direct.c

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/*
 * linux/fs/nfs/direct.c
 *
 * Copyright (C) 2003 by Chuck Lever <[email protected]>
 *
 * 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
 * 04 May 2005  support O_DIRECT with aio  --cel
 *
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/kref.h>
#include <linux/slab.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/module.h>

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

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

#include "internal.h"
#include "iostat.h"
#include "pnfs.h"

#define NFSDBG_FACILITY     NFSDBG_VFS

static struct kmem_cache *nfs_direct_cachep;

/*
 * This represents a set of asynchronous requests that we're waiting on
 */
struct nfs_direct_req {
    struct kref     kref;       /* release manager */

    /* I/O parameters */
    struct nfs_open_context *ctx;       /* file open context info */
    struct nfs_lock_context *l_ctx;     /* Lock context info */
    struct kiocb *      iocb;       /* controlling i/o request */
    struct inode *      inode;      /* target file of i/o */

    /* completion state */
    atomic_t        io_count;   /* i/os we're waiting for */
    spinlock_t      lock;       /* protect completion state */
    ssize_t         count,      /* bytes actually processed */
                bytes_left, /* bytes left to be sent */
                error;      /* any reported error */
    struct completion   completion; /* wait for i/o completion */

    /* commit state */
    struct nfs_mds_commit_info mds_cinfo;   /* Storage for cinfo */
    struct pnfs_ds_commit_info ds_cinfo;    /* Storage for cinfo */
    struct work_struct  work;
    int         flags;
#define NFS_ODIRECT_DO_COMMIT       (1) /* an unstable reply was received */
#define NFS_ODIRECT_RESCHED_WRITES  (2) /* write verification failed */
    struct nfs_writeverf    verf;       /* unstable write verifier */
};

static const struct nfs_pgio_completion_ops nfs_direct_write_completion_ops;
static const struct nfs_commit_completion_ops nfs_direct_commit_completion_ops;
static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode);
static void nfs_direct_write_schedule_work(struct work_struct *work);

static inline void get_dreq(struct nfs_direct_req *dreq)
{
    atomic_inc(&dreq->io_count);
}

static inline int put_dreq(struct nfs_direct_req *dreq)
{
    return atomic_dec_and_test(&dreq->io_count);
}

ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
{
#ifndef CONFIG_NFS_SWAP
    dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
            iocb->ki_filp->f_path.dentry->d_name.name,
            (long long) pos, nr_segs);

    return -EINVAL;
#else
    VM_BUG_ON(iocb->ki_left != PAGE_SIZE);
    VM_BUG_ON(iocb->ki_nbytes != PAGE_SIZE);

    if (rw == READ || rw == KERNEL_READ)
        return nfs_file_direct_read(iocb, iov, nr_segs, pos,
                rw == READ ? true : false);
    return nfs_file_direct_write(iocb, iov, nr_segs, pos,
                rw == WRITE ? true : false);
#endif /* CONFIG_NFS_SWAP */
}

static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
{
    unsigned int i;
    for (i = 0; i < npages; i++)
        page_cache_release(pages[i]);
}

void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
                  struct nfs_direct_req *dreq)
{
    cinfo->lock = &dreq->lock;
    cinfo->mds = &dreq->mds_cinfo;
    cinfo->ds = &dreq->ds_cinfo;
    cinfo->dreq = dreq;
    cinfo->completion_ops = &nfs_direct_commit_completion_ops;
}

static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
{
    struct nfs_direct_req *dreq;

    dreq = kmem_cache_zalloc(nfs_direct_cachep, GFP_KERNEL);
    if (!dreq)
        return NULL;

    kref_init(&dreq->kref);
    kref_get(&dreq->kref);
    init_completion(&dreq->completion);
    INIT_LIST_HEAD(&dreq->mds_cinfo.list);
    INIT_WORK(&dreq->work, nfs_direct_write_schedule_work);
    spin_lock_init(&dreq->lock);

    return dreq;
}

static void nfs_direct_req_free(struct kref *kref)
{
    struct nfs_direct_req *dreq = container_of(kref, struct nfs_direct_req, kref);

    if (dreq->l_ctx != NULL)
        nfs_put_lock_context(dreq->l_ctx);
    if (dreq->ctx != NULL)
        put_nfs_open_context(dreq->ctx);
    kmem_cache_free(nfs_direct_cachep, dreq);
}

static void nfs_direct_req_release(struct nfs_direct_req *dreq)
{
    kref_put(&dreq->kref, nfs_direct_req_free);
}

ssize_t nfs_dreq_bytes_left(struct nfs_direct_req *dreq)
{
    return dreq->bytes_left;
}
EXPORT_SYMBOL_GPL(nfs_dreq_bytes_left);

