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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 <libblock.h>
  44. #include <ipc/ipc.h>
  45. #include <ipc/services.h>
  46. #include <ipc/devmap.h>
  47. #include <async.h>
  48. #include <errno.h>
  49. #include <string.h>
  50. #include <byteorder.h>
  51. #include <libadt/hash_table.h>
  52. #include <libadt/list.h>
  53. #include <assert.h>
  54. #include <futex.h>
  55. #include <sys/mman.h>
  56. #include <align.h>
  57.  
  58. /** Futex protecting the list of cached free FAT nodes. */
  59. static futex_t ffn_futex = FUTEX_INITIALIZER;
  60.  
  61. /** List of cached free FAT nodes. */
  62. static LIST_INITIALIZE(ffn_head);
  63.  
  64. static void fat_node_initialize(fat_node_t *node)
  65. {
  66.     futex_initialize(&node->lock, 1);
  67.     node->idx = NULL;
  68.     node->type = 0;
  69.     link_initialize(&node->ffn_link);
  70.     node->size = 0;
  71.     node->lnkcnt = 0;
  72.     node->refcnt = 0;
  73.     node->dirty = false;
  74. }
  75.  
  76. static void fat_node_sync(fat_node_t *node)
  77. {
  78.     block_t *b;
  79.     fat_bs_t *bs;
  80.     fat_dentry_t *d;
  81.     uint16_t bps;
  82.     unsigned dps;
  83.    
  84.     assert(node->dirty);
  85.  
  86.     bs = block_bb_get(node->idx->dev_handle);
  87.     bps = uint16_t_le2host(bs->bps);
  88.     dps = bps / sizeof(fat_dentry_t);
  89.    
  90.     /* Read the block that contains the dentry of interest. */
  91.     b = _fat_block_get(bs, node->idx->dev_handle, node->idx->pfc,
  92.         (node->idx->pdi * sizeof(fat_dentry_t)) / bps);
  93.  
  94.     d = ((fat_dentry_t *)b->data) + (node->idx->pdi % dps);
  95.  
  96.     d->firstc = host2uint16_t_le(node->firstc);
  97.     if (node->type == FAT_FILE)
  98.         d->size = host2uint32_t_le(node->size);
  99.     /* TODO: update other fields? (e.g time fields, attr field) */
  100.    
  101.     b->dirty = true;        /* need to sync block */
  102.     block_put(b);
  103. }
  104.  
  105. /** Internal version of fat_node_get().
  106.  *
  107.  * @param idxp      Locked index structure.
  108.  */
  109. static void *fat_node_get_core(fat_idx_t *idxp)
  110. {
  111.     block_t *b;
  112.     fat_bs_t *bs;
  113.     fat_dentry_t *d;
  114.     fat_node_t *nodep = NULL;
  115.     unsigned bps;
  116.     unsigned dps;
  117.  
  118.     if (idxp->nodep) {
  119.         /*
  120.          * We are lucky.
  121.          * The node is already instantiated in memory.
  122.          */
  123.         futex_down(&idxp->nodep->lock);
  124.         if (!idxp->nodep->refcnt++)
  125.             list_remove(&idxp->nodep->ffn_link);
  126.         futex_up(&idxp->nodep->lock);
  127.         return idxp->nodep;
  128.     }
  129.  
  130.     /*
  131.      * We must instantiate the node from the file system.
  132.      */
  133.    
  134.     assert(idxp->pfc);
  135.  
  136.     futex_down(&ffn_futex);
  137.     if (!list_empty(&ffn_head)) {
  138.         /* Try to use a cached free node structure. */
  139.         fat_idx_t *idxp_tmp;
  140.         nodep = list_get_instance(ffn_head.next, fat_node_t, ffn_link);
  141.         if (futex_trydown(&nodep->lock) == ESYNCH_WOULD_BLOCK)
  142.             goto skip_cache;
  143.         idxp_tmp = nodep->idx;
  144.         if (futex_trydown(&idxp_tmp->lock) == ESYNCH_WOULD_BLOCK) {
  145.             futex_up(&nodep->lock);
  146.             goto skip_cache;
  147.         }
  148.         list_remove(&nodep->ffn_link);
  149.         futex_up(&ffn_futex);
  150.         if (nodep->dirty)
  151.             fat_node_sync(nodep);
  152.         idxp_tmp->nodep = NULL;
  153.         futex_up(&nodep->lock);
  154.         futex_up(&idxp_tmp->lock);
  155.     } else {
  156. skip_cache:
  157.         /* Try to allocate a new node structure. */
  158.         futex_up(&ffn_futex);
  159.         nodep = (fat_node_t *)malloc(sizeof(fat_node_t));
  160.         if (!nodep)
  161.             return NULL;
  162.     }
  163.     fat_node_initialize(nodep);
  164.  
