Automatic merge of rsync://rsync.kernel.org/pub/scm/linux/kernel/git/gregkh/driver...

[linux-2.6/verdex.git] / fs / nfs / direct.c

/*
 * linux/fs/nfs/direct.c
 *
 * Copyright (C) 2003 by Chuck Lever <cel@netapp.com>
 *
 * High-performance uncached I/O for the Linux NFS client
 *
 * There are important applications whose performance or correctness
 * depends on uncached access to file data.  Database clusters
 * (multiple copies of the same instance running on separate hosts) 
 * implement their own cache coherency protocol that subsumes file
 * system cache protocols.  Applications that process datasets 
 * considerably larger than the client's memory do not always benefit 
 * from a local cache.  A streaming video server, for instance, has no 
 * need to cache the contents of a file.
 *
 * When an application requests uncached I/O, all read and write requests
 * are made directly to the server; data stored or fetched via these
 * requests is not cached in the Linux page cache.  The client does not
 * correct unaligned requests from applications.  All requested bytes are
 * held on permanent storage before a direct write system call returns to
 * an application.
 *
 * Solaris implements an uncached I/O facility called directio() that
 * is used for backups and sequential I/O to very large files.  Solaris
 * also supports uncaching whole NFS partitions with "-o forcedirectio,"
 * an undocumented mount option.
 *
 * Designed by Jeff Kimmel, Chuck Lever, and Trond Myklebust, with
 * help from Andrew Morton.
 *
 * 18 Dec 2001  Initial implementation for 2.4  --cel
 * 08 Jul 2002  Version for 2.4.19, with bug fixes --trondmy
 * 08 Jun 2003  Port to 2.5 APIs  --cel
 * 31 Mar 2004  Handle direct I/O without VFS support  --cel
 * 15 Sep 2004  Parallel async reads  --cel
 *
 */

#include <linux/config.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/smp_lock.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/kref.h>

#include <linux/nfs_fs.h>
#include <linux/nfs_page.h>
#include <linux/sunrpc/clnt.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/atomic.h>

#define NFSDBG_FACILITY         NFSDBG_VFS
#define MAX_DIRECTIO_SIZE       (4096UL << PAGE_SHIFT)

static kmem_cache_t *nfs_direct_cachep;

/*
 * This represents a set of asynchronous requests that we're waiting on
 */
struct nfs_direct_req {
        struct kref             kref;           /* release manager */
        struct list_head        list;           /* nfs_read_data structs */
        wait_queue_head_t       wait;           /* wait for i/o completion */
        struct page **          pages;          /* pages in our buffer */
        unsigned int            npages;         /* count of pages */
        atomic_t                complete,       /* i/os we're waiting for */
                                count,          /* bytes actually processed */
                                error;          /* any reported error */
};


/**
 * nfs_get_user_pages - find and set up pages underlying user's buffer
 * rw: direction (read or write)
 * user_addr: starting address of this segment of user's buffer
 * count: size of this segment
 * @pages: returned array of page struct pointers underlying user's buffer
 */
static inline int
nfs_get_user_pages(int rw, unsigned long user_addr, size_t size,
                struct page ***pages)
{
        int result = -ENOMEM;
        unsigned long page_count;
        size_t array_size;

        /* set an arbitrary limit to prevent type overflow */
        /* XXX: this can probably be as large as INT_MAX */
        if (size > MAX_DIRECTIO_SIZE) {
                *pages = NULL;
                return -EFBIG;
        }

        page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
        page_count -= user_addr >> PAGE_SHIFT;

        array_size = (page_count * sizeof(struct page *));
        *pages = kmalloc(array_size, GFP_KERNEL);
        if (*pages) {
                down_read(&current->mm->mmap_sem);
                result = get_user_pages(current, current->mm, user_addr,
                                        page_count, (rw == READ), 0,
                                        *pages, NULL);
                up_read(&current->mm->mmap_sem);
        }
        return result;
}

/**
 * nfs_free_user_pages - tear down page struct array
 * @pages: array of page struct pointers underlying target buffer
 * @npages: number of pages in the array
 * @do_dirty: dirty the pages as we release them
 */
static void
nfs_free_user_pages(struct page **pages, int npages, int do_dirty)
{
        int i;
        for (i = 0; i < npages; i++) {
                if (do_dirty)
                        set_page_dirty_lock(pages[i]);
                page_cache_release(pages[i]);
        }
        kfree(pages);
}

