nfs: patches backported from 2.6 upstream

[tomato.git] / release / src / linux / linux / 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/swap.h>
#include <linux/pagemap.h>
#include <linux/file.h>

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

#define NFSDBG_FACILITY         NFSDBG_PAGECACHE

/*
 * Local structures
 *
 * This is the struct where the WRITE/COMMIT arguments go.
 */
struct nfs_write_data {
        struct rpc_task         task;
        struct inode            *inode;
        struct rpc_cred         *cred;
        struct nfs_writeargs    args;           /* argument struct */
        struct nfs_writeres     res;            /* result struct */
        struct nfs_fattr        fattr;
        struct nfs_writeverf    verf;
        struct list_head        pages;          /* Coalesced requests we wish to flush */
        struct page             *pagevec[NFS_WRITE_MAXIOV];
};

/*
 * Local function declarations
 */
static struct nfs_page * nfs_update_request(struct file*, struct inode *,
                                            struct page *,
                                            unsigned int, unsigned int);
static void     nfs_strategy(struct inode *inode);
static void     nfs_writeback_done(struct rpc_task *);
#ifdef CONFIG_NFS_V3
static void     nfs_commit_done(struct rpc_task *);
#endif

/* Hack for future NFS swap support */
#ifndef IS_SWAPFILE
# define IS_SWAPFILE(inode)     (0)
#endif

static kmem_cache_t *nfs_wdata_cachep;

static __inline__ struct nfs_write_data *nfs_writedata_alloc(void)
{
        struct nfs_write_data   *p;
        p = kmem_cache_alloc(nfs_wdata_cachep, SLAB_NOFS);
        if (p) {
                memset(p, 0, sizeof(*p));
                INIT_LIST_HEAD(&p->pages);
                p->args.pages = p->pagevec;
        }
        return p;
}

static __inline__ void nfs_writedata_free(struct nfs_write_data *p)
{
        kmem_cache_free(nfs_wdata_cachep, p);
}

static void nfs_writedata_release(struct rpc_task *task)
{
        struct nfs_write_data   *wdata = (struct nfs_write_data *)task->tk_calldata;
        nfs_writedata_free(wdata);
}

/*
 * Write a page synchronously.
 * Offset is the data offset within the page.
 */
static int
nfs_writepage_sync(struct file *file, struct inode *inode, struct page *page,
                   unsigned int offset, unsigned int count)
{
        struct rpc_cred *cred = NULL;
        loff_t          base;
        unsigned int    wsize = NFS_SERVER(inode)->wsize;
        int             result, refresh = 0, written = 0, flags;
        u8              *buffer;
        struct nfs_fattr fattr;
        struct nfs_writeverf verf;


        if (file)
                cred = get_rpccred(nfs_file_cred(file));
        if (!cred)
                cred = get_rpccred(NFS_I(inode)->mm_cred);

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

        base = page_offset(page) + offset;

        flags = ((IS_SWAPFILE(inode)) ? NFS_RW_SWAP : 0) | NFS_RW_SYNC;

        do {
                if (count < wsize && !IS_SWAPFILE(inode))
                        wsize = count;

                result = NFS_PROTO(inode)->write(inode, cred, &fattr, flags,
                                                 offset, wsize, page, &verf);
                nfs_write_attributes(inode, &fattr);

                if (result < 0) {
                        /* Must mark the page invalid after I/O error */
                        ClearPageUptodate(page);
                        goto io_error;
                }
                if (result != wsize)
                        printk("NFS: short write, wsize=%u, result=%d\n",
                        wsize, result);
                refresh = 1;
                buffer  += wsize;
                base    += wsize;
                offset  += wsize;
                written += wsize;
                count   -= wsize;
                /*
                 * If we've extended the file, update the inode
                 * now so we don't invalidate the cache.
                 */
                if (base > inode->i_size)
                        inode->i_size = base;
        } while (count);