  165.     bs = block_bb_get(idxp->dev_handle);
  166.     bps = uint16_t_le2host(bs->bps);
  167.     dps = bps / sizeof(fat_dentry_t);
  168.  
  169.     /* Read the block that contains the dentry of interest. */
  170.     b = _fat_block_get(bs, idxp->dev_handle, idxp->pfc,
  171.         (idxp->pdi * sizeof(fat_dentry_t)) / bps);
  172.     assert(b);
  173.  
  174.     d = ((fat_dentry_t *)b->data) + (idxp->pdi % dps);
  175.     if (d->attr & FAT_ATTR_SUBDIR) {
  176.         /*
  177.          * The only directory which does not have this bit set is the
  178.          * root directory itself. The root directory node is handled
  179.          * and initialized elsewhere.
  180.          */
  181.         nodep->type = FAT_DIRECTORY;
  182.         /*
  183.          * Unfortunately, the 'size' field of the FAT dentry is not
  184.          * defined for the directory entry type. We must determine the
  185.          * size of the directory by walking the FAT.
  186.          */
  187.         nodep->size = bps * _fat_blcks_get(bs, idxp->dev_handle,
  188.             uint16_t_le2host(d->firstc), NULL);
  189.     } else {
  190.         nodep->type = FAT_FILE;
  191.         nodep->size = uint32_t_le2host(d->size);
  192.     }
  193.     nodep->firstc = uint16_t_le2host(d->firstc);
  194.     nodep->lnkcnt = 1;
  195.     nodep->refcnt = 1;
  196.  
  197.     block_put(b);
  198.  
  199.     /* Link the idx structure with the node structure. */
  200.     nodep->idx = idxp;
  201.     idxp->nodep = nodep;
  202.  
  203.     return nodep;
  204. }
  205.  
  206. /** Instantiate a FAT in-core node. */
  207. static void *fat_node_get(dev_handle_t dev_handle, fs_index_t index)
  208. {
  209.     void *node;
  210.     fat_idx_t *idxp;
  211.  
  212.     idxp = fat_idx_get_by_index(dev_handle, index);
  213.     if (!idxp)
  214.         return NULL;
  215.     /* idxp->lock held */
  216.     node = fat_node_get_core(idxp);
  217.     futex_up(&idxp->lock);
  218.     return node;
  219. }
  220.  
  221. static void fat_node_put(void *node)
  222. {
  223.     fat_node_t *nodep = (fat_node_t *)node;
  224.  
  225.     futex_down(&nodep->lock);
  226.     if (!--nodep->refcnt) {
  227.         futex_down(&ffn_futex);
  228.         list_append(&nodep->ffn_link, &ffn_head);
  229.         futex_up(&ffn_futex);
  230.     }
  231.     futex_up(&nodep->lock);
  232. }
  233.  
  234. static void *fat_create(int flags)
  235. {
  236.     return NULL;    /* not supported at the moment */
  237. }
  238.  
  239. static int fat_destroy(void *node)
  240. {
  241.     return ENOTSUP; /* not supported at the moment */
  242. }
  243.  
  244. static bool fat_link(void *prnt, void *chld, const char *name)
  245. {
  246.     return false;   /* not supported at the moment */
  247. }
  248.  
  249. static int fat_unlink(void *prnt, void *chld)
  250. {
  251.     return ENOTSUP; /* not supported at the moment */
  252. }
  253.  
  254. static void *fat_match(void *prnt, const char *component)
  255. {
  256.     fat_bs_t *bs;
  257.     fat_node_t *parentp = (fat_node_t *)prnt;
  258.     char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];
  259.     unsigned i, j;
  260.     unsigned bps;       /* bytes per sector */
  261.     unsigned dps;       /* dentries per sector */
  262.     unsigned blocks;
  263.     fat_dentry_t *d;
  264.     block_t *b;
  265.  
