// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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
 * 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 <linux/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;

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 */

        loff_t                  io_start;       /* Start offset for I/O */
        ssize_t                 count,          /* bytes actually processed */
                                max_count,      /* max expected count */
                                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;
        /* for write */
#define NFS_ODIRECT_DO_COMMIT           (1)     /* an unstable reply was received */
#define NFS_ODIRECT_RESCHED_WRITES      (2)     /* write verification failed */
        /* for read */
#define NFS_ODIRECT_SHOULD_DIRTY        (3)     /* dirty user-space page after read */
        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);
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);
}

static void
nfs_direct_handle_truncated(struct nfs_direct_req *dreq,
                            const struct nfs_pgio_header *hdr,
                            ssize_t dreq_len)
{
        if (!(test_bit(NFS_IOHDR_ERROR, &hdr->flags) ||
              test_bit(NFS_IOHDR_EOF, &hdr->flags)))
                return;
        if (dreq->max_count >= dreq_len) {
                dreq->max_count = dreq_len;
                if (dreq->count > dreq_len)
                        dreq->count = dreq_len;

                if (test_bit(NFS_IOHDR_ERROR, &hdr->flags))
                        dreq->error = hdr->error;
                else /* Clear outstanding error if this is EOF */
                        dreq->error = 0;
        }
}

static void
nfs_direct_count_bytes(struct nfs_direct_req *dreq,
                       const struct nfs_pgio_header *hdr)
{
        loff_t hdr_end = hdr->io_start + hdr->good_bytes;
        ssize_t dreq_len = 0;

        if (hdr_end > dreq->io_start)
                dreq_len = hdr_end - dreq->io_start;

        nfs_direct_handle_truncated(dreq, hdr, dreq_len);

        if (dreq_len > dreq->max_count)
                dreq_len = dreq->max_count;

        if (dreq->count < dreq_len)
                dreq->count = dreq_len;
}

/*
 * nfs_direct_select_verf - select the right verifier
 * @dreq - direct request possibly spanning multiple servers
 * @ds_clp - nfs_client of data server or NULL if MDS / non-pnfs
 * @commit_idx - commit bucket index for the DS
 *
 * returns the correct verifier to use given the role of the server
 */
static struct nfs_writeverf *
nfs_direct_select_verf(struct nfs_direct_req *dreq,
                       struct nfs_client *ds_clp,
                       int commit_idx)
{
        struct nfs_writeverf *verfp = &dreq->verf;

#ifdef CONFIG_NFS_V4_1
        /*
         * pNFS is in use, use the DS verf except commit_through_mds is set
         * for layout segment where nbuckets is zero.
         */
        if (ds_clp && dreq->ds_cinfo.nbuckets > 0) {
                if (commit_idx >= 0 && commit_idx < dreq->ds_cinfo.nbuckets)
                        verfp = &dreq->ds_cinfo.buckets[commit_idx].direct_verf;
                else
                        WARN_ON_ONCE(1);
        }
#endif
        return verfp;
}


/*
 * nfs_direct_set_hdr_verf - set the write/commit verifier
 * @dreq - direct request possibly spanning multiple servers
 * @hdr - pageio header to validate against previously seen verfs
 *
 * Set the server's (MDS or DS) "seen" verifier
 */
static void nfs_direct_set_hdr_verf(struct nfs_direct_req *dreq,
                                    struct nfs_pgio_header *hdr)
{
        struct nfs_writeverf *verfp;

        verfp = nfs_direct_select_verf(dreq, hdr->ds_clp, hdr->ds_commit_idx);
        WARN_ON_ONCE(verfp->committed >= 0);
        memcpy(verfp, &hdr->verf, sizeof(struct nfs_writeverf));
        WARN_ON_ONCE(verfp->committed < 0);
}

static int nfs_direct_cmp_verf(const struct nfs_writeverf *v1,
                const struct nfs_writeverf *v2)
{
        return nfs_write_verifier_cmp(&v1->verifier, &v2->verifier);
}