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

io_error:
        if (cred)
                put_rpccred(cred);

        return written? written : result;
}

static int
nfs_writepage_async(struct file *file, struct inode *inode, struct page *page,
                    unsigned int offset, unsigned int count)
{
        struct nfs_page *req;
        loff_t          end;
        int             status;

        req = nfs_update_request(file, inode, page, offset, count);
        status = (IS_ERR(req)) ? PTR_ERR(req) : 0;
        if (status < 0)
                goto out;
        if (!req->wb_cred)
                req->wb_cred = get_rpccred(NFS_I(inode)->mm_cred);
        nfs_unlock_request(req);
        nfs_strategy(inode);
        end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
        if (inode->i_size < end)
                inode->i_size = end;

 out:
        return status;
}

/*
 * Write an mmapped page to the server.
 */
int
nfs_writepage(struct page *page)
{
        struct inode *inode = page->mapping->host;
        unsigned long end_index;
        unsigned offset = PAGE_CACHE_SIZE;
        int inode_referenced = 0;
        int err;

        /*
         * 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 = inode->i_size >> PAGE_CACHE_SHIFT;

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

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

        /* OK, are we completely out? */
        err = -EIO;
        if (page->index >= end_index+1 || !offset)
                goto out;
do_it:
        lock_kernel();
        if (NFS_SERVER(inode)->wsize >= PAGE_CACHE_SIZE && !IS_SYNC(inode) &&
                        inode_referenced) {
                err = nfs_writepage_async(NULL, inode, page, 0, offset);
                if (err >= 0)
                        err = 0;
        } else {
                err = nfs_writepage_sync(NULL, inode, page, 0, offset); 
                if (err == offset)
                        err = 0;
        }
        unlock_kernel();
out:
        UnlockPage(page);
        if (inode_referenced)
                iput(inode);
        return err;
}

/*
 * Check whether the file range we want to write to is locked by
 * us.
 */
static int
region_locked(struct inode *inode, struct nfs_page *req)
{
        struct file_lock        *fl;
        loff_t                  rqstart, rqend;

        /* Don't optimize writes if we don't use NLM */
        if (NFS_SERVER(inode)->flags & NFS_MOUNT_NONLM)
                return 0;

        rqstart = page_offset(req->wb_page) + req->wb_offset;
        rqend = rqstart + req->wb_bytes;
        for (fl = inode->i_flock; fl; fl = fl->fl_next) {
                if (fl->fl_owner == current->files && (fl->fl_flags & FL_POSIX)
                    && fl->fl_type == F_WRLCK
                    && fl->fl_start <= rqstart && rqend <= fl->fl_end) {
                        return 1;
                }
        }

        return 0;
}

/*
 * Insert a write request into an inode
 * Note: we sort the list in order to be able to optimize nfs_find_request()
 *       & co. for the 'write append' case. For 2.5 we may want to consider
 *       some form of hashing so as to perform well on random writes.
 */
static inline void
nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
{
        struct list_head *pos, *head;
        unsigned long pg_idx = page_index(req->wb_page);

        if (!list_empty(&req->wb_hash))
                return;
        if (!NFS_WBACK_BUSY(req))
                printk(KERN_ERR "NFS: unlocked request attempted hashed!\n");
        head = &inode->u.nfs_i.writeback;
        if (list_empty(head))
                igrab(inode);
        list_for_each_prev(pos, head) {
                struct nfs_page *entry = nfs_inode_wb_entry(pos);
                if (page_index(entry->wb_page) < pg_idx)
                        break;
        }
        inode->u.nfs_i.npages++;
        list_add(&req->wb_hash, pos);
        req->wb_count++;
}

/*
 * Insert a write request into an inode
 */
static inline void
nfs_inode_remove_request(struct nfs_page *req)
{
        struct inode *inode;
        spin_lock(&nfs_wreq_lock);
        if (list_empty(&req->wb_hash)) {
                spin_unlock(&nfs_wreq_lock);
                return;
        }
        if (!NFS_WBACK_BUSY(req))
                printk(KERN_ERR "NFS: unlocked request attempted unhashed!\n");
        inode = req->wb_inode;
        list_del(&req->wb_hash);
        INIT_LIST_HEAD(&req->wb_hash);
        inode->u.nfs_i.npages--;
        if ((inode->u.nfs_i.npages == 0) != list_empty(&inode->u.nfs_i.writeback))
                printk(KERN_ERR "NFS: desynchronized value of nfs_i.npages.\n");
        if (list_empty(&inode->u.nfs_i.writeback)) {
                spin_unlock(&nfs_wreq_lock);
                iput(inode);
        } else
                spin_unlock(&nfs_wreq_lock);
        nfs_clear_request(req);
        nfs_release_request(req);
}