  266.     futex_down(&parentp->idx->lock);
  267.     bs = block_bb_get(parentp->idx->dev_handle);
  268.     bps = uint16_t_le2host(bs->bps);
  269.     dps = bps / sizeof(fat_dentry_t);
  270.     blocks = parentp->size / bps;
  271.     for (i = 0; i < blocks; i++) {
  272.         b = fat_block_get(bs, parentp, i);
  273.         for (j = 0; j < dps; j++) {
  274.             d = ((fat_dentry_t *)b->data) + j;
  275.             switch (fat_classify_dentry(d)) {
  276.             case FAT_DENTRY_SKIP:
  277.                 continue;
  278.             case FAT_DENTRY_LAST:
  279.                 block_put(b);
  280.                 futex_up(&parentp->idx->lock);
  281.                 return NULL;
  282.             default:
  283.             case FAT_DENTRY_VALID:
  284.                 dentry_name_canonify(d, name);
  285.                 break;
  286.             }
  287.             if (stricmp(name, component) == 0) {
  288.                 /* hit */
  289.                 void *node;
  290.                 /*
  291.                  * Assume tree hierarchy for locking.  We
  292.                  * already have the parent and now we are going
  293.                  * to lock the child.  Never lock in the oposite
  294.                  * order.
  295.                  */
  296.                 fat_idx_t *idx = fat_idx_get_by_pos(
  297.                     parentp->idx->dev_handle, parentp->firstc,
  298.                     i * dps + j);
  299.                 futex_up(&parentp->idx->lock);
  300.                 if (!idx) {
  301.                     /*
  302.                      * Can happen if memory is low or if we
  303.                      * run out of 32-bit indices.
  304.                      */
  305.                     block_put(b);
  306.                     return NULL;
  307.                 }
  308.                 node = fat_node_get_core(idx);
  309.                 futex_up(&idx->lock);
  310.                 block_put(b);
  311.                 return node;
  312.             }
  313.         }
  314.         block_put(b);
  315.     }
  316.  
  317.     futex_up(&parentp->idx->lock);
  318.     return NULL;
  319. }
  320.  
  321. static fs_index_t fat_index_get(void *node)
  322. {
  323.     fat_node_t *fnodep = (fat_node_t *)node;
  324.     if (!fnodep)
  325.         return 0;
  326.     return fnodep->idx->index;
  327. }
  328.  
  329. static size_t fat_size_get(void *node)
  330. {
  331.     return ((fat_node_t *)node)->size;
  332. }
  333.  
  334. static unsigned fat_lnkcnt_get(void *node)
  335. {
  336.     return ((fat_node_t *)node)->lnkcnt;
  337. }
  338.  
  339. static bool fat_has_children(void *node)
  340. {
  341.     fat_bs_t *bs;
  342.     fat_node_t *nodep = (fat_node_t *)node;
  343.     unsigned bps;
  344.     unsigned dps;
  345.     unsigned blocks;
  346.     block_t *b;
  347.     unsigned i, j;
  348.  
  349.     if (nodep->type != FAT_DIRECTORY)
  350.         return false;
  351.    
  352.     futex_down(&nodep->idx->lock);
  353.     bs = block_bb_get(nodep->idx->dev_handle);
  354.     bps = uint16_t_le2host(bs->bps);
  355.     dps = bps / sizeof(fat_dentry_t);
  356.  
  357.     blocks = nodep->size / bps;
  358.  
  359.     for (i = 0; i < blocks; i++) {
  360.         fat_dentry_t *d;
  361.    
  362.         b = fat_block_get(bs, nodep, i);
  363.         for (j = 0; j < dps; j++) {
  364.             d = ((fat_dentry_t *)b->data) + j;
  365.             switch (fat_classify_dentry(d)) {
  366.             case FAT_DENTRY_SKIP:
  367.                 continue;
  368.             case FAT_DENTRY_LAST:
  369.                 block_put(b);
  370.                 futex_up(&nodep->idx->lock);
  371.                 return false;
  372.             default:
  373.             case FAT_DENTRY_VALID:
  374.                 block_put(b);
  375.                 futex_up(&nodep->idx->lock);
  376.                 return true;
  377.             }
  378.             block_put(b);
  379.             futex_up(&nodep->idx->lock);
  380.             return true;
  381.         }
  382.         block_put(b);
  383.     }
  384.  
  385.     futex_up(&nodep->idx->lock);
  386.     return false;
  387. }
  388.  