/*
 * nfs_direct_cmp_hdr_verf - compare verifier for pgio header
 * @dreq - direct request possibly spanning multiple servers
 * @hdr - pageio header to validate against previously seen verf
 *
 * set the server's "seen" verf if not initialized.
 * returns result of comparison between @hdr->verf and the "seen"
 * verf of the server used by @hdr (DS or MDS)
 */
static int nfs_direct_set_or_cmp_hdr_verf(struct nfs_direct_req *dreq,
                                          struct nfs_pgio_header *hdr)
{
        struct nfs_writeverf *verfp;

        verfp = nfs_direct_select_verf(dreq, hdr->ds_clp, hdr->ds_commit_idx);
        if (verfp->committed < 0) {
                nfs_direct_set_hdr_verf(dreq, hdr);
                return 0;
        }
        return nfs_direct_cmp_verf(verfp, &hdr->verf);
}

/*
 * nfs_direct_cmp_commit_data_verf - compare verifier for commit data
 * @dreq - direct request possibly spanning multiple servers
 * @data - commit data to validate against previously seen verf
 *
 * returns result of comparison between @data->verf and the verf of
 * the server used by @data (DS or MDS)
 */
static int nfs_direct_cmp_commit_data_verf(struct nfs_direct_req *dreq,
                                           struct nfs_commit_data *data)
{
        struct nfs_writeverf *verfp;

        verfp = nfs_direct_select_verf(dreq, data->ds_clp,
                                         data->ds_commit_index);

        /* verifier not set so always fail */
        if (verfp->committed < 0)
                return 1;

        return nfs_direct_cmp_verf(verfp, &data->verf);
}

/**
 * nfs_direct_IO - NFS address space operation for direct I/O
 * @iocb: target I/O control block
 * @iter: I/O buffer
 *
 * The presence of this routine in the address space ops vector means
 * the NFS client supports direct I/O. However, for most direct IO, we
 * shunt off direct read and write requests before the VFS gets them,
 * so this method is only ever called for swap.
 */
ssize_t nfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
{
        struct inode *inode = iocb->ki_filp->f_mapping->host;

        /* we only support swap file calling nfs_direct_IO */
        if (!IS_SWAPFILE(inode))
                return 0;

        VM_BUG_ON(iov_iter_count(iter) != PAGE_SIZE);

        if (iov_iter_rw(iter) == READ)
                return nfs_file_direct_read(iocb, iter);
        return nfs_file_direct_write(iocb, iter);
}

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

void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
                              struct nfs_direct_req *dreq)
{
        cinfo->inode = dreq->inode;
        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);
        dreq->verf.committed = NFS_INVALID_STABLE_HOW;  /* not set yet */
        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);

        nfs_free_pnfs_ds_cinfo(&dreq->ds_cinfo);
        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->count;
                WARN_ON_ONCE(dreq->count < 0);
        }
        if (!result)
                result = dreq->error;

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)
{
        struct inode *inode = dreq->inode;

        inode_dio_end(inode);

        if (dreq->iocb) {
                long res = (long) dreq->error;
                if (dreq->count != 0) {
                        res = (long) dreq->count;
                        WARN_ON_ONCE(dreq->count < 0);
                }
                dreq->iocb->ki_complete(dreq->iocb, res, 0);
        }

        complete(&dreq->completion);

        nfs_direct_req_release(dreq);
}

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

        spin_lock(&dreq->lock);
        if (test_bit(NFS_IOHDR_REDO, &hdr->flags)) {
                spin_unlock(&dreq->lock);
                goto out_put;
        }

        nfs_direct_count_bytes(dreq, hdr);
        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 (!PageCompound(page) && bytes < hdr->good_bytes &&
                    (dreq->flags == NFS_ODIRECT_SHOULD_DIRTY))
                        set_page_dirty(page);
                bytes += req->wb_bytes;
                nfs_list_remove_request(req);
                nfs_release_request(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, int error)
{
        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_iovec(struct nfs_direct_req *dreq,
                                              struct iov_iter *iter,
                                              loff_t pos)
{
        struct nfs_pageio_descriptor desc;
        struct inode *inode = dreq->inode;
        ssize_t result = -EINVAL;
        size_t requested_bytes = 0;
        size_t rsize = max_t(size_t, NFS_SERVER(inode)->rsize, PAGE_SIZE);

