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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    fat_idx.c
  35.  * @brief   Layer for translating FAT entities to VFS node indices.
  36.  */
  37.  
  38. #include "fat.h"
  39. #include "../../vfs/vfs.h"
  40. #include <errno.h>
  41. #include <string.h>
  42. #include <libadt/hash_table.h>
  43. #include <libadt/list.h>
  44. #include <assert.h>
  45. #include <futex.h>
  46.  
  47. /** Each instance of this type describes one interval of freed VFS indices. */
  48. typedef struct {
  49.     link_t      link;
  50.     fs_index_t  first;
  51.     fs_index_t  last;
  52. } freed_t;
  53.  
  54. /**
  55.  * Each instance of this type describes state of all VFS indices that
  56.  * are currently unused.
  57.  */
  58. typedef struct {
  59.     link_t      link;
  60.     dev_handle_t    dev_handle;
  61.  
  62.     /** Next unassigned index. */
  63.     fs_index_t  next;
  64.     /** Number of remaining unassigned indices. */
  65.     uint64_t    remaining;
  66.  
  67.     /** Sorted list of intervals of freed indices. */
  68.     link_t      freed_head;
  69. } unused_t;
  70.  
  71. /** Futex protecting the list of unused structures. */
  72. static futex_t unused_futex = FUTEX_INITIALIZER;
  73.  
  74. /** List of unused structures. */
  75. static LIST_INITIALIZE(unused_head);
  76.  
  77. /** Futex protecting the up_hash and ui_hash. */
  78. static futex_t used_futex = FUTEX_INITIALIZER;
  79.  
  80. /**
  81.  * Global hash table of all used fat_idx_t structures.
  82.  * The index structures are hashed by the dev_handle, parent node's first
  83.  * cluster and index within the parent directory.
  84.  */
  85. static hash_table_t up_hash;
  86.  
  87. #define UPH_BUCKETS_LOG 12
  88. #define UPH_BUCKETS (1 << UPH_BUCKETS_LOG)
  89.  
  90. #define UPH_DH_KEY  0
  91. #define UPH_PFC_KEY 1
  92. #define UPH_PDI_KEY 2
  93.  
  94. static hash_index_t pos_hash(unsigned long key[])
  95. {
  96.     dev_handle_t dev_handle = (dev_handle_t)key[UPH_DH_KEY];
  97.     fat_cluster_t pfc = (fat_cluster_t)key[UPH_PFC_KEY];
  98.     unsigned pdi = (unsigned)key[UPH_PDI_KEY];
  99.  
  100.     hash_index_t h;
  101.  
  102.     /*
  103.      * The least significant half of all bits are the least significant bits
  104.      * of the parent node's first cluster.
  105.      *
  106.      * The least significant half of the most significant half of all bits
  107.      * are the least significant bits of the node's dentry index within the
  108.      * parent directory node.
  109.      *
  110.      * The most significant half of the most significant half of all bits
  111.      * are the least significant bits of the device handle.
  112.      */
  113.     h = pfc & ((1 << (UPH_BUCKETS_LOG / 2)) - 1);
  114.     h |= (pdi & ((1 << (UPH_BUCKETS_LOG / 4)) - 1)) <<
  115.         (UPH_BUCKETS_LOG / 2);
  116.     h |= (dev_handle & ((1 << (UPH_BUCKETS_LOG / 4)) - 1)) <<
  117.         (3 * (UPH_BUCKETS_LOG / 4));
  118.  
  119.     return h;
  120. }
  121.  
  122. static int pos_compare(unsigned long key[], hash_count_t keys, link_t *item)
  123. {
  124.     dev_handle_t dev_handle = (dev_handle_t)key[UPH_DH_KEY];
  125.     fat_cluster_t pfc = (fat_cluster_t)key[UPH_PFC_KEY];
  126.     unsigned pdi = (unsigned)key[UPH_PDI_KEY];
  127.     fat_idx_t *fidx = list_get_instance(item, fat_idx_t, uph_link);
  128.  
  129.     return (dev_handle == fidx->dev_handle) && (pfc == fidx->pfc) &&
  130.         (pdi == fidx->pdi);
  131. }
  132.  
  133. static void pos_remove_callback(link_t *item)
  134. {
  135.     /* nothing to do */
  136. }
  137.  
  138. static hash_table_operations_t uph_ops = {
  139.     .hash = pos_hash,
  140.     .compare = pos_compare,
  141.     .remove_callback = pos_remove_callback,
  142. };
  143.  
  144. /**
  145.  * Global hash table of all used fat_idx_t structures.
  146.  * The index structures are hashed by the dev_handle and index.
  147.  */
  148. static hash_table_t ui_hash;
  149.  
  150. #define UIH_BUCKETS_LOG 12
  151. #define UIH_BUCKETS (1 << UIH_BUCKETS_LOG)
  152.  