/*
 * Collects and returns the final error value/byte-count.
 */
static ssize_t nfs_direct_wait(struct nfs_direct_req *dreq)
{
    ssize_t result = -EIOCBQUEUED;

    /* Async requests don't wait here */
    if (dreq->iocb)
        goto out;

    result = wait_for_completion_killable(&dreq->completion);

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

out:
    return (ssize_t) result;
}

/*
 * Synchronous I/O uses a stack-allocated iocb.  Thus we can't trust
 * the iocb is still valid here if this is a synchronous request.
 */
static void nfs_direct_complete(struct nfs_direct_req *dreq)
{
    if (dreq->iocb) {
        long res = (long) dreq->error;
        if (!res)
            res = (long) dreq->count;
        aio_complete(dreq->iocb, res, 0);
    }
    complete_all(&dreq->completion);

    nfs_direct_req_release(dreq);
}

static void nfs_direct_readpage_release(struct nfs_page *req)
{
    dprintk("NFS: direct read done (%s/%lld %d@%lld)\n",
        req->wb_context->dentry->d_inode->i_sb->s_id,
        (long long)NFS_FILEID(req->wb_context->dentry->d_inode),
        req->wb_bytes,
        (long long)req_offset(req));
    nfs_release_request(req);
}

static void nfs_direct_read_completion(struct nfs_pgio_header *hdr)
{
    unsigned long bytes = 0;
    struct nfs_direct_req *dreq = hdr->dreq;

    if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
        goto out_put;

    spin_lock(&dreq->lock);
    if (test_bit(NFS_IOHDR_ERROR, &hdr->flags) && (hdr->good_bytes == 0))
        dreq->error = hdr->error;
    else
        dreq->count += hdr->good_bytes;
    spin_unlock(&dreq->lock);

    while (!list_empty(&hdr->pages)) {
        struct nfs_page *req = nfs_list_entry(hdr->pages.next);
        struct page *page = req->wb_page;

        if (test_bit(NFS_IOHDR_EOF, &hdr->flags)) {
            if (bytes > hdr->good_bytes)
                zero_user(page, 0, PAGE_SIZE);
            else if (hdr->good_bytes - bytes < PAGE_SIZE)
                zero_user_segment(page,
                    hdr->good_bytes & ~PAGE_MASK,
                    PAGE_SIZE);
        }
        if (!PageCompound(page)) {
            if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
                if (bytes < hdr->good_bytes)
                    set_page_dirty(page);
            } else
                set_page_dirty(page);
        }
        bytes += req->wb_bytes;
        nfs_list_remove_request(req);
        nfs_direct_readpage_release(req);
    }
out_put:
    if (put_dreq(dreq))
        nfs_direct_complete(dreq);
    hdr->release(hdr);
}

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

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

static void nfs_direct_pgio_init(struct nfs_pgio_header *hdr)
{
    get_dreq(hdr->dreq);
}

static const struct nfs_pgio_completion_ops nfs_direct_read_completion_ops = {
    .error_cleanup = nfs_read_sync_pgio_error,
    .init_hdr = nfs_direct_pgio_init,
    .completion = nfs_direct_read_completion,
};