        nfs_pageio_init_read(&desc, dreq->inode, false,
                             &nfs_direct_read_completion_ops);
        get_dreq(dreq);
        desc.pg_dreq = dreq;
        inode_dio_begin(inode);

        while (iov_iter_count(iter)) {
                struct page **pagevec;
                size_t bytes;
                size_t pgbase;
                unsigned npages, i;

                result = iov_iter_get_pages_alloc(iter, &pagevec, 
                                                  rsize, &pgbase);
                if (result < 0)
                        break;
        
                bytes = result;
                iov_iter_advance(iter, bytes);
                npages = (result + pgbase + PAGE_SIZE - 1) / PAGE_SIZE;
                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, 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;
                        requested_bytes += req_len;
                        pos += req_len;
                        dreq->bytes_left -= req_len;
                }
                nfs_direct_release_pages(pagevec, npages);
                kvfree(pagevec);
                if (result < 0)
                        break;
        }

        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_end(inode);
                nfs_direct_req_release(dreq);
                return result < 0 ? result : -EIO;
        }

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

/**
 * nfs_file_direct_read - file direct read operation for NFS files
 * @iocb: target I/O control block
 * @iter: vector of user buffers into which to read data
 *
 * 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.  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, struct iov_iter *iter)
{
        struct file *file = iocb->ki_filp;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct nfs_direct_req *dreq;
        struct nfs_lock_context *l_ctx;
        ssize_t result = -EINVAL, requested;
        size_t count = iov_iter_count(iter);
        nfs_add_stats(mapping->host, NFSIOS_DIRECTREADBYTES, count);

        dfprintk(FILE, "NFS: direct read(%pD2, %zd@%Ld)\n",
                file, count, (long long) iocb->ki_pos);

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

        task_io_account_read(count);

        result = -ENOMEM;
        dreq = nfs_direct_req_alloc();
        if (dreq == NULL)
                goto out;

        dreq->inode = inode;
        dreq->bytes_left = dreq->max_count = count;
        dreq->io_start = iocb->ki_pos;
        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;

        if (iter_is_iovec(iter))
                dreq->flags = NFS_ODIRECT_SHOULD_DIRTY;

        nfs_start_io_direct(inode);

        NFS_I(inode)->read_io += count;
        requested = nfs_direct_read_schedule_iovec(dreq, iter, iocb->ki_pos);

        nfs_end_io_direct(inode);

        if (requested > 0) {
                result = nfs_direct_wait(dreq);
                if (result > 0) {
                        requested -= result;
                        iocb->ki_pos += result;
                }
                iov_iter_revert(iter, requested);
        } else {
                result = requested;
        }

out_release:
        nfs_direct_req_release(dreq);
out:
        return result;
}

static void
nfs_direct_write_scan_commit_list(struct inode *inode,
                                  struct list_head *list,
                                  struct nfs_commit_info *cinfo)
{
        mutex_lock(&NFS_I(cinfo->inode)->commit_mutex);
#ifdef CONFIG_NFS_V4_1
        if (cinfo->ds != NULL && cinfo->ds->nwritten != 0)
                NFS_SERVER(inode)->pnfs_curr_ld->recover_commit_reqs(list, cinfo);
#endif
        nfs_scan_commit_list(&cinfo->mds->list, list, cinfo, 0);
        mutex_unlock(&NFS_I(cinfo->inode)->commit_mutex);
}

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);
        nfs_direct_write_scan_commit_list(dreq->inode, &reqs, &cinfo);

        dreq->count = 0;
        dreq->max_count = 0;
        list_for_each_entry(req, &reqs, wb_list)
                dreq->max_count += req->wb_bytes;
        dreq->verf.committed = NFS_INVALID_STABLE_HOW;
        nfs_clear_pnfs_ds_commit_verifiers(&dreq->ds_cinfo);
        get_dreq(dreq);

        nfs_pageio_init_write(&desc, dreq->inode, FLUSH_STABLE, false,
                              &nfs_direct_write_completion_ops);
        desc.pg_dreq = dreq;

        list_for_each_entry_safe(req, tmp, &reqs, wb_list) {
                /* Bump the transmission count */
                req->wb_nio++;
                if (!nfs_pageio_add_request(&desc, req)) {
                        nfs_list_move_request(req, &failed);
                        spin_lock(&cinfo.inode->i_lock);
                        dreq->flags = 0;
                        if (desc.pg_error < 0)
                                dreq->error = desc.pg_error;
                        else
                                dreq->error = -EIO;
                        spin_unlock(&cinfo.inode->i_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);
}

