/*
* 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 <libadt/hash_table.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.
*
* @return VFS node corresponding to the given triplet.
*/
vfs_node_t *vfs_node_get(vfs_triplet_t *triplet)
{
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;
link_initialize(&node->nh_link);
hash_table_insert(&nodes, key, &node->nh_link);
} else {
node = hash_table_get_instance(tmp, vfs_node_t, nh_link);
}
_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);
}
/**
* @}
*/