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  1. /*
  2.  * Copyright (c) 2008 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. #include <assert.h>
  46.  
  47. /** Futex protecting the VFS node hash table. */
  48. atomic_t nodes_futex = FUTEX_INITIALIZER;
  49.  
  50. #define NODES_BUCKETS_LOG   8
  51. #define NODES_BUCKETS       (1 << NODES_BUCKETS_LOG)
  52.  
  53. /** VFS node hash table containing all active, in-memory VFS nodes. */
  54. hash_table_t nodes;
  55.  
  56. #define KEY_FS_HANDLE   0
  57. #define KEY_DEV_HANDLE  1
  58. #define KEY_INDEX   2
  59.  
  60. static hash_index_t nodes_hash(unsigned long []);
  61. static int nodes_compare(unsigned long [], hash_count_t, link_t *);
  62. static void nodes_remove_callback(link_t *);
  63.  
  64. /** VFS node hash table operations. */
  65. hash_table_operations_t nodes_ops = {
  66.     .hash = nodes_hash,
  67.     .compare = nodes_compare,
  68.     .remove_callback = nodes_remove_callback
  69. };
  70.  
  71. /** Initialize the VFS node hash table.
  72.  *
  73.  * @return      Return true on success, false on failure.
  74.  */
  75. bool vfs_nodes_init(void)
  76. {
  77.     return hash_table_create(&nodes, NODES_BUCKETS, 3, &nodes_ops);
  78. }
  79.  
  80. static inline void _vfs_node_addref(vfs_node_t *node)
  81. {
  82.     node->refcnt++;
  83. }
  84.  
  85. /** Increment reference count of a VFS node.
  86.  *
  87.  * @param node      VFS node that will have its refcnt incremented.
  88.  */
  89. void vfs_node_addref(vfs_node_t *node)
  90. {
  91.     futex_down(&nodes_futex);
  92.     _vfs_node_addref(node);
  93.     futex_up(&nodes_futex);
  94. }
  95.  
  96. /** Decrement reference count of a VFS node.
  97.  *
  98.  * This function handles the case when the reference count drops to zero.
  99.  *
  100.  * @param node      VFS node that will have its refcnt decremented.
  101.  */
  102. void vfs_node_delref(vfs_node_t *node)
  103. {
  104.     futex_down(&nodes_futex);
  105.     if (node->refcnt-- == 1) {
  106.         unsigned long key[] = {
  107.             [KEY_FS_HANDLE] = node->fs_handle,
  108.             [KEY_DEV_HANDLE] = node->dev_handle,
  109.             [KEY_INDEX] = node->index
  110.         };
  111.         hash_table_remove(&nodes, key, 3);
  112.     }
  113.     futex_up(&nodes_futex);
  114. }
  115.  
  116. /** Find VFS node.
  117.  *
  118.  * This function will try to lookup the given triplet in the VFS node hash
  119.  * table. In case the triplet is not found there, a new VFS node is created.
  120.  * In any case, the VFS node will have its reference count incremented. Every
  121.  * node returned by this call should be eventually put back by calling
  122.  * vfs_node_put() on it.
  123.  *
  124.  * @param result    Populated lookup result structure.
  125.  *
  126.  * @return      VFS node corresponding to the given triplet.
  127.  */
  128. vfs_node_t *vfs_node_get(vfs_lookup_res_t *result)
  129. {
  130.     unsigned long key[] = {
  131.         [KEY_FS_HANDLE] = result->triplet.fs_handle,
  132.         [KEY_DEV_HANDLE] = result->triplet.dev_handle,
  133.         [KEY_INDEX] = result->triplet.index
  134.     };
  135.     link_t *tmp;
  136.     vfs_node_t *node;
  137.  
  138.     futex_down(&nodes_futex);
  139.     tmp = hash_table_find(&nodes, key);
  140.     if (!tmp) {
  141.         node = (vfs_node_t *) malloc(sizeof(vfs_node_t));
  142.         if (!node) {
  143.             futex_up(&nodes_futex);
  144.             return NULL;
  145.         }
  146.         memset(node, 0, sizeof(vfs_node_t));
  147.         node->fs_handle = result->triplet.fs_handle;
  148.         node->dev_handle = result->triplet.fs_handle;
  149.         node->index = result->triplet.index;
  150.         node->size = result->size;
  151.         link_initialize(&node->nh_link);
  152.         rwlock_initialize(&node->contents_rwlock);
  153.         hash_table_insert(&nodes, key, &node->nh_link);
  154.     } else {
  155.         node = hash_table_get_instance(tmp, vfs_node_t, nh_link);  
  156.     }
  157.  
  158.     assert(node->size == result->size);
  159.  
  160.     _vfs_node_addref(node);
  161.     futex_up(&nodes_futex);
  162.  
  163.     return node;
  164. }
  165.  
  166. /** Return VFS node when no longer needed by the caller.
  167.  *
  168.  * This function will remove the reference on the VFS node created by
  169.  * vfs_node_get(). This function can only be called as a closing bracket to the
  170.  * preceding vfs_node_get() call.
  171.  *
  172.  * @param node      VFS node being released.
  173.  */
  174. void vfs_node_put(vfs_node_t *node)
  175. {
  176.     vfs_node_delref(node);
  177. }
  178.  
  179. hash_index_t nodes_hash(unsigned long key[])
  180. {
  181.     hash_index_t a = key[KEY_FS_HANDLE] << (NODES_BUCKETS_LOG / 4);
  182.     hash_index_t b = (a | key[KEY_DEV_HANDLE]) << (NODES_BUCKETS_LOG / 2);
  183.    
  184.     return (b | key[KEY_INDEX]) & (NODES_BUCKETS - 1);
  185. }
  186.  
  187. int nodes_compare(unsigned long key[], hash_count_t keys, link_t *item)
  188. {
  189.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  190.     return (node->fs_handle == key[KEY_FS_HANDLE]) &&
  191.         (node->dev_handle == key[KEY_DEV_HANDLE]) &&
  192.         (node->index == key[KEY_INDEX]);
  193. }
  194.  
  195. void nodes_remove_callback(link_t *item)
  196. {
  197.     vfs_node_t *node = hash_table_get_instance(item, vfs_node_t, nh_link);
  198.     free(node);
  199. }
  200.  
  201. /**
  202.  * @}
  203.  */
  204.