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 || nfs_direct_cmp_commit_data_verf(dreq, data))
                dreq->flags = NFS_ODIRECT_RESCHED_WRITES;

        while (!list_empty(&data->pages)) {
                req = nfs_list_entry(data->pages.next);
                nfs_list_remove_request(req);
                if (dreq->flags == NFS_ODIRECT_RESCHED_WRITES) {
                        /*
                         * Despite the reboot, the write was successful,
                         * so reset wb_nio.
                         */
                        req->wb_nio = 0;
                        /* Note the rewrite will go through mds */
                        nfs_mark_request_commit(req, NULL, &cinfo, 0);
                } 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);
}

static void nfs_direct_resched_write(struct nfs_commit_info *cinfo,
                struct nfs_page *req)
{
        struct nfs_direct_req *dreq = cinfo->dreq;

        spin_lock(&dreq->lock);
        dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
        spin_unlock(&dreq->lock);
        nfs_mark_request_commit(req, NULL, cinfo, 0);
}

static const struct nfs_commit_completion_ops nfs_direct_commit_completion_ops = {
        .completion = nfs_direct_commit_complete,
        .resched_write = nfs_direct_resched_write,
};

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_zap_mapping(dreq->inode, dreq->inode->i_mapping);
                        nfs_direct_complete(dreq);
        }
}

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

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

        nfs_init_cinfo_from_dreq(&cinfo, dreq);

        spin_lock(&dreq->lock);
        if (test_bit(NFS_IOHDR_REDO, &hdr->flags)) {
                spin_unlock(&dreq->lock);
                goto out_put;
        }

        nfs_direct_count_bytes(dreq, hdr);
        if (hdr->good_bytes != 0) {
                if (nfs_write_need_commit(hdr)) {
                        if (dreq->flags == NFS_ODIRECT_RESCHED_WRITES)
                                request_commit = true;
                        else if (dreq->flags == 0) {
                                nfs_direct_set_hdr_verf(dreq, hdr);
                                request_commit = true;
                                dreq->flags = NFS_ODIRECT_DO_COMMIT;
                        } else if (dreq->flags == NFS_ODIRECT_DO_COMMIT) {
                                request_commit = true;
                                if (nfs_direct_set_or_cmp_hdr_verf(dreq, hdr))
                                        dreq->flags =
                                                NFS_ODIRECT_RESCHED_WRITES;
                        }
                }
        }
        spin_unlock(&dreq->lock);

        while (!list_empty(&hdr->pages)) {

                req = nfs_list_entry(hdr->pages.next);
                nfs_list_remove_request(req);
                if (request_commit) {
                        kref_get(&req->wb_kref);
                        nfs_mark_request_commit(req, hdr->lseg, &cinfo,
                                hdr->ds_commit_idx);
                }
                nfs_unlock_and_release_request(req);
        }

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

static void nfs_write_sync_pgio_error(struct list_head *head, int error)
{
        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 void nfs_direct_write_reschedule_io(struct nfs_pgio_header *hdr)
{
        struct nfs_direct_req *dreq = hdr->dreq;

        spin_lock(&dreq->lock);
        if (dreq->error == 0) {
                dreq->flags = NFS_ODIRECT_RESCHED_WRITES;
                /* fake unstable write to let common nfs resend pages */
                hdr->verf.committed = NFS_UNSTABLE;
                hdr->good_bytes = hdr->args.count;
        }
        spin_unlock(&dreq->lock);
}

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,
        .reschedule_io = nfs_direct_write_reschedule_io,
};


