC_NONE);
        if (ret == -EAGAIN) {
                redirty_page_for_writepage(wbc, page);
                ret = 0;
        }
        return ret;
}

/*
 * 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 && nfs_have_delegation(inode, FMODE_WRITE))
                inode->i_version++;
        set_bit(PG_MAPPED, &req->wb_flags);
        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->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);
        clear_bit(PG_MAPPED, &req->wb_flags);
        radix_tree_delete(&nfsi->nfs_page_tree, req->wb_index);
        nfsi->npages--;
        spin_unlock(&inode->i_lock);
        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 pnfs_layout_segment *lseg)
{
        struct inode *inode = req->wb_context->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);
        nfsi->ncommit++;
        spin_unlock(&inode->i_lock);
        pnfs_mark_request_commit(req, lseg);
        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)
{
        if (data->verf.committed == NFS_DATA_SYNC)
                return data->lseg == NULL;
        else
                return data->verf.committed != NFS_FILE_SYNC;
}

static inline
int nfs_reschedule_unstable_write(struct nfs_page *req,
                                  struct nfs_write_data *data)
{
        if (test_and_clear_bit(PG_NEED_COMMIT, &req->wb_flags)) {
                nfs_mark_request_commit(req, data->lseg);
                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, struct pnfs_layout_segment *lseg)
{
}

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,
                                  struct nfs_write_data *data)
{
        return 0;
}
#endif

#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);
        int ret;

        if (!nfs_need_commit(nfsi))
                return 0;

        spin_lock(&inode->i_lock);
        ret = nfs_scan_list(nfsi, dst, idx_start, npages, NFS_PAGE_TAG_COMMIT);
        if (ret > 0)
                nfsi->ncommit -= ret;
        spin_unlock(&inode->i_lock);

        if (nfs_need_commit(NFS_I(inode)))
                __mark_inode_dirty(inode, I_DIRTY_DATASYNC);

        return ret;
}
#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) != NULL) {
                NFS_I(inode)->ncommit--;
                pnfs_clear_request_commit(req);
        }

        /* 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_mark_request_dirty(req);
        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 ||
                        req->wb_lock_context->lockowner != current->files ||
                        req->wb_lock_context->pid != current->tgid;
                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)\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 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_DSYNC)) {
                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)\n",
                        status, (long long)i_size_read(inode));
        return status;
}

static void nfs_writepage_release(struct nfs_page *req,
                                  struct nfs_write_data *data)
{
        struct page *page = req->wb_page;

        if (PageError(req->wb_page) || !nfs_reschedule_unstable_write(req, data))
                nfs_inode_remove_request(req);
        nfs_clear_page_tag_locked(req);
        nfs_end_page_writeback(page);
}

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;
}

int nfs_initiate_write(struct nfs_write_data *data,
                       struct rpc_clnt *clnt,
                       const struct rpc_call_ops *call_ops,
                       int how)
{
        struct inode *inode = data->inode;
        int priority = flush_task_priority(how);
        struct rpc_task *task;
        struct rpc_message msg = {
                .rpc_argp = &data->args,
                .rpc_resp = &data->res,
                .rpc_cred = data->cred,
        };
        struct rpc_task_setup task_setup_data = {
                .rpc_client = clnt,
                .task = &data->task,
                .rpc_message = &msg,
                .callback_ops = call_ops,
                .callback_data = data,
                .workqueue = nfsiod_workqueue,
                .flags = RPC_TASK_ASYNC,
                .priority = priority,
        };
        int ret = 0;

        /* 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)\n",
                data->task.tk_pid,
                inode->i_sb->s_id,
                (long long)NFS_FILEID(inode),
                data->args.count,
                (unsigned long long)data->args.offset);

        task = rpc_run_task(&task_setup_data);
        if (IS_ERR(task)) {
                ret = PTR_ERR(task);
                goto out;
        }
        if (how & FLUSH_SYNC) {
                ret = rpc_wait_for_completion_task(task);
                if (ret == 0)
                        ret = task->tk_status;
        }
        rpc_put_task(task);
out:
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_initiate_write);

/*
 * 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,
                unsigned int count, unsigned int offset,
                int how)
{
        struct inode *inode = req->wb_context->dentry->d_inode;