  389. static void *fat_root_get(dev_handle_t dev_handle)
  390. {
  391.     return fat_node_get(dev_handle, 0);
  392. }
  393.  
  394. static char fat_plb_get_char(unsigned pos)
  395. {
  396.     return fat_reg.plb_ro[pos % PLB_SIZE];
  397. }
  398.  
  399. static bool fat_is_directory(void *node)
  400. {
  401.     return ((fat_node_t *)node)->type == FAT_DIRECTORY;
  402. }
  403.  
  404. static bool fat_is_file(void *node)
  405. {
  406.     return ((fat_node_t *)node)->type == FAT_FILE;
  407. }
  408.  
  409. /** libfs operations */
  410. libfs_ops_t fat_libfs_ops = {
  411.     .match = fat_match,
  412.     .node_get = fat_node_get,
  413.     .node_put = fat_node_put,
  414.     .create = fat_create,
  415.     .destroy = fat_destroy,
  416.     .link = fat_link,
  417.     .unlink = fat_unlink,
  418.     .index_get = fat_index_get,
  419.     .size_get = fat_size_get,
  420.     .lnkcnt_get = fat_lnkcnt_get,
  421.     .has_children = fat_has_children,
  422.     .root_get = fat_root_get,
  423.     .plb_get_char = fat_plb_get_char,
  424.     .is_directory = fat_is_directory,
  425.     .is_file = fat_is_file
  426. };
  427.  
  428. void fat_mounted(ipc_callid_t rid, ipc_call_t *request)
  429. {
  430.     dev_handle_t dev_handle = (dev_handle_t) IPC_GET_ARG1(*request);
  431.     fat_bs_t *bs;
  432.     uint16_t bps;
  433.     uint16_t rde;
  434.     int rc;
  435.  
  436.     /* initialize libblock */
  437.     rc = block_init(dev_handle, BS_SIZE, BS_BLOCK * BS_SIZE, BS_SIZE);
  438.     if (rc != EOK) {
  439.         ipc_answer_0(rid, 0);
  440.         return;
  441.     }
  442.  
  443.     /* get the buffer with the boot sector */
  444.     bs = block_bb_get(dev_handle);
  445.    
  446.     /* Read the number of root directory entries. */
  447.     bps = uint16_t_le2host(bs->bps);
  448.     rde = uint16_t_le2host(bs->root_ent_max);
  449.  
  450.     if (bps != BS_SIZE) {
  451.         block_fini(dev_handle);
  452.         ipc_answer_0(rid, ENOTSUP);
  453.         return;
  454.     }
  455.  
  456.     rc = fat_idx_init_by_dev_handle(dev_handle);
  457.     if (rc != EOK) {
  458.         block_fini(dev_handle);
  459.         ipc_answer_0(rid, rc);
  460.         return;
  461.     }
  462.  
  463.     /* Initialize the root node. */
  464.     fat_node_t *rootp = (fat_node_t *)malloc(sizeof(fat_node_t));
  465.     if (!rootp) {
  466.         block_fini(dev_handle);
  467.         fat_idx_fini_by_dev_handle(dev_handle);
  468.         ipc_answer_0(rid, ENOMEM);
  469.         return;
  470.     }
  471.     fat_node_initialize(rootp);
  472.  
  473.     fat_idx_t *ridxp = fat_idx_get_by_pos(dev_handle, FAT_CLST_ROOTPAR, 0);
  474.     if (!ridxp) {
  475.         block_fini(dev_handle);
  476.         free(rootp);
  477.         fat_idx_fini_by_dev_handle(dev_handle);
  478.         ipc_answer_0(rid, ENOMEM);
  479.         return;
  480.     }
  481.     assert(ridxp->index == 0);
  482.     /* ridxp->lock held */
  483.  
  484.     rootp->type = FAT_DIRECTORY;
  485.     rootp->firstc = FAT_CLST_ROOT;
  486.     rootp->refcnt = 1;
  487.     rootp->lnkcnt = 0;  /* FS root is not linked */
  488.     rootp->size = rde * sizeof(fat_dentry_t);
  489.     rootp->idx = ridxp;
  490.     ridxp->nodep = rootp;
  491.    
  492.     futex_up(&ridxp->lock);
  493.  
  494.     ipc_answer_3(rid, EOK, ridxp->index, rootp->size, rootp->lnkcnt);
  495. }
  496.  
