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/*

 * Copyright (c) 2008 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup fs

 * @{

 */ 

/**

 * @file	fat_ops.c

 * @brief	Implementation of VFS operations for the FAT file system server.

 */

#include "fat.h"

#include "fat_dentry.h"

#include "fat_fat.h"

#include "../../vfs/vfs.h"

#include <libfs.h>

#include <libblock.h>

#include <ipc/ipc.h>

#include <ipc/services.h>

#include <ipc/devmap.h>

#include <async.h>

#include <errno.h>

#include <string.h>

#include <byteorder.h>

#include <libadt/hash_table.h>

#include <libadt/list.h>

#include <assert.h>

#include <futex.h>

#include <sys/mman.h>

#include <align.h>

/** Futex protecting the list of cached free FAT nodes. */

static futex_t ffn_futex = FUTEX_INITIALIZER;

/** List of cached free FAT nodes. */

static LIST_INITIALIZE(ffn_head);

static void fat_node_initialize(fat_node_t *node)

{

	futex_initialize(&node->lock, 1);

	node->idx = NULL;

	node->type = 0;

	link_initialize(&node->ffn_link);

	node->size = 0;

	node->lnkcnt = 0;

	node->refcnt = 0;

	node->dirty = false;

}

static void fat_node_sync(fat_node_t *node)

{

	block_t *b;

	fat_bs_t *bs;

	fat_dentry_t *d;

	uint16_t bps;

	unsigned dps;

	assert(node->dirty);

	bs = block_bb_get(node->idx->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	dps = bps / sizeof(fat_dentry_t);

	/* Read the block that contains the dentry of interest. */

	b = _fat_block_get(bs, node->idx->dev_handle, node->idx->pfc,

	    (node->idx->pdi * sizeof(fat_dentry_t)) / bps, BLOCK_FLAGS_NONE);

	d = ((fat_dentry_t *)b->data) + (node->idx->pdi % dps);

	d->firstc = host2uint16_t_le(node->firstc);

	if (node->type == FAT_FILE) {

		d->size = host2uint32_t_le(node->size);

	} else if (node->type == FAT_DIRECTORY) {

		d->attr = FAT_ATTR_SUBDIR;

	}

	/* TODO: update other fields? (e.g time fields) */

	b->dirty = true;		/* need to sync block */

	block_put(b);

}

static fat_node_t *fat_node_get_new(void)

{

	fat_node_t *nodep;

	futex_down(&ffn_futex);

	if (!list_empty(&ffn_head)) {

		/* Try to use a cached free node structure. */

		fat_idx_t *idxp_tmp;

		nodep = list_get_instance(ffn_head.next, fat_node_t, ffn_link);

		if (futex_trydown(&nodep->lock) == ESYNCH_WOULD_BLOCK)

			goto skip_cache;

		idxp_tmp = nodep->idx;

		if (futex_trydown(&idxp_tmp->lock) == ESYNCH_WOULD_BLOCK) {

			futex_up(&nodep->lock);

			goto skip_cache;

		}

		list_remove(&nodep->ffn_link);

		futex_up(&ffn_futex);

		if (nodep->dirty)

			fat_node_sync(nodep);

		idxp_tmp->nodep = NULL;

		futex_up(&nodep->lock);

		futex_up(&idxp_tmp->lock);

	} else {

skip_cache:

		/* Try to allocate a new node structure. */

		futex_up(&ffn_futex);

		nodep = (fat_node_t *)malloc(sizeof(fat_node_t));

		if (!nodep)

			return NULL;

	}

	fat_node_initialize(nodep);

	return nodep;

}

/** Internal version of fat_node_get().

 *

 * @param idxp		Locked index structure.

 */

static void *fat_node_get_core(fat_idx_t *idxp)

{

	block_t *b;

	fat_bs_t *bs;

	fat_dentry_t *d;

	fat_node_t *nodep = NULL;

	unsigned bps;

	unsigned spc;

	unsigned dps;

	if (idxp->nodep) {

		/*

		 * We are lucky.

		 * The node is already instantiated in memory.

		 */

		futex_down(&idxp->nodep->lock);

		if (!idxp->nodep->refcnt++)

			list_remove(&idxp->nodep->ffn_link);

		futex_up(&idxp->nodep->lock);

		return idxp->nodep;

	}

	/*

	 * We must instantiate the node from the file system.

