write.c

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/*
 * linux/fs/nfs/write.c
 *
 * Write file data over NFS.
 *
 * Copyright (C) 1996, 1997, Olaf Kirch <[email protected]>
 */

#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_redirty_request(struct nfs_page *req);
static const struct rpc_call_ops nfs_write_common_ops;
static const struct rpc_call_ops nfs_commit_ops;
static const struct nfs_pgio_completion_ops nfs_async_write_completion_ops;
static const struct nfs_commit_completion_ops nfs_commit_completion_ops;

static struct kmem_cache *nfs_wdata_cachep;
static mempool_t *nfs_wdata_mempool;
static struct kmem_cache *nfs_cdata_cachep;
static mempool_t *nfs_commit_mempool;

struct nfs_commit_data *nfs_commitdata_alloc(void)
{
    struct nfs_commit_data *p = mempool_alloc(nfs_commit_mempool, GFP_NOIO);

    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_commit_data *p)
{
    mempool_free(p, nfs_commit_mempool);
}
EXPORT_SYMBOL_GPL(nfs_commit_free);

struct nfs_write_header *nfs_writehdr_alloc(void)
{
    struct nfs_write_header *p = mempool_alloc(nfs_wdata_mempool, GFP_NOIO);

    if (p) {
        struct nfs_pgio_header *hdr = &p->header;

        memset(p, 0, sizeof(*p));
        INIT_LIST_HEAD(&hdr->pages);
        INIT_LIST_HEAD(&hdr->rpc_list);
        spin_lock_init(&hdr->lock);
        atomic_set(&hdr->refcnt, 0);
        hdr->verf = &p->verf;
    }
    return p;
}
EXPORT_SYMBOL_GPL(nfs_writehdr_alloc);

static struct nfs_write_data *nfs_writedata_alloc(struct nfs_pgio_header *hdr,
                          unsigned int pagecount)
{
    struct nfs_write_data *data, *prealloc;

    prealloc = &container_of(hdr, struct nfs_write_header, header)->rpc_data;
    if (prealloc->header == NULL)
        data = prealloc;
    else
        data = kzalloc(sizeof(*data), GFP_KERNEL);
    if (!data)
        goto out;

    if (nfs_pgarray_set(&data->pages, pagecount)) {
        data->header = hdr;
        atomic_inc(&hdr->refcnt);
    } else {
        if (data != prealloc)
            kfree(data);
        data = NULL;
    }
out:
    return data;
}

void nfs_writehdr_free(struct nfs_pgio_header *hdr)
{
    struct nfs_write_header *whdr = container_of(hdr, struct nfs_write_header, header);
    mempool_free(whdr, nfs_wdata_mempool);
}
EXPORT_SYMBOL_GPL(nfs_writehdr_free);

void nfs_writedata_release(struct nfs_write_data *wdata)
{
    struct nfs_pgio_header *hdr = wdata->header;
    struct nfs_write_header *write_header = container_of(hdr, struct nfs_write_header, header);

    put_nfs_open_context(wdata->args.context);
    if (wdata->pages.pagevec != wdata->pages.page_array)
        kfree(wdata->pages.pagevec);
    if (wdata != &write_header->rpc_data)
        kfree(wdata);
    else
        wdata->header = NULL;
    if (atomic_dec_and_test(&hdr->refcnt))
        hdr->completion_ops->completion(hdr);
}
EXPORT_SYMBOL_GPL(nfs_writedata_release);

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 nfs_inode *nfsi, struct page *page)
{
    struct nfs_page *req = NULL;

    if (PagePrivate(page))
        req = (struct nfs_page *)page_private(page);
    else if (unlikely(PageSwapCache(page))) {
        struct nfs_page *freq, *t;

