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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_ops.c
  35.  * @brief   Implementation of VFS operations for the FAT file system server.
  36.  */
  37.  
  38. #include "fat.h"
  39. #include "fat_dentry.h"
  40. #include "fat_fat.h"
  41. #include "../../vfs/vfs.h"
  42. #include <libfs.h>
  43. #include <ipc/ipc.h>
  44. #include <ipc/services.h>
  45. #include <ipc/devmap.h>
  46. #include <async.h>
  47. #include <errno.h>
  48. #include <string.h>
  49. #include <byteorder.h>
  50. #include <libadt/hash_table.h>
  51. #include <libadt/list.h>
  52. #include <assert.h>
  53. #include <futex.h>
  54. #include <sys/mman.h>
  55. #include <align.h>
  56.  
  57. /** Futex protecting the list of cached free FAT nodes. */
  58. static futex_t ffn_futex = FUTEX_INITIALIZER;
  59.  
  60. /** List of cached free FAT nodes. */
  61. static LIST_INITIALIZE(ffn_head);
  62.  
  63. static int dev_phone = -1;      /* FIXME */
  64. static void *dev_buffer = NULL;     /* FIXME */
  65.  
  66. block_t *block_get(dev_handle_t dev_handle, off_t offset, size_t bs)
  67. {
  68.     /* FIXME */
  69.     block_t *b;
  70.     off_t bufpos = 0;
  71.     size_t buflen = 0;
  72.     off_t pos = offset * bs;
  73.  
  74.     assert(dev_phone != -1);
  75.     assert(dev_buffer);
  76.  
  77.     b = malloc(sizeof(block_t));
  78.     if (!b)
  79.         return NULL;
  80.    
  81.     b->data = malloc(bs);
  82.     if (!b->data) {
  83.         free(b);
  84.         return NULL;
  85.     }
  86.     b->size = bs;
  87.  
  88.     if (!libfs_blockread(dev_phone, dev_buffer, &bufpos, &buflen, &pos,
  89.         b->data, bs, bs)) {
  90.         free(b->data);
  91.         free(b);
  92.         return NULL;
  93.     }
  94.  
  95.     return b;
  96. }
  97.  
  98. void block_put(block_t *block)
  99. {
  100.     /* FIXME */
  101.     free(block->data);
  102.     free(block);
  103. }
  104.  
  105. static void fat_node_initialize(fat_node_t *node)
  106. {
  107.     futex_initialize(&node->lock, 1);
  108.     node->idx = NULL;
  109.     node->type = 0;
  110.     link_initialize(&node->ffn_link);
  111.     node->size = 0;
  112.     node->lnkcnt = 0;
  113.     node->refcnt = 0;
  114.     node->dirty = false;
  115. }
  116.  
  117. static void fat_node_sync(fat_node_t *node)
  118. {
  119.     /* TODO */
  120. }
  121.  
  122. /** Internal version of fat_node_get().
  123.  *
  124.  * @param idxp      Locked index structure.
  125.  */
  126. static void *fat_node_get_core(fat_idx_t *idxp)
  127. {
  128.     block_t *b;
  129.     fat_dentry_t *d;
  130.     fat_node_t *nodep = NULL;
  131.     unsigned bps;
  132.     unsigned dps;
  133.  
  134.     if (idxp->nodep) {
  135.         /*
  136.          * We are lucky.
  137.          * The node is already instantiated in memory.
  138.          */
  139.         futex_down(&idxp->nodep->lock);
  140.         if (!idxp->nodep->refcnt++)
  141.             list_remove(&idxp->nodep->ffn_link);
  142.         futex_up(&idxp->nodep->lock);
  143.         return idxp->nodep;
  144.     }
  145.  
  146.     /*
  147.      * We must instantiate the node from the file system.
  148.      */
  149.    
  150.     assert(idxp->pfc);
  151.  