/**
 * nfs_direct_req_release - release  nfs_direct_req structure for direct read
 * @kref: kref object embedded in an nfs_direct_req structure
 *
 */
static void nfs_direct_req_release(struct kref *kref)
{
        struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);
        kmem_cache_free(nfs_direct_cachep, dreq);
}

/**
 * nfs_direct_read_alloc - allocate nfs_read_data structures for direct read
 * @count: count of bytes for the read request
 * @rsize: local rsize setting
 *
 * Note we also set the number of requests we have in the dreq when we are
 * done.  This prevents races with I/O completion so we will always wait
 * until all requests have been dispatched and completed.
 */
static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, unsigned int rsize)
{
        struct list_head *list;
        struct nfs_direct_req *dreq;
        unsigned int reads = 0;

        dreq = kmem_cache_alloc(nfs_direct_cachep, SLAB_KERNEL);
        if (!dreq)
                return NULL;

        kref_init(&dreq->kref);
        init_waitqueue_head(&dreq->wait);
        INIT_LIST_HEAD(&dreq->list);
        atomic_set(&dreq->count, 0);
        atomic_set(&dreq->error, 0);

        list = &dreq->list;
        for(;;) {
                struct nfs_read_data *data = nfs_readdata_alloc();

                if (unlikely(!data)) {
                        while (!list_empty(list)) {
                                data = list_entry(list->next,
                                                  struct nfs_read_data, pages);
                                list_del(&data->pages);
                                nfs_readdata_free(data);
                        }
                        kref_put(&dreq->kref, nfs_direct_req_release);
                        return NULL;
                }

                INIT_LIST_HEAD(&data->pages);
                list_add(&data->pages, list);

                data->req = (struct nfs_page *) dreq;
                reads++;
                if (nbytes <= rsize)
                        break;
                nbytes -= rsize;
        }
        kref_get(&dreq->kref);
        atomic_set(&dreq->complete, reads);
        return dreq;
}

/**
 * nfs_direct_read_result - handle a read reply for a direct read request
 * @data: address of NFS READ operation control block
 * @status: status of this NFS READ operation
 *
 * We must hold a reference to all the pages in this direct read request
 * until the RPCs complete.  This could be long *after* we are woken up in
 * nfs_direct_read_wait (for instance, if someone hits ^C on a slow server).
 */
static void nfs_direct_read_result(struct nfs_read_data *data, int status)
{
        struct nfs_direct_req *dreq = (struct nfs_direct_req *) data->req;

        if (likely(status >= 0))
                atomic_add(data->res.count, &dreq->count);
        else
                atomic_set(&dreq->error, status);

        if (unlikely(atomic_dec_and_test(&dreq->complete))) {
                nfs_free_user_pages(dreq->pages, dreq->npages, 1);
                wake_up(&dreq->wait);
                kref_put(&dreq->kref, nfs_direct_req_release);
        }
}

/**
 * nfs_direct_read_schedule - dispatch NFS READ operations for a direct read
 * @dreq: address of nfs_direct_req struct for this request
 * @inode: target inode
 * @ctx: target file open context
 * @user_addr: starting address of this segment of user's buffer
 * @count: size of this segment
 * @file_offset: offset in file to begin the operation
 *
 * For each nfs_read_data struct that was allocated on the list, dispatch
 * an NFS READ operation
 */
static void nfs_direct_read_schedule(struct nfs_direct_req *dreq,
                struct inode *inode, struct nfs_open_context *ctx,
                unsigned long user_addr, size_t count, loff_t file_offset)
{
        struct list_head *list = &dreq->list;
        struct page **pages = dreq->pages;
        unsigned int curpage, pgbase;
        unsigned int rsize = NFS_SERVER(inode)->rsize;

        curpage = 0;
        pgbase = user_addr & ~PAGE_MASK;
        do {
                struct nfs_read_data *data;
                unsigned int bytes;

                bytes = rsize;
                if (count < rsize)
                        bytes = count;

                data = list_entry(list->next, struct nfs_read_data, pages);
                list_del_init(&data->pages);

                data->inode = inode;
                data->cred = ctx->cred;
                data->args.fh = NFS_FH(inode);
                data->args.context = ctx;
                data->args.offset = file_offset;
                data->args.pgbase = pgbase;
                data->args.pages = &pages[curpage];
                data->args.count = bytes;
                data->res.fattr = &data->fattr;
                data->res.eof = 0;
                data->res.count = bytes;