        /* Linearly search the commit list for the correct req */
        list_for_each_entry_safe(freq, t, &nfsi->commit_info.list, wb_list) {
            if (freq->wb_page == page) {
                req = freq;
                break;
            }
        }
    }

    if (req)
        kref_get(&req->wb_kref);

    return req;
}

static struct nfs_page *nfs_page_find_request(struct page *page)
{
    struct inode *inode = page_file_mapping(page)->host;
    struct nfs_page *req = NULL;

    spin_lock(&inode->i_lock);
    req = nfs_page_find_request_locked(NFS_I(inode), 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_file_mapping(page)->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_file_index(page) < end_index)
        goto out;
    end = page_file_offset(page) + ((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_file_mapping(page)->host, page_file_mapping(page));
}

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

        if (atomic_long_inc_return(&nfss->writeback) >
                NFS_CONGESTION_ON_THRESH) {
            set_bdi_congested(&nfss->backing_dev_info,
                        BLK_RW_ASYNC);
        }
    }
    return ret;
}

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

    end_page_writeback(page);
    if (atomic_long_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
        clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
}

static struct nfs_page *nfs_find_and_lock_request(struct page *page, bool nonblock)
{
    struct inode *inode = page_file_mapping(page)->host;
    struct nfs_page *req;
    int ret;

    spin_lock(&inode->i_lock);
    for (;;) {
        req = nfs_page_find_request_locked(NFS_I(inode), page);
        if (req == NULL)
            break;
        if (nfs_lock_request(req))
            break;
        /* Note: If we hold the page lock, as is the case in nfs_writepage,
         *   then the call to nfs_lock_request() 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_file_mapping(page)->host;
    int ret;

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

    nfs_pageio_cond_complete(pgio, page_file_index(page));
    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_PROTO(page_file_mapping(page)->host)->write_pageio_init(&pgio,
                              page->mapping->host,
                              wb_priority(wbc),
                              &nfs_async_write_completion_ops);
    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_PROTO(inode)->write_pageio_init(&pgio, inode, wb_priority(wbc), &nfs_async_write_completion_ops);
    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 void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
{
    struct nfs_inode *nfsi = NFS_I(inode);

    /* Lock the request! */
    nfs_lock_request(req);

    spin_lock(&inode->i_lock);
    if (!nfsi->npages && NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
        inode->i_version++;
    /*
     * Swap-space should not get truncated. Hence no need to plug the race
     * with invalidate/truncate.
     */
    if (likely(!PageSwapCache(req->wb_page))) {
        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);
    spin_unlock(&inode->i_lock);
}

/*
 * 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);
    if (likely(!PageSwapCache(req->wb_page))) {
        set_page_private(req->wb_page, 0);
        ClearPagePrivate(req->wb_page);
        clear_bit(PG_MAPPED, &req->wb_flags);
    }
    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 IS_ENABLED(CONFIG_NFS_V3) || IS_ENABLED(CONFIG_NFS_V4)

void
nfs_request_add_commit_list(struct nfs_page *req, struct list_head *dst,
                struct nfs_commit_info *cinfo)
{
    set_bit(PG_CLEAN, &(req)->wb_flags);
    spin_lock(cinfo->lock);
    nfs_list_add_request(req, dst);
    cinfo->mds->ncommit++;
    spin_unlock(cinfo->lock);
    if (!cinfo->dreq) {
        inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
        inc_bdi_stat(page_file_mapping(req->wb_page)->backing_dev_info,
                 BDI_RECLAIMABLE);
        __mark_inode_dirty(req->wb_context->dentry->d_inode,
                   I_DIRTY_DATASYNC);
    }
}
EXPORT_SYMBOL_GPL(nfs_request_add_commit_list);

void
nfs_request_remove_commit_list(struct nfs_page *req,
                   struct nfs_commit_info *cinfo)
{
    if (!test_and_clear_bit(PG_CLEAN, &(req)->wb_flags))
        return;
    nfs_list_remove_request(req);
    cinfo->mds->ncommit--;
}
EXPORT_SYMBOL_GPL(nfs_request_remove_commit_list);

static void nfs_init_cinfo_from_inode(struct nfs_commit_info *cinfo,
                      struct inode *inode)
{
    cinfo->lock = &inode->i_lock;
    cinfo->mds = &NFS_I(inode)->commit_info;
    cinfo->ds = pnfs_get_ds_info(inode);
    cinfo->dreq = NULL;
    cinfo->completion_ops = &nfs_commit_completion_ops;
}

void nfs_init_cinfo(struct nfs_commit_info *cinfo,
            struct inode *inode,
            struct nfs_direct_req *dreq)
{
    if (dreq)
        nfs_init_cinfo_from_dreq(cinfo, dreq);
    else
        nfs_init_cinfo_from_inode(cinfo, inode);
}
EXPORT_SYMBOL_GPL(nfs_init_cinfo);

