/*
 * V9FS cache definitions.
 *
 *  Copyright (C) 2009 by Abhishek Kulkarni <adkulkar@umail.iu.edu>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to:
 *  Free Software Foundation
 *  51 Franklin Street, Fifth Floor
 *  Boston, MA  02111-1301  USA
 *
 */

#include <linux/jiffies.h>
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <net/9p/9p.h>

#include "v9fs.h"
#include "cache.h"

#define CACHETAG_LEN  11

struct fscache_netfs v9fs_cache_netfs = {
        .name           = "9p",
        .version        = 0,
};

/**
 * v9fs_random_cachetag - Generate a random tag to be associated
 *                        with a new cache session.
 *
 * The value of jiffies is used for a fairly randomly cache tag.
 */

static
int v9fs_random_cachetag(struct v9fs_session_info *v9ses)
{
        v9ses->cachetag = kmalloc(CACHETAG_LEN, GFP_KERNEL);
        if (!v9ses->cachetag)
                return -ENOMEM;

        return scnprintf(v9ses->cachetag, CACHETAG_LEN, "%lu", jiffies);
}

const struct fscache_cookie_def v9fs_cache_session_index_def = {
        .name           = "9P.session",
        .type           = FSCACHE_COOKIE_TYPE_INDEX,
};

void v9fs_cache_session_get_cookie(struct v9fs_session_info *v9ses)
{
        /* If no cache session tag was specified, we generate a random one. */
        if (!v9ses->cachetag) {
                if (v9fs_random_cachetag(v9ses) < 0) {
                        v9ses->fscache = NULL;
                        return;
                }
        }

        v9ses->fscache = fscache_acquire_cookie(v9fs_cache_netfs.primary_index,
                                                &v9fs_cache_session_index_def,
                                                v9ses->cachetag,
                                                strlen(v9ses->cachetag),
                                                NULL, 0,
                                                v9ses, 0, true);
        p9_debug(P9_DEBUG_FSC, "session %p get cookie %p\n",
                 v9ses, v9ses->fscache);
}

void v9fs_cache_session_put_cookie(struct v9fs_session_info *v9ses)
{
        p9_debug(P9_DEBUG_FSC, "session %p put cookie %p\n",
                 v9ses, v9ses->fscache);
        fscache_relinquish_cookie(v9ses->fscache, NULL, false);
        v9ses->fscache = NULL;
}

static enum
fscache_checkaux v9fs_cache_inode_check_aux(void *cookie_netfs_data,
                                            const void *buffer,
                                            uint16_t buflen,
                                            loff_t object_size)
{
        const struct v9fs_inode *v9inode = cookie_netfs_data;

        if (buflen != sizeof(v9inode->qid.version))
                return FSCACHE_CHECKAUX_OBSOLETE;

        if (memcmp(buffer, &v9inode->qid.version,
                   sizeof(v9inode->qid.version)))
                return FSCACHE_CHECKAUX_OBSOLETE;

        return FSCACHE_CHECKAUX_OKAY;
}

const struct fscache_cookie_def v9fs_cache_inode_index_def = {
        .name           = "9p.inode",
        .type           = FSCACHE_COOKIE_TYPE_DATAFILE,
        .check_aux      = v9fs_cache_inode_check_aux,
};

void v9fs_cache_inode_get_cookie(struct inode *inode)
{
        struct v9fs_inode *v9inode;
        struct v9fs_session_info *v9ses;

        if (!S_ISREG(inode->i_mode))
                return;

        v9inode = V9FS_I(inode);
        if (v9inode->fscache)
                return;

        v9ses = v9fs_inode2v9ses(inode);
        v9inode->fscache = fscache_acquire_cookie(v9ses->fscache,
                                                  &v9fs_cache_inode_index_def,
                                                  &v9inode->qid.path,
                                                  sizeof(v9inode->qid.path),
                                                  &v9inode->qid.version,
                                                  sizeof(v9inode->qid.version),
                                                  v9inode,
                                                  i_size_read(&v9inode->vfs_inode),
                                                  true);

        p9_debug(P9_DEBUG_FSC, "inode %p get cookie %p\n",
                 inode, v9inode->fscache);
}

void v9fs_cache_inode_put_cookie(struct inode *inode)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);

        if (!v9inode->fscache)
                return;
        p9_debug(P9_DEBUG_FSC, "inode %p put cookie %p\n",
                 inode, v9inode->fscache);

        fscache_relinquish_cookie(v9inode->fscache, &v9inode->qid.version,
                                  false);
        v9inode->fscache = NULL;
}

void v9fs_cache_inode_flush_cookie(struct inode *inode)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);

        if (!v9inode->fscache)
                return;
        p9_debug(P9_DEBUG_FSC, "inode %p flush cookie %p\n",
                 inode, v9inode->fscache);

        fscache_relinquish_cookie(v9inode->fscache, NULL, true);
        v9inode->fscache = NULL;
}

void v9fs_cache_inode_set_cookie(struct inode *inode, struct file *filp)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);

        if (!v9inode->fscache)
                return;

        mutex_lock(&v9inode->fscache_lock);

        if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
                v9fs_cache_inode_flush_cookie(inode);
        else
                v9fs_cache_inode_get_cookie(inode);

        mutex_unlock(&v9inode->fscache_lock);
}

void v9fs_cache_inode_reset_cookie(struct inode *inode)
{
        struct v9fs_inode *v9inode = V9FS_I(inode);
        struct v9fs_session_info *v9ses;
        struct fscache_cookie *old;