  153. #define UIH_DH_KEY  0
  154. #define UIH_INDEX_KEY   1
  155.  
  156. static hash_index_t idx_hash(unsigned long key[])
  157. {
  158.     dev_handle_t dev_handle = (dev_handle_t)key[UIH_DH_KEY];
  159.     fs_index_t index = (fs_index_t)key[UIH_INDEX_KEY];
  160.  
  161.     hash_index_t h;
  162.  
  163.     h = dev_handle & ((1 << (UIH_BUCKETS_LOG / 2)) - 1);
  164.     h |= (index & ((1 << (UIH_BUCKETS_LOG / 2)) - 1)) <<
  165.         (UIH_BUCKETS_LOG / 2);
  166.  
  167.     return h;
  168. }
  169.  
  170. static int idx_compare(unsigned long key[], hash_count_t keys, link_t *item)
  171. {
  172.     dev_handle_t dev_handle = (dev_handle_t)key[UIH_DH_KEY];
  173.     fs_index_t index = (fs_index_t)key[UIH_INDEX_KEY];
  174.     fat_idx_t *fidx = list_get_instance(item, fat_idx_t, uih_link);
  175.  
  176.     return (dev_handle == fidx->dev_handle) && (index == fidx->index);
  177. }
  178.  
  179. static void idx_remove_callback(link_t *item)
  180. {
  181.     /* nothing to do */
  182. }
  183.  
  184. static hash_table_operations_t uih_ops = {
  185.     .hash = idx_hash,
  186.     .compare = idx_compare,
  187.     .remove_callback = idx_remove_callback,
  188. };
  189.  
  190. /** Allocate a VFS index which is not currently in use. */
  191. static bool fat_idx_alloc(dev_handle_t dev_handle, fs_index_t *index)
  192. {
  193.     link_t *l;
  194.     unused_t *u;
  195.    
  196.     assert(index);
  197.     futex_down(&unused_futex);
  198.     for (l = unused_head.next; l != &unused_head; l = l->next) {
  199.         u = list_get_instance(l, unused_t, link);
  200.         if (u->dev_handle == dev_handle)
  201.             goto hit;
  202.     }
  203.     futex_up(&unused_futex);
  204.    
  205.     /* dev_handle not found */
  206.     return false;  
  207.  
  208. hit:
  209.     if (list_empty(&u->freed_head)) {
  210.         if (u->remaining) {
  211.             /*
  212.              * There are no freed indices, allocate one directly
  213.              * from the counter.
  214.              */
  215.             *index = u->next++;
  216.             --u->remaining;
  217.             futex_up(&unused_futex);
  218.             return true;
  219.         }
  220.     } else {
  221.         /* There are some freed indices which we can reuse. */
  222.         freed_t *f = list_get_instance(u->freed_head.next, freed_t,
  223.             link);
  224.         *index = f->first;
  225.         if (f->first++ == f->last) {
  226.             /* Destroy the interval. */
  227.             list_remove(&f->link);
  228.             free(f);
  229.         }
  230.         futex_up(&unused_futex);
  231.         return true;
  232.     }
  233.     /*
  234.      * We ran out of indices, which is extremely unlikely with FAT16, but
  235.      * theoretically still possible (e.g. too many open unlinked nodes or
  236.      * too many zero-sized nodes).
  237.      */
  238.     futex_up(&unused_futex);
  239.     return false;
  240. }
  241.  
  242. /** If possible, coalesce two intervals of freed indices. */
  243. static void try_coalesce_intervals(link_t *l, link_t *r, link_t *cur)
  244. {
  245.     freed_t *fl = list_get_instance(l, freed_t, link);
  246.     freed_t *fr = list_get_instance(r, freed_t, link);
  247.  
  248.     if (fl->last + 1 == fr->first) {
  249.         if (cur == l) {
  250.             fl->last = fr->last;
  251.             list_remove(r);
  252.             free(r);
  253.         } else {
  254.             fr->first = fl->first;
  255.             list_remove(l);
  256.             free(l);
  257.         }
  258.     }
  259. }
  260.  
  261. /** Free a VFS index, which is no longer in use. */
  262. static void fat_idx_free(dev_handle_t dev_handle, fs_index_t index)
  263. {
  264.     link_t *l;
  265.     unused_t *u;
  266.  
  267.     futex_down(&unused_futex);
  268.     for (l = unused_head.next; l != &unused_head; l = l->next) {
  269.         u = list_get_instance(l, unused_t, link);
  270.         if (u->dev_handle == dev_handle)
  271.             goto hit;
  272.     }
  273.     futex_up(&unused_futex);
  274.  
  275.     /* should not happen */
  276.     assert(0);
  277.  
