/*
 * 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/nfs3.h>
#include <linux/nfs4.h>
#include <linux/nfs_page.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>

#include "internal.h"

static struct kmem_cache *nfs_page_cachep;

static inline struct nfs_page *
nfs_page_alloc(void)
{
        struct nfs_page *p;
        p = kmem_cache_alloc(nfs_page_cachep, GFP_KERNEL);
        if (p) {
                memset(p, 0, sizeof(*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.
 * @file: file descriptor 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;

        for (;;) {
                /* try to allocate the request struct */
                req = nfs_page_alloc();
                if (req != NULL)
                        break;

                if (fatal_signal_pending(current))
                        return ERR_PTR(-ERESTARTSYS);
                yield();
        }

        /* 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_set_page_tag_locked - Tag a request as locked
 * @req:
 */
int nfs_set_page_tag_locked(struct nfs_page *req)
{
        struct nfs_inode *nfsi = NFS_I(req->wb_context->path.dentry->d_inode);

        if (!nfs_lock_request_dontget(req))
                return 0;
        if (req->wb_page != NULL)
                radix_tree_tag_set(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
        return 1;
}

/**
 * nfs_clear_page_tag_locked - Clear request tag and wake up sleepers
 */
void nfs_clear_page_tag_locked(struct nfs_page *req)
{
        struct inode *inode = req->wb_context->path.dentry->d_inode;
        struct nfs_inode *nfsi = NFS_I(inode);

        if (req->wb_page != NULL) {
                spin_lock(&inode->i_lock);
                radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_LOCKED);
                nfs_unlock_request(req);
                spin_unlock(&inode->i_lock);
        } else
                nfs_unlock_request(req);
}

/**
 * nfs_clear_request - Free up all resources allocated to the request
 * @req:
 *
 * Release page resources associated with a write request after it
 * has completed.
 */
void nfs_clear_request(struct nfs_page *req)
{
        struct page *page = req->wb_page;
        if (page != NULL) {
                page_cache_release(page);
                req->wb_page = 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 or cached credential */
        nfs_clear_request(req);
        put_nfs_open_context(req->wb_context);
        nfs_page_free(req);
}

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

/**
 * 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)
{
        int ret = 0;

        if (!test_bit(PG_BUSY, &req->wb_flags))
                goto out;
        ret = out_of_line_wait_on_bit(&req->wb_flags, PG_BUSY,
                        nfs_wait_bit_killable, TASK_KILLABLE);
out:
        return ret;
}

/**
 * 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,
                     int (*doio)(struct inode *, struct list_head *, unsigned int, size_t, int),
                     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_inode = inode;
        desc->pg_doio = doio;
        desc->pg_ioflags = io_flags;
        desc->pg_error = 0;
}

/**
 * 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 int nfs_can_coalesce_requests(struct nfs_page *prev,
                                     struct nfs_page *req)
{
        if (req->wb_context->cred != prev->wb_context->cred)
                return 0;
        if (req->wb_context->lockowner != prev->wb_context->lockowner)
                return 0;
        if (req->wb_context->state != prev->wb_context->state)
                return 0;
        if (req->wb_index != (prev->wb_index + 1))
                return 0;
        if (req->wb_pgbase != 0)
                return 0;
        if (prev->wb_pgbase + prev->wb_bytes != PAGE_CACHE_SIZE)
                return 0;
        return 1;
}

/**
 * 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)
{
        size_t newlen = req->wb_bytes;

        if (desc->pg_count != 0) {
                struct nfs_page *prev;

                /*
                 * 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;
                newlen += desc->pg_count;
                if (newlen > desc->pg_bsize)
                        return 0;
                prev = nfs_list_entry(desc->pg_list.prev);
                if (!nfs_can_coalesce_requests(prev, req))
                        return 0;
        } else
                desc->pg_base = req->wb_pgbase;
        nfs_list_remove_request(req);
        nfs_list_add_request(req, &desc->pg_list);
        desc->pg_count = newlen;
        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_doio(desc->pg_inode,
                                          &desc->pg_list,
                                          nfs_page_array_len(desc->pg_base,
                                                             desc->pg_count),
                                          desc->pg_count,
                                          desc->pg_ioflags);
                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'.
 */
int nfs_pageio_add_request(struct nfs_pageio_descriptor *desc,
                           struct nfs_page *req)
{
        while (!nfs_pageio_do_add_request(desc, req)) {
                nfs_pageio_doio(desc);
                if (desc->pg_error < 0)
                        return 0;
        }
        return 1;
}

/**
 * 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)
{
        nfs_pageio_doio(desc);
}

/**
 * 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_doio(desc);
        }
}

#define NFS_SCAN_MAXENTRIES 16
/**
 * nfs_scan_list - Scan a list for matching requests
 * @nfsi: NFS inode
 * @dst: Destination list
 * @idx_start: lower bound of page->index to scan
 * @npages: idx_start + npages sets the upper bound to scan.
 * @tag: tag to scan for
 *
 * Moves elements from one of the inode request lists.
 * If the number of requests is set to 0, the entire address_space
 * starting at index idx_start, is scanned.
 * The requests are *not* checked to ensure that they form a contiguous set.
 * You must be holding the inode's i_lock when calling this function
 */
int nfs_scan_list(struct nfs_inode *nfsi,
                struct list_head *dst, pgoff_t idx_start,
                unsigned int npages, int tag)
{
        struct nfs_page *pgvec[NFS_SCAN_MAXENTRIES];
        struct nfs_page *req;
        pgoff_t idx_end;
        int found, i;
        int res;

        res = 0;
        if (npages == 0)
                idx_end = ~0;
        else
                idx_end = idx_start + npages - 1;

        for (;;) {
                found = radix_tree_gang_lookup_tag(&nfsi->nfs_page_tree,
                                (void **)&pgvec[0], idx_start,
                                NFS_SCAN_MAXENTRIES, tag);
                if (found <= 0)
                        break;
                for (i = 0; i < found; i++) {
                        req = pgvec[i];
                        if (req->wb_index > idx_end)
                                goto out;
                        idx_start = req->wb_index + 1;
                        if (nfs_set_page_tag_locked(req)) {
                                kref_get(&req->wb_kref);
                                nfs_list_remove_request(req);
                                radix_tree_tag_clear(&nfsi->nfs_page_tree,
                                                req->wb_index, tag);
                                nfs_list_add_request(req, dst);
                                res++;
                                if (res == INT_MAX)
                                        goto out;
                        }
                }
                /* for latency reduction */
                cond_resched_lock(&nfsi->vfs_inode.i_lock);
        }
out:
        return res;
}

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);
}