/*
 * Find a request
 */
static inline struct nfs_page *
_nfs_find_request(struct inode *inode, struct page *page)
{
        struct list_head        *head, *pos;
        unsigned long pg_idx = page_index(page);

        head = &inode->u.nfs_i.writeback;
        list_for_each_prev(pos, head) {
                struct nfs_page *req = nfs_inode_wb_entry(pos);
                unsigned long found_idx = page_index(req->wb_page);

                if (pg_idx < found_idx)
                        continue;
                if (pg_idx != found_idx)
                        break;
                req->wb_count++;
                return req;
        }
        return NULL;
}

static struct nfs_page *
nfs_find_request(struct inode *inode, struct page *page)
{
        struct nfs_page         *req;

        spin_lock(&nfs_wreq_lock);
        req = _nfs_find_request(inode, page);
        spin_unlock(&nfs_wreq_lock);
        return req;
}

/*
 * Add a request to the inode's dirty list.
 */
static inline void
nfs_mark_request_dirty(struct nfs_page *req)
{
        struct inode *inode = req->wb_inode;

        spin_lock(&nfs_wreq_lock);
        nfs_list_add_request(req, &inode->u.nfs_i.dirty);
        inode->u.nfs_i.ndirty++;
        __nfs_del_lru(req);
        __nfs_add_lru(&NFS_SERVER(inode)->lru_dirty, req);
        spin_unlock(&nfs_wreq_lock);
        mark_inode_dirty(inode);
}

/*
 * Check if a request is dirty
 */
static inline int
nfs_dirty_request(struct nfs_page *req)
{
        struct inode *inode = req->wb_inode;
        return !list_empty(&req->wb_list) && req->wb_list_head == &inode->u.nfs_i.dirty;
}

#ifdef CONFIG_NFS_V3
/*
 * Add a request to the inode's commit list.
 */
static inline void
nfs_mark_request_commit(struct nfs_page *req)
{
        struct inode *inode = req->wb_inode;

        spin_lock(&nfs_wreq_lock);
        nfs_list_add_request(req, &inode->u.nfs_i.commit);
        inode->u.nfs_i.ncommit++;
        __nfs_del_lru(req);
        __nfs_add_lru(&NFS_SERVER(inode)->lru_commit, req);
        spin_unlock(&nfs_wreq_lock);
        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 list_head        *p, *head;
        unsigned long           idx_end;
        unsigned int            res = 0;
        int                     error;

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

        head = &inode->u.nfs_i.writeback;
 restart:
        spin_lock(&nfs_wreq_lock);
        list_for_each_prev(p, head) {
                unsigned long pg_idx;
                struct nfs_page *req = nfs_inode_wb_entry(p);

                pg_idx = page_index(req->wb_page);
                if (pg_idx < idx_start)
                        break;
                if (pg_idx > idx_end)
                        continue;

                if (!NFS_WBACK_BUSY(req))
                        continue;
                req->wb_count++;
                spin_unlock(&nfs_wreq_lock);
                error = nfs_wait_on_request(req);
                nfs_release_request(req);
                if (error < 0)
                        return error;
                res++;
                goto restart;
        }
        spin_unlock(&nfs_wreq_lock);
        return res;
}

/**
 * nfs_scan_lru_dirty_timeout - Scan LRU list for timed out dirty requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
 * The elements are checked to ensure that they form a contiguous set
 * of pages, and that they originated from the same file.
 */
int
nfs_scan_lru_dirty_timeout(struct nfs_server *server, struct list_head *dst)
{
        struct inode *inode;
        int npages;

        npages = nfs_scan_lru_timeout(&server->lru_dirty, dst, server->wpages);
        if (npages) {
                inode = nfs_list_entry(dst->next)->wb_inode;
                inode->u.nfs_i.ndirty -= npages;
        }
        return npages;
}

/**
 * nfs_scan_lru_dirty - Scan LRU list for dirty requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Moves a maximum of 'wpages' requests from the NFS dirty page LRU list.
 * The elements are checked to ensure that they form a contiguous set
 * of pages, and that they originated from the same file.
 */
int
nfs_scan_lru_dirty(struct nfs_server *server, struct list_head *dst)
{
        struct inode *inode;
        int npages;

        npages = nfs_scan_lru(&server->lru_dirty, dst, server->wpages);
        if (npages) {
                inode = nfs_list_entry(dst->next)->wb_inode;
                inode->u.nfs_i.ndirty -= npages;
        }
        return npages;
}

