NFS: Cleanup of NFS write code in preparation for asynchronous o_direct

[linux-2.6.22.y-op.git] / fs / nfs / write.c

/*
 * linux/fs/nfs/write.c
 *
 * Writing file data over NFS.
 *
 * We do it like this: When a (user) process wishes to write data to an
 * NFS file, a write request is allocated that contains the RPC task data
 * plus some info on the page to be written, and added to the inode's
 * write chain. If the process writes past the end of the page, an async
 * RPC call to write the page is scheduled immediately; otherwise, the call
 * is delayed for a few seconds.
 *
 * Just like readahead, no async I/O is performed if wsize < PAGE_SIZE.
 *
 * Write requests are kept on the inode's writeback list. Each entry in
 * that list references the page (portion) to be written. When the
 * cache timeout has expired, the RPC task is woken up, and tries to
 * lock the page. As soon as it manages to do so, the request is moved
 * from the writeback list to the writelock list.
 *
 * Note: we must make sure never to confuse the inode passed in the
 * write_page request with the one in page->inode. As far as I understand
 * it, these are different when doing a swap-out.
 *
 * To understand everything that goes on here and in the NFS read code,
 * one should be aware that a page is locked in exactly one of the following
 * cases:
 *
 *  -   A write request is in progress.
 *  -   A user process is in generic_file_write/nfs_update_page
 *  -   A user process is in generic_file_read
 *
 * Also note that because of the way pages are invalidated in
 * nfs_revalidate_inode, the following assertions hold:
 *
 *  -   If a page is dirty, there will be no read requests (a page will
 *      not be re-read unless invalidated by nfs_revalidate_inode).
 *  -   If the page is not uptodate, there will be no pending write
 *      requests, and no process will be in nfs_update_page.
 *
 * FIXME: Interaction with the vmscan routines is not optimal yet.
 * Either vmscan must be made nfs-savvy, or we need a different page
 * reclaim concept that supports something like FS-independent
 * buffer_heads with a b_ops-> field.
 *
 * Copyright (C) 1996, 1997, Olaf Kirch <okir@monad.swb.de>
 */

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

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

#include "delegation.h"
#include "iostat.h"

#define NFSDBG_FACILITY         NFSDBG_PAGECACHE

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

/*
 * Local function declarations
 */
static struct nfs_page * nfs_update_request(struct nfs_open_context*,
                                            struct inode *,
                                            struct page *,
                                            unsigned int, unsigned int);
static int nfs_writeback_done(struct rpc_task *, struct nfs_write_data *);
static int nfs_wait_on_write_congestion(struct address_space *, int);
static int nfs_wait_on_requests(struct inode *, unsigned long, unsigned int);
static int nfs_flush_inode(struct inode *inode, unsigned long idx_start,
                           unsigned int npages, int how);
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 kmem_cache_t *nfs_wdata_cachep;
mempool_t *nfs_wdata_mempool;
static mempool_t *nfs_commit_mempool;

static DECLARE_WAIT_QUEUE_HEAD(nfs_write_congestion);

static inline struct nfs_write_data *nfs_commit_alloc(unsigned int pagecount)
{
        struct nfs_write_data *p = mempool_alloc(nfs_commit_mempool, SLAB_NOFS);

        if (p) {
                memset(p, 0, sizeof(*p));
                INIT_LIST_HEAD(&p->pages);
                if (pagecount < NFS_PAGEVEC_SIZE)
                        p->pagevec = &p->page_array[0];
                else {
                        size_t size = ++pagecount * sizeof(struct page *);
                        p->pagevec = kzalloc(size, GFP_NOFS);
                        if (!p->pagevec) {
                                mempool_free(p, nfs_commit_mempool);
                                p = NULL;
                        }
                }
        }
        return p;
}

static inline 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);
}

void nfs_writedata_release(void *wdata)
{
        nfs_writedata_free(wdata);
}

/* Adjust the file length if we're writing beyond the end */
static void nfs_grow_file(struct page *page, unsigned int offset, unsigned int count)
{
        struct inode *inode = page->mapping->host;
        loff_t end, i_size = i_size_read(inode);
        unsigned long end_index = (i_size - 1) >> PAGE_CACHE_SHIFT;

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

/* 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)
{
        loff_t end_offs;

        if (PageUptodate(page))
                return;
        if (base != 0)
                return;
        if (count == PAGE_CACHE_SIZE) {
                SetPageUptodate(page);
                return;
        }

        end_offs = i_size_read(page->mapping->host) - 1;
        if (end_offs < 0)
                return;
        /* Is this the last page? */
        if (page->index != (unsigned long)(end_offs >> PAGE_CACHE_SHIFT))
                return;
        /* This is the last page: set PG_uptodate if we cover the entire
         * extent of the data, then zero the rest of the page.
         */
        if (count == (unsigned int)(end_offs & (PAGE_CACHE_SIZE - 1)) + 1) {
                memclear_highpage_flush(page, count, PAGE_CACHE_SIZE - count);
                SetPageUptodate(page);
        }
}