	 */

	assert(idxp->pfc);

	nodep = fat_node_get_new();

	if (!nodep)

		return NULL;

	bs = block_bb_get(idxp->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	spc = bs->spc;

	dps = bps / sizeof(fat_dentry_t);

	/* Read the block that contains the dentry of interest. */

	b = _fat_block_get(bs, idxp->dev_handle, idxp->pfc,

	    (idxp->pdi * sizeof(fat_dentry_t)) / bps, BLOCK_FLAGS_NONE);

	assert(b);

	d = ((fat_dentry_t *)b->data) + (idxp->pdi % dps);

	if (d->attr & FAT_ATTR_SUBDIR) {

		/* 

		 * The only directory which does not have this bit set is the

		 * root directory itself. The root directory node is handled

		 * and initialized elsewhere.

		 */

		nodep->type = FAT_DIRECTORY;

		/*

		 * Unfortunately, the 'size' field of the FAT dentry is not

		 * defined for the directory entry type. We must determine the

		 * size of the directory by walking the FAT.

		 */

		nodep->size = bps * spc * fat_clusters_get(bs, idxp->dev_handle,

		    uint16_t_le2host(d->firstc));

	} else {

		nodep->type = FAT_FILE;

		nodep->size = uint32_t_le2host(d->size);

	}

	nodep->firstc = uint16_t_le2host(d->firstc);

	nodep->lnkcnt = 1;

	nodep->refcnt = 1;

	block_put(b);

	/* Link the idx structure with the node structure. */

	nodep->idx = idxp;

	idxp->nodep = nodep;

	return nodep;

}

/*

 * Forward declarations of FAT libfs operations.

 */

static void *fat_node_get(dev_handle_t, fs_index_t);

static void fat_node_put(void *);

static void *fat_create_node(dev_handle_t, int);

static int fat_destroy_node(void *);

static int fat_link(void *, void *, const char *);

static int fat_unlink(void *, void *);

static void *fat_match(void *, const char *);

static fs_index_t fat_index_get(void *);

static size_t fat_size_get(void *);

static unsigned fat_lnkcnt_get(void *);

static bool fat_has_children(void *);

static void *fat_root_get(dev_handle_t);

static char fat_plb_get_char(unsigned);

static bool fat_is_directory(void *);

static bool fat_is_file(void *node);

/*

 * FAT libfs operations.

 */

/** Instantiate a FAT in-core node. */

void *fat_node_get(dev_handle_t dev_handle, fs_index_t index)

{

	void *node;

	fat_idx_t *idxp;

	idxp = fat_idx_get_by_index(dev_handle, index);

	if (!idxp)

		return NULL;

	/* idxp->lock held */

	node = fat_node_get_core(idxp);

	futex_up(&idxp->lock);

	return node;

}

void fat_node_put(void *node)

{

	fat_node_t *nodep = (fat_node_t *)node;

	bool destroy = false;

	futex_down(&nodep->lock);

	if (!--nodep->refcnt) {

		if (nodep->idx) {

			futex_down(&ffn_futex);

			list_append(&nodep->ffn_link, &ffn_head);

			futex_up(&ffn_futex);

		} else {

			/*

			 * The node does not have any index structure associated

			 * with itself. This can only mean that we are releasing

			 * the node after a failed attempt to allocate the index

			 * structure for it.

			 */

			destroy = true;

		}

	}

	futex_up(&nodep->lock);

	if (destroy)

		free(node);

}

void *fat_create_node(dev_handle_t dev_handle, int flags)

{

	fat_idx_t *idxp;

	fat_node_t *nodep;

	fat_bs_t *bs;

	fat_cluster_t mcl, lcl;

	uint16_t bps;

	int rc;

	bs = block_bb_get(dev_handle);

	bps = uint16_t_le2host(bs->bps);

	if (flags & L_DIRECTORY) {

		/* allocate a cluster */

		rc = fat_alloc_clusters(bs, dev_handle, 1, &mcl, &lcl);

		if (rc != EOK) 

			return NULL;

	}

	nodep = fat_node_get_new();

	if (!nodep) {

		fat_free_clusters(bs, dev_handle, mcl);	

		return NULL;

	}

	idxp = fat_idx_get_new(dev_handle);

	if (!idxp) {

		fat_free_clusters(bs, dev_handle, mcl);	

		fat_node_put(nodep);

		return NULL;

	}

	/* idxp->lock held */

	if (flags & L_DIRECTORY) {

		int i;

		block_t *b;

		/*

		 * Populate the new cluster with unused dentries.

		 * We don't create the '.' and '..' entries, since they are

		 * optional and HelenOS VFS does not need them.