/*
 * Add a request to the inode's commit list.
 */
void
nfs_mark_request_commit(struct nfs_page *req, struct pnfs_layout_segment *lseg,
            struct nfs_commit_info *cinfo)
{
    if (pnfs_mark_request_commit(req, lseg, cinfo))
        return;
    nfs_request_add_commit_list(req, &cinfo->mds->list, cinfo);
}

static void
nfs_clear_page_commit(struct page *page)
{
    dec_zone_page_state(page, NR_UNSTABLE_NFS);
    dec_bdi_stat(page_file_mapping(page)->backing_dev_info, BDI_RECLAIMABLE);
}

static void
nfs_clear_request_commit(struct nfs_page *req)
{
    if (test_bit(PG_CLEAN, &req->wb_flags)) {
        struct inode *inode = req->wb_context->dentry->d_inode;
        struct nfs_commit_info cinfo;

        nfs_init_cinfo_from_inode(&cinfo, inode);
        if (!pnfs_clear_request_commit(req, &cinfo)) {
            spin_lock(cinfo.lock);
            nfs_request_remove_commit_list(req, &cinfo);
            spin_unlock(cinfo.lock);
        }
        nfs_clear_page_commit(req->wb_page);
    }
}

static inline
int nfs_write_need_commit(struct nfs_write_data *data)
{
    if (data->verf.committed == NFS_DATA_SYNC)
        return data->header->lseg == NULL;
    return data->verf.committed != NFS_FILE_SYNC;
}

#else
static void nfs_init_cinfo_from_inode(struct nfs_commit_info *cinfo,
                      struct inode *inode)
{
}

void nfs_init_cinfo(struct nfs_commit_info *cinfo,
            struct inode *inode,
            struct nfs_direct_req *dreq)
{
}

void
nfs_mark_request_commit(struct nfs_page *req, struct pnfs_layout_segment *lseg,
            struct nfs_commit_info *cinfo)
{
}

static void
nfs_clear_request_commit(struct nfs_page *req)
{
}

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

#endif

static void nfs_write_completion(struct nfs_pgio_header *hdr)
{
    struct nfs_commit_info cinfo;
    unsigned long bytes = 0;

    if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
        goto out;
    nfs_init_cinfo_from_inode(&cinfo, hdr->inode);
    while (!list_empty(&hdr->pages)) {
        struct nfs_page *req = nfs_list_entry(hdr->pages.next);

        bytes += req->wb_bytes;
        nfs_list_remove_request(req);
        if (test_bit(NFS_IOHDR_ERROR, &hdr->flags) &&
            (hdr->good_bytes < bytes)) {
            nfs_set_pageerror(req->wb_page);
            nfs_context_set_write_error(req->wb_context, hdr->error);
            goto remove_req;
        }
        if (test_bit(NFS_IOHDR_NEED_RESCHED, &hdr->flags)) {
            nfs_mark_request_dirty(req);
            goto next;
        }
        if (test_bit(NFS_IOHDR_NEED_COMMIT, &hdr->flags)) {
            memcpy(&req->wb_verf, &hdr->verf->verifier, sizeof(req->wb_verf));
            nfs_mark_request_commit(req, hdr->lseg, &cinfo);
            goto next;
        }
remove_req:
        nfs_inode_remove_request(req);
next:
        nfs_unlock_request(req);
        nfs_end_page_writeback(req->wb_page);
        nfs_release_request(req);
    }
out:
    hdr->release(hdr);
}