        if (!v9inode->fscache)
                return;

        old = v9inode->fscache;

        mutex_lock(&v9inode->fscache_lock);
        fscache_relinquish_cookie(v9inode->fscache, NULL, true);

        v9ses = v9fs_inode2v9ses(inode);
        v9inode->fscache = fscache_acquire_cookie(v9ses->fscache,
                                                  &v9fs_cache_inode_index_def,
                                                  &v9inode->qid.path,
                                                  sizeof(v9inode->qid.path),
                                                  &v9inode->qid.version,
                                                  sizeof(v9inode->qid.version),
                                                  v9inode,
                                                  i_size_read(&v9inode->vfs_inode),
                                                  true);
        p9_debug(P9_DEBUG_FSC, "inode %p revalidating cookie old %p new %p\n",
                 inode, old, v9inode->fscache);

        mutex_unlock(&v9inode->fscache_lock);
}

int __v9fs_fscache_release_page(struct page *page, gfp_t gfp)
{
        struct inode *inode = page->mapping->host;
        struct v9fs_inode *v9inode = V9FS_I(inode);

        BUG_ON(!v9inode->fscache);

        return fscache_maybe_release_page(v9inode->fscache, page, gfp);
}

void __v9fs_fscache_invalidate_page(struct page *page)
{
        struct inode *inode = page->mapping->host;
        struct v9fs_inode *v9inode = V9FS_I(inode);

        BUG_ON(!v9inode->fscache);

        if (PageFsCache(page)) {
                fscache_wait_on_page_write(v9inode->fscache, page);
                BUG_ON(!PageLocked(page));
                fscache_uncache_page(v9inode->fscache, page);
        }
}

static void v9fs_vfs_readpage_complete(struct page *page, void *data,
                                       int error)
{
        if (!error)
                SetPageUptodate(page);

        unlock_page(page);
}

/**
 * __v9fs_readpage_from_fscache - read a page from cache
 *
 * Returns 0 if the pages are in cache and a BIO is submitted,
 * 1 if the pages are not in cache and -error otherwise.
 */

int __v9fs_readpage_from_fscache(struct inode *inode, struct page *page)
{
        int ret;
        const struct v9fs_inode *v9inode = V9FS_I(inode);

        p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
        if (!v9inode->fscache)
                return -ENOBUFS;

        ret = fscache_read_or_alloc_page(v9inode->fscache,
                                         page,
                                         v9fs_vfs_readpage_complete,
                                         NULL,
                                         GFP_KERNEL);
        switch (ret) {
        case -ENOBUFS:
        case -ENODATA:
                p9_debug(P9_DEBUG_FSC, "page/inode not in cache %d\n", ret);
                return 1;
        case 0:
                p9_debug(P9_DEBUG_FSC, "BIO submitted\n");
                return ret;
        default:
                p9_debug(P9_DEBUG_FSC, "ret %d\n", ret);
                return ret;
        }
}

/**
 * __v9fs_readpages_from_fscache - read multiple pages from cache
 *
 * Returns 0 if the pages are in cache and a BIO is submitted,
 * 1 if the pages are not in cache and -error otherwise.
 */

int __v9fs_readpages_from_fscache(struct inode *inode,
                                  struct address_space *mapping,
                                  struct list_head *pages,
                                  unsigned *nr_pages)
{
        int ret;
        const struct v9fs_inode *v9inode = V9FS_I(inode);

        p9_debug(P9_DEBUG_FSC, "inode %p pages %u\n", inode, *nr_pages);
        if (!v9inode->fscache)
                return -ENOBUFS;

        ret = fscache_read_or_alloc_pages(v9inode->fscache,
                                          mapping, pages, nr_pages,
                                          v9fs_vfs_readpage_complete,
                                          NULL,
                                          mapping_gfp_mask(mapping));
        switch (ret) {
        case -ENOBUFS:
        case -ENODATA:
                p9_debug(P9_DEBUG_FSC, "pages/inodes not in cache %d\n", ret);
                return 1;
        case 0:
                BUG_ON(!list_empty(pages));
                BUG_ON(*nr_pages != 0);
                p9_debug(P9_DEBUG_FSC, "BIO submitted\n");
                return ret;
        default:
                p9_debug(P9_DEBUG_FSC, "ret %d\n", ret);
                return ret;
        }
}

/**
 * __v9fs_readpage_to_fscache - write a page to the cache
 *
 */

void __v9fs_readpage_to_fscache(struct inode *inode, struct page *page)
{
        int ret;
        const struct v9fs_inode *v9inode = V9FS_I(inode);

        p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
        ret = fscache_write_page(v9inode->fscache, page,
                                 i_size_read(&v9inode->vfs_inode), GFP_KERNEL);
        p9_debug(P9_DEBUG_FSC, "ret =  %d\n", ret);
        if (ret != 0)
                v9fs_uncache_page(inode, page);
}

/*
 * wait for a page to complete writing to the cache
 */
void __v9fs_fscache_wait_on_page_write(struct inode *inode, struct page *page)
{
        const struct v9fs_inode *v9inode = V9FS_I(inode);
        p9_debug(P9_DEBUG_FSC, "inode %p page %p\n", inode, page);
        if (PageFsCache(page))
                fscache_wait_on_page_write(v9inode->fscache, page);
}