/*
 * For each rsize'd chunk of the user's buffer, dispatch an NFS READ
 * operation.  If nfs_readdata_alloc() or get_user_pages() fails,
 * bail and stop sending more reads.  Read length accounting is
 * handled automatically by nfs_direct_read_result().  Otherwise, if
 * no requests have been sent, just return an error.
 */
static ssize_t nfs_direct_read_schedule_segment(struct nfs_pageio_descriptor *desc,
                        const struct iovec *iov,
                        loff_t pos, bool uio)
{
    struct nfs_direct_req *dreq = desc->pg_dreq;
    struct nfs_open_context *ctx = dreq->ctx;
    struct inode *inode = ctx->dentry->d_inode;
    unsigned long user_addr = (unsigned long)iov->iov_base;
    size_t count = iov->iov_len;
    size_t rsize = NFS_SERVER(inode)->rsize;
    unsigned int pgbase;
    int result;
    ssize_t started = 0;
    struct page **pagevec = NULL;
    unsigned int npages;

    do {
        size_t bytes;
        int i;

        pgbase = user_addr & ~PAGE_MASK;
        bytes = min(max_t(size_t, rsize, PAGE_SIZE), count);

        result = -ENOMEM;
        npages = nfs_page_array_len(pgbase, bytes);
        if (!pagevec)
            pagevec = kmalloc(npages * sizeof(struct page *),
                      GFP_KERNEL);
        if (!pagevec)
            break;
        if (uio) {
            down_read(&current->mm->mmap_sem);
            result = get_user_pages(current, current->mm, user_addr,
                    npages, 1, 0, pagevec, NULL);
            up_read(&current->mm->mmap_sem);
            if (result < 0)
                break;
        } else {
            WARN_ON(npages != 1);
            result = get_kernel_page(user_addr, 1, pagevec);
            if (WARN_ON(result != 1))
                break;
        }

        if ((unsigned)result < npages) {
            bytes = result * PAGE_SIZE;
            if (bytes <= pgbase) {
                nfs_direct_release_pages(pagevec, result);
                break;
            }
            bytes -= pgbase;
            npages = result;
        }

        for (i = 0; i < npages; i++) {
            struct nfs_page *req;
            unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase);
            /* XXX do we need to do the eof zeroing found in async_filler? */
            req = nfs_create_request(dreq->ctx, dreq->inode,
                         pagevec[i],
                         pgbase, req_len);
            if (IS_ERR(req)) {
                result = PTR_ERR(req);
                break;
            }
            req->wb_index = pos >> PAGE_SHIFT;
            req->wb_offset = pos & ~PAGE_MASK;
            if (!nfs_pageio_add_request(desc, req)) {
                result = desc->pg_error;
                nfs_release_request(req);
                break;
            }
            pgbase = 0;
            bytes -= req_len;
            started += req_len;
            user_addr += req_len;
            pos += req_len;
            count -= req_len;
            dreq->bytes_left -= req_len;
        }
        /* The nfs_page now hold references to these pages */
        nfs_direct_release_pages(pagevec, npages);
    } while (count != 0 && result >= 0);

    kfree(pagevec);

    if (started)
        return started;
    return result < 0 ? (ssize_t) result : -EFAULT;
}

static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
                          const struct iovec *iov,
                          unsigned long nr_segs,
                          loff_t pos, bool uio)
{
    struct nfs_pageio_descriptor desc;
    ssize_t result = -EINVAL;
    size_t requested_bytes = 0;
    unsigned long seg;

    NFS_PROTO(dreq->inode)->read_pageio_init(&desc, dreq->inode,
                 &nfs_direct_read_completion_ops);
    get_dreq(dreq);
    desc.pg_dreq = dreq;

    for (seg = 0; seg < nr_segs; seg++) {
        const struct iovec *vec = &iov[seg];
        result = nfs_direct_read_schedule_segment(&desc, vec, pos, uio);
        if (result < 0)
            break;
        requested_bytes += result;
        if ((size_t)result < vec->iov_len)
            break;
        pos += vec->iov_len;
    }

    nfs_pageio_complete(&desc);