#if  IS_ENABLED(CONFIG_NFS_V3) || IS_ENABLED(CONFIG_NFS_V4)
static unsigned long
nfs_reqs_to_commit(struct nfs_commit_info *cinfo)
{
    return cinfo->mds->ncommit;
}

/* cinfo->lock held by caller */
int
nfs_scan_commit_list(struct list_head *src, struct list_head *dst,
             struct nfs_commit_info *cinfo, int max)
{
    struct nfs_page *req, *tmp;
    int ret = 0;

    list_for_each_entry_safe(req, tmp, src, wb_list) {
        if (!nfs_lock_request(req))
            continue;
        kref_get(&req->wb_kref);
        if (cond_resched_lock(cinfo->lock))
            list_safe_reset_next(req, tmp, wb_list);
        nfs_request_remove_commit_list(req, cinfo);
        nfs_list_add_request(req, dst);
        ret++;
        if ((ret == max) && !cinfo->dreq)
            break;
    }
    return ret;
}

/*
 * nfs_scan_commit - Scan an inode for commit requests
 * @inode: NFS inode to scan
 * @dst: mds destination list
 * @cinfo: mds and ds lists of reqs ready to commit
 *
 * Moves requests from the inode's 'commit' request list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
int
nfs_scan_commit(struct inode *inode, struct list_head *dst,
        struct nfs_commit_info *cinfo)
{
    int ret = 0;

    spin_lock(cinfo->lock);
    if (cinfo->mds->ncommit > 0) {
        const int max = INT_MAX;

        ret = nfs_scan_commit_list(&cinfo->mds->list, dst,
                       cinfo, max);
        ret += pnfs_scan_commit_lists(inode, cinfo, max - ret);
    }
    spin_unlock(cinfo->lock);
    return ret;
}

#else
static unsigned long nfs_reqs_to_commit(struct nfs_commit_info *cinfo)
{
    return 0;
}

int nfs_scan_commit(struct inode *inode, struct list_head *dst,
            struct nfs_commit_info *cinfo)
{
    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(NFS_I(inode), 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_lock_request(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);
    }

    /* 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);
    if (req)
        nfs_clear_request_commit(req);
    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_file_mapping(page)->host;
    struct nfs_page *req;

    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;
    nfs_inode_add_request(inode, req);
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_unlock_and_release_request(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_lock_context *l_ctx;
    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;
        l_ctx = req->wb_lock_context;
        do_flush = req->wb_page != page || req->wb_context != ctx;
        if (l_ctx) {
            do_flush |= l_ctx->lockowner.l_owner != current->files
                || l_ctx->lockowner.l_pid != current->tgid;
        }
        nfs_release_request(req);
        if (!do_flush)
            return 0;
        status = nfs_wb_page(page_file_mapping(page)->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 bool nfs_write_pageuptodate(struct page *page, struct inode *inode)
{
    if (nfs_have_delegated_attributes(inode))
        goto out;
    if (NFS_I(inode)->cache_validity & NFS_INO_REVAL_PAGECACHE)
        return false;
out:
    return PageUptodate(page) != 0;
}

/*
 * 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_file_mapping(page)->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_file_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 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 rpc_clnt *clnt,
               struct nfs_write_data *data,
               const struct rpc_call_ops *call_ops,
               int how, int flags)
{
    struct inode *inode = data->header->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->header->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 | flags,
        .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_write_data *data,
        unsigned int count, unsigned int offset,
        int how, struct nfs_commit_info *cinfo)
{
    struct nfs_page *req = data->header->req;

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

    data->args.fh     = NFS_FH(data->header->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->pages.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_reqs_to_commit(cinfo))
            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->header->inode;

    return nfs_initiate_write(NFS_CLIENT(inode), data, call_ops, how, 0);
}

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_first_entry(head, 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)
{
    nfs_mark_request_dirty(req);
    nfs_unlock_request(req);
    nfs_end_page_writeback(req->wb_page);
    nfs_release_request(req);
}

static void nfs_async_write_error(struct list_head *head)
{
    struct nfs_page *req;