/*
 * 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)
{
        int     res;
        res = nfs_scan_list(&inode->u.nfs_i.dirty, dst, idx_start, npages);
        inode->u.nfs_i.ndirty -= res;
        if ((inode->u.nfs_i.ndirty == 0) != list_empty(&inode->u.nfs_i.dirty))
                printk(KERN_ERR "NFS: desynchronized value of nfs_i.ndirty.\n");
        return res;
}

#ifdef CONFIG_NFS_V3
/**
 * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Finds the first a timed out request in the NFS commit LRU list and moves it
 * to the list dst. If such an element is found, we move all other commit
 * requests that apply to the same inode.
 * The assumption is that doing everything in a single commit-to-disk is
 * the cheaper alternative.
 */
int
nfs_scan_lru_commit_timeout(struct nfs_server *server, struct list_head *dst)
{
        struct inode *inode;
        int npages;

        npages = nfs_scan_lru_timeout(&server->lru_commit, dst, 1);
        if (npages) {
                inode = nfs_list_entry(dst->next)->wb_inode;
                npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, 0, 0);
                inode->u.nfs_i.ncommit -= npages;
        }
        return npages;
}


/**
 * nfs_scan_lru_commit_timeout - Scan LRU list for timed out commit requests
 * @server: NFS superblock data
 * @dst: destination list
 *
 * Finds the first request in the NFS commit LRU list and moves it
 * to the list dst. If such an element is found, we move all other commit
 * requests that apply to the same inode.
 * The assumption is that doing everything in a single commit-to-disk is
 * the cheaper alternative.
 */
int
nfs_scan_lru_commit(struct nfs_server *server, struct list_head *dst)
{
        struct inode *inode;
        int npages;

        npages = nfs_scan_lru(&server->lru_commit, dst, 1);
        if (npages) {
                inode = nfs_list_entry(dst->next)->wb_inode;
                npages += nfs_scan_list(&inode->u.nfs_i.commit, dst, 0, 0);
                inode->u.nfs_i.ncommit -= npages;
        }
        return npages;
}

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


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

        end = offset + bytes;

        for (;;) {
                /* Loop over all inode entries and see if we find
                 * A request for the page we wish to update
                 */
                spin_lock(&nfs_wreq_lock);
                req = _nfs_find_request(inode, page);
                if (req) {
                        if (!nfs_lock_request_dontget(req)) {
                                int error;
                                spin_unlock(&nfs_wreq_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(&nfs_wreq_lock);
                        if (new)
                                nfs_release_request(new);
                        break;
                }

                if (new) {
                        nfs_lock_request_dontget(new);
                        nfs_inode_add_request(inode, new);
                        spin_unlock(&nfs_wreq_lock);
                        nfs_mark_request_dirty(new);
                        return new;
                }
                spin_unlock(&nfs_wreq_lock);

                new = nfs_create_request(nfs_file_cred(file), inode, page, offset, bytes);
                if (IS_ERR(new))
                        return new;
                if (file) {
                        new->wb_file = file;
                        get_file(file);
                }
                /* If the region is locked, adjust the timeout */
                if (region_locked(inode, new))
                        new->wb_timeout = jiffies + NFS_WRITEBACK_LOCKDELAY;
                else
                        new->wb_timeout = jiffies + NFS_WRITEBACK_DELAY;
        }

        /* 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_file != file
            || 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_bytes = rqend - req->wb_offset;
        }

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

        return req;
}

/*
 * This is the strategy routine for NFS.
 * It is called by nfs_updatepage whenever the user wrote up to the end
 * of a page.
 *
 * We always try to submit a set of requests in parallel so that the
 * server's write code can gather writes. This is mainly for the benefit
 * of NFSv2.
 *
 * We never submit more requests than we think the remote can handle.
 * For UDP sockets, we make sure we don't exceed the congestion window;
 * for TCP, we limit the number of requests to 8.
 *
 * NFS_STRATEGY_PAGES gives the minimum number of requests for NFSv2 that
 * should be sent out in one go. This is for the benefit of NFSv2 servers
 * that perform write gathering.
 *
 * FIXME: Different servers may have different sweet spots.
 * Record the average congestion window in server struct?
 */
#define NFS_STRATEGY_PAGES      8
static void
nfs_strategy(struct inode *inode)
{
        unsigned int    dirty, wpages;