/*
 * Write a page synchronously.
 * Offset is the data offset within the page.
 */
static int nfs_writepage_sync(struct nfs_open_context *ctx, struct inode *inode,
                struct page *page, unsigned int offset, unsigned int count,
                int how)
{
        unsigned int    wsize = NFS_SERVER(inode)->wsize;
        int             result, written = 0;
        struct nfs_write_data *wdata;

        wdata = nfs_writedata_alloc(1);
        if (!wdata)
                return -ENOMEM;

        wdata->flags = how;
        wdata->cred = ctx->cred;
        wdata->inode = inode;
        wdata->args.fh = NFS_FH(inode);
        wdata->args.context = ctx;
        wdata->args.pages = &page;
        wdata->args.stable = NFS_FILE_SYNC;
        wdata->args.pgbase = offset;
        wdata->args.count = wsize;
        wdata->res.fattr = &wdata->fattr;
        wdata->res.verf = &wdata->verf;

        dprintk("NFS:      nfs_writepage_sync(%s/%Ld %d@%Ld)\n",
                inode->i_sb->s_id,
                (long long)NFS_FILEID(inode),
                count, (long long)(page_offset(page) + offset));

        set_page_writeback(page);
        nfs_begin_data_update(inode);
        do {
                if (count < wsize)
                        wdata->args.count = count;
                wdata->args.offset = page_offset(page) + wdata->args.pgbase;

                result = NFS_PROTO(inode)->write(wdata);

                if (result < 0) {
                        /* Must mark the page invalid after I/O error */
                        ClearPageUptodate(page);
                        goto io_error;
                }
                if (result < wdata->args.count)
                        printk(KERN_WARNING "NFS: short write, count=%u, result=%d\n",
                                        wdata->args.count, result);

                wdata->args.offset += result;
                wdata->args.pgbase += result;
                written += result;
                count -= result;
                nfs_add_stats(inode, NFSIOS_SERVERWRITTENBYTES, result);
        } while (count);
        /* Update file length */
        nfs_grow_file(page, offset, written);
        /* Set the PG_uptodate flag? */
        nfs_mark_uptodate(page, offset, written);

        if (PageError(page))
                ClearPageError(page);

io_error:
        nfs_end_data_update(inode);
        end_page_writeback(page);
        nfs_writedata_free(wdata);
        return written ? written : result;
}

static int nfs_writepage_async(struct nfs_open_context *ctx,
                struct inode *inode, struct page *page,
                unsigned int offset, unsigned int count)
{
        struct nfs_page *req;

        req = nfs_update_request(ctx, inode, page, offset, count);
        if (IS_ERR(req))
                return PTR_ERR(req);
        /* Update file length */
        nfs_grow_file(page, offset, count);
        /* Set the PG_uptodate flag? */
        nfs_mark_uptodate(page, offset, count);
        nfs_unlock_request(req);
        return 0;
}

static int wb_priority(struct writeback_control *wbc)
{
        if (wbc->for_reclaim)
                return FLUSH_HIGHPRI;
        if (wbc->for_kupdate)
                return FLUSH_LOWPRI;
        return 0;
}

/*
 * Write an mmapped page to the server.
 */
int nfs_writepage(struct page *page, struct writeback_control *wbc)
{
        struct nfs_open_context *ctx;
        struct inode *inode = page->mapping->host;
        unsigned long end_index;
        unsigned offset = PAGE_CACHE_SIZE;
        loff_t i_size = i_size_read(inode);
        int inode_referenced = 0;
        int priority = wb_priority(wbc);
        int err;

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

        /*
         * Note: We need to ensure that we have a reference to the inode
         *       if we are to do asynchronous writes. If not, waiting
         *       in nfs_wait_on_request() may deadlock with clear_inode().
         *
         *       If igrab() fails here, then it is in any case safe to
         *       call nfs_wb_page(), since there will be no pending writes.
         */
        if (igrab(inode) != 0)
                inode_referenced = 1;
        end_index = i_size >> PAGE_CACHE_SHIFT;

        /* Ensure we've flushed out any previous writes */
        nfs_wb_page_priority(inode, page, priority);

        /* easy case */
        if (page->index < end_index)
                goto do_it;
        /* things got complicated... */
        offset = i_size & (PAGE_CACHE_SIZE-1);