        /* 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->dentry->d_inode;
        data->cred = req->wb_context->cred;

        data->args.fh     = NFS_FH(inode);
        data->args.offset = req_offset(req) + offset;
        /* pnfs_set_layoutcommit needs this */
        data->mds_offset = data->args.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.lock_context = req->wb_lock_context;
        data->args.stable  = NFS_UNSTABLE;
        switch (how & (FLUSH_STABLE | FLUSH_COND_STABLE)) {
        case 0:
                break;
        case FLUSH_COND_STABLE:
                if (nfs_need_commit(NFS_I(inode)))
                        break;
        default:
                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);
}

static int nfs_do_write(struct nfs_write_data *data,
                const struct rpc_call_ops *call_ops,
                int how)
{
        struct inode *inode = data->args.context->dentry->d_inode;

        return nfs_initiate_write(data, NFS_CLIENT(inode), call_ops, how);
}

static int nfs_do_multiple_writes(struct list_head *head,
                const struct rpc_call_ops *call_ops,
                int how)
{
        struct nfs_write_data *data;
        int ret = 0;

        while (!list_empty(head)) {
                int ret2;

                data = list_entry(head->next, struct nfs_write_data, list);
                list_del_init(&data->list);
                
                ret2 = nfs_do_write(data, call_ops, how);
                 if (ret == 0)
                         ret = ret2;
        }
        return ret;
}

/* 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)
{
        struct page *page = req->wb_page;

        nfs_mark_request_dirty(req);
        nfs_clear_page_tag_locked(req);
        nfs_end_page_writeback(page);
}

/*
 * Generate multiple small requests to write out a single
 * contiguous dirty area on one page.
 */
static int nfs_flush_multi(struct nfs_pageio_descriptor *desc, struct list_head *res)
{
        struct nfs_page *req = nfs_list_entry(desc->pg_list.next);
        struct page *page = req->wb_page;
        struct nfs_write_data *data;
        size_t wsize = desc->pg_bsize, nbytes;
        unsigned int offset;
        int requests = 0;
        int ret = 0;

        nfs_list_remove_request(req);

        if ((desc->pg_ioflags & FLUSH_COND_STABLE) &&
            (desc->pg_moreio || NFS_I(desc->pg_inode)->ncommit ||
             desc->pg_count > wsize))
                desc->pg_ioflags &= ~FLUSH_COND_STABLE;


        offset = 0;
        nbytes = desc->pg_count;
        do {
                size_t len = min(nbytes, wsize);

                data = nfs_writedata_alloc(1);
                if (!data)
                        goto out_bad;
                data->pagevec[0] = page;
                nfs_write_rpcsetup(req, data, len, offset, desc->pg_ioflags);
                list_add(&data->list, res);
                requests++;
                nbytes -= len;
                offset += len;
        } while (nbytes != 0);
        atomic_set(&req->wb_complete, requests);
        desc->pg_rpc_callops = &nfs_write_partial_ops;
        return ret;

out_bad:
        while (!list_empty(res)) {
                data = list_entry(res->next, struct nfs_write_data, list);
                list_del(&data->list);
                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 nfs_pageio_descriptor *desc, struct list_head *res)
{
        struct nfs_page         *req;
        struct page             **pages;
        struct nfs_write_data   *data;
        struct list_head *head = &desc->pg_list;
        int ret = 0;

        data = nfs_writedata_alloc(nfs_page_array_len(desc->pg_base,
                                                      desc->pg_count));
        if (!data) {
                while (!list_empty(head)) {
                        req = nfs_list_entry(head->next);
                        nfs_list_remove_request(req);
                        nfs_redirty_request(req);
                }
                ret = -ENOMEM;
                goto out;
        }
        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);
                *pages++ = req->wb_page;
        }
        req = nfs_list_entry(data->pages.next);

        if ((desc->pg_ioflags & FLUSH_COND_STABLE) &&
            (desc->pg_moreio || NFS_I(desc->pg_inode)->ncommit))
                desc->pg_ioflags &= ~FLUSH_COND_STABLE;