        dirty  = inode->u.nfs_i.ndirty;
        wpages = NFS_SERVER(inode)->wpages;
#ifdef CONFIG_NFS_V3
        if (NFS_PROTO(inode)->version == 2) {
                if (dirty >= NFS_STRATEGY_PAGES * wpages)
                        nfs_flush_file(inode, 0, 0, 0);
        } else if (dirty >= wpages)
                nfs_flush_file(inode, 0, 0, 0);
#else
        if (dirty >= NFS_STRATEGY_PAGES * wpages)
                nfs_flush_file(inode, 0, 0, 0);
#endif
}

int
nfs_flush_incompatible(struct file *file, struct page *page)
{
        struct rpc_cred *cred = nfs_file_cred(file);
        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);
        if (req) {
                if (req->wb_file != file || req->wb_cred != cred || req->wb_page != page)
                        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 dentry   *dentry = file->f_dentry;
        struct inode    *inode = page->mapping->host;
        struct nfs_page *req;
        loff_t          end;
        int             status = 0;

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

        /*
         * If wsize is smaller than page size, update and write
         * page synchronously.
         */
        if (NFS_SERVER(inode)->wsize < PAGE_CACHE_SIZE || IS_SYNC(inode)) {
                status = nfs_writepage_sync(file, inode, page, offset, count);
                if (status > 0) {
                        if (offset == 0 && status == PAGE_CACHE_SIZE)
                                SetPageUptodate(page);
                        return 0;
                }
                return status;
        }

        /*
         * 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(file, 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;
        end = ((loff_t)page->index<<PAGE_CACHE_SHIFT) + (loff_t)(offset + count);
        if (inode->i_size < end)
                inode->i_size = end;

        /* If we wrote past the end of the page.
         * Call the strategy routine so it can send out a bunch
         * of requests.
         */
        if (req->wb_offset == 0 && req->wb_bytes == PAGE_CACHE_SIZE) {
                SetPageUptodate(page);
                nfs_unlock_request(req);
                nfs_strategy(inode);
        } else
                nfs_unlock_request(req);
done:
        dprintk("NFS:      nfs_updatepage returns %d (isize %Ld)\n",
                                                status, (long long)inode->i_size);
        if (status < 0)
                ClearPageUptodate(page);
        return status;
}

/*
 * Set up the argument/result storage required for the RPC call.
 */
static void
nfs_write_rpcsetup(struct list_head *head, struct nfs_write_data *data)
{
        struct nfs_page         *req;
        struct page             **pages;
        unsigned int            count;

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

        pages = data->args.pages;
        count = 0;
        while (!list_empty(head)) {
                struct nfs_page *req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_list_add_request(req, &data->pages);
                *pages++ = req->wb_page;
                count += req->wb_bytes;
        }
        req = nfs_list_entry(data->pages.next);
        data->inode = req->wb_inode;
        data->cred = req->wb_cred;
        data->args.fh     = NFS_FH(req->wb_inode);
        data->args.offset = page_offset(req->wb_page) + req->wb_offset;
        data->args.pgbase = req->wb_offset;
        data->args.count  = count;
        data->res.fattr   = &data->fattr;
        data->res.count   = count;
        data->res.verf    = &data->verf;
}


/*
 * 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 rpc_clnt         *clnt = NFS_CLIENT(inode);
        struct nfs_write_data   *data;
        struct rpc_task         *task;
        struct rpc_message      msg;
        int                     flags,
                                nfsvers = NFS_PROTO(inode)->version,
                                async = !(how & FLUSH_SYNC),
                                stable = (how & FLUSH_STABLE);
        sigset_t                oldset;


        data = nfs_writedata_alloc();
        if (!data)
                goto out_bad;
        task = &data->task;

        /* Set the initial flags for the task.  */
        flags = (async) ? RPC_TASK_ASYNC : 0;

        /* Set up the argument struct */
        nfs_write_rpcsetup(head, data);
        if (nfsvers < 3)
                data->args.stable = NFS_FILE_SYNC;
        else if (stable) {
                if (!inode->u.nfs_i.ncommit)
                        data->args.stable = NFS_FILE_SYNC;
                else
                        data->args.stable = NFS_DATA_SYNC;
        } else
                data->args.stable = NFS_UNSTABLE;

        /* Finalize the task. */
        rpc_init_task(task, clnt, nfs_writeback_done, flags);
        task->tk_calldata = data;
        /* Release requests */
        task->tk_release = nfs_writedata_release;