        /* OK, are we completely out? */
        err = 0; /* potential race with truncate - ignore */
        if (page->index >= end_index+1 || !offset)
                goto out;
do_it:
        ctx = nfs_find_open_context(inode, NULL, FMODE_WRITE);
        if (ctx == NULL) {
                err = -EBADF;
                goto out;
        }
        lock_kernel();
        if (!IS_SYNC(inode) && inode_referenced) {
                err = nfs_writepage_async(ctx, inode, page, 0, offset);
                if (!wbc->for_writepages)
                        nfs_flush_inode(inode, 0, 0, wb_priority(wbc));
        } else {
                err = nfs_writepage_sync(ctx, inode, page, 0,
                                                offset, priority);
                if (err >= 0) {
                        if (err != offset)
                                redirty_page_for_writepage(wbc, page);
                        err = 0;
                }
        }
        unlock_kernel();
        put_nfs_open_context(ctx);
out:
        unlock_page(page);
        if (inode_referenced)
                iput(inode);
        return err; 
}

/*
 * Note: causes nfs_update_request() to block on the assumption
 *       that the writeback is generated due to memory pressure.
 */
int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct backing_dev_info *bdi = mapping->backing_dev_info;
        struct inode *inode = mapping->host;
        int err;

        nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGES);

        err = generic_writepages(mapping, wbc);
        if (err)
                return err;
        while (test_and_set_bit(BDI_write_congested, &bdi->state) != 0) {
                if (wbc->nonblocking)
                        return 0;
                nfs_wait_on_write_congestion(mapping, 0);
        }
        err = nfs_flush_inode(inode, 0, 0, wb_priority(wbc));
        if (err < 0)
                goto out;
        nfs_add_stats(inode, NFSIOS_WRITEPAGES, err);
        wbc->nr_to_write -= err;
        if (!wbc->nonblocking && wbc->sync_mode == WB_SYNC_ALL) {
                err = nfs_wait_on_requests(inode, 0, 0);
                if (err < 0)
                        goto out;
        }
        err = nfs_commit_inode(inode, wb_priority(wbc));
        if (err > 0) {
                wbc->nr_to_write -= err;
                err = 0;
        }
out:
        clear_bit(BDI_write_congested, &bdi->state);
        wake_up_all(&nfs_write_congestion);
        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_insert(&nfsi->nfs_page_tree, req->wb_index, req);
        BUG_ON(error == -EEXIST);
        if (error)
                return error;
        if (!nfsi->npages) {
                igrab(inode);
                nfs_begin_data_update(inode);
                if (nfs_have_delegation(inode, FMODE_WRITE))
                        nfsi->change_attr++;
        }
        nfsi->npages++;
        atomic_inc(&req->wb_count);
        return 0;
}

/*
 * Insert a write request into 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(&nfsi->req_lock);
        radix_tree_delete(&nfsi->nfs_page_tree, req->wb_index);
        nfsi->npages--;
        if (!nfsi->npages) {
                spin_unlock(&nfsi->req_lock);
                nfs_end_data_update(inode);
                iput(inode);
        } else
                spin_unlock(&nfsi->req_lock);
        nfs_clear_request(req);
        nfs_release_request(req);
}

/*
 * Find a request
 */
static inline struct nfs_page *
_nfs_find_request(struct inode *inode, unsigned long index)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        struct nfs_page *req;

        req = (struct nfs_page*)radix_tree_lookup(&nfsi->nfs_page_tree, index);
        if (req)
                atomic_inc(&req->wb_count);
        return req;
}

static struct nfs_page *
nfs_find_request(struct inode *inode, unsigned long index)
{
        struct nfs_page         *req;
        struct nfs_inode        *nfsi = NFS_I(inode);

        spin_lock(&nfsi->req_lock);
        req = _nfs_find_request(inode, index);
        spin_unlock(&nfsi->req_lock);
        return req;
}

/*
 * Add a request to the inode's dirty list.
 */
static void
nfs_mark_request_dirty(struct nfs_page *req)
{
        struct inode *inode = req->wb_context->dentry->d_inode;
        struct nfs_inode *nfsi = NFS_I(inode);

        spin_lock(&nfsi->req_lock);
        radix_tree_tag_set(&nfsi->nfs_page_tree,
                        req->wb_index, NFS_PAGE_TAG_DIRTY);
        nfs_list_add_request(req, &nfsi->dirty);
        nfsi->ndirty++;
        spin_unlock(&nfsi->req_lock);
        inc_page_state(nr_dirty);
        mark_inode_dirty(inode);
}