  497. void fat_mount(ipc_callid_t rid, ipc_call_t *request)
  498. {
  499.     ipc_answer_0(rid, ENOTSUP);
  500. }
  501.  
  502. void fat_lookup(ipc_callid_t rid, ipc_call_t *request)
  503. {
  504.     libfs_lookup(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
  505. }
  506.  
  507. void fat_read(ipc_callid_t rid, ipc_call_t *request)
  508. {
  509.     dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);
  510.     fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);
  511.     off_t pos = (off_t)IPC_GET_ARG3(*request);
  512.     fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);
  513.     fat_bs_t *bs;
  514.     uint16_t bps;
  515.     size_t bytes;
  516.     block_t *b;
  517.  
  518.     if (!nodep) {
  519.         ipc_answer_0(rid, ENOENT);
  520.         return;
  521.     }
  522.  
  523.     ipc_callid_t callid;
  524.     size_t len;
  525.     if (!ipc_data_read_receive(&callid, &len)) {
  526.         fat_node_put(nodep);
  527.         ipc_answer_0(callid, EINVAL);
  528.         ipc_answer_0(rid, EINVAL);
  529.         return;
  530.     }
  531.  
  532.     bs = block_bb_get(dev_handle);
  533.     bps = uint16_t_le2host(bs->bps);
  534.  
  535.     if (nodep->type == FAT_FILE) {
  536.         /*
  537.          * Our strategy for regular file reads is to read one block at
  538.          * most and make use of the possibility to return less data than
  539.          * requested. This keeps the code very simple.
  540.          */
  541.         if (pos >= nodep->size) {
  542.             /* reading beyond the EOF */
  543.             bytes = 0;
  544.             (void) ipc_data_read_finalize(callid, NULL, 0);
  545.         } else {
  546.             bytes = min(len, bps - pos % bps);
  547.             bytes = min(bytes, nodep->size - pos);
  548.             b = fat_block_get(bs, nodep, pos / bps);
  549.             (void) ipc_data_read_finalize(callid, b->data + pos % bps,
  550.                 bytes);
  551.             block_put(b);
  552.         }
  553.     } else {
  554.         unsigned bnum;
  555.         off_t spos = pos;
  556.         char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];
  557.         fat_dentry_t *d;
  558.  
  559.         assert(nodep->type == FAT_DIRECTORY);
  560.         assert(nodep->size % bps == 0);
  561.         assert(bps % sizeof(fat_dentry_t) == 0);
  562.  
  563.         /*
  564.          * Our strategy for readdir() is to use the position pointer as
  565.          * an index into the array of all dentries. On entry, it points
  566.          * to the first unread dentry. If we skip any dentries, we bump
  567.          * the position pointer accordingly.
  568.          */
  569.         bnum = (pos * sizeof(fat_dentry_t)) / bps;
  570.         while (bnum < nodep->size / bps) {
  571.             off_t o;
  572.  
  573.             b = fat_block_get(bs, nodep, bnum);
  574.             for (o = pos % (bps / sizeof(fat_dentry_t));
  575.                 o < bps / sizeof(fat_dentry_t);
  576.                 o++, pos++) {
  577.                 d = ((fat_dentry_t *)b->data) + o;
  578.                 switch (fat_classify_dentry(d)) {
  579.                 case FAT_DENTRY_SKIP:
  580.                     continue;
  581.                 case FAT_DENTRY_LAST:
  582.                     block_put(b);
  583.                     goto miss;
  584.                 default:
  585.                 case FAT_DENTRY_VALID:
  586.                     dentry_name_canonify(d, name);
  587.                     block_put(b);
  588.                     goto hit;
  589.                 }
  590.             }
  591.             block_put(b);
  592.             bnum++;
  593.         }
  594. miss:
  595.         fat_node_put(nodep);
  596.         ipc_answer_0(callid, ENOENT);
  597.         ipc_answer_1(rid, ENOENT, 0);
  598.         return;
  599. hit:
  600.         (void) ipc_data_read_finalize(callid, name, strlen(name) + 1);
  601.         bytes = (pos - spos) + 1;
  602.     }
  603.  
  604.     fat_node_put(nodep);
  605.     ipc_answer_1(rid, EOK, (ipcarg_t)bytes);
  606. }
  607.  