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

static const struct nfs_pgio_completion_ops nfs_async_write_completion_ops = {
    .error_cleanup = nfs_async_write_error,
    .completion = nfs_write_completion,
};

static void nfs_flush_error(struct nfs_pageio_descriptor *desc,
        struct nfs_pgio_header *hdr)
{
    set_bit(NFS_IOHDR_REDO, &hdr->flags);
    while (!list_empty(&hdr->rpc_list)) {
        struct nfs_write_data *data = list_first_entry(&hdr->rpc_list,
                struct nfs_write_data, list);
        list_del(&data->list);
        nfs_writedata_release(data);
    }
    desc->pg_completion_ops->error_cleanup(&desc->pg_list);
}

/*
 * 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 nfs_pgio_header *hdr)
{
    struct nfs_page *req = hdr->req;
    struct page *page = req->wb_page;
    struct nfs_write_data *data;
    size_t wsize = desc->pg_bsize, nbytes;
    unsigned int offset;
    int requests = 0;
    struct nfs_commit_info cinfo;

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

    if ((desc->pg_ioflags & FLUSH_COND_STABLE) &&
        (desc->pg_moreio || nfs_reqs_to_commit(&cinfo) ||
         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(hdr, 1);
        if (!data) {
            nfs_flush_error(desc, hdr);
            return -ENOMEM;
        }
        data->pages.pagevec[0] = page;
        nfs_write_rpcsetup(data, len, offset, desc->pg_ioflags, &cinfo);
        list_add(&data->list, &hdr->rpc_list);
        requests++;
        nbytes -= len;
        offset += len;
    } while (nbytes != 0);
    nfs_list_remove_request(req);
    nfs_list_add_request(req, &hdr->pages);
    desc->pg_rpc_callops = &nfs_write_common_ops;
    return 0;
}

/*
 * 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 nfs_pgio_header *hdr)
{
    struct nfs_page     *req;
    struct page     **pages;
    struct nfs_write_data   *data;
    struct list_head *head = &desc->pg_list;
    struct nfs_commit_info cinfo;

    data = nfs_writedata_alloc(hdr, nfs_page_array_len(desc->pg_base,
                               desc->pg_count));
    if (!data) {
        nfs_flush_error(desc, hdr);
        return -ENOMEM;
    }

    nfs_init_cinfo(&cinfo, desc->pg_inode, desc->pg_dreq);
    pages = data->pages.pagevec;
    while (!list_empty(head)) {
        req = nfs_list_entry(head->next);
        nfs_list_remove_request(req);
        nfs_list_add_request(req, &hdr->pages);
        *pages++ = req->wb_page;
    }

    if ((desc->pg_ioflags & FLUSH_COND_STABLE) &&
        (desc->pg_moreio || nfs_reqs_to_commit(&cinfo)))
        desc->pg_ioflags &= ~FLUSH_COND_STABLE;

    /* Set up the argument struct */
    nfs_write_rpcsetup(data, desc->pg_count, 0, desc->pg_ioflags, &cinfo);
    list_add(&data->list, &hdr->rpc_list);
    desc->pg_rpc_callops = &nfs_write_common_ops;
    return 0;
}

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

static int nfs_generic_pg_writepages(struct nfs_pageio_descriptor *desc)
{
    struct nfs_write_header *whdr;
    struct nfs_pgio_header *hdr;
    int ret;

    whdr = nfs_writehdr_alloc();
    if (!whdr) {
        desc->pg_completion_ops->error_cleanup(&desc->pg_list);
        return -ENOMEM;
    }
    hdr = &whdr->header;
    nfs_pgheader_init(desc, hdr, nfs_writehdr_free);
    atomic_inc(&hdr->refcnt);
    ret = nfs_generic_flush(desc, hdr);
    if (ret == 0)
        ret = nfs_do_multiple_writes(&hdr->rpc_list,
                         desc->pg_rpc_callops,
                         desc->pg_ioflags);
    if (atomic_dec_and_test(&hdr->refcnt))
        hdr->completion_ops->completion(hdr);
    return ret;
}