/*
 * Check if a request is dirty
 */
static inline int
nfs_dirty_request(struct nfs_page *req)
{
        struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
        return !list_empty(&req->wb_list) && req->wb_list_head == &nfsi->dirty;
}

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
/*
 * Add a request to the inode's commit list.
 */
static void
nfs_mark_request_commit(struct nfs_page *req)
{
        struct inode *inode = req->wb_context->dentry->d_inode;
        struct nfs_inode *nfsi = NFS_I(inode);

        spin_lock(&nfsi->req_lock);
        nfs_list_add_request(req, &nfsi->commit);
        nfsi->ncommit++;
        spin_unlock(&nfsi->req_lock);
        inc_page_state(nr_unstable);
        mark_inode_dirty(inode);
}
#endif

/*
 * Wait for a request to complete.
 *
 * Interruptible by signals only if mounted with intr flag.
 */
static int
nfs_wait_on_requests(struct inode *inode, unsigned long idx_start, unsigned int npages)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        struct nfs_page *req;
        unsigned long           idx_end, next;
        unsigned int            res = 0;
        int                     error;

        if (npages == 0)
                idx_end = ~0;
        else
                idx_end = idx_start + npages - 1;

        spin_lock(&nfsi->req_lock);
        next = idx_start;
        while (radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree, (void **)&req, next, 1, NFS_PAGE_TAG_WRITEBACK)) {
                if (req->wb_index > idx_end)
                        break;

                next = req->wb_index + 1;
                BUG_ON(!NFS_WBACK_BUSY(req));

                atomic_inc(&req->wb_count);
                spin_unlock(&nfsi->req_lock);
                error = nfs_wait_on_request(req);
                nfs_release_request(req);
                if (error < 0)
                        return error;
                spin_lock(&nfsi->req_lock);
                res++;
        }
        spin_unlock(&nfsi->req_lock);
        return res;
}

/*
 * nfs_scan_dirty - Scan an inode for dirty 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 dirty page list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
static int
nfs_scan_dirty(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        int res = 0;

        if (nfsi->ndirty != 0) {
                res = nfs_scan_lock_dirty(nfsi, dst, idx_start, npages);
                nfsi->ndirty -= res;
                sub_page_state(nr_dirty,res);
                if ((nfsi->ndirty == 0) != list_empty(&nfsi->dirty))
                        printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
        }
        return res;
}

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
/*
 * nfs_scan_commit - Scan an inode for commit requests
 * @inode: NFS inode to scan
 * @dst: destination list
 * @idx_start: lower bound of page->index to scan.
 * @npages: idx_start + npages sets the upper bound to scan.
 *
 * Moves requests from the inode's 'commit' request list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
static int
nfs_scan_commit(struct inode *inode, struct list_head *dst, unsigned long idx_start, unsigned int npages)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        int res = 0;

        if (nfsi->ncommit != 0) {
                res = nfs_scan_list(&nfsi->commit, dst, idx_start, npages);
                nfsi->ncommit -= res;
                if ((nfsi->ncommit == 0) != list_empty(&nfsi->commit))
                        printk(KERN_ERR "NFS: desynchronized value of nfs_i.ncommit.\n");
        }
        return res;
}
#endif

static int nfs_wait_on_write_congestion(struct address_space *mapping, int intr)
{
        struct backing_dev_info *bdi = mapping->backing_dev_info;
        DEFINE_WAIT(wait);
        int ret = 0;

        might_sleep();

        if (!bdi_write_congested(bdi))
                return 0;

        nfs_inc_stats(mapping->host, NFSIOS_CONGESTIONWAIT);

        if (intr) {
                struct rpc_clnt *clnt = NFS_CLIENT(mapping->host);
                sigset_t oldset;

                rpc_clnt_sigmask(clnt, &oldset);
                prepare_to_wait(&nfs_write_congestion, &wait, TASK_INTERRUPTIBLE);
                if (bdi_write_congested(bdi)) {
                        if (signalled())
                                ret = -ERESTARTSYS;
                        else
                                schedule();
                }
                rpc_clnt_sigunmask(clnt, &oldset);
        } else {
                prepare_to_wait(&nfs_write_congestion, &wait, TASK_UNINTERRUPTIBLE);
                if (bdi_write_congested(bdi))
                        schedule();
        }
        finish_wait(&nfs_write_congestion, &wait);
        return ret;
}