    /*
     * If no bytes were started, return the error, and let the
     * generic layer handle the completion.
     */
    if (requested_bytes == 0) {
        nfs_direct_req_release(dreq);
        return result < 0 ? result : -EIO;
    }

    if (put_dreq(dreq))
        nfs_direct_complete(dreq);
    return 0;
}

static ssize_t nfs_direct_read(struct kiocb *iocb, const struct iovec *iov,
                   unsigned long nr_segs, loff_t pos, bool uio)
{
    ssize_t result = -ENOMEM;
    struct inode *inode = iocb->ki_filp->f_mapping->host;
    struct nfs_direct_req *dreq;
    struct nfs_lock_context *l_ctx;

    dreq = nfs_direct_req_alloc();
    if (dreq == NULL)
        goto out;

    dreq->inode = inode;
    dreq->bytes_left = iov_length(iov, nr_segs);
    dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
    l_ctx = nfs_get_lock_context(dreq->ctx);
    if (IS_ERR(l_ctx)) {
        result = PTR_ERR(l_ctx);
        goto out_release;
    }
    dreq->l_ctx = l_ctx;
    if (!is_sync_kiocb(iocb))
        dreq->iocb = iocb;

    NFS_I(inode)->read_io += iov_length(iov, nr_segs);
    result = nfs_direct_read_schedule_iovec(dreq, iov, nr_segs, pos, uio);
    if (!result)
        result = nfs_direct_wait(dreq);
out_release:
    nfs_direct_req_release(dreq);
out:
    return result;
}

static void nfs_inode_dio_write_done(struct inode *inode)
{
    nfs_zap_mapping(inode, inode->i_mapping);
    inode_dio_done(inode);
}

#if IS_ENABLED(CONFIG_NFS_V3) || IS_ENABLED(CONFIG_NFS_V4)
static void nfs_direct_write_reschedule(struct nfs_direct_req *dreq)
{
    struct nfs_pageio_descriptor desc;
    struct nfs_page *req, *tmp;
    LIST_HEAD(reqs);
    struct nfs_commit_info cinfo;
    LIST_HEAD(failed);

    nfs_init_cinfo_from_dreq(&cinfo, dreq);
    pnfs_recover_commit_reqs(dreq->inode, &reqs, &cinfo);
    spin_lock(cinfo.lock);
    nfs_scan_commit_list(&cinfo.mds->list, &reqs, &cinfo, 0);
    spin_unlock(cinfo.lock);

    dreq->count = 0;
    get_dreq(dreq);

    NFS_PROTO(dreq->inode)->write_pageio_init(&desc, dreq->inode, FLUSH_STABLE,
                  &nfs_direct_write_completion_ops);
    desc.pg_dreq = dreq;

    list_for_each_entry_safe(req, tmp, &reqs, wb_list) {
        if (!nfs_pageio_add_request(&desc, req)) {
            nfs_list_remove_request(req);
            nfs_list_add_request(req, &failed);
            spin_lock(cinfo.lock);
            dreq->flags = 0;
            dreq->error = -EIO;
            spin_unlock(cinfo.lock);
        }
        nfs_release_request(req);
    }
    nfs_pageio_complete(&desc);

    while (!list_empty(&failed)) {
        req = nfs_list_entry(failed.next);
        nfs_list_remove_request(req);
        nfs_unlock_and_release_request(req);
    }

    if (put_dreq(dreq))
        nfs_direct_write_complete(dreq, dreq->inode);
}

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

    nfs_init_cinfo_from_dreq(&cinfo, dreq);
    if (status < 0) {
        dprintk("NFS: %5u commit failed with error %d.\n",
            data->task.tk_pid, status);
        dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
    } else if (memcmp(&dreq->verf, &data->verf, sizeof(data->verf))) {
        dprintk("NFS: %5u commit verify failed\n", data->task.tk_pid);
        dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
    }

    dprintk("NFS: %5u commit returned %d\n", data->task.tk_pid, status);
    while (!list_empty(&data->pages)) {
        req = nfs_list_entry(data->pages.next);
        nfs_list_remove_request(req);
        if (dreq->flags == NFS_ODIRECT_RESCHED_WRITES) {
            /* Note the rewrite will go through mds */
            nfs_mark_request_commit(req, NULL, &cinfo);
        } else
            nfs_release_request(req);
        nfs_unlock_and_release_request(req);
    }

    if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
        nfs_direct_write_complete(dreq, data->inode);
}

static void nfs_direct_error_cleanup(struct nfs_inode *nfsi)
{
    /* There is no lock to clear */
}

static const struct nfs_commit_completion_ops nfs_direct_commit_completion_ops = {
    .completion = nfs_direct_commit_complete,
    .error_cleanup = nfs_direct_error_cleanup,
};