  152.     futex_down(&ffn_futex);
  153.     if (!list_empty(&ffn_head)) {
  154.         /* Try to use a cached free node structure. */
  155.         fat_idx_t *idxp_tmp;
  156.         nodep = list_get_instance(ffn_head.next, fat_node_t, ffn_link);
  157.         if (futex_trydown(&nodep->lock) == ESYNCH_WOULD_BLOCK)
  158.             goto skip_cache;
  159.         idxp_tmp = nodep->idx;
  160.         if (futex_trydown(&idxp_tmp->lock) == ESYNCH_WOULD_BLOCK) {
  161.             futex_up(&nodep->lock);
  162.             goto skip_cache;
  163.         }
  164.         list_remove(&nodep->ffn_link);
  165.         futex_up(&ffn_futex);
  166.         if (nodep->dirty)
  167.             fat_node_sync(nodep);
  168.         idxp_tmp->nodep = NULL;
  169.         futex_up(&nodep->lock);
  170.         futex_up(&idxp_tmp->lock);
  171.     } else {
  172. skip_cache:
  173.         /* Try to allocate a new node structure. */
  174.         futex_up(&ffn_futex);
  175.         nodep = (fat_node_t *)malloc(sizeof(fat_node_t));
  176.         if (!nodep)
  177.             return NULL;
  178.     }
  179.     fat_node_initialize(nodep);
  180.  
  181.     bps = fat_bps_get(idxp->dev_handle);
  182.     dps = bps / sizeof(fat_dentry_t);
  183.  
  184.     /* Read the block that contains the dentry of interest. */
  185.     b = _fat_block_get(idxp->dev_handle, idxp->pfc,
  186.         (idxp->pdi * sizeof(fat_dentry_t)) / bps);
  187.     assert(b);
  188.  
  189.     d = ((fat_dentry_t *)b->data) + (idxp->pdi % dps);
  190.     if (d->attr & FAT_ATTR_SUBDIR) {
  191.         /*
  192.          * The only directory which does not have this bit set is the
  193.          * root directory itself. The root directory node is handled
  194.          * and initialized elsewhere.
  195.          */
  196.         nodep->type = FAT_DIRECTORY;
  197.         /*
  198.          * Unfortunately, the 'size' field of the FAT dentry is not
  199.          * defined for the directory entry type. We must determine the
  200.          * size of the directory by walking the FAT.
  201.          */
  202.         nodep->size = bps * _fat_blcks_get(idxp->dev_handle,
  203.             uint16_t_le2host(d->firstc), NULL);
  204.     } else {
  205.         nodep->type = FAT_FILE;
  206.         nodep->size = uint32_t_le2host(d->size);
  207.     }
  208.     nodep->firstc = uint16_t_le2host(d->firstc);
  209.     nodep->lnkcnt = 1;
  210.     nodep->refcnt = 1;
  211.  
  212.     block_put(b);
  213.  
  214.     /* Link the idx structure with the node structure. */
  215.     nodep->idx = idxp;
  216.     idxp->nodep = nodep;
  217.  
  218.     return nodep;
  219. }
  220.  
  221. /** Instantiate a FAT in-core node. */
  222. static void *fat_node_get(dev_handle_t dev_handle, fs_index_t index)
  223. {
  224.     void *node;
  225.     fat_idx_t *idxp;
  226.  
  227.     idxp = fat_idx_get_by_index(dev_handle, index);
  228.     if (!idxp)
  229.         return NULL;
  230.     /* idxp->lock held */
  231.     node = fat_node_get_core(idxp);
  232.     futex_up(&idxp->lock);
  233.     return node;
  234. }
  235.  
  236. static void fat_node_put(void *node)
  237. {
  238.     fat_node_t *nodep = (fat_node_t *)node;
  239.  
  240.     futex_down(&nodep->lock);
  241.     if (!--nodep->refcnt) {
  242.         futex_down(&ffn_futex);
  243.         list_append(&nodep->ffn_link, &ffn_head);
  244.         futex_up(&ffn_futex);
  245.     }
  246.     futex_up(&nodep->lock);
  247. }
  248.  