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

        end = offset + bytes;

        if (nfs_wait_on_write_congestion(page->mapping, server->flags & NFS_MOUNT_INTR))
                return ERR_PTR(-ERESTARTSYS);
        for (;;) {
                /* Loop over all inode entries and see if we find
                 * A request for the page we wish to update
                 */
                spin_lock(&nfsi->req_lock);
                req = _nfs_find_request(inode, page->index);
                if (req) {
                        if (!nfs_lock_request_dontget(req)) {
                                int error;
                                spin_unlock(&nfsi->req_lock);
                                error = nfs_wait_on_request(req);
                                nfs_release_request(req);
                                if (error < 0) {
                                        if (new)
                                                nfs_release_request(new);
                                        return ERR_PTR(error);
                                }
                                continue;
                        }
                        spin_unlock(&nfsi->req_lock);
                        if (new)
                                nfs_release_request(new);
                        break;
                }

                if (new) {
                        int error;
                        nfs_lock_request_dontget(new);
                        error = nfs_inode_add_request(inode, new);
                        if (error) {
                                spin_unlock(&nfsi->req_lock);
                                nfs_unlock_request(new);
                                return ERR_PTR(error);
                        }
                        spin_unlock(&nfsi->req_lock);
                        nfs_mark_request_dirty(new);
                        return new;
                }
                spin_unlock(&nfsi->req_lock);

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

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

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

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

        return req;
}

int nfs_flush_incompatible(struct file *file, struct page *page)
{
        struct nfs_open_context *ctx = (struct nfs_open_context *)file->private_data;
        struct inode    *inode = page->mapping->host;
        struct nfs_page *req;
        int             status = 0;
        /*
         * 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.
         */
        req = nfs_find_request(inode, page->index);
        if (req) {
                if (req->wb_page != page || ctx != req->wb_context)
                        status = nfs_wb_page(inode, page);
                nfs_release_request(req);
        }
        return (status < 0) ? status : 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 = (struct nfs_open_context *)file->private_data;
        struct inode    *inode = page->mapping->host;
        struct nfs_page *req;
        int             status = 0;

        nfs_inc_stats(inode, NFSIOS_VFSUPDATEPAGE);

        dprintk("NFS:      nfs_updatepage(%s/%s %d@%Ld)\n",
                file->f_dentry->d_parent->d_name.name,
                file->f_dentry->d_name.name, count,
                (long long)(page_offset(page) +offset));

        if (IS_SYNC(inode)) {
                status = nfs_writepage_sync(ctx, inode, page, offset, count, 0);
                if (status > 0) {
                        if (offset == 0 && status == PAGE_CACHE_SIZE)
                                SetPageUptodate(page);
                        return 0;
                }
                return status;
        }

        /* If we're not using byte range locks, and we know the page
         * is entirely in cache, it may be more efficient to avoid
         * fragmenting write requests.
         */
        if (PageUptodate(page) && inode->i_flock == NULL && !(file->f_mode & O_SYNC)) {
                loff_t end_offs = i_size_read(inode) - 1;
                unsigned long end_index = end_offs >> PAGE_CACHE_SHIFT;

                count += offset;
                offset = 0;
                if (unlikely(end_offs < 0)) {
                        /* Do nothing */
                } else if (page->index == end_index) {
                        unsigned int pglen;
                        pglen = (unsigned int)(end_offs & (PAGE_CACHE_SIZE-1)) + 1;
                        if (count < pglen)
                                count = pglen;
                } else if (page->index < end_index)
                        count = PAGE_CACHE_SIZE;
        }

        /*
         * Try to find an NFS request corresponding to this page
         * and update it.
         * If the existing request cannot be updated, we must flush
         * it out now.
         */
        do {
                req = nfs_update_request(ctx, inode, page, offset, count);
                status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
                if (status != -EBUSY)
                        break;
                /* Request could not be updated. Flush it out and try again */
                status = nfs_wb_page(inode, page);
        } while (status >= 0);
        if (status < 0)
                goto done;

        status = 0;

        /* Update file length */
        nfs_grow_file(page, offset, count);
        /* Set the PG_uptodate flag? */
        nfs_mark_uptodate(page, req->wb_pgbase, req->wb_bytes);
        nfs_unlock_request(req);
done:
        dprintk("NFS:      nfs_updatepage returns %d (isize %Ld)\n",
                        status, (long long)i_size_read(inode));
        if (status < 0)
                ClearPageUptodate(page);
        return status;
}

static void nfs_writepage_release(struct nfs_page *req)
{
        end_page_writeback(req->wb_page);

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
        if (!PageError(req->wb_page)) {
                if (NFS_NEED_RESCHED(req)) {
                        nfs_mark_request_dirty(req);
                        goto out;
                } else if (NFS_NEED_COMMIT(req)) {
                        nfs_mark_request_commit(req);
                        goto out;
                }
        }
        nfs_inode_remove_request(req);

out:
        nfs_clear_commit(req);
        nfs_clear_reschedule(req);
#else
        nfs_inode_remove_request(req);
#endif
        nfs_clear_page_writeback(req);
}

static inline int flush_task_priority(int how)
{
        switch (how & (FLUSH_HIGHPRI|FLUSH_LOWPRI)) {
                case FLUSH_HIGHPRI:
                        return RPC_PRIORITY_HIGH;
                case FLUSH_LOWPRI:
                        return RPC_PRIORITY_LOW;
        }
        return RPC_PRIORITY_NORMAL;
}