#ifdef CONFIG_NFS_V3
        msg.rpc_proc = (nfsvers == 3) ? NFS3PROC_WRITE : NFSPROC_WRITE;
#else
        msg.rpc_proc = NFSPROC_WRITE;
#endif
        msg.rpc_argp = &data->args;
        msg.rpc_resp = &data->res;
        msg.rpc_cred = data->cred;

        dprintk("NFS: %4d initiated write call (req %x/%Ld count %u)\n",
                task->tk_pid, 
                inode->i_dev,
                (long long)NFS_FILEID(inode),
                data->args.count);

        rpc_clnt_sigmask(clnt, &oldset);
        rpc_call_setup(task, &msg, 0);
        lock_kernel();
        rpc_execute(task);
        unlock_kernel();
        rpc_clnt_sigunmask(clnt, &oldset);
        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_unlock_request(req);
        }
        return -ENOMEM;
}

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_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_unlock_request(req);
        }
        return error;
}


/*
 * This function is called when the WRITE call is complete.
 */
static void
nfs_writeback_done(struct rpc_task *task)
{
        struct nfs_write_data   *data = (struct nfs_write_data *) task->tk_calldata;
        struct nfs_writeargs    *argp = &data->args;
        struct nfs_writeres     *resp = &data->res;
        struct inode            *inode = data->inode;
        struct nfs_page         *req;
        struct page             *page;

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

        if (nfs_async_handle_jukebox(task))
                return;

        /* We can't handle that yet but we check for it nevertheless */
        if (resp->count < argp->count && task->tk_status >= 0) {
                static unsigned long    complain;
                if (time_before(complain, jiffies)) {
                        printk(KERN_WARNING
                               "NFS: Server wrote less than requested.\n");
                        complain = jiffies + 300 * HZ;
                }
                /* Can't do anything about it right now except throw
                 * an error. */
                task->tk_status = -EIO;
        }
#ifdef CONFIG_NFS_V3
        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 NFSv3 server %s:"
                                " (committed = %d) != (stable = %d)\n",
                                NFS_SERVER(inode)->hostname,
                                resp->verf->committed, argp->stable);
                        complain = jiffies + 300 * HZ;
                }
        }
#endif

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

                dprintk("NFS: write (%x/%Ld %d@%Ld)",
                        req->wb_inode->i_dev,
                        (long long)NFS_FILEID(req->wb_inode),
                        req->wb_bytes,
                        (long long)(page_offset(page) + req->wb_offset));

                if (task->tk_status < 0) {
                        ClearPageUptodate(page);
                        SetPageError(page);
                        if (req->wb_file)
                                req->wb_file->f_error = task->tk_status;
                        nfs_inode_remove_request(req);
                        dprintk(", error = %d\n", task->tk_status);
                        goto next;
                }

#ifdef CONFIG_NFS_V3
                if (argp->stable != NFS_UNSTABLE || resp->verf->committed == NFS_FILE_SYNC) {
                        nfs_inode_remove_request(req);
                        dprintk(" OK\n");
                        goto next;
                }
                memcpy(&req->wb_verf, resp->verf, sizeof(req->wb_verf));
                req->wb_timeout = jiffies + NFS_COMMIT_DELAY;
                nfs_mark_request_commit(req);
                dprintk(" marked for commit\n");
#else
                nfs_inode_remove_request(req);
#endif
        next:
                nfs_unlock_request(req);
        }
}


#ifdef CONFIG_NFS_V3
/*
 * 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)
{
        struct nfs_page         *first, *last;
        struct inode            *inode;
        loff_t                  start, end, len;

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

        list_splice(head, &data->pages);
        INIT_LIST_HEAD(head);
        first = nfs_list_entry(data->pages.next);
        last = nfs_list_entry(data->pages.prev);
        inode = first->wb_inode;

        /*
         * Determine the offset range of requests in the COMMIT call.
         * We rely on the fact that data->pages is an ordered list...
         */
        start = page_offset(first->wb_page) + first->wb_offset;
        end = page_offset(last->wb_page) + (last->wb_offset + last->wb_bytes);
        len = end - start;
        /* If 'len' is not a 32-bit quantity, pass '0' in the COMMIT call */
        if (end >= inode->i_size || len < 0 || len > (~((u32)0) >> 1))
                len = 0;

        data->inode       = inode;
        data->cred        = first->wb_cred;
        data->args.fh     = NFS_FH(inode);
        data->args.offset = start;
        data->res.count   = data->args.count = (u32)len;
        data->res.fattr   = &data->fattr;
        data->res.verf    = &data->verf;
}

