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  1. /*
  2.  * Copyright (c) 2007 Jakub Jermar
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup fs
  30.  * @{
  31.  */
  32.  
  33. /**
  34.  * @file    vfs_node.c
  35.  * @brief   Various operations on VFS nodes have their home in this file.
  36.  */
  37.  
  38. #include "vfs.h"
  39. #include <stdlib.h>
  40. #include <string.h>
  41. #include <atomic.h>
  42. #include <futex.h>
  43. #include <rwlock.h>
  44. #include <libadt/hash_table.h>
  45.  
  46. /** Futex protecting the VFS node hash table. */
  47. atomic_t nodes_futex = FUTEX_INITIALIZER;
  48.  
  49. #define NODES_BUCKETS_LOG   8
  50. #define NODES_BUCKETS       (1 << NODES_BUCKETS_LOG)
  51.  
  52. /** VFS node hash table containing all active, in-memory VFS nodes. */
  53. hash_table_t nodes;
  54.  
  55. #define KEY_FS_HANDLE   0
  56. #define KEY_DEV_HANDLE  1
  57. #define KEY_INDEX   2
  58.  
  59. static hash_index_t nodes_hash(unsigned long []);
  60. static int nodes_compare(unsigned long [], hash_count_t, link_t *);
  61. static void nodes_remove_callback(link_t *);
  62.  
  63. /** VFS node hash table operations. */
  64. hash_table_operations_t nodes_ops = {
  65.     .hash = nodes_hash,
  66.     .compare = nodes_compare,
  67.     .remove_callback = nodes_remove_callback
  68. };
  69.  
  70. /** Initialize the VFS node hash table.
  71.  *
  72.  * @return      Return true on success, false on failure.
  73.  */
  74. bool vfs_nodes_init(void)
  75. {
  76.     return hash_table_create(&nodes, NODES_BUCKETS, 3, &nodes_ops);
  77. }
  78.  
  79. static inline void _vfs_node_addref(vfs_node_t *node)
  80. {
  81.     node->refcnt++;
  82. }
  83.  
  84. /** Increment reference count of a VFS node.
  85.  *
  86.  * @param node      VFS node that will have its refcnt incremented.
  87.  */
  88. void vfs_node_addref(vfs_node_t *node)
  89. {
  90.     futex_down(&nodes_futex);
  91.     _vfs_node_addref(node);
  92.     futex_up(&nodes_futex);
  93. }
  94.  
  95. /** Decrement reference count of a VFS node.
  96.  *
  97.  * This function handles the case when the reference count drops to zero.
  98.  *
  99.  * @param node      VFS node that will have its refcnt decremented.
  100.  */
  101. void vfs_node_delref(vfs_node_t *node)
  102. {
  103.     futex_down(&nodes_futex);
  104.     if (node->refcnt-- == 1) {
  105.         unsigned long key[] = {
  106.             [KEY_FS_HANDLE] = node->fs_handle,
  107.             [KEY_DEV_HANDLE] = node->dev_handle,
  108.             [KEY_INDEX] = node->index
  109.         };
  110.         hash_table_remove(&nodes, key, 3);
  111.     }
  112.     futex_up(&nodes_futex);
  113. }
  114.  
  115. /** Find VFS node.
  116.  *
  117.  * This function will try to lookup the given triplet in the VFS node hash
  118.  * table. In case the triplet is not found there, a new VFS node is created.
  119.  * In any case, the VFS node will have its reference count incremented. Every
  120.  * node returned by this call should be eventually put back by calling
  121.  * vfs_node_put() on it.
  122.  *
  123.  * @param triplet   Triplet encoding the identity of the VFS node.
  124.  *
  125.  * @return      VFS node corresponding to the given triplet.
  126.  */
  127. vfs_node_t *vfs_node_get(vfs_triplet_t *triplet)
  128. {
  129.     unsigned long key[] = {
  130.         [KEY_FS_HANDLE] = triplet->fs_handle,
  131.         [KEY_DEV_HANDLE] = triplet->dev_handle,
  132.         [KEY_INDEX] = triplet->index
  133.     };
  134.     link_t *tmp;
  135.     vfs_node_t *node;
  136.  
  137.     futex_down(&nodes_futex);
  138.     tmp = hash_table_find(&nodes, key);
  139.     if (!tmp) {
  140.         node = (vfs_node_t *) malloc(sizeof(vfs_node_t));
  141.         if (!node) {
  142.             futex_up(&nodes_futex);
  143.             return NULL;
  144.         }
  145.         memset(node, 0, sizeof(vfs_node_t));
  146.         node->fs_handle = triplet->fs_handle;
  147.         node->dev_handle = triplet->fs_handle;
  148.         node->index = triplet->index;
  149.         link_initialize(&node->nh_link);
  150.         rwlock_initialize(&node->contents_rwlock);
  151.         hash_table_insert(&nodes, key, &node->nh_link);
  152.     } else {
  153.         node = hash_table_get_instance(tmp, vfs_node_t, nh_link);  
  154.     }
  155.     _vfs_node_addref(node);
  156.     futex_up(&nodes_futex);
  157.  
  158.     return node;
  159. }
  160.  
  161. /** Return VFS node when no longer needed by the caller.
  162.  *
  163.  * This function will remove the reference on the VFS node created by
  164.  * vfs_node_get(). This function can only be called as a closing bracket to the
  165.  * preceding vfs_node_get() call.
  166.  *
  167.  * @param node      VFS node being released.
  168.  */
  169. void vfs_node_put(vfs_node_t *node)
  170. {
  171.     vfs_node_delref(node);
  172. }
  173.  
  174. hash_index_t nodes_hash(unsigned long key[])
  175. {
  176.     hash_index_t a = key[KEY_FS_HANDLE] << (NODES_BUCKETS_LOG / 4);
  177.     hash_index_t b = (a | key[KEY_DEV_HANDLE]) << (NODES_BUCKETS_LOG / 2);
  178.    
  179.     return (b | key[KEY_INDEX]) & (NODES_BUCKETS - 1);
  180. }
  181.  
  182. int nodes_compare(unsigned long key[], hash_count_t keys, link_t *item)
  183. {
  184.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  185.     return (node->fs_handle == key[KEY_FS_HANDLE]) &&
  186.         (node->dev_handle == key[KEY_DEV_HANDLE]) &&
  187.         (node->index == key[KEY_INDEX]);
  188. }
  189.  
  190. void nodes_remove_callback(link_t *item)
  191. {
  192.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  193.     free(node);
  194. }
  195.  
  196. /**
  197.  * @}
  198.  */
  199.