        /* Set up the argument struct */
        nfs_write_rpcsetup(req, data, desc->pg_count, 0, desc->pg_ioflags);
        list_add(&data->list, res);
        desc->pg_rpc_callops = &nfs_write_full_ops;
out:
        return ret;
}

int nfs_generic_flush(struct nfs_pageio_descriptor *desc, struct list_head *head)
{
        if (desc->pg_bsize < PAGE_CACHE_SIZE)
                return nfs_flush_multi(desc, head);
        return nfs_flush_one(desc, head);
}

static int nfs_generic_pg_writepages(struct nfs_pageio_descriptor *desc)
{
        LIST_HEAD(head);
        int ret;

        ret = nfs_generic_flush(desc, &head);
        if (ret == 0)
                ret = nfs_do_multiple_writes(&head, desc->pg_rpc_callops,
                                desc->pg_ioflags);
        return ret;
}

static const struct nfs_pageio_ops nfs_pageio_write_ops = {
        .pg_test = nfs_generic_pg_test,
        .pg_doio = nfs_generic_pg_writepages,
};

static void nfs_pageio_init_write_mds(struct nfs_pageio_descriptor *pgio,
                                  struct inode *inode, int ioflags)
{
        nfs_pageio_init(pgio, inode, &nfs_pageio_write_ops,
                                NFS_SERVER(inode)->wsize, ioflags);
}

void nfs_pageio_reset_write_mds(struct nfs_pageio_descriptor *pgio)
{
        pgio->pg_ops = &nfs_pageio_write_ops;
        pgio->pg_bsize = NFS_SERVER(pgio->pg_inode)->wsize;
}
EXPORT_SYMBOL_GPL(nfs_pageio_reset_write_mds);

static void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
                                  struct inode *inode, int ioflags)
{
        if (!pnfs_pageio_init_write(pgio, inode, ioflags))
                nfs_pageio_init_write_mds(pgio, inode, 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->dentry->d_inode->i_sb->s_id,
                (long long)
                  NFS_FILEID(data->req->wb_context->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\n", 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, data);
        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;

        if (nfs4_setup_sequence(NFS_SERVER(data->inode),
                                &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 ret, status = data->task.tk_status;
        struct nfs_pageio_descriptor pgio;

        if (data->pnfs_error) {
                nfs_pageio_init_write_mds(&pgio, data->inode, FLUSH_STABLE);
                pgio.pg_recoalesce = 1;
        }

        /* 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->dentry->d_inode->i_sb->s_id,
                        (long long)NFS_FILEID(req->wb_context->dentry->d_inode),
                        req->wb_bytes,
                        (long long)req_offset(req));

                if (data->pnfs_error) {
                        dprintk(", pnfs error = %d\n", data->pnfs_error);
                        goto next;
                }

                if (status < 0) {
                        nfs_set_pageerror(page);
                        nfs_context_set_write_error(req->wb_context, status);
                        dprintk(", error = %d\n", 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, data->lseg);
                        dprintk(" marked for commit\n");
                        goto next;
                }
                dprintk(" OK\n");
remove_request:
                nfs_inode_remove_request(req);
        next:
                nfs_clear_page_tag_locked(req);
                nfs_end_page_writeback(page);
                if (data->pnfs_error) {
                        lock_page(page);
                        nfs_pageio_cond_complete(&pgio, page->index);
                        ret = nfs_page_async_flush(&pgio, page, 0);
                        if (ret) {
                                nfs_set_pageerror(page);
                                dprintk("rewrite to MDS error = %d\n", ret);
                        }
                        unlock_page(page);
                }
        }
        if (data->pnfs_error)
                nfs_pageio_complete(&pgio);
        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.
 */
void 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;
        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;

                /* Note this will print the MDS for a DS write */
                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 */
                                data->mds_offset += resp->count;
                                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_prepare(task);
                        return;
                }
                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;
}


#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
static int nfs_commit_set_lock(struct nfs_inode *nfsi, int may_wait)
{
        int ret;

        if (!test_and_set_bit(NFS_INO_COMMIT, &nfsi->flags))
                return 1;
        if (!may_wait)
                return 0;
        ret = out_of_line_wait_on_bit_lock(&nfsi->flags,
                                NFS_INO_COMMIT,
                                nfs_wait_bit_killable,
                                TASK_KILLABLE);
        return (ret < 0) ? ret : 1;
}

void nfs_commit_clear_lock(struct nfs_inode *nfsi)
{
        clear_bit(NFS_INO_COMMIT, &nfsi->flags);
        smp_mb__after_clear_bit();
        wake_up_bit(&nfsi->flags, NFS_INO_COMMIT);
}
EXPORT_SYMBOL_GPL(nfs_commit_clear_lock);

void nfs_commitdata_release(void *data)
{
        struct nfs_write_data *wdata = data;