                NFS_PROTO(inode)->read_setup(data);

                data->task.tk_cookie = (unsigned long) inode;
                data->task.tk_calldata = data;
                data->task.tk_release = nfs_readdata_release;
                data->complete = nfs_direct_read_result;

                lock_kernel();
                rpc_execute(&data->task);
                unlock_kernel();

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

                file_offset += bytes;
                pgbase += bytes;
                curpage += pgbase >> PAGE_SHIFT;
                pgbase &= ~PAGE_MASK;

                count -= bytes;
        } while (count != 0);
}

/**
 * nfs_direct_read_wait - wait for I/O completion for direct reads
 * @dreq: request on which we are to wait
 * @intr: whether or not this wait can be interrupted
 *
 * Collects and returns the final error value/byte-count.
 */
static ssize_t nfs_direct_read_wait(struct nfs_direct_req *dreq, int intr)
{
        int result = 0;

        if (intr) {
                result = wait_event_interruptible(dreq->wait,
                                        (atomic_read(&dreq->complete) == 0));
        } else {
                wait_event(dreq->wait, (atomic_read(&dreq->complete) == 0));
        }

        if (!result)
                result = atomic_read(&dreq->error);
        if (!result)
                result = atomic_read(&dreq->count);

        kref_put(&dreq->kref, nfs_direct_req_release);
        return (ssize_t) result;
}

/**
 * nfs_direct_read_seg - Read in one iov segment.  Generate separate
 *                        read RPCs for each "rsize" bytes.
 * @inode: target inode
 * @ctx: target file open context
 * @user_addr: starting address of this segment of user's buffer
 * @count: size of this segment
 * @file_offset: offset in file to begin the operation
 * @pages: array of addresses of page structs defining user's buffer
 * @nr_pages: number of pages in the array
 *
 */
static ssize_t nfs_direct_read_seg(struct inode *inode,
                struct nfs_open_context *ctx, unsigned long user_addr,
                size_t count, loff_t file_offset, struct page **pages,
                unsigned int nr_pages)
{
        ssize_t result;
        sigset_t oldset;
        struct rpc_clnt *clnt = NFS_CLIENT(inode);
        struct nfs_direct_req *dreq;

        dreq = nfs_direct_read_alloc(count, NFS_SERVER(inode)->rsize);
        if (!dreq)
                return -ENOMEM;

        dreq->pages = pages;
        dreq->npages = nr_pages;

        rpc_clnt_sigmask(clnt, &oldset);
        nfs_direct_read_schedule(dreq, inode, ctx, user_addr, count,
                                 file_offset);
        result = nfs_direct_read_wait(dreq, clnt->cl_intr);
        rpc_clnt_sigunmask(clnt, &oldset);

        return result;
}

/**
 * nfs_direct_read - For each iov segment, map the user's buffer
 *                   then generate read RPCs.
 * @inode: target inode
 * @ctx: target file open context
 * @iov: array of vectors that define I/O buffer
 * file_offset: offset in file to begin the operation
 * nr_segs: size of iovec array
 *
 * We've already pushed out any non-direct writes so that this read
 * will see them when we read from the server.
 */
static ssize_t
nfs_direct_read(struct inode *inode, struct nfs_open_context *ctx,
                const struct iovec *iov, loff_t file_offset,
                unsigned long nr_segs)
{
        ssize_t tot_bytes = 0;
        unsigned long seg = 0;

        while ((seg < nr_segs) && (tot_bytes >= 0)) {
                ssize_t result;
                int page_count;
                struct page **pages;
                const struct iovec *vec = &iov[seg++];
                unsigned long user_addr = (unsigned long) vec->iov_base;
                size_t size = vec->iov_len;

                page_count = nfs_get_user_pages(READ, user_addr, size, &pages);
                if (page_count < 0) {
                        nfs_free_user_pages(pages, 0, 0);
                        if (tot_bytes > 0)
                                break;
                        return page_count;
                }

