/*
 * linux/fs/nfs/pagelist.c
 *
 * A set of helper functions for managing NFS read and write requests.
 * The main purpose of these routines is to provide support for the
 * coalescing of several requests into a single RPC call.
 *
 * Copyright 2000, 2001 (c) Trond Myklebust <trond.myklebust@fys.uio.no>
 *
 */

#include <linux/slab.h>
#include <linux/file.h>
#include <linux/sched.h>
#include <linux/sunrpc/clnt.h>
#include <linux/nfs.h>
#include <linux/nfs3.h>
#include <linux/nfs4.h>
#include <linux/nfs_page.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/export.h>

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

static struct kmem_cache *nfs_page_cachep;

static inline struct nfs_page *
nfs_page_alloc(void)
{
        struct nfs_page *p = kmem_cache_zalloc(nfs_page_cachep, GFP_KERNEL);
        if (p)
                INIT_LIST_HEAD(&p->wb_list);
        return p;
}

static inline void
nfs_page_free(struct nfs_page *p)
{
        kmem_cache_free(nfs_page_cachep, p);
}

/**
 * nfs_create_request - Create an NFS read/write request.
 * @ctx: open context to use
 * @inode: inode to which the request is attached
 * @page: page to write
 * @offset: starting offset within the page for the write
 * @count: number of bytes to read/write
 *
 * The page must be locked by the caller. This makes sure we never
 * create two different requests for the same page.
 * User should ensure it is safe to sleep in this function.
 */
struct nfs_page *
nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
                   struct page *page,
                   unsigned int offset, unsigned int count)
{
        struct nfs_page         *req;

        /* try to allocate the request struct */
        req = nfs_page_alloc();
        if (req == NULL)
                return ERR_PTR(-ENOMEM);

        /* get lock context early so we can deal with alloc failures */
        req->wb_lock_context = nfs_get_lock_context(ctx);
        if (req->wb_lock_context == NULL) {
                nfs_page_free(req);
                return ERR_PTR(-ENOMEM);
        }

        /* Initialize the request struct. Initially, we assume a
         * long write-back delay. This will be adjusted in
         * update_nfs_request below if the region is not locked. */
        req->wb_page    = page;
        atomic_set(&req->wb_complete, 0);
        req->wb_index   = page->index;
        page_cache_get(page);
        BUG_ON(PagePrivate(page));
        BUG_ON(!PageLocked(page));
        BUG_ON(page->mapping->host != inode);
        req->wb_offset  = offset;
        req->wb_pgbase  = offset;
        req->wb_bytes   = count;
        req->wb_context = get_nfs_open_context(ctx);
        kref_init(&req->wb_kref);
        return req;
}

/**
 * nfs_unlock_request - Unlock request and wake up sleepers.
 * @req:
 */
void nfs_unlock_request(struct nfs_page *req)
{
        if (!NFS_WBACK_BUSY(req)) {
                printk(KERN_ERR "NFS: Invalid unlock attempted\n");
                BUG();
        }
        smp_mb__before_clear_bit();
        clear_bit(PG_BUSY, &req->wb_flags);
        smp_mb__after_clear_bit();
        wake_up_bit(&req->wb_flags, PG_BUSY);
        nfs_release_request(req);
}

/*
 * nfs_clear_request - Free up all resources allocated to the request
 * @req:
 *
 * Release page and open context resources associated with a read/write
 * request after it has completed.
 */
static void nfs_clear_request(struct nfs_page *req)
{
        struct page *page = req->wb_page;
        struct nfs_open_context *ctx = req->wb_context;
        struct nfs_lock_context *l_ctx = req->wb_lock_context;

        if (page != NULL) {
                page_cache_release(page);
                req->wb_page = NULL;
        }
        if (l_ctx != NULL) {
                nfs_put_lock_context(l_ctx);
                req->wb_lock_context = NULL;
        }
        if (ctx != NULL) {
                put_nfs_open_context(ctx);
                req->wb_context = NULL;
        }
}


/**
 * nfs_release_request - Release the count on an NFS read/write request
 * @req: request to release
 *
 * Note: Should never be called with the spinlock held!
 */
static void nfs_free_request(struct kref *kref)
{
        struct nfs_page *req = container_of(kref, struct nfs_page, wb_kref);