        put_lseg(wdata->lseg);
        put_nfs_open_context(wdata->args.context);
        nfs_commit_free(wdata);
}
EXPORT_SYMBOL_GPL(nfs_commitdata_release);

int nfs_initiate_commit(struct nfs_write_data *data, struct rpc_clnt *clnt,
                        const struct rpc_call_ops *call_ops,
                        int how)
{
        struct rpc_task *task;
        int priority = flush_task_priority(how);
        struct rpc_message msg = {
                .rpc_argp = &data->args,
                .rpc_resp = &data->res,
                .rpc_cred = data->cred,
        };
        struct rpc_task_setup task_setup_data = {
                .task = &data->task,
                .rpc_client = clnt,
                .rpc_message = &msg,
                .callback_ops = call_ops,
                .callback_data = data,
                .workqueue = nfsiod_workqueue,
                .flags = RPC_TASK_ASYNC,
                .priority = priority,
        };
        /* Set up the initial task struct.  */
        NFS_PROTO(data->inode)->commit_setup(data, &msg);

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

        task = rpc_run_task(&task_setup_data);
        if (IS_ERR(task))
                return PTR_ERR(task);
        if (how & FLUSH_SYNC)
                rpc_wait_for_completion_task(task);
        rpc_put_task(task);
        return 0;
}
EXPORT_SYMBOL_GPL(nfs_initiate_commit);

/*
 * Set up the argument/result storage required for the RPC call.
 */
void nfs_init_commit(struct nfs_write_data *data,
                            struct list_head *head,
                            struct pnfs_layout_segment *lseg)
{
        struct nfs_page *first = nfs_list_entry(head->next);
        struct inode *inode = first->wb_context->dentry->d_inode;

        /* 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        = first->wb_context->cred;
        data->lseg        = lseg; /* reference transferred */
        data->mds_ops     = &nfs_commit_ops;

        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);
}
EXPORT_SYMBOL_GPL(nfs_init_commit);

void nfs_retry_commit(struct list_head *page_list,
                      struct pnfs_layout_segment *lseg)
{
        struct nfs_page *req;

        while (!list_empty(page_list)) {
                req = nfs_list_entry(page_list->next);
                nfs_list_remove_request(req);
                nfs_mark_request_commit(req, lseg);
                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);
        }
}
EXPORT_SYMBOL_GPL(nfs_retry_commit);

/*
 * Commit dirty pages
 */
static int
nfs_commit_list(struct inode *inode, struct list_head *head, int how)
{
        struct nfs_write_data   *data;

        data = nfs_commitdata_alloc();

        if (!data)
                goto out_bad;

        /* Set up the argument struct */
        nfs_init_commit(data, head, NULL);
        return nfs_initiate_commit(data, NFS_CLIENT(inode), data->mds_ops, how);
 out_bad:
        nfs_retry_commit(head, NULL);
        nfs_commit_clear_lock(NFS_I(inode));
        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)\n",
                                task->tk_pid, task->tk_status);

        /* Call the NFS version-specific code */
        NFS_PROTO(data->inode)->commit_done(task, data);
}

void nfs_commit_release_pages(struct nfs_write_data *data)
{
        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->dentry->d_sb->s_id,
                        (long long)NFS_FILEID(req->wb_context->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\n", 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\n");
                        goto next;
                }
                /* We have a mismatch. Write the page again */
                dprintk(" mismatch\n");
                nfs_mark_request_dirty(req);
        next:
                nfs_clear_page_tag_locked(req);
        }
}
EXPORT_SYMBOL_GPL(nfs_commit_release_pages);

static void nfs_commit_release(void *calldata)
{
        struct nfs_write_data *data = calldata;

        nfs_commit_release_pages(data);
        nfs_commit_clear_lock(NFS_I(data->inode));
        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 may_wait = how & FLUSH_SYNC;
        int res;

        res = nfs_commit_set_lock(NFS_I(inode), may_wait);
        if (res <= 0)
                goto out_mark_dirty;
        res = nfs_scan_commit(inode, &head, 0, 0);
        if (res) {
                int error;

                error = pnfs_commit_list(inode, &head, how);
                if (error == PNFS_NOT_ATTEMPTED)
                        error = nfs_commit_list(inode, &head, how);
                if (error < 0)
                        return error;
                if (!may_wait)
                        goto out_mark_dirty;
                error = wait_on_bit(&NFS_I(inode)->flags,
                                NFS_INO_COMMIT,
                                nfs_wait_bit_killable,
                                TASK_KILLABLE);
                if (error < 0)
                        return error;
        } else
                nfs_commit_clear_lock(NFS_I(inode));
        return res;
        /* Note: If we exit without ensuring that the commit is complete,
         * we must mark the inode as dirty. Otherwise, future calls to
         * sync_inode() with the WB_SYNC_ALL flag set will fail to ensure
         * that the data is on the disk.
         */
out_mark_dirty:
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        return res;
}

static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_control *wbc)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        int flags = FLUSH_SYNC;
        int ret = 0;