  249. static void *fat_create(int flags)
  250. {
  251.     return NULL;    /* not supported at the moment */
  252. }
  253.  
  254. static int fat_destroy(void *node)
  255. {
  256.     return ENOTSUP; /* not supported at the moment */
  257. }
  258.  
  259. static bool fat_link(void *prnt, void *chld, const char *name)
  260. {
  261.     return false;   /* not supported at the moment */
  262. }
  263.  
  264. static int fat_unlink(void *prnt, void *chld)
  265. {
  266.     return ENOTSUP; /* not supported at the moment */
  267. }
  268.  
  269. static void *fat_match(void *prnt, const char *component)
  270. {
  271.     fat_node_t *parentp = (fat_node_t *)prnt;
  272.     char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];
  273.     unsigned i, j;
  274.     unsigned bps;       /* bytes per sector */
  275.     unsigned dps;       /* dentries per sector */
  276.     unsigned blocks;
  277.     fat_dentry_t *d;
  278.     block_t *b;
  279.  
  280.     futex_down(&parentp->idx->lock);
  281.     bps = fat_bps_get(parentp->idx->dev_handle);
  282.     dps = bps / sizeof(fat_dentry_t);
  283.     blocks = parentp->size / bps + (parentp->size % bps != 0);
  284.     for (i = 0; i < blocks; i++) {
  285.         unsigned dentries;
  286.        
  287.         b = fat_block_get(parentp, i);
  288.         dentries = (i == blocks - 1) ?
  289.             parentp->size % sizeof(fat_dentry_t) :
  290.             dps;
  291.         for (j = 0; j < dentries; j++) {
  292.             d = ((fat_dentry_t *)b->data) + j;
  293.             switch (fat_classify_dentry(d)) {
  294.             case FAT_DENTRY_SKIP:
  295.                 continue;
  296.             case FAT_DENTRY_LAST:
  297.                 block_put(b);
  298.                 futex_up(&parentp->idx->lock);
  299.                 return NULL;
  300.             default:
  301.             case FAT_DENTRY_VALID:
  302.                 dentry_name_canonify(d, name);
  303.                 break;
  304.             }
  305.             if (stricmp(name, component) == 0) {
  306.                 /* hit */
  307.                 void *node;
  308.                 /*
  309.                  * Assume tree hierarchy for locking.  We
  310.                  * already have the parent and now we are going
  311.                  * to lock the child.  Never lock in the oposite
  312.                  * order.
  313.                  */
  314.                 fat_idx_t *idx = fat_idx_get_by_pos(
  315.                     parentp->idx->dev_handle, parentp->firstc,
  316.                     i * dps + j);
  317.                 futex_up(&parentp->idx->lock);
  318.                 if (!idx) {
  319.                     /*
  320.                      * Can happen if memory is low or if we
  321.                      * run out of 32-bit indices.
  322.                      */
  323.                     block_put(b);
  324.                     return NULL;
  325.                 }
  326.                 node = fat_node_get_core(idx);
  327.                 futex_up(&idx->lock);
  328.                 block_put(b);
  329.                 return node;
  330.             }
  331.         }
  332.         block_put(b);
  333.     }
  334.     futex_up(&parentp->idx->lock);
  335.     return NULL;
  336. }
  337.  
  338. static fs_index_t fat_index_get(void *node)
  339. {
  340.     fat_node_t *fnodep = (fat_node_t *)node;
  341.     if (!fnodep)
  342.         return 0;
  343.     return fnodep->idx->index;
  344. }
  345.  
  346. static size_t fat_size_get(void *node)
  347. {
  348.     return ((fat_node_t *)node)->size;
  349. }
  350.  
  351. static unsigned fat_lnkcnt_get(void *node)
  352. {
  353.     return ((fat_node_t *)node)->lnkcnt;
  354. }
  355.  