                result = nfs_direct_read_seg(inode, ctx, user_addr, size,
                                file_offset, pages, page_count);

                if (result <= 0) {
                        if (tot_bytes > 0)
                                break;
                        return result;
                }
                tot_bytes += result;
                file_offset += result;
                if (result < size)
                        break;
        }

        return tot_bytes;
}

/**
 * nfs_direct_write_seg - Write out one iov segment.  Generate separate
 *                        write RPCs for each "wsize" bytes, then commit.
 * @inode: target inode
 * @ctx: target file open context
 * user_addr: starting address of this segment of user's buffer
 * count: size of this segment
 * file_offset: offset in file to begin the operation
 * @pages: array of addresses of page structs defining user's buffer
 * nr_pages: size of pages array
 */
static ssize_t nfs_direct_write_seg(struct inode *inode,
                struct nfs_open_context *ctx, unsigned long user_addr,
                size_t count, loff_t file_offset, struct page **pages,
                int nr_pages)
{
        const unsigned int wsize = NFS_SERVER(inode)->wsize;
        size_t request;
        int curpage, need_commit;
        ssize_t result, tot_bytes;
        struct nfs_writeverf first_verf;
        struct nfs_write_data *wdata;

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

        wdata->inode = inode;
        wdata->cred = ctx->cred;
        wdata->args.fh = NFS_FH(inode);
        wdata->args.context = ctx;
        wdata->args.stable = NFS_UNSTABLE;
        if (IS_SYNC(inode) || NFS_PROTO(inode)->version == 2 || count <= wsize)
                wdata->args.stable = NFS_FILE_SYNC;
        wdata->res.fattr = &wdata->fattr;
        wdata->res.verf = &wdata->verf;

        nfs_begin_data_update(inode);
retry:
        need_commit = 0;
        tot_bytes = 0;
        curpage = 0;
        request = count;
        wdata->args.pgbase = user_addr & ~PAGE_MASK;
        wdata->args.offset = file_offset;
        do {
                wdata->args.count = request;
                if (wdata->args.count > wsize)
                        wdata->args.count = wsize;
                wdata->args.pages = &pages[curpage];

                dprintk("NFS: direct write: c=%u o=%Ld ua=%lu, pb=%u, cp=%u\n",
                        wdata->args.count, (long long) wdata->args.offset,
                        user_addr + tot_bytes, wdata->args.pgbase, curpage);

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

                if (result <= 0) {
                        if (tot_bytes > 0)
                                break;
                        goto out;
                }

                if (tot_bytes == 0)
                        memcpy(&first_verf.verifier, &wdata->verf.verifier,
                                                sizeof(first_verf.verifier));
                if (wdata->verf.committed != NFS_FILE_SYNC) {
                        need_commit = 1;
                        if (memcmp(&first_verf.verifier, &wdata->verf.verifier,
                                        sizeof(first_verf.verifier)));
                                goto sync_retry;
                }

                tot_bytes += result;

                /* in case of a short write: stop now, let the app recover */
                if (result < wdata->args.count)
                        break;

                wdata->args.offset += result;
                wdata->args.pgbase += result;
                curpage += wdata->args.pgbase >> PAGE_SHIFT;
                wdata->args.pgbase &= ~PAGE_MASK;
                request -= result;
        } while (request != 0);

        /*
         * Commit data written so far, even in the event of an error
         */
        if (need_commit) {
                wdata->args.count = tot_bytes;
                wdata->args.offset = file_offset;

                lock_kernel();
                result = NFS_PROTO(inode)->commit(wdata);
                unlock_kernel();

                if (result < 0 || memcmp(&first_verf.verifier,
                                         &wdata->verf.verifier,
                                         sizeof(first_verf.verifier)) != 0)
                        goto sync_retry;
        }
        result = tot_bytes;

out:
        nfs_end_data_update_defer(inode);
        nfs_writedata_free(wdata);
        return result;