/*
 * 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_iovec(struct nfs_direct_req *dreq,
                                               struct iov_iter *iter,
                                               loff_t pos)
{
        struct nfs_pageio_descriptor desc;
        struct inode *inode = dreq->inode;
        ssize_t result = 0;
        size_t requested_bytes = 0;
        size_t wsize = max_t(size_t, NFS_SERVER(inode)->wsize, PAGE_SIZE);

        nfs_pageio_init_write(&desc, inode, FLUSH_COND_STABLE, false,
                              &nfs_direct_write_completion_ops);
        desc.pg_dreq = dreq;
        get_dreq(dreq);
        inode_dio_begin(inode);

        NFS_I(inode)->write_io += iov_iter_count(iter);
        while (iov_iter_count(iter)) {
                struct page **pagevec;
                size_t bytes;
                size_t pgbase;
                unsigned npages, i;

                result = iov_iter_get_pages_alloc(iter, &pagevec, 
                                                  wsize, &pgbase);
                if (result < 0)
                        break;

                bytes = result;
                iov_iter_advance(iter, bytes);
                npages = (result + pgbase + PAGE_SIZE - 1) / PAGE_SIZE;
                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, pagevec[i],
                                                 pgbase, req_len);
                        if (IS_ERR(req)) {
                                result = PTR_ERR(req);
                                break;
                        }

                        if (desc.pg_error < 0) {
                                nfs_free_request(req);
                                result = desc.pg_error;
                                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;
                        requested_bytes += req_len;
                        pos += req_len;
                        dreq->bytes_left -= req_len;
                }
                nfs_direct_release_pages(pagevec, npages);
                kvfree(pagevec);
                if (result < 0)
                        break;
        }
        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_end(inode);
                nfs_direct_req_release(dreq);
                return result < 0 ? result : -EIO;
        }

        if (put_dreq(dreq))
                nfs_direct_write_complete(dreq);
        return requested_bytes;
}

/**
 * nfs_file_direct_write - file direct write operation for NFS files
 * @iocb: target I/O control block
 * @iter: vector of user buffers from which to write data
 *
 * 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 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, struct iov_iter *iter)
{
        ssize_t result = -EINVAL, requested;
        size_t count;
        struct file *file = iocb->ki_filp;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        struct nfs_direct_req *dreq;
        struct nfs_lock_context *l_ctx;
        loff_t pos, end;

        dfprintk(FILE, "NFS: direct write(%pD2, %zd@%Ld)\n",
                file, iov_iter_count(iter), (long long) iocb->ki_pos);

        result = generic_write_checks(iocb, iter);
        if (result <= 0)
                return result;
        count = result;
        nfs_add_stats(mapping->host, NFSIOS_DIRECTWRITTENBYTES, count);

        pos = iocb->ki_pos;
        end = (pos + iov_iter_count(iter) - 1) >> PAGE_SHIFT;

        task_io_account_write(count);

        result = -ENOMEM;
        dreq = nfs_direct_req_alloc();
        if (!dreq)
                goto out;

        dreq->inode = inode;
        dreq->bytes_left = dreq->max_count = count;
        dreq->io_start = pos;
        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_start_io_direct(inode);

        requested = nfs_direct_write_schedule_iovec(dreq, iter, pos);

        if (mapping->nrpages) {
                invalidate_inode_pages2_range(mapping,
                                              pos >> PAGE_SHIFT, end);
        }

        nfs_end_io_direct(inode);

        if (requested > 0) {
                result = nfs_direct_wait(dreq);
                if (result > 0) {
                        requested -= result;
                        iocb->ki_pos = pos + result;
                        /* XXX: should check the generic_write_sync retval */
                        generic_write_sync(iocb, result);
                }
                iov_iter_revert(iter, requested);
        } else {
                result = requested;
        }
out_release:
        nfs_direct_req_release(dreq);
out:
        return result;
}

/**
 * nfs_init_directcache - create a slab cache for nfs_direct_req structures
 *
 */
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;
}

/**
 * nfs_destroy_directcache - destroy the slab cache for nfs_direct_req structures
 *
 */
void nfs_destroy_directcache(void)
{
        kmem_cache_destroy(nfs_direct_cachep);
}