Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 808 insertions, 0 deletions

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
new file mode 100644
index 000000000000..68df803f27ca
--- /dev/null
+++ b/fs/nfs/direct.c
@@ -0,0 +1,808 @@
+/*
+ * 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");
+}