/*
 * Commit dirty pages
 */
int
nfs_commit_list(struct list_head *head, int how)
{
        struct rpc_message      msg;
        struct rpc_clnt         *clnt;
        struct nfs_write_data   *data;
        struct rpc_task         *task;
        struct nfs_page         *req;
        int                     flags,
                                async = !(how & FLUSH_SYNC);
        sigset_t                oldset;

        data = nfs_writedata_alloc();

        if (!data)
                goto out_bad;
        task = &data->task;

        flags = (async) ? RPC_TASK_ASYNC : 0;

        /* Set up the argument struct */
        nfs_commit_rpcsetup(head, data);
        req = nfs_list_entry(data->pages.next);
        clnt = NFS_CLIENT(req->wb_inode);

        rpc_init_task(task, clnt, nfs_commit_done, flags);
        task->tk_calldata = data;
        /* Release requests */
        task->tk_release = nfs_writedata_release;

        msg.rpc_proc = NFS3PROC_COMMIT;
        msg.rpc_argp = &data->args;
        msg.rpc_resp = &data->res;
        msg.rpc_cred = data->cred;

        dprintk("NFS: %4d initiated commit call\n", task->tk_pid);
        rpc_clnt_sigmask(clnt, &oldset);
        rpc_call_setup(task, &msg, 0);
        lock_kernel();
        rpc_execute(task);
        unlock_kernel();
        rpc_clnt_sigunmask(clnt, &oldset);
        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_unlock_request(req);
        }
        return -ENOMEM;
}

/*
 * COMMIT call returned
 */
static void
nfs_commit_done(struct rpc_task *task)
{
        struct nfs_write_data   *data = (struct nfs_write_data *)task->tk_calldata;
        struct nfs_writeres     *resp = &data->res;
        struct nfs_page         *req;
        struct inode            *inode = data->inode;

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

        if (nfs_async_handle_jukebox(task))
                return;

        nfs_write_attributes(inode, resp->fattr);
        while (!list_empty(&data->pages)) {
                req = nfs_list_entry(data->pages.next);
                nfs_list_remove_request(req);

                dprintk("NFS: commit (%x/%Ld %d@%Ld)",
                        req->wb_inode->i_dev,
                        (long long)NFS_FILEID(req->wb_inode),
                        req->wb_bytes,
                        (long long)(page_offset(req->wb_page) + req->wb_offset));
                if (task->tk_status < 0) {
                        if (req->wb_file)
                                req->wb_file->f_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_unlock_request(req);
        }
}
#endif

int nfs_flush_file(struct inode *inode, unsigned long idx_start,
                   unsigned int npages, int how)
{
        LIST_HEAD(head);
        int                     res,
                                error = 0;

        spin_lock(&nfs_wreq_lock);
        res = nfs_scan_dirty(inode, &head, idx_start, npages);
        spin_unlock(&nfs_wreq_lock);
        if (res)
                error = nfs_flush_list(&head, NFS_SERVER(inode)->wpages, how);
        if (error < 0)
                return error;
        return res;
}

#ifdef CONFIG_NFS_V3
int nfs_commit_file(struct inode *inode, int how)
{
        LIST_HEAD(head);
        int                     res,
                                error = 0;

        spin_lock(&nfs_wreq_lock);
        res = nfs_scan_commit(inode, &head, 0, 0);
        spin_unlock(&nfs_wreq_lock);
        if (res)
                error = nfs_commit_list(&head, how);
        if (error < 0)
                return error;
        return res;
}
#endif

int nfs_sync_file(struct inode *inode, unsigned long idx_start,
                  unsigned int npages, int how)
{
        int     error,
                wait;

        wait = how & FLUSH_WAIT;
        how &= ~FLUSH_WAIT;

        do {
                error = 0;
                if (wait)
                        error = nfs_wait_on_requests(inode, idx_start, npages);
                if (error == 0)
                        error = nfs_flush_file(inode, idx_start, npages, how);
#ifdef CONFIG_NFS_V3
                if (error == 0)
                        error = nfs_commit_file(inode, how);
#endif
        } 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;

        return 0;
}

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