  356. static bool fat_has_children(void *node)
  357. {
  358.     fat_node_t *nodep = (fat_node_t *)node;
  359.     unsigned bps;
  360.     unsigned dps;
  361.     unsigned blocks;
  362.     block_t *b;
  363.     unsigned i, j;
  364.  
  365.     if (nodep->type != FAT_DIRECTORY)
  366.         return false;
  367.  
  368.     futex_down(&nodep->idx->lock);
  369.     bps = fat_bps_get(nodep->idx->dev_handle);
  370.     dps = bps / sizeof(fat_dentry_t);
  371.  
  372.     blocks = nodep->size / bps + (nodep->size % bps != 0);
  373.  
  374.     for (i = 0; i < blocks; i++) {
  375.         unsigned dentries;
  376.         fat_dentry_t *d;
  377.    
  378.         b = fat_block_get(nodep, i);
  379.         dentries = (i == blocks - 1) ?
  380.             nodep->size % sizeof(fat_dentry_t) :
  381.             dps;
  382.         for (j = 0; j < dentries; j++) {
  383.             d = ((fat_dentry_t *)b->data) + j;
  384.             switch (fat_classify_dentry(d)) {
  385.             case FAT_DENTRY_SKIP:
  386.                 continue;
  387.             case FAT_DENTRY_LAST:
  388.                 block_put(b);
  389.                 futex_up(&nodep->idx->lock);
  390.                 return false;
  391.             default:
  392.             case FAT_DENTRY_VALID:
  393.                 block_put(b);
  394.                 futex_up(&nodep->idx->lock);
  395.                 return true;
  396.             }
  397.             block_put(b);
  398.             futex_up(&nodep->idx->lock);
  399.             return true;
  400.         }
  401.         block_put(b);
  402.     }
  403.  
  404.     futex_up(&nodep->idx->lock);
  405.     return false;
  406. }
  407.  
  408. static void *fat_root_get(dev_handle_t dev_handle)
  409. {
  410.     return fat_node_get(dev_handle, 0);
  411. }
  412.  
  413. static char fat_plb_get_char(unsigned pos)
  414. {
  415.     return fat_reg.plb_ro[pos % PLB_SIZE];
  416. }
  417.  
  418. static bool fat_is_directory(void *node)
  419. {
  420.     return ((fat_node_t *)node)->type == FAT_DIRECTORY;
  421. }
  422.  
  423. static bool fat_is_file(void *node)
  424. {
  425.     return ((fat_node_t *)node)->type == FAT_FILE;
  426. }
  427.  
  428. /** libfs operations */
  429. libfs_ops_t fat_libfs_ops = {
  430.     .match = fat_match,
  431.     .node_get = fat_node_get,
  432.     .node_put = fat_node_put,
  433.     .create = fat_create,
  434.     .destroy = fat_destroy,
  435.     .link = fat_link,
  436.     .unlink = fat_unlink,
  437.     .index_get = fat_index_get,
  438.     .size_get = fat_size_get,
  439.     .lnkcnt_get = fat_lnkcnt_get,
  440.     .has_children = fat_has_children,
  441.     .root_get = fat_root_get,
  442.     .plb_get_char = fat_plb_get_char,
  443.     .is_directory = fat_is_directory,
  444.     .is_file = fat_is_file
  445. };
  446.  
  447. void fat_mounted(ipc_callid_t rid, ipc_call_t *request)
  448. {
  449.     dev_handle_t dev_handle = (dev_handle_t) IPC_GET_ARG1(*request);
  450.     block_t *bb;
  451.     uint16_t bps;
  452.     uint16_t rde;
  453.     int rc;
  454.  
  455.     /*
  456.      * For now, we don't bother to remember dev_handle, dev_phone or
  457.      * dev_buffer in some data structure. We use global variables because we
  458.      * know there will be at most one mount on this file system.
  459.      * Of course, this is a huge TODO item.