sync_retry:
        wdata->args.stable = NFS_FILE_SYNC;
        goto retry;
}

/**
 * nfs_direct_write - For each iov segment, map the user's buffer
 *                    then generate write and commit RPCs.
 * @inode: target inode
 * @ctx: target file open context
 * @iov: array of vectors that define I/O buffer
 * file_offset: offset in file to begin the operation
 * nr_segs: size of iovec array
 *
 * Upon return, generic_file_direct_IO invalidates any cached pages
 * that non-direct readers might access, so they will pick up these
 * writes immediately.
 */
static ssize_t nfs_direct_write(struct inode *inode,
                struct nfs_open_context *ctx, const struct iovec *iov,
                loff_t file_offset, unsigned long nr_segs)
{
        ssize_t tot_bytes = 0;
        unsigned long seg = 0;

        while ((seg < nr_segs) && (tot_bytes >= 0)) {
                ssize_t result;
                int page_count;
                struct page **pages;
                const struct iovec *vec = &iov[seg++];
                unsigned long user_addr = (unsigned long) vec->iov_base;
                size_t size = vec->iov_len;

                page_count = nfs_get_user_pages(WRITE, user_addr, size, &pages);
                if (page_count < 0) {
                        nfs_free_user_pages(pages, 0, 0);
                        if (tot_bytes > 0)
                                break;
                        return page_count;
                }

                result = nfs_direct_write_seg(inode, ctx, user_addr, size,
                                file_offset, pages, page_count);
                nfs_free_user_pages(pages, page_count, 0);

                if (result <= 0) {
                        if (tot_bytes > 0)
                                break;
                        return result;
                }
                tot_bytes += result;
                file_offset += result;
                if (result < size)
                        break;
        }
        return tot_bytes;
}

/**
 * nfs_direct_IO - NFS address space operation for direct I/O
 * rw: direction (read or write)
 * @iocb: target I/O control block
 * @iov: array of vectors that define I/O buffer
 * file_offset: offset in file to begin the operation
 * nr_segs: size of iovec array
 *
 */
ssize_t
nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                loff_t file_offset, unsigned long nr_segs)
{
        ssize_t result = -EINVAL;
        struct file *file = iocb->ki_filp;
        struct nfs_open_context *ctx;
        struct dentry *dentry = file->f_dentry;
        struct inode *inode = dentry->d_inode;

        /*
         * No support for async yet
         */
        if (!is_sync_kiocb(iocb))
                return result;

        ctx = (struct nfs_open_context *)file->private_data;
        switch (rw) {
        case READ:
                dprintk("NFS: direct_IO(read) (%s) off/no(%Lu/%lu)\n",
                                dentry->d_name.name, file_offset, nr_segs);

                result = nfs_direct_read(inode, ctx, iov,
                                                file_offset, nr_segs);
                break;
        case WRITE:
                dprintk("NFS: direct_IO(write) (%s) off/no(%Lu/%lu)\n",
                                dentry->d_name.name, file_offset, nr_segs);

                result = nfs_direct_write(inode, ctx, iov,
                                                file_offset, nr_segs);
                break;
        default:
                break;
        }
        return result;
}

/**
 * nfs_file_direct_read - file direct read operation for NFS files
 * @iocb: target I/O control block
 * @buf: user's buffer into which to read data
 * count: number of bytes to read
 * pos: byte offset in file where reading starts
 *
 * We use this function for direct reads instead of calling
 * generic_file_aio_read() in order to avoid gfar's check to see if
 * the request starts before the end of the file.  For that check
 * to work, we must generate a GETATTR before each direct read, and
 * even then there is a window between the GETATTR and the subsequent
 * READ where the file size could change.  So our preference is simply
 * to do all reads the application wants, and the server will take
 * care of managing the end of file boundary.
 * 
 * This function also eliminates unnecessarily updating the file's
 * atime locally, as the NFS server sets the file's atime, and this
 * client must read the updated atime from the server back into its
 * cache.
 */
ssize_t
nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
{
        ssize_t retval = -EINVAL;
        loff_t *ppos = &iocb->ki_pos;
        struct file *file = iocb->ki_filp;
        struct nfs_open_context *ctx =
                        (struct nfs_open_context *) file->private_data;
        struct dentry *dentry = file->f_dentry;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct iovec iov = {
                .iov_base = buf,
                .iov_len = count,
        };

        dprintk("nfs: direct read(%s/%s, %lu@%lu)\n",
                dentry->d_parent->d_name.name, dentry->d_name.name,
                (unsigned long) count, (unsigned long) pos);