/*
 * Set up the argument/result storage required for the RPC call.
 */
static void nfs_write_rpcsetup(struct nfs_page *req,
                struct nfs_write_data *data,
                const struct rpc_call_ops *call_ops,
                unsigned int count, unsigned int offset,
                int how)
{
        struct inode            *inode;
        int flags;

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

        data->req = req;
        data->inode = inode = req->wb_context->dentry->d_inode;
        data->cred = req->wb_context->cred;

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

        data->res.fattr   = &data->fattr;
        data->res.count   = count;
        data->res.verf    = &data->verf;
        nfs_fattr_init(&data->fattr);

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

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

        dprintk("NFS: %4d initiated write call (req %s/%Ld, %u bytes @ offset %Lu)\n",
                data->task.tk_pid,
                inode->i_sb->s_id,
                (long long)NFS_FILEID(inode),
                count,
                (unsigned long long)data->args.offset);
}

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

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

/*
 * Generate multiple small requests to write out a single
 * contiguous dirty area on one page.
 */
static int nfs_flush_multi(struct list_head *head, struct inode *inode, int how)
{
        struct nfs_page *req = nfs_list_entry(head->next);
        struct page *page = req->wb_page;
        struct nfs_write_data *data;
        unsigned int wsize = NFS_SERVER(inode)->wsize;
        unsigned int nbytes, offset;
        int requests = 0;
        LIST_HEAD(list);

        nfs_list_remove_request(req);

        nbytes = req->wb_bytes;
        for (;;) {
                data = nfs_writedata_alloc(1);
                if (!data)
                        goto out_bad;
                list_add(&data->pages, &list);
                requests++;
                if (nbytes <= wsize)
                        break;
                nbytes -= wsize;
        }
        atomic_set(&req->wb_complete, requests);

        ClearPageError(page);
        set_page_writeback(page);
        offset = 0;
        nbytes = req->wb_bytes;
        do {
                data = list_entry(list.next, struct nfs_write_data, pages);
                list_del_init(&data->pages);

                data->pagevec[0] = page;

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

        return 0;

out_bad:
        while (!list_empty(&list)) {
                data = list_entry(list.next, struct nfs_write_data, pages);
                list_del(&data->pages);
                nfs_writedata_free(data);
        }
        nfs_mark_request_dirty(req);
        nfs_clear_page_writeback(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 list_head *head, struct inode *inode, int how)
{
        struct nfs_page         *req;
        struct page             **pages;
        struct nfs_write_data   *data;
        unsigned int            count;

        if (NFS_SERVER(inode)->wsize < PAGE_CACHE_SIZE)
                return nfs_flush_multi(head, inode, how);

        data = nfs_writedata_alloc(NFS_SERVER(inode)->wpages);
        if (!data)
                goto out_bad;

        pages = data->pagevec;
        count = 0;
        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_list_add_request(req, &data->pages);
                ClearPageError(req->wb_page);
                set_page_writeback(req->wb_page);
                *pages++ = req->wb_page;
                count += req->wb_bytes;
        }
        req = nfs_list_entry(data->pages.next);

        /* Set up the argument struct */
        nfs_write_rpcsetup(req, data, &nfs_write_full_ops, count, 0, how);

        nfs_execute_write(data);
        return 0;
 out_bad:
        while (!list_empty(head)) {
                struct nfs_page *req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_mark_request_dirty(req);
                nfs_clear_page_writeback(req);
        }
        return -ENOMEM;
}

static int
nfs_flush_list(struct list_head *head, int wpages, int how)
{
        LIST_HEAD(one_request);
        struct nfs_page         *req;
        int                     error = 0;
        unsigned int            pages = 0;

        while (!list_empty(head)) {
                pages += nfs_coalesce_requests(head, &one_request, wpages);
                req = nfs_list_entry(one_request.next);
                error = nfs_flush_one(&one_request, req->wb_context->dentry->d_inode, how);
                if (error < 0)
                        break;
        }
        if (error >= 0)
                return pages;

        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_mark_request_dirty(req);
                nfs_clear_page_writeback(req);
        }
        return error;
}