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

void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
                   struct inode *inode, int ioflags,
                   const struct nfs_pgio_completion_ops *compl_ops)
{
    nfs_pageio_init(pgio, inode, &nfs_pageio_write_ops, compl_ops,
                NFS_SERVER(inode)->wsize, ioflags);
}
EXPORT_SYMBOL_GPL(nfs_pageio_init_write);

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);


void nfs_write_prepare(struct rpc_task *task, void *calldata)
{
    struct nfs_write_data *data = calldata;
    NFS_PROTO(data->header->inode)->write_rpc_prepare(task, data);
}

void nfs_commit_prepare(struct rpc_task *task, void *calldata)
{
    struct nfs_commit_data *data = calldata;

    NFS_PROTO(data->inode)->commit_rpc_prepare(task, data);
}

/*
 * 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_common(struct rpc_task *task, void *calldata)
{
    struct nfs_write_data   *data = calldata;

    nfs_writeback_done(task, data);
}

static void nfs_writeback_release_common(void *calldata)
{
    struct nfs_write_data   *data = calldata;
    struct nfs_pgio_header *hdr = data->header;
    int status = data->task.tk_status;

    if ((status >= 0) && nfs_write_need_commit(data)) {
        spin_lock(&hdr->lock);
        if (test_bit(NFS_IOHDR_NEED_RESCHED, &hdr->flags))
            ; /* Do nothing */
        else if (!test_and_set_bit(NFS_IOHDR_NEED_COMMIT, &hdr->flags))
            memcpy(hdr->verf, &data->verf, sizeof(*hdr->verf));
        else if (memcmp(hdr->verf, &data->verf, sizeof(*hdr->verf)))
            set_bit(NFS_IOHDR_NEED_RESCHED, &hdr->flags);
        spin_unlock(&hdr->lock);
    }
    nfs_writedata_release(data);
}

static const struct rpc_call_ops nfs_write_common_ops = {
    .rpc_call_prepare = nfs_write_prepare,
    .rpc_call_done = nfs_writeback_done_common,
    .rpc_release = nfs_writeback_release_common,
};


/*
 * 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;
    struct inode        *inode = data->header->inode;
    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(inode)->write_done(task, data);
    if (status != 0)
        return;
    nfs_add_stats(inode, NFSIOS_SERVERWRITTENBYTES, resp->count);

#if IS_ENABLED(CONFIG_NFS_V3) || IS_ENABLED(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(inode)->nfs_client->cl_hostname,
                resp->verf->committed, argp->stable);
            complain = jiffies + 300 * HZ;
        }
    }
#endif
    if (task->tk_status < 0)
        nfs_set_pgio_error(data->header, task->tk_status, argp->offset);
    else if (resp->count < argp->count) {
        static unsigned long    complain;

        /* This a short write! */
        nfs_inc_stats(inode, NFSIOS_SHORTWRITE);

        /* Has the server at least made some progress? */
        if (resp->count == 0) {
            if (time_before(complain, jiffies)) {
                printk(KERN_WARNING
                       "NFS: Server wrote zero bytes, expected %u.\n",
                       argp->count);
                complain = jiffies + 300 * HZ;
            }
            nfs_set_pgio_error(data->header, -EIO, argp->offset);
            task->tk_status = -EIO;
            return;
        }
        /* 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);
    }
}


#if IS_ENABLED(CONFIG_NFS_V3) || IS_ENABLED(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;
}

static 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);
}

void nfs_commitdata_release(struct nfs_commit_data *data)
{
    put_nfs_open_context(data->context);
    nfs_commit_free(data);
}
EXPORT_SYMBOL_GPL(nfs_commitdata_release);

int nfs_initiate_commit(struct rpc_clnt *clnt, struct nfs_commit_data *data,
            const struct rpc_call_ops *call_ops,
            int how, int flags)
{
    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 | flags,
        .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_commit_data *data,
             struct list_head *head,
             struct pnfs_layout_segment *lseg,
             struct nfs_commit_info *cinfo)
{
    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->completion_ops = cinfo->completion_ops;
    data->dreq    = cinfo->dreq;

