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/*

 * Copyright (c) 2007 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup fs

 * @{

 */

/**

 * @file    vfs_node.c

 * @brief   Various operations on VFS nodes have their home in this file.

 */

#include "vfs.h"

#include <stdlib.h>

#include <string.h>

#include <atomic.h>

#include <futex.h>

#include <rwlock.h>

#include <libadt/hash_table.h>

#include <assert.h>

/** Futex protecting the VFS node hash table. */

atomic_t nodes_futex = FUTEX_INITIALIZER;

#define NODES_BUCKETS_LOG   8

#define NODES_BUCKETS       (1 << NODES_BUCKETS_LOG)

/** VFS node hash table containing all active, in-memory VFS nodes. */

hash_table_t nodes;

#define KEY_FS_HANDLE   0

#define KEY_DEV_HANDLE  1

#define KEY_INDEX   2

static hash_index_t nodes_hash(unsigned long []);

static int nodes_compare(unsigned long [], hash_count_t, link_t *);

static void nodes_remove_callback(link_t *);

/** VFS node hash table operations. */

hash_table_operations_t nodes_ops = {

    .hash = nodes_hash,

    .compare = nodes_compare,

    .remove_callback = nodes_remove_callback

};

/** Initialize the VFS node hash table.

 *

 * @return      Return true on success, false on failure.

 */

bool vfs_nodes_init(void)

{

    return hash_table_create(&nodes, NODES_BUCKETS, 3, &nodes_ops);

}

static inline void _vfs_node_addref(vfs_node_t *node)

{

    node->refcnt++;

}

/** Increment reference count of a VFS node.

 *

 * @param node      VFS node that will have its refcnt incremented.

 */

void vfs_node_addref(vfs_node_t *node)

{

    futex_down(&nodes_futex);

    _vfs_node_addref(node);

    futex_up(&nodes_futex);

}

/** Decrement reference count of a VFS node.

 *

 * This function handles the case when the reference count drops to zero.

 *

 * @param node      VFS node that will have its refcnt decremented.

 */

void vfs_node_delref(vfs_node_t *node)

{

    futex_down(&nodes_futex);

    if (node->refcnt-- == 1) {

        unsigned long key[] = {

            [KEY_FS_HANDLE] = node->fs_handle,

            [KEY_DEV_HANDLE] = node->dev_handle,

            [KEY_INDEX] = node->index

        };

        hash_table_remove(&nodes, key, 3);

    }

    futex_up(&nodes_futex);

}

/** Find VFS node.

 *

 * This function will try to lookup the given triplet in the VFS node hash

 * table. In case the triplet is not found there, a new VFS node is created.

 * In any case, the VFS node will have its reference count incremented. Every

 * node returned by this call should be eventually put back by calling

 * vfs_node_put() on it.

 *

 * @param triplet   Triplet encoding the identity of the VFS node.

 * @param size      Size of the node as filled by vfs_lookup_internal().

 *

 * @return      VFS node corresponding to the given triplet.

 */

vfs_node_t *vfs_node_get(vfs_triplet_t *triplet, size_t size)

{

    unsigned long key[] = {

        [KEY_FS_HANDLE] = triplet->fs_handle,

        [KEY_DEV_HANDLE] = triplet->dev_handle,

        [KEY_INDEX] = triplet->index

    };

    link_t *tmp;

    vfs_node_t *node;

    futex_down(&nodes_futex);

    tmp = hash_table_find(&nodes, key);

    if (!tmp) {

        node = (vfs_node_t *) malloc(sizeof(vfs_node_t));

        if (!node) {

            futex_up(&nodes_futex);

            return NULL;

        }

        memset(node, 0, sizeof(vfs_node_t));

        node->fs_handle = triplet->fs_handle;

        node->dev_handle = triplet->fs_handle;

        node->index = triplet->index;

        node->size = size;

        link_initialize(&node->nh_link);

        rwlock_initialize(&node->contents_rwlock);

        hash_table_insert(&nodes, key, &node->nh_link);

    } else {

        node = hash_table_get_instance(tmp, vfs_node_t, nh_link);  

    }

    assert(node->size == size);

    _vfs_node_addref(node);

    futex_up(&nodes_futex);

    return node;

}

/** Return VFS node when no longer needed by the caller.

 *

 * This function will remove the reference on the VFS node created by

 * vfs_node_get(). This function can only be called as a closing bracket to the

 * preceding vfs_node_get() call.

 *

 * @param node      VFS node being released.

 */

void vfs_node_put(vfs_node_t *node)

{

    vfs_node_delref(node);

}

hash_index_t nodes_hash(unsigned long key[])

{

    hash_index_t a = key[KEY_FS_HANDLE] << (NODES_BUCKETS_LOG / 4);

    hash_index_t b = (a | key[KEY_DEV_HANDLE]) << (NODES_BUCKETS_LOG / 2);

    return (b | key[KEY_INDEX]) & (NODES_BUCKETS - 1);

}

int nodes_compare(unsigned long key[], hash_count_t keys, link_t *item)

{

    vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);

    return (node->fs_handle == key[KEY_FS_HANDLE]) &&

        (node->dev_handle == key[KEY_DEV_HANDLE]) &&

        (node->index == key[KEY_INDEX]);

}

void nodes_remove_callback(link_t *item)

{

    vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);

    free(node);

}

/**

 * @}

 */