static void nfs_direct_commit_schedule(struct nfs_direct_req *dreq)
{
    int res;
    struct nfs_commit_info cinfo;
    LIST_HEAD(mds_list);

    nfs_init_cinfo_from_dreq(&cinfo, dreq);
    nfs_scan_commit(dreq->inode, &mds_list, &cinfo);
    res = nfs_generic_commit_list(dreq->inode, &mds_list, 0, &cinfo);
    if (res < 0) /* res == -ENOMEM */
        nfs_direct_write_reschedule(dreq);
}

static void nfs_direct_write_schedule_work(struct work_struct *work)
{
    struct nfs_direct_req *dreq = container_of(work, struct nfs_direct_req, work);
    int flags = dreq->flags;

    dreq->flags = 0;
    switch (flags) {
        case NFS_ODIRECT_DO_COMMIT:
            nfs_direct_commit_schedule(dreq);
            break;
        case NFS_ODIRECT_RESCHED_WRITES:
            nfs_direct_write_reschedule(dreq);
            break;
        default:
            nfs_inode_dio_write_done(dreq->inode);
            nfs_direct_complete(dreq);
    }
}

static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
{
    schedule_work(&dreq->work); /* Calls nfs_direct_write_schedule_work */
}

#else
static void nfs_direct_write_schedule_work(struct work_struct *work)
{
}

static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode *inode)
{
    nfs_inode_dio_write_done(inode);
    nfs_direct_complete(dreq);
}
#endif

/*
 * NB: Return the value of the first error return code.  Subsequent
 *     errors after the first one are ignored.
 */
/*
 * For each wsize'd chunk of the user's buffer, dispatch an NFS WRITE
 * operation.  If nfs_writedata_alloc() or get_user_pages() fails,
 * bail and stop sending more writes.  Write length accounting is
 * handled automatically by nfs_direct_write_result().  Otherwise, if
 * no requests have been sent, just return an error.
 */
static ssize_t nfs_direct_write_schedule_segment(struct nfs_pageio_descriptor *desc,
                         const struct iovec *iov,
                         loff_t pos, bool uio)
{
    struct nfs_direct_req *dreq = desc->pg_dreq;
    struct nfs_open_context *ctx = dreq->ctx;
    struct inode *inode = ctx->dentry->d_inode;
    unsigned long user_addr = (unsigned long)iov->iov_base;
    size_t count = iov->iov_len;
    size_t wsize = NFS_SERVER(inode)->wsize;
    unsigned int pgbase;
    int result;
    ssize_t started = 0;
    struct page **pagevec = NULL;
    unsigned int npages;

    do {
        size_t bytes;
        int i;

        pgbase = user_addr & ~PAGE_MASK;
        bytes = min(max_t(size_t, wsize, PAGE_SIZE), count);

        result = -ENOMEM;
        npages = nfs_page_array_len(pgbase, bytes);
        if (!pagevec)
            pagevec = kmalloc(npages * sizeof(struct page *), GFP_KERNEL);
        if (!pagevec)
            break;

        if (uio) {
            down_read(&current->mm->mmap_sem);
            result = get_user_pages(current, current->mm, user_addr,
                        npages, 0, 0, pagevec, NULL);
            up_read(&current->mm->mmap_sem);
            if (result < 0)
                break;
        } else {
            WARN_ON(npages != 1);
            result = get_kernel_page(user_addr, 0, pagevec);
            if (WARN_ON(result != 1))
                break;
        }

        if ((unsigned)result < npages) {
            bytes = result * PAGE_SIZE;
            if (bytes <= pgbase) {
                nfs_direct_release_pages(pagevec, result);
                break;
            }
            bytes -= pgbase;
            npages = result;
        }

        for (i = 0; i < npages; i++) {
            struct nfs_page *req;
            unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase);