/*
 * Handle a write reply that flushed part of a page.
 */
static void nfs_writeback_done_partial(struct rpc_task *task, void *calldata)
{
        struct nfs_write_data   *data = calldata;
        struct nfs_page         *req = data->req;
        struct page             *page = req->wb_page;

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

        if (task->tk_status < 0) {
                ClearPageUptodate(page);
                SetPageError(page);
                req->wb_context->error = task->tk_status;
                dprintk(", error = %d\n", task->tk_status);
        } else {
#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
                if (data->verf.committed < NFS_FILE_SYNC) {
                        if (!NFS_NEED_COMMIT(req)) {
                                nfs_defer_commit(req);
                                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))) {
                                nfs_defer_reschedule(req);
                                dprintk(" server reboot detected\n");
                        }
                } else
#endif
                        dprintk(" OK\n");
        }

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

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

/*
 * Handle a write reply that flushes a whole page.
 *
 * FIXME: There is an inherent race with invalidate_inode_pages and
 *        writebacks since the page->count is kept > 1 for as long
 *        as the page has a write request pending.
 */
static void nfs_writeback_done_full(struct rpc_task *task, void *calldata)
{
        struct nfs_write_data   *data = calldata;
        struct nfs_page         *req;
        struct page             *page;

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

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

                dprintk("NFS: write (%s/%Ld %d@%Ld)",
                        req->wb_context->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 (task->tk_status < 0) {
                        ClearPageUptodate(page);
                        SetPageError(page);
                        req->wb_context->error = task->tk_status;
                        end_page_writeback(page);
                        nfs_inode_remove_request(req);
                        dprintk(", error = %d\n", task->tk_status);
                        goto next;
                }
                end_page_writeback(page);

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
                if (data->args.stable != NFS_UNSTABLE || data->verf.committed == NFS_FILE_SYNC) {
                        nfs_inode_remove_request(req);
                        dprintk(" OK\n");
                        goto next;
                }
                memcpy(&req->wb_verf, &data->verf, sizeof(req->wb_verf));
                nfs_mark_request_commit(req);
                dprintk(" marked for commit\n");
#else
                nfs_inode_remove_request(req);
#endif
        next:
                nfs_clear_page_writeback(req);
        }
}

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


/*
 * This function is called when the WRITE call is complete.
 */
static int nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data)
{
        struct nfs_writeargs    *argp = &data->args;
        struct nfs_writeres     *resp = &data->res;
        int status;

        dprintk("NFS: %4d nfs_writeback_done (status %d)\n",
                task->tk_pid, task->tk_status);

        /* Call the NFS version-specific code */
        status = NFS_PROTO(data->inode)->write_done(task, data);
        if (status != 0)
                return status;
        nfs_add_stats(data->inode, NFSIOS_SERVERWRITTENBYTES, resp->count);

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

                if (time_before(complain, jiffies)) {
                        dprintk("NFS: faulty NFS server %s:"
                                " (committed = %d) != (stable = %d)\n",
                                NFS_SERVER(data->inode)->hostname,
                                resp->verf->committed, argp->stable);
                        complain = jiffies + 300 * HZ;
                }
        }
#endif
        /* Is this a short write? */
        if (task->tk_status >= 0 && resp->count < argp->count) {
                static unsigned long    complain;

                nfs_inc_stats(data->inode, NFSIOS_SHORTWRITE);

                /* Has the server at least made some progress? */
                if (resp->count != 0) {
                        /* Was this an NFSv2 write or an NFSv3 stable write? */
                        if (resp->verf->committed != NFS_UNSTABLE) {
                                /* Resend from where the server left off */
                                argp->offset += resp->count;
                                argp->pgbase += resp->count;
                                argp->count -= resp->count;
                        } else {
                                /* Resend as a stable write in order to avoid
                                 * headaches in the case of a server crash.
                                 */
                                argp->stable = NFS_FILE_SYNC;
                        }
                        rpc_restart_call(task);
                        return -EAGAIN;
                }
                if (time_before(complain, jiffies)) {
                        printk(KERN_WARNING
                               "NFS: Server wrote zero bytes, expected %u.\n",
                                        argp->count);
                        complain = jiffies + 300 * HZ;
                }
                /* Can't do anything about it except throw an error. */
                task->tk_status = -EIO;
        }
        return 0;
}


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

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

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

        list_splice_init(head, &data->pages);
        first = nfs_list_entry(data->pages.next);
        inode = first->wb_context->dentry->d_inode;

        data->inode       = inode;
        data->cred        = first->wb_context->cred;

        data->args.fh     = NFS_FH(data->inode);
        /* Note: we always request a commit of the entire inode */
        data->args.offset = 0;
        data->args.count  = 0;
        data->res.count   = 0;
        data->res.fattr   = &data->fattr;
        data->res.verf    = &data->verf;
        nfs_fattr_init(&data->fattr);