    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->context     = get_nfs_open_context(first->wb_context);
    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_commit_info *cinfo)
{
    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, cinfo);
        if (!cinfo->dreq) {
            dec_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
            dec_bdi_stat(page_file_mapping(req->wb_page)->backing_dev_info,
                     BDI_RECLAIMABLE);
        }
        nfs_unlock_and_release_request(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_commit_info *cinfo)
{
    struct nfs_commit_data  *data;

    data = nfs_commitdata_alloc();

    if (!data)
        goto out_bad;

    /* Set up the argument struct */
    nfs_init_commit(data, head, NULL, cinfo);
    atomic_inc(&cinfo->mds->rpcs_out);
    return nfs_initiate_commit(NFS_CLIENT(inode), data, data->mds_ops,
                   how, 0);
 out_bad:
    nfs_retry_commit(head, NULL, cinfo);
    cinfo->completion_ops->error_cleanup(NFS_I(inode));
    return -ENOMEM;
}

/*
 * COMMIT call returned
 */
static void nfs_commit_done(struct rpc_task *task, void *calldata)
{
    struct nfs_commit_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);
}

static void nfs_commit_release_pages(struct nfs_commit_data *data)
{
    struct nfs_page *req;
    int status = data->task.tk_status;
    struct nfs_commit_info cinfo;

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

        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, &data->verf.verifier, sizeof(req->wb_verf))) {
            /* 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);
        set_bit(NFS_CONTEXT_RESEND_WRITES, &req->wb_context->flags);
    next:
        nfs_unlock_and_release_request(req);
    }
    nfs_init_cinfo(&cinfo, data->inode, data->dreq);
    if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
        nfs_commit_clear_lock(NFS_I(data->inode));
}

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

    data->completion_ops->completion(data);
    nfs_commitdata_release(calldata);
}

static const struct rpc_call_ops nfs_commit_ops = {
    .rpc_call_prepare = nfs_commit_prepare,
    .rpc_call_done = nfs_commit_done,
    .rpc_release = nfs_commit_release,
};

static const struct nfs_commit_completion_ops nfs_commit_completion_ops = {
    .completion = nfs_commit_release_pages,
    .error_cleanup = nfs_commit_clear_lock,
};

int nfs_generic_commit_list(struct inode *inode, struct list_head *head,
                int how, struct nfs_commit_info *cinfo)
{
    int status;

    status = pnfs_commit_list(inode, head, how, cinfo);
    if (status == PNFS_NOT_ATTEMPTED)
        status = nfs_commit_list(inode, head, how, cinfo);
    return status;
}

int nfs_commit_inode(struct inode *inode, int how)
{
    LIST_HEAD(head);
    struct nfs_commit_info cinfo;
    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;
    nfs_init_cinfo_from_inode(&cinfo, inode);
    res = nfs_scan_commit(inode, &head, &cinfo);
    if (res) {
        int error;

        error = nfs_generic_commit_list(inode, &head, how, &cinfo);
        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->commit_info.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->commit_info.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)
{
    return nfs_commit_unstable_pages(inode, wbc);
}
EXPORT_SYMBOL_GPL(nfs_write_inode);

/*
 * 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);
}
EXPORT_SYMBOL_GPL(nfs_wb_all);

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(req)) {
            nfs_clear_request_commit(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_and_release_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_file_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_header),
                         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_cdata_cachep = kmem_cache_create("nfs_commit_data",
                         sizeof(struct nfs_commit_data),
                         0, SLAB_HWCACHE_ALIGN,
                         NULL);
    if (nfs_cdata_cachep == NULL)
        goto out_destroy_write_mempool;

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

    /*
     * 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_commit_cache:
    kmem_cache_destroy(nfs_cdata_cachep);
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);
    kmem_cache_destroy(nfs_cdata_cachep);
    mempool_destroy(nfs_wdata_mempool);
    kmem_cache_destroy(nfs_wdata_cachep);
}