            req = nfs_create_request(dreq->ctx, dreq->inode,
                         pagevec[i],
                         pgbase, req_len);
            if (IS_ERR(req)) {
                result = PTR_ERR(req);
                break;
            }
            nfs_lock_request(req);
            req->wb_index = pos >> PAGE_SHIFT;
            req->wb_offset = pos & ~PAGE_MASK;
            if (!nfs_pageio_add_request(desc, req)) {
                result = desc->pg_error;
                nfs_unlock_and_release_request(req);
                break;
            }
            pgbase = 0;
            bytes -= req_len;
            started += req_len;
            user_addr += req_len;
            pos += req_len;
            count -= req_len;
            dreq->bytes_left -= req_len;
        }
        /* The nfs_page now hold references to these pages */
        nfs_direct_release_pages(pagevec, npages);
    } while (count != 0 && result >= 0);

    kfree(pagevec);

    if (started)
        return started;
    return result < 0 ? (ssize_t) result : -EFAULT;
}

static void nfs_direct_write_completion(struct nfs_pgio_header *hdr)
{
    struct nfs_direct_req *dreq = hdr->dreq;
    struct nfs_commit_info cinfo;
    int bit = -1;
    struct nfs_page *req = nfs_list_entry(hdr->pages.next);

    if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
        goto out_put;

    nfs_init_cinfo_from_dreq(&cinfo, dreq);

    spin_lock(&dreq->lock);

    if (test_bit(NFS_IOHDR_ERROR, &hdr->flags)) {
        dreq->flags = 0;
        dreq->error = hdr->error;
    }
    if (dreq->error != 0)
        bit = NFS_IOHDR_ERROR;
    else {
        dreq->count += hdr->good_bytes;
        if (test_bit(NFS_IOHDR_NEED_RESCHED, &hdr->flags)) {
            dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
            bit = NFS_IOHDR_NEED_RESCHED;
        } else if (test_bit(NFS_IOHDR_NEED_COMMIT, &hdr->flags)) {
            if (dreq->flags == NFS_ODIRECT_RESCHED_WRITES)
                bit = NFS_IOHDR_NEED_RESCHED;
            else if (dreq->flags == 0) {
                memcpy(&dreq->verf, hdr->verf,
                       sizeof(dreq->verf));
                bit = NFS_IOHDR_NEED_COMMIT;
                dreq->flags = NFS_ODIRECT_DO_COMMIT;
            } else if (dreq->flags == NFS_ODIRECT_DO_COMMIT) {
                if (memcmp(&dreq->verf, hdr->verf, sizeof(dreq->verf))) {
                    dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
                    bit = NFS_IOHDR_NEED_RESCHED;
                } else
                    bit = NFS_IOHDR_NEED_COMMIT;
            }
        }
    }
    spin_unlock(&dreq->lock);

    while (!list_empty(&hdr->pages)) {
        req = nfs_list_entry(hdr->pages.next);
        nfs_list_remove_request(req);
        switch (bit) {
        case NFS_IOHDR_NEED_RESCHED:
        case NFS_IOHDR_NEED_COMMIT:
            kref_get(&req->wb_kref);
            nfs_mark_request_commit(req, hdr->lseg, &cinfo);
        }
        nfs_unlock_and_release_request(req);
    }

out_put:
    if (put_dreq(dreq))
        nfs_direct_write_complete(dreq, hdr->inode);
    hdr->release(hdr);
}

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

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

static const struct nfs_pgio_completion_ops nfs_direct_write_completion_ops = {
    .error_cleanup = nfs_write_sync_pgio_error,
    .init_hdr = nfs_direct_pgio_init,
    .completion = nfs_direct_write_completion,
};

static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
                           const struct iovec *iov,
                           unsigned long nr_segs,
                           loff_t pos, bool uio)
{
    struct nfs_pageio_descriptor desc;
    struct inode *inode = dreq->inode;
    ssize_t result = 0;
    size_t requested_bytes = 0;
    unsigned long seg;

    NFS_PROTO(inode)->write_pageio_init(&desc, inode, FLUSH_COND_STABLE,
                  &nfs_direct_write_completion_ops);
    desc.pg_dreq = dreq;
    get_dreq(dreq);
    atomic_inc(&inode->i_dio_count);

    NFS_I(dreq->inode)->write_io += iov_length(iov, nr_segs);
    for (seg = 0; seg < nr_segs; seg++) {
        const struct iovec *vec = &iov[seg];
        result = nfs_direct_write_schedule_segment(&desc, vec, pos, uio);
        if (result < 0)
            break;
        requested_bytes += result;
        if ((size_t)result < vec->iov_len)
            break;
        pos += vec->iov_len;
    }
    nfs_pageio_complete(&desc);