        if (!is_sync_kiocb(iocb))
                goto out;
        if (count < 0)
                goto out;
        retval = -EFAULT;
        if (!access_ok(VERIFY_WRITE, iov.iov_base, iov.iov_len))
                goto out;
        retval = 0;
        if (!count)
                goto out;

        if (mapping->nrpages) {
                retval = filemap_fdatawrite(mapping);
                if (retval == 0)
                        retval = nfs_wb_all(inode);
                if (retval == 0)
                        retval = filemap_fdatawait(mapping);
                if (retval)
                        goto out;
        }

        retval = nfs_direct_read(inode, ctx, &iov, pos, 1);
        if (retval > 0)
                *ppos = pos + retval;

out:
        return retval;
}

/**
 * nfs_file_direct_write - file direct write operation for NFS files
 * @iocb: target I/O control block
 * @buf: user's buffer from which to write data
 * count: number of bytes to write
 * pos: byte offset in file where writing starts
 *
 * We use this function for direct writes instead of calling
 * generic_file_aio_write() in order to avoid taking the inode
 * semaphore and updating the i_size.  The NFS server will set
 * the new i_size and this client must read the updated size
 * back into its cache.  We let the server do generic write
 * parameter checking and report problems.
 *
 * We also avoid an unnecessary invocation of generic_osync_inode(),
 * as it is fairly meaningless to sync the metadata of an NFS file.
 *
 * We eliminate local atime updates, see direct read above.
 *
 * We avoid unnecessary page cache invalidations for normal cached
 * readers of this file.
 *
 * Note that O_APPEND is not supported for NFS direct writes, as there
 * is no atomic O_APPEND write facility in the NFS protocol.
 */
ssize_t
nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
{
        ssize_t retval = -EINVAL;
        loff_t *ppos = &iocb->ki_pos;
        unsigned long limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
        struct file *file = iocb->ki_filp;
        struct nfs_open_context *ctx =
                        (struct nfs_open_context *) file->private_data;
        struct dentry *dentry = file->f_dentry;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct iovec iov = {
                .iov_base = (char __user *)buf,
                .iov_len = count,
        };

        dfprintk(VFS, "nfs: direct write(%s/%s(%ld), %lu@%lu)\n",
                dentry->d_parent->d_name.name, dentry->d_name.name,
                inode->i_ino, (unsigned long) count, (unsigned long) pos);

        if (!is_sync_kiocb(iocb))
                goto out;
        if (count < 0)
                goto out;
        if (pos < 0)
                goto out;
        retval = -EFAULT;
        if (!access_ok(VERIFY_READ, iov.iov_base, iov.iov_len))
                goto out;
        if (file->f_error) {
                retval = file->f_error;
                file->f_error = 0;
                goto out;
        }
        retval = -EFBIG;
        if (limit != RLIM_INFINITY) {
                if (pos >= limit) {
                        send_sig(SIGXFSZ, current, 0);
                        goto out;
                }
                if (count > limit - (unsigned long) pos)
                        count = limit - (unsigned long) pos;
        }
        retval = 0;
        if (!count)
                goto out;

        if (mapping->nrpages) {
                retval = filemap_fdatawrite(mapping);
                if (retval == 0)
                        retval = nfs_wb_all(inode);
                if (retval == 0)
                        retval = filemap_fdatawait(mapping);
                if (retval)
                        goto out;
        }

        retval = nfs_direct_write(inode, ctx, &iov, pos, 1);
        if (mapping->nrpages)
                invalidate_inode_pages2(mapping);
        if (retval > 0)
                *ppos = pos + retval;

out:
        return retval;
}

int nfs_init_directcache(void)
{
        nfs_direct_cachep = kmem_cache_create("nfs_direct_cache",
                                                sizeof(struct nfs_direct_req),
                                                0, SLAB_RECLAIM_ACCOUNT,
                                                NULL, NULL);
        if (nfs_direct_cachep == NULL)
                return -ENOMEM;

        return 0;
}

void nfs_destroy_directcache(void)
{
        if (kmem_cache_destroy(nfs_direct_cachep))
                printk(KERN_INFO "nfs_direct_cache: not all structures were freed\n");
}