  460.      */
  461.     dev_buffer = mmap(NULL, BS_SIZE, PROTO_READ | PROTO_WRITE,
  462.         MAP_ANONYMOUS | MAP_PRIVATE, 0, 0);
  463.    
  464.     if (!dev_buffer) {
  465.         ipc_answer_0(rid, ENOMEM);
  466.         return;
  467.     }
  468.  
  469.     dev_phone = ipc_connect_me_to(PHONE_NS, SERVICE_DEVMAP,
  470.         DEVMAP_CONNECT_TO_DEVICE, dev_handle);
  471.  
  472.     if (dev_phone < 0) {
  473.         munmap(dev_buffer, BS_SIZE);
  474.         ipc_answer_0(rid, dev_phone);
  475.         return;
  476.     }
  477.  
  478.     rc = ipc_share_out_start(dev_phone, dev_buffer,
  479.         AS_AREA_READ | AS_AREA_WRITE);
  480.     if (rc != EOK) {
  481.             munmap(dev_buffer, BS_SIZE);
  482.         ipc_answer_0(rid, rc);
  483.         return;
  484.     }
  485.  
  486.     /* Read the number of root directory entries. */
  487.     bb = block_get(dev_handle, BS_BLOCK, BS_SIZE);
  488.     bps = uint16_t_le2host(FAT_BS(bb)->bps);
  489.     rde = uint16_t_le2host(FAT_BS(bb)->root_ent_max);
  490.     block_put(bb);
  491.  
  492.     if (bps != BS_SIZE) {
  493.         munmap(dev_buffer, BS_SIZE);
  494.         ipc_answer_0(rid, ENOTSUP);
  495.         return;
  496.     }
  497.  
  498.     rc = fat_idx_init_by_dev_handle(dev_handle);
  499.     if (rc != EOK) {
  500.             munmap(dev_buffer, BS_SIZE);
  501.         ipc_answer_0(rid, rc);
  502.         return;
  503.     }
  504.  
  505.     /* Initialize the root node. */
  506.     fat_node_t *rootp = (fat_node_t *)malloc(sizeof(fat_node_t));
  507.     if (!rootp) {
  508.             munmap(dev_buffer, BS_SIZE);
  509.         fat_idx_fini_by_dev_handle(dev_handle);
  510.         ipc_answer_0(rid, ENOMEM);
  511.         return;
  512.     }
  513.     fat_node_initialize(rootp);
  514.  
  515.     fat_idx_t *ridxp = fat_idx_get_by_pos(dev_handle, FAT_CLST_ROOTPAR, 0);
  516.     if (!ridxp) {
  517.             munmap(dev_buffer, BS_SIZE);
  518.         free(rootp);
  519.         fat_idx_fini_by_dev_handle(dev_handle);
  520.         ipc_answer_0(rid, ENOMEM);
  521.         return;
  522.     }
  523.     assert(ridxp->index == 0);
  524.     /* ridxp->lock held */
  525.  
  526.     rootp->type = FAT_DIRECTORY;
  527.     rootp->firstc = FAT_CLST_ROOT;
  528.     rootp->refcnt = 1;
  529.     rootp->lnkcnt = 0;  /* FS root is not linked */
  530.     rootp->size = rde * sizeof(fat_dentry_t);
  531.     rootp->idx = ridxp;
  532.     ridxp->nodep = rootp;
  533.    
  534.     futex_up(&ridxp->lock);
  535.  
  536.     ipc_answer_3(rid, EOK, ridxp->index, rootp->size, rootp->lnkcnt);
  537. }
  538.  
  539. void fat_mount(ipc_callid_t rid, ipc_call_t *request)
  540. {
  541.     ipc_answer_0(rid, ENOTSUP);
  542. }
  543.  
  544. void fat_lookup(ipc_callid_t rid, ipc_call_t *request)
  545. {
  546.     libfs_lookup(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
  547. }
  548.  