    /*
     * If no bytes were started, return the error, and let the
     * generic layer handle the completion.
     */
    if (requested_bytes == 0) {
        inode_dio_done(inode);
        nfs_direct_req_release(dreq);
        return result < 0 ? result : -EIO;
    }

    if (put_dreq(dreq))
        nfs_direct_write_complete(dreq, dreq->inode);
    return 0;
}

static ssize_t nfs_direct_write(struct kiocb *iocb, const struct iovec *iov,
                unsigned long nr_segs, loff_t pos,
                size_t count, bool uio)
{
    ssize_t result = -ENOMEM;
    struct inode *inode = iocb->ki_filp->f_mapping->host;
    struct nfs_direct_req *dreq;
    struct nfs_lock_context *l_ctx;

    dreq = nfs_direct_req_alloc();
    if (!dreq)
        goto out;

    dreq->inode = inode;
    dreq->bytes_left = count;
    dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
    l_ctx = nfs_get_lock_context(dreq->ctx);
    if (IS_ERR(l_ctx)) {
        result = PTR_ERR(l_ctx);
        goto out_release;
    }
    dreq->l_ctx = l_ctx;
    if (!is_sync_kiocb(iocb))
        dreq->iocb = iocb;

    result = nfs_direct_write_schedule_iovec(dreq, iov, nr_segs, pos, uio);
    if (!result)
        result = nfs_direct_wait(dreq);
out_release:
    nfs_direct_req_release(dreq);
out:
    return result;
}

ssize_t nfs_file_direct_read(struct kiocb *iocb, const struct iovec *iov,
                unsigned long nr_segs, loff_t pos, bool uio)
{
    ssize_t retval = -EINVAL;
    struct file *file = iocb->ki_filp;
    struct address_space *mapping = file->f_mapping;
    size_t count;

    count = iov_length(iov, nr_segs);
    nfs_add_stats(mapping->host, NFSIOS_DIRECTREADBYTES, count);

    dfprintk(FILE, "NFS: direct read(%s/%s, %zd@%Ld)\n",
        file->f_path.dentry->d_parent->d_name.name,
        file->f_path.dentry->d_name.name,
        count, (long long) pos);

    retval = 0;
    if (!count)
        goto out;

    retval = nfs_sync_mapping(mapping);
    if (retval)
        goto out;

    task_io_account_read(count);

    retval = nfs_direct_read(iocb, iov, nr_segs, pos, uio);
    if (retval > 0)
        iocb->ki_pos = pos + retval;

out:
    return retval;
}

ssize_t nfs_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
                unsigned long nr_segs, loff_t pos, bool uio)
{
    ssize_t retval = -EINVAL;
    struct file *file = iocb->ki_filp;
    struct address_space *mapping = file->f_mapping;
    size_t count;

    count = iov_length(iov, nr_segs);
    nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES, count);

    dfprintk(FILE, "NFS: direct write(%s/%s, %zd@%Ld)\n",
        file->f_path.dentry->d_parent->d_name.name,
        file->f_path.dentry->d_name.name,
        count, (long long) pos);

    retval = generic_write_checks(file, &pos, &count, 0);
    if (retval)
        goto out;

    retval = -EINVAL;
    if ((ssize_t) count < 0)
        goto out;
    retval = 0;
    if (!count)
        goto out;

    retval = nfs_sync_mapping(mapping);
    if (retval)
        goto out;

    task_io_account_write(count);

    retval = nfs_direct_write(iocb, iov, nr_segs, pos, count, uio);
    if (retval > 0) {
        struct inode *inode = mapping->host;

        iocb->ki_pos = pos + retval;
        spin_lock(&inode->i_lock);
        if (i_size_read(inode) < iocb->ki_pos)
            i_size_write(inode, iocb->ki_pos);
        spin_unlock(&inode->i_lock);
    }
out:
    return retval;
}

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

    return 0;
}

void nfs_destroy_directcache(void)
{
    kmem_cache_destroy(nfs_direct_cachep);
}