  278. hit:
  279.     if (u->next == index + 1) {
  280.         /* The index can be returned directly to the counter. */
  281.         u->next--;
  282.         u->remaining++;
  283.     } else {
  284.         /*
  285.          * The index must be returned either to an existing freed
  286.          * interval or a new interval must be created.
  287.          */
  288.         link_t *lnk;
  289.         freed_t *n;
  290.         for (lnk = u->freed_head.next; lnk != &u->freed_head;
  291.             lnk = lnk->next) {
  292.             freed_t *f = list_get_instance(lnk, freed_t, link);
  293.             if (f->first == index + 1) {
  294.                 f->first--;
  295.                 if (lnk->prev != &u->freed_head)
  296.                     try_coalesce_intervals(lnk->prev, lnk,
  297.                         lnk);
  298.                 futex_up(&unused_futex);
  299.                 return;
  300.             }
  301.             if (f->last == index - 1) {
  302.                 f->last++;
  303.                 if (lnk->next != &u->freed_head)
  304.                     try_coalesce_intervals(lnk, lnk->next,
  305.                         lnk);
  306.                 futex_up(&unused_futex);
  307.                 return;
  308.             }
  309.             if (index > f->first) {
  310.                 n = malloc(sizeof(freed_t));
  311.                 /* TODO: sleep until allocation succeeds */
  312.                 assert(n);
  313.                 link_initialize(&n->link);
  314.                 n->first = index;
  315.                 n->last = index;
  316.                 list_insert_before(&n->link, lnk);
  317.                 futex_up(&unused_futex);
  318.                 return;
  319.             }
  320.  
  321.         }
  322.         /* The index will form the last interval. */
  323.         n = malloc(sizeof(freed_t));
  324.         /* TODO: sleep until allocation succeeds */
  325.         assert(n);
  326.         link_initialize(&n->link);
  327.         n->first = index;
  328.         n->last = index;
  329.         list_append(&n->link, &u->freed_head);
  330.     }
  331.     futex_up(&unused_futex);
  332. }
  333.  
  334. fat_idx_t *
  335. fat_idx_get_by_pos(dev_handle_t dev_handle, fat_cluster_t pfc, unsigned pdi)
  336. {
  337.     fat_idx_t *fidx;
  338.     link_t *l;
  339.     unsigned long pkey[] = {
  340.         [UPH_DH_KEY] = dev_handle,
  341.         [UPH_PFC_KEY] = pfc,
  342.         [UPH_PDI_KEY] = pdi,
  343.     };
  344.  
  345.     futex_down(&used_futex);
  346.     l = hash_table_find(&up_hash, pkey);
  347.     if (l) {
  348.         fidx = hash_table_get_instance(l, fat_idx_t, uph_link);
  349.     } else {
  350.         fidx = (fat_idx_t *) malloc(sizeof(fat_idx_t));
  351.         if (!fidx) {
  352.             futex_up(&used_futex);
  353.             return NULL;
  354.         }
  355.         if (!fat_idx_alloc(dev_handle, &fidx->index)) {
  356.             free(fidx);
  357.             futex_up(&used_futex);
  358.             return NULL;
  359.         }
  360.        
  361.         unsigned long ikey[] = {
  362.             [UIH_DH_KEY] = dev_handle,
  363.             [UIH_INDEX_KEY] = fidx->index,
  364.         };
  365.    
  366.         link_initialize(&fidx->uph_link);
  367.         link_initialize(&fidx->uih_link);
  368.         futex_initialize(&fidx->lock, 1);
  369.         fidx->dev_handle = dev_handle;
  370.         fidx->pfc = pfc;
  371.         fidx->pdi = pdi;
  372.         fidx->nodep = NULL;
  373.  
  374.         hash_table_insert(&up_hash, pkey, &fidx->uph_link);
  375.         hash_table_insert(&ui_hash, ikey, &fidx->uih_link);
  376.     }
  377.     futex_down(&fidx->lock);
  378.     futex_up(&used_futex);
  379.  
  380.     return fidx;
  381. }
  382.  
  383. fat_idx_t *
  384. fat_idx_get_by_index(dev_handle_t dev_handle, fs_index_t index)
  385. {
  386.     fat_idx_t *fidx = NULL;
  387.     link_t *l;
  388.     unsigned long ikey[] = {
  389.         [UIH_DH_KEY] = dev_handle,
  390.         [UIH_INDEX_KEY] = index,
  391.     };
  392.  
  393.     futex_down(&used_futex);
  394.     l = hash_table_find(&ui_hash, ikey);
  395.     if (l) {
  396.         fidx = hash_table_get_instance(l, fat_idx_t, uih_link);
  397.         futex_down(&fidx->lock);
  398.     }
  399.     futex_up(&used_futex);
  400.  
  401.     return fidx;
  402. }
  403.  
  404.