        /* no commits means nothing needs to be done */
        if (!nfsi->ncommit)
                return ret;

        if (wbc->sync_mode == WB_SYNC_NONE) {
                /* Don't commit yet if this is a non-blocking flush and there
                 * are a lot of outstanding writes for this mapping.
                 */
                if (nfsi->ncommit <= (nfsi->npages >> 1))
                        goto out_mark_dirty;

                /* don't wait for the COMMIT response */
                flags = 0;
        }

        ret = nfs_commit_inode(inode, flags);
        if (ret >= 0) {
                if (wbc->sync_mode == WB_SYNC_NONE) {
                        if (ret < wbc->nr_to_write)
                                wbc->nr_to_write -= ret;
                        else
                                wbc->nr_to_write = 0;
                }
                return 0;
        }
out_mark_dirty:
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        return ret;
}
#else
static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_control *wbc)
{
        return 0;
}
#endif

int nfs_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        int ret;

        ret = nfs_commit_unstable_pages(inode, wbc);
        if (ret >= 0 && test_bit(NFS_INO_LAYOUTCOMMIT, &NFS_I(inode)->flags)) {
                int status;
                bool sync = true;

                if (wbc->sync_mode == WB_SYNC_NONE)
                        sync = false;

                status = pnfs_layoutcommit_inode(inode, sync);
                if (status < 0)
                        return status;
        }
        return ret;
}

/*
 * flush the inode to disk.
 */
int nfs_wb_all(struct inode *inode)
{
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = LONG_MAX,
                .range_start = 0,
                .range_end = LLONG_MAX,
        };

        return sync_inode(inode, &wbc);
}

int nfs_wb_page_cancel(struct inode *inode, struct page *page)
{
        struct nfs_page *req;
        int ret = 0;

        BUG_ON(!PageLocked(page));
        for (;;) {
                wait_on_page_writeback(page);
                req = nfs_page_find_request(page);
                if (req == NULL)
                        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);
                nfs_release_request(req);
                if (ret < 0)
                        break;
        }
        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)
{
        loff_t range_start = page_offset(page);
        loff_t range_end = range_start + (loff_t)(PAGE_CACHE_SIZE - 1);
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = 0,
                .range_start = range_start,
                .range_end = range_end,
        };
        int ret;

        for (;;) {
                wait_on_page_writeback(page);
                if (clear_page_dirty_for_io(page)) {
                        ret = nfs_writepage_locked(page, &wbc);
                        if (ret < 0)
                                goto out_error;
                        continue;
                }
                if (!PagePrivate(page))
                        break;
                ret = nfs_commit_inode(inode, FLUSH_SYNC);
                if (ret < 0)
                        goto out_error;
        }
        return 0;
out_error:
        return ret;
}

#ifdef CONFIG_MIGRATION
int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
                struct page *page, enum migrate_mode mode)
{
        /*
         * If PagePrivate is set, then the page is currently associated with
         * an in-progress read or write request. Don't try to migrate it.
         *
         * FIXME: we could do this in principle, but we'll need a way to ensure
         *        that we can safely release the inode reference while holding
         *        the page lock.
         */
        if (PagePrivate(page))
                return -EBUSY;

        nfs_fscache_release_page(page, GFP_KERNEL);

        return migrate_page(mapping, newpage, page, mode);
}
#endif

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)
                goto out_destroy_write_cache;

        nfs_commit_mempool = mempool_create_slab_pool(MIN_POOL_COMMIT,
                                                      nfs_wdata_cachep);
        if (nfs_commit_mempool == NULL)
                goto out_destroy_write_mempool;

        /*
         * 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;

out_destroy_write_mempool:
        mempool_destroy(nfs_wdata_mempool);
out_destroy_write_cache:
        kmem_cache_destroy(nfs_wdata_cachep);
        return -ENOMEM;
}

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