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

        data->task.tk_priority = flush_task_priority(how);
        data->task.tk_cookie = (unsigned long)inode;
        
        dprintk("NFS: %4d initiated commit call\n", data->task.tk_pid);
}

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

        data = nfs_commit_alloc(NFS_SERVER(inode)->wpages);

        if (!data)
                goto out_bad;

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

        nfs_execute_write(data);
        return 0;
 out_bad:
        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_mark_request_commit(req);
                nfs_clear_page_writeback(req);
        }
        return -ENOMEM;
}

/*
 * COMMIT call returned
 */
static void nfs_commit_done(struct rpc_task *task, void *calldata)
{
        struct nfs_write_data   *data = calldata;
        struct nfs_page         *req;
        int res = 0;

        dprintk("NFS: %4d nfs_commit_done (status %d)\n",
                                task->tk_pid, task->tk_status);

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

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

                dprintk("NFS: commit (%s/%Ld %d@%Ld)",
                        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 (task->tk_status < 0) {
                        req->wb_context->error = task->tk_status;
                        nfs_inode_remove_request(req);
                        dprintk(", error = %d\n", task->tk_status);
                        goto next;
                }

                /* Okay, COMMIT succeeded, apparently. Check the verifier
                 * returned by the server against all stored verfs. */
                if (!memcmp(req->wb_verf.verifier, data->verf.verifier, sizeof(data->verf.verifier))) {
                        /* We have a match */
                        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_writeback(req);
                res++;
        }
        sub_page_state(nr_unstable,res);
}

static const struct rpc_call_ops nfs_commit_ops = {
        .rpc_call_done = nfs_commit_done,
        .rpc_release = nfs_commit_release,
};
#endif

static int nfs_flush_inode(struct inode *inode, unsigned long idx_start,
                           unsigned int npages, int how)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        LIST_HEAD(head);
        int                     res,
                                error = 0;

        spin_lock(&nfsi->req_lock);
        res = nfs_scan_dirty(inode, &head, idx_start, npages);
        spin_unlock(&nfsi->req_lock);
        if (res) {
                struct nfs_server *server = NFS_SERVER(inode);

                /* For single writes, FLUSH_STABLE is more efficient */
                if (res == nfsi->npages && nfsi->npages <= server->wpages) {
                        if (res > 1 || nfs_list_entry(head.next)->wb_bytes <= server->wsize)
                                how |= FLUSH_STABLE;
                }
                error = nfs_flush_list(&head, server->wpages, how);
        }
        if (error < 0)
                return error;
        return res;
}

#if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
int nfs_commit_inode(struct inode *inode, int how)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        LIST_HEAD(head);
        int                     res,
                                error = 0;

        spin_lock(&nfsi->req_lock);
        res = nfs_scan_commit(inode, &head, 0, 0);
        spin_unlock(&nfsi->req_lock);
        if (res) {
                error = nfs_commit_list(inode, &head, how);
                if (error < 0)
                        return error;
        }
        return res;
}
#endif

int nfs_sync_inode(struct inode *inode, unsigned long idx_start,
                  unsigned int npages, int how)
{
        int nocommit = how & FLUSH_NOCOMMIT;
        int wait = how & FLUSH_WAIT;
        int error;

        how &= ~(FLUSH_WAIT|FLUSH_NOCOMMIT);

        do {
                if (wait) {
                        error = nfs_wait_on_requests(inode, idx_start, npages);
                        if (error != 0)
                                continue;
                }
                error = nfs_flush_inode(inode, idx_start, npages, how);
                if (error != 0)
                        continue;
                if (!nocommit)
                        error = nfs_commit_inode(inode, how);
        } while (error > 0);
        return error;
}

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

        nfs_wdata_mempool = mempool_create(MIN_POOL_WRITE,
                                           mempool_alloc_slab,
                                           mempool_free_slab,
                                           nfs_wdata_cachep);
        if (nfs_wdata_mempool == NULL)
                return -ENOMEM;

        nfs_commit_mempool = mempool_create(MIN_POOL_COMMIT,
                                           mempool_alloc_slab,
                                           mempool_free_slab,
                                           nfs_wdata_cachep);
        if (nfs_commit_mempool == NULL)
                return -ENOMEM;

        return 0;
}

void nfs_destroy_writepagecache(void)
{
        mempool_destroy(nfs_commit_mempool);
        mempool_destroy(nfs_wdata_mempool);
        if (kmem_cache_destroy(nfs_wdata_cachep))
                printk(KERN_INFO "nfs_write_data: not all structures were freed\n");
}