        /* Release struct file and open context */
        nfs_clear_request(req);
        nfs_page_free(req);
}

void nfs_release_request(struct nfs_page *req)
{
        kref_put(&req->wb_kref, nfs_free_request);
}

static int nfs_wait_bit_uninterruptible(void *word)
{
        io_schedule();
        return 0;
}

/**
 * nfs_wait_on_request - Wait for a request to complete.
 * @req: request to wait upon.
 *
 * Interruptible by fatal signals only.
 * The user is responsible for holding a count on the request.
 */
int
nfs_wait_on_request(struct nfs_page *req)
{
        return wait_on_bit(&req->wb_flags, PG_BUSY,
                        nfs_wait_bit_uninterruptible,
                        TASK_UNINTERRUPTIBLE);
}

bool nfs_generic_pg_test(struct nfs_pageio_descriptor *desc, struct nfs_page *prev, struct nfs_page *req)
{
        /*
         * FIXME: ideally we should be able to coalesce all requests
         * that are not block boundary aligned, but currently this
         * is problematic for the case of bsize < PAGE_CACHE_SIZE,
         * since nfs_flush_multi and nfs_pagein_multi assume you
         * can have only one struct nfs_page.
         */
        if (desc->pg_bsize < PAGE_SIZE)
                return 0;

        return desc->pg_count + req->wb_bytes <= desc->pg_bsize;
}
EXPORT_SYMBOL_GPL(nfs_generic_pg_test);

/**
 * nfs_pageio_init - initialise a page io descriptor
 * @desc: pointer to descriptor
 * @inode: pointer to inode
 * @doio: pointer to io function
 * @bsize: io block size
 * @io_flags: extra parameters for the io function
 */
void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
                     struct inode *inode,
                     const struct nfs_pageio_ops *pg_ops,
                     size_t bsize,
                     int io_flags)
{
        INIT_LIST_HEAD(&desc->pg_list);
        desc->pg_bytes_written = 0;
        desc->pg_count = 0;
        desc->pg_bsize = bsize;
        desc->pg_base = 0;
        desc->pg_moreio = 0;
        desc->pg_recoalesce = 0;
        desc->pg_inode = inode;
        desc->pg_ops = pg_ops;
        desc->pg_ioflags = io_flags;
        desc->pg_error = 0;
        desc->pg_lseg = NULL;
}

/**
 * nfs_can_coalesce_requests - test two requests for compatibility
 * @prev: pointer to nfs_page
 * @req: pointer to nfs_page
 *
 * The nfs_page structures 'prev' and 'req' are compared to ensure that the
 * page data area they describe is contiguous, and that their RPC
 * credentials, NFSv4 open state, and lockowners are the same.
 *
 * Return 'true' if this is the case, else return 'false'.
 */
static bool nfs_can_coalesce_requests(struct nfs_page *prev,
                                      struct nfs_page *req,
                                      struct nfs_pageio_descriptor *pgio)
{
        if (req->wb_context->cred != prev->wb_context->cred)
                return false;
        if (req->wb_lock_context->lockowner != prev->wb_lock_context->lockowner)
                return false;
        if (req->wb_context->state != prev->wb_context->state)
                return false;
        if (req->wb_index != (prev->wb_index + 1))
                return false;
        if (req->wb_pgbase != 0)
                return false;
        if (prev->wb_pgbase + prev->wb_bytes != PAGE_CACHE_SIZE)
                return false;
        return pgio->pg_ops->pg_test(pgio, prev, req);
}

/**
 * nfs_pageio_do_add_request - Attempt to coalesce a request into a page list.
 * @desc: destination io descriptor
 * @req: request
 *
 * Returns true if the request 'req' was successfully coalesced into the
 * existing list of pages 'desc'.
 */
static int nfs_pageio_do_add_request(struct nfs_pageio_descriptor *desc,
                                     struct nfs_page *req)
{
        if (desc->pg_count != 0) {
                struct nfs_page *prev;

                prev = nfs_list_entry(desc->pg_list.prev);
                if (!nfs_can_coalesce_requests(prev, req, desc))
                        return 0;
        } else {
                if (desc->pg_ops->pg_init)
                        desc->pg_ops->pg_init(desc, req);
                desc->pg_base = req->wb_pgbase;
        }
        nfs_list_remove_request(req);
        nfs_list_add_request(req, &desc->pg_list);
        desc->pg_count += req->wb_bytes;
        return 1;
}