  549. void fat_read(ipc_callid_t rid, ipc_call_t *request)
  550. {
  551.     dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);
  552.     fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);
  553.     off_t pos = (off_t)IPC_GET_ARG3(*request);
  554.     fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);
  555.     uint16_t bps = fat_bps_get(dev_handle);
  556.     size_t bytes;
  557.     block_t *b;
  558.  
  559.     if (!nodep) {
  560.         ipc_answer_0(rid, ENOENT);
  561.         return;
  562.     }
  563.  
  564.     ipc_callid_t callid;
  565.     size_t len;
  566.     if (!ipc_data_read_receive(&callid, &len)) {
  567.         fat_node_put(nodep);
  568.         ipc_answer_0(callid, EINVAL);
  569.         ipc_answer_0(rid, EINVAL);
  570.         return;
  571.     }
  572.  
  573.     if (nodep->type == FAT_FILE) {
  574.         /*
  575.          * Our strategy for regular file reads is to read one block at
  576.          * most and make use of the possibility to return less data than
  577.          * requested. This keeps the code very simple.
  578.          */
  579.         bytes = min(len, bps - pos % bps);
  580.         b = fat_block_get(nodep, pos / bps);
  581.         (void) ipc_data_read_finalize(callid, b->data + pos % bps,
  582.             bytes);
  583.         block_put(b);
  584.     } else {
  585.         unsigned bnum;
  586.         off_t spos = pos;
  587.         char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];
  588.         fat_dentry_t *d;
  589.  
  590.         assert(nodep->type == FAT_DIRECTORY);
  591.         assert(nodep->size % bps == 0);
  592.         assert(bps % sizeof(fat_dentry_t) == 0);
  593.  
  594.         /*
  595.          * Our strategy for readdir() is to use the position pointer as
  596.          * an index into the array of all dentries. On entry, it points
  597.          * to the first unread dentry. If we skip any dentries, we bump
  598.          * the position pointer accordingly.
  599.          */
  600.         bnum = (pos * sizeof(fat_dentry_t)) / bps;
  601.         while (bnum < nodep->size / bps) {
  602.             off_t o;
  603.  
  604.             b = fat_block_get(nodep, bnum);
  605.             for (o = pos % (bps / sizeof(fat_dentry_t));
  606.                 o < bps / sizeof(fat_dentry_t);
  607.                 o++, pos++) {
  608.                 d = ((fat_dentry_t *)b->data) + o;
  609.                 switch (fat_classify_dentry(d)) {
  610.                 case FAT_DENTRY_SKIP:
  611.                     continue;
  612.                 case FAT_DENTRY_LAST:
  613.                     block_put(b);
  614.                     goto miss;
  615.                 default:
  616.                 case FAT_DENTRY_VALID:
  617.                     dentry_name_canonify(d, name);
  618.                     block_put(b);
  619.                     goto hit;
  620.                 }
  621.             }
  622.             block_put(b);
  623.             bnum++;
  624.         }
  625. miss:
  626.         fat_node_put(nodep);
  627.         ipc_answer_0(callid, ENOENT);
  628.         ipc_answer_1(rid, ENOENT, 0);
  629.         return;
  630. hit:
  631.         (void) ipc_data_read_finalize(callid, name, strlen(name) + 1);
  632.         bytes = (pos - spos) + 1;
  633.     }
  634.  
  635.     fat_node_put(nodep);
  636.     ipc_answer_1(rid, EOK, (ipcarg_t)bytes);
  637. }
  638.  
  639. void fat_write(ipc_callid_t rid, ipc_call_t *request)
  640. {
  641.     dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);
  642.     fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);
  643.     off_t pos = (off_t)IPC_GET_ARG3(*request);
  644.     fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);
  645.     size_t bytes;
  646.     block_t *b, *bb;
  647.     uint16_t bps;
  648.     unsigned spc;
  649.     off_t boundary;
  650.    
  651.     if (!nodep) {
  652.         ipc_answer_0(rid, ENOENT);
  653.         return;
  654.     }
  655.    