  608. void fat_write(ipc_callid_t rid, ipc_call_t *request)
  609. {
  610.     dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);
  611.     fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);
  612.     off_t pos = (off_t)IPC_GET_ARG3(*request);
  613.     fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);
  614.     fat_bs_t *bs;
  615.     size_t bytes;
  616.     block_t *b;
  617.     uint16_t bps;
  618.     unsigned spc;
  619.     off_t boundary;
  620.    
  621.     if (!nodep) {
  622.         ipc_answer_0(rid, ENOENT);
  623.         return;
  624.     }
  625.    
  626.     /* XXX remove me when you are ready */
  627.     {
  628.         ipc_answer_0(rid, ENOTSUP);
  629.         fat_node_put(nodep);
  630.         return;
  631.     }
  632.  
  633.     ipc_callid_t callid;
  634.     size_t len;
  635.     if (!ipc_data_write_receive(&callid, &len)) {
  636.         fat_node_put(nodep);
  637.         ipc_answer_0(callid, EINVAL);
  638.         ipc_answer_0(rid, EINVAL);
  639.         return;
  640.     }
  641.  
  642.     /*
  643.      * In all scenarios, we will attempt to write out only one block worth
  644.      * of data at maximum. There might be some more efficient approaches,
  645.      * but this one greatly simplifies fat_write(). Note that we can afford
  646.      * to do this because the client must be ready to handle the return
  647.      * value signalizing a smaller number of bytes written.
  648.      */
  649.     bytes = min(len, bps - pos % bps);
  650.  
  651.     bs = block_bb_get(dev_handle);
  652.     bps = uint16_t_le2host(bs->bps);
  653.     spc = bs->spc;
  654.    
  655.     boundary = ROUND_UP(nodep->size, bps * spc);
  656.     if (pos < boundary) {
  657.         /*
  658.          * This is the easier case - we are either overwriting already
  659.          * existing contents or writing behind the EOF, but still within
  660.          * the limits of the last cluster. The node size may grow to the
  661.          * next block size boundary.
  662.          */
  663.         fat_fill_gap(bs, nodep, FAT_CLST_RES0, pos);
  664.         b = fat_block_get(bs, nodep, pos / bps);
  665.         (void) ipc_data_write_finalize(callid, b->data + pos % bps,
  666.             bytes);
  667.         b->dirty = true;        /* need to sync block */
  668.         block_put(b);
  669.         if (pos + bytes > nodep->size) {
  670.             nodep->size = pos + bytes;
  671.             nodep->dirty = true;    /* need to sync node */
  672.         }
  673.         fat_node_put(nodep);
  674.         ipc_answer_1(rid, EOK, bytes); 
  675.         return;
  676.     } else {
  677.         /*
  678.          * This is the more difficult case. We must allocate new
  679.          * clusters for the node and zero them out.
  680.          */
  681.         int status;
  682.         unsigned nclsts;
  683.         fat_cluster_t mcl, lcl;
  684.    
  685.         nclsts = (ROUND_UP(pos + bytes, bps * spc) - boundary) /
  686.             bps * spc;
  687.         /* create an independent chain of nclsts clusters in all FATs */
  688.         status = fat_alloc_clusters(bs, dev_handle, nclsts, &mcl,
  689.             &lcl);
  690.         if (status != EOK) {
  691.             /* could not allocate a chain of nclsts clusters */
  692.             fat_node_put(nodep);
  693.             ipc_answer_0(callid, status);
  694.             ipc_answer_0(rid, status);
  695.             return;
  696.         }
  697.         /* zero fill any gaps */
  698.         fat_fill_gap(bs, nodep, mcl, pos);
  699.         b = _fat_block_get(bs, dev_handle, lcl,
  700.             (pos / bps) % spc);
  701.         (void) ipc_data_write_finalize(callid, b->data + pos % bps,
  702.             bytes);
  703.         b->dirty = true;        /* need to sync block */
  704.         block_put(b);
  705.         /*
  706.          * Append the cluster chain starting in mcl to the end of the
  707.          * node's cluster chain.
  708.          */
  709.         fat_append_clusters(bs, nodep, mcl);
  710.         nodep->size = pos + bytes;
  711.         nodep->dirty = true;        /* need to sync node */
  712.         fat_node_put(nodep);
  713.         ipc_answer_1(rid, EOK, bytes);
  714.         return;
  715.     }
  716. }
  717.  
  718. /**
  719.  * @}
  720.  */
  721.