/*
 * Helper for nfs_pageio_add_request and nfs_pageio_complete
 */
static void nfs_pageio_doio(struct nfs_pageio_descriptor *desc)
{
        if (!list_empty(&desc->pg_list)) {
                int error = desc->pg_ops->pg_doio(desc);
                if (error < 0)
                        desc->pg_error = error;
                else
                        desc->pg_bytes_written += desc->pg_count;
        }
        if (list_empty(&desc->pg_list)) {
                desc->pg_count = 0;
                desc->pg_base = 0;
        }
}

/**
 * nfs_pageio_add_request - Attempt to coalesce a request into a page list.
 * @desc: destination io descriptor
 * @req: request
 *
 * Returns true if the request 'req' was successfully coalesced into the
 * existing list of pages 'desc'.
 */
static int __nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
                           struct nfs_page *req)
{
        while (!nfs_pageio_do_add_request(desc, req)) {
                desc->pg_moreio = 1;
                nfs_pageio_doio(desc);
                if (desc->pg_error < 0)
                        return 0;
                desc->pg_moreio = 0;
                if (desc->pg_recoalesce)
                        return 0;
        }
        return 1;
}

static int nfs_do_recoalesce(struct nfs_pageio_descriptor *desc)
{
        LIST_HEAD(head);

        do {
                list_splice_init(&desc->pg_list, &head);
                desc->pg_bytes_written -= desc->pg_count;
                desc->pg_count = 0;
                desc->pg_base = 0;
                desc->pg_recoalesce = 0;

                while (!list_empty(&head)) {
                        struct nfs_page *req;

                        req = list_first_entry(&head, struct nfs_page, wb_list);
                        nfs_list_remove_request(req);
                        if (__nfs_pageio_add_request(desc, req))
                                continue;
                        if (desc->pg_error < 0)
                                return 0;
                        break;
                }
        } while (desc->pg_recoalesce);
        return 1;
}

int nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
                struct nfs_page *req)
{
        int ret;

        do {
                ret = __nfs_pageio_add_request(desc, req);
                if (ret)
                        break;
                if (desc->pg_error < 0)
                        break;
                ret = nfs_do_recoalesce(desc);
        } while (ret);
        return ret;
}

/**
 * nfs_pageio_complete - Complete I/O on an nfs_pageio_descriptor
 * @desc: pointer to io descriptor
 */
void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
{
        for (;;) {
                nfs_pageio_doio(desc);
                if (!desc->pg_recoalesce)
                        break;
                if (!nfs_do_recoalesce(desc))
                        break;
        }
}

/**
 * nfs_pageio_cond_complete - Conditional I/O completion
 * @desc: pointer to io descriptor
 * @index: page index
 *
 * It is important to ensure that processes don't try to take locks
 * on non-contiguous ranges of pages as that might deadlock. This
 * function should be called before attempting to wait on a locked
 * nfs_page. It will complete the I/O if the page index 'index'
 * is not contiguous with the existing list of pages in 'desc'.
 */
void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
{
        if (!list_empty(&desc->pg_list)) {
                struct nfs_page *prev = nfs_list_entry(desc->pg_list.prev);
                if (index != prev->wb_index + 1)
                        nfs_pageio_complete(desc);
        }
}

int __init nfs_init_nfspagecache(void)
{
        nfs_page_cachep = kmem_cache_create("nfs_page",
                                            sizeof(struct nfs_page),
                                            0, SLAB_HWCACHE_ALIGN,
                                            NULL);
        if (nfs_page_cachep == NULL)
                return -ENOMEM;

        return 0;
}

void nfs_destroy_nfspagecache(void)
{
        kmem_cache_destroy(nfs_page_cachep);
}