  656.     /* XXX remove me when you are ready */
  657.     {
  658.         ipc_answer_0(rid, ENOTSUP);
  659.         fat_node_put(nodep);
  660.         return;
  661.     }
  662.  
  663.     ipc_callid_t callid;
  664.     size_t len;
  665.     if (!ipc_data_write_receive(&callid, &len)) {
  666.         fat_node_put(nodep);
  667.         ipc_answer_0(callid, EINVAL);
  668.         ipc_answer_0(rid, EINVAL);
  669.         return;
  670.     }
  671.  
  672.     /*
  673.      * In all scenarios, we will attempt to write out only one block worth
  674.      * of data at maximum. There might be some more efficient approaches,
  675.      * but this one greatly simplifies fat_write(). Note that we can afford
  676.      * to do this because the client must be ready to handle the return
  677.      * value signalizing a smaller number of bytes written.
  678.      */
  679.     bytes = min(len, bps - pos % bps);
  680.  
  681.     bb = block_get(dev_handle, BS_BLOCK, BS_SIZE);
  682.     bps = uint16_t_le2host(FAT_BS(bb)->bps);
  683.     spc = FAT_BS(bb)->spc;
  684.     block_put(bb);
  685.    
  686.     boundary = ROUND_UP(nodep->size, bps * spc);
  687.     if (pos < boundary) {
  688.         /*
  689.          * This is the easier case - we are either overwriting already
  690.          * existing contents or writing behind the EOF, but still within
  691.          * the limits of the last cluster. The node size may grow to the
  692.          * next block size boundary.
  693.          */
  694.         fat_fill_gap(nodep, FAT_CLST_RES0, pos);
  695.         b = fat_block_get(nodep, pos / bps);
  696.         (void) ipc_data_write_finalize(callid, b->data + pos % bps,
  697.             bytes);
  698.         b->dirty = true;        /* need to sync block */
  699.         block_put(b);
  700.         if (pos + bytes > nodep->size) {
  701.             nodep->size = pos + bytes;
  702.             nodep->dirty = true;    /* need to sync node */
  703.         }
  704.         fat_node_put(nodep);
  705.         ipc_answer_1(rid, EOK, bytes); 
  706.         return;
  707.     } else {
  708.         /*
  709.          * This is the more difficult case. We must allocate new
  710.          * clusters for the node and zero them out.
  711.          */
  712.         int status;
  713.         unsigned nclsts;
  714.         fat_cluster_t mcl, lcl;
  715.    
  716.         nclsts = (ROUND_UP(pos + bytes, bps * spc) - boundary) /
  717.             bps * spc;
  718.         /* create an independent chain of nclsts clusters in all FATs */
  719.         status = fat_alloc_clusters(dev_handle, nclsts, &mcl, &lcl);
  720.         if (status != EOK) {
  721.             /* could not allocate a chain of nclsts clusters */
  722.             fat_node_put(nodep);
  723.             ipc_answer_0(callid, status);
  724.             ipc_answer_0(rid, status);
  725.             return;
  726.         }
  727.         /* zero fill any gaps */
  728.         fat_fill_gap(nodep, mcl, pos);
  729.         b = _fat_block_get(dev_handle, lcl, (pos / bps) % spc);
  730.         (void) ipc_data_write_finalize(callid, b->data + pos % bps,
  731.             bytes);
  732.         b->dirty = true;        /* need to sync block */
  733.         block_put(b);
  734.         /*
  735.          * Append the cluster chain starting in mcl to the end of the
  736.          * node's cluster chain.
  737.          */
  738.         fat_append_clusters(nodep, mcl);
  739.         nodep->size = pos + bytes;
  740.         nodep->dirty = true;        /* need to sync node */
  741.         fat_node_put(nodep);
  742.         ipc_answer_1(rid, EOK, bytes);
  743.         return;
  744.     }
  745. }
  746.  
  747. /**
  748.  * @}
  749.  */
  750.