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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 <libadt/hash_table.h>
  44.  
  45. /** Futex protecting the VFS node hash table. */
  46. atomic_t nodes_futex = FUTEX_INITIALIZER;
  47.  
  48. #define NODES_BUCKETS_LOG   8
  49. #define NODES_BUCKETS       (1 << NODES_BUCKETS_LOG)
  50.  
  51. /** VFS node hash table containing all active, in-memory VFS nodes. */
  52. hash_table_t nodes;
  53.  
  54. #define KEY_FS_HANDLE   0
  55. #define KEY_DEV_HANDLE  1
  56. #define KEY_INDEX   2
  57.  
  58. static hash_index_t nodes_hash(unsigned long []);
  59. static int nodes_compare(unsigned long [], hash_count_t, link_t *);
  60. static void nodes_remove_callback(link_t *);
  61.  
  62. /** VFS node hash table operations. */
  63. hash_table_operations_t nodes_ops = {
  64.     .hash = nodes_hash,
  65.     .compare = nodes_compare,
  66.     .remove_callback = nodes_remove_callback
  67. };
  68.  
  69. /** Initialize the VFS node hash table.
  70.  *
  71.  * @return      Return true on success, false on failure.
  72.  */
  73. bool vfs_nodes_init(void)
  74. {
  75.     return hash_table_create(&nodes, NODES_BUCKETS, 3, &nodes_ops);
  76. }
  77.  
  78. static inline void _vfs_node_addref(vfs_node_t *node)
  79. {
  80.     node->refcnt++;
  81. }
  82.  
  83. /** Increment reference count of a VFS node.
  84.  *
  85.  * @param node      VFS node that will have its refcnt incremented.
  86.  */
  87. void vfs_node_addref(vfs_node_t *node)
  88. {
  89.     futex_down(&nodes_futex);
  90.     _vfs_node_addref(node);
  91.     futex_up(&nodes_futex);
  92. }
  93.  
  94. /** Decrement reference count of a VFS node.
  95.  *
  96.  * This function handles the case when the reference count drops to zero.
  97.  *
  98.  * @param node      VFS node that will have its refcnt decremented.
  99.  */
  100. void vfs_node_delref(vfs_node_t *node)
  101. {
  102.     futex_down(&nodes_futex);
  103.     if (node->refcnt-- == 1) {
  104.         unsigned long key[] = {
  105.             [KEY_FS_HANDLE] = node->fs_handle,
  106.             [KEY_DEV_HANDLE] = node->dev_handle,
  107.             [KEY_INDEX] = node->index
  108.         };
  109.         hash_table_remove(&nodes, key, 3);
  110.     }
  111.     futex_up(&nodes_futex);
  112. }
  113.  
  114. /** Find VFS node.
  115.  *
  116.  * This function will try to lookup the given triplet in the VFS node hash
  117.  * table. In case the triplet is not found there, a new VFS node is created.
  118.  * In any case, the VFS node will have its reference count incremented. Every
  119.  * node returned by this call should be eventually put back by calling
  120.  * vfs_node_put() on it.
  121.  *
  122.  * @param triplet   Triplet encoding the identity of the VFS node.
  123.  *
  124.  * @return      VFS node corresponding to the given triplet.
  125.  */
  126. vfs_node_t *vfs_node_get(vfs_triplet_t *triplet)
  127. {
  128.     unsigned long key[] = {
  129.         [KEY_FS_HANDLE] = triplet->fs_handle,
  130.         [KEY_DEV_HANDLE] = triplet->dev_handle,
  131.         [KEY_INDEX] = triplet->index
  132.     };
  133.     link_t *tmp;
  134.     vfs_node_t *node;
  135.  
  136.     futex_down(&nodes_futex);
  137.     tmp = hash_table_find(&nodes, key);
  138.     if (!tmp) {
  139.         node = (vfs_node_t *) malloc(sizeof(vfs_node_t));
  140.         if (!node) {
  141.             futex_up(&nodes_futex);
  142.             return NULL;
  143.         }
  144.         memset(node, 0, sizeof(vfs_node_t));
  145.         node->fs_handle = triplet->fs_handle;
  146.         node->dev_handle = triplet->fs_handle;
  147.         node->index = triplet->index;
  148.         link_initialize(&node->nh_link);
  149.         hash_table_insert(&nodes, key, &node->nh_link);
  150.     } else {
  151.         node = hash_table_get_instance(tmp, vfs_node_t, nh_link);  
  152.     }
  153.     _vfs_node_addref(node);
  154.     futex_up(&nodes_futex);
  155.  
  156.     return node;
  157. }
  158.  
  159. /** Return VFS node when no longer needed by the caller.
  160.  *
  161.  * This function will remove the reference on the VFS node created by
  162.  * vfs_node_get(). This function can only be called as a closing bracket to the
  163.  * preceding vfs_node_get() call.
  164.  *
  165.  * @param node      VFS node being released.
  166.  */
  167. void vfs_node_put(vfs_node_t *node)
  168. {
  169.     vfs_node_delref(node);
  170. }
  171.  
  172. hash_index_t nodes_hash(unsigned long key[])
  173. {
  174.     hash_index_t a = key[KEY_FS_HANDLE] << (NODES_BUCKETS_LOG / 4);
  175.     hash_index_t b = (a | key[KEY_DEV_HANDLE]) << (NODES_BUCKETS_LOG / 2);
  176.    
  177.     return (b | key[KEY_INDEX]) & (NODES_BUCKETS - 1);
  178. }
  179.  
  180. int nodes_compare(unsigned long key[], hash_count_t keys, link_t *item)
  181. {
  182.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  183.     return (node->fs_handle == key[KEY_FS_HANDLE]) &&
  184.         (node->dev_handle == key[KEY_DEV_HANDLE]) &&
  185.         (node->index == key[KEY_INDEX]);
  186. }
  187.  
  188. void nodes_remove_callback(link_t *item)
  189. {
  190.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  191.     free(node);
  192. }
  193.  
  194. /**
  195.  * @}
  196.  */
  197.