		 */

		for (i = 0; i < bs->spc; i++) {

			b = _fat_block_get(bs, dev_handle, mcl, i,

			    BLOCK_FLAGS_NOREAD);

			/* mark all dentries as never-used */

			memset(b->data, 0, bps);

			b->dirty = false;

			block_put(b);

		}

		nodep->type = FAT_DIRECTORY;

		nodep->firstc = mcl;

		nodep->size = bps * bs->spc;

	} else {

		nodep->type = FAT_FILE;

		nodep->firstc = FAT_CLST_RES0;

		nodep->size = 0;

	}

	nodep->lnkcnt = 0;	/* not linked anywhere */

	nodep->refcnt = 1;

	nodep->dirty = true;

	nodep->idx = idxp;

	idxp->nodep = nodep;

	futex_up(&idxp->lock);

	return nodep;

}

int fat_destroy_node(void *node)

{

	fat_node_t *nodep = (fat_node_t *)node;

	fat_bs_t *bs;

	/*

	 * The node is not reachable from the file system. This means that the

	 * link count should be zero and that the index structure cannot be

	 * found in the position hash. Obviously, we don't need to lock the node

	 * nor its index structure.

	 */

	assert(nodep->lnkcnt == 0);

	/*

	 * The node may not have any children.

	 */

	assert(fat_has_children(node) == false);

	bs = block_bb_get(nodep->idx->dev_handle);

	if (nodep->firstc != FAT_CLST_RES0) {

		assert(nodep->size);

		/* Free all clusters allocated to the node. */

		fat_free_clusters(bs, nodep->idx->dev_handle, nodep->firstc);

	}

	fat_idx_destroy(nodep->idx);

	free(nodep);

	return EOK;

}

int fat_link(void *prnt, void *chld, const char *name)

{

	fat_node_t *parentp = (fat_node_t *)prnt;

	fat_node_t *childp = (fat_node_t *)chld;

	fat_dentry_t *d;

	fat_bs_t *bs;

	block_t *b;

	int i, j;

	uint16_t bps;

	unsigned dps;

	unsigned blocks;

	futex_down(&childp->lock);

	if (childp->lnkcnt == 1) {

		/*

		 * On FAT, we don't support multiple hard links.

		 */

		futex_up(&childp->lock);

		return EMLINK;

	}

	assert(childp->lnkcnt == 0);

	futex_up(&childp->lock);

	if (!fat_dentry_name_verify(name)) {

		/*

		 * Attempt to create unsupported name.

		 */

		return ENOTSUP;

	}

	/*

	 * Get us an unused parent node's dentry or grow the parent and allocate

	 * a new one.

	 */

	futex_down(&parentp->idx->lock);

	bs = block_bb_get(parentp->idx->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	dps = bps / sizeof(fat_dentry_t);

	blocks = parentp->size / bps;

	for (i = 0; i < blocks; i++) {

		b = fat_block_get(bs, parentp, i, BLOCK_FLAGS_NONE);

		for (j = 0; j < dps; j++) {

			d = ((fat_dentry_t *)b->data) + j;

			switch (fat_classify_dentry(d)) {

			case FAT_DENTRY_SKIP:

			case FAT_DENTRY_VALID:

				/* skipping used and meta entries */

				continue;

			case FAT_DENTRY_FREE:

			case FAT_DENTRY_LAST:

				/* found an empty slot */

				goto hit;

			}

		}

		block_put(b);

	}

	/*

	 * We need to grow the parent in order to create a new unused dentry.

	 */

	futex_up(&parentp->idx->lock);

	return ENOTSUP;	/* XXX */

hit:

	/*

	 * At this point we only establish the link between the parent and the

	 * child.  The dentry, except of the name and the extension, will remain

	 * uninitialized until the the corresponding node is synced. Thus the

	 * valid dentry data is kept in the child node structure.

	 */

	memset(d, 0, sizeof(fat_dentry_t));

	fat_dentry_name_set(d, name);

	b->dirty = true;		/* need to sync block */

	block_put(b);

	futex_up(&parentp->idx->lock);

	futex_down(&childp->idx->lock);

	childp->idx->pfc = parentp->firstc;

	childp->idx->pdi = i * dps + j;

	futex_up(&childp->idx->lock);

	futex_down(&childp->lock);

	childp->lnkcnt = 1;

	childp->dirty = true;		/* need to sync node */

	futex_up(&childp->lock);

	/*

	 * Hash in the index structure into the position hash.

	 */

	fat_idx_hashin(childp->idx);

	return EOK;

}

int fat_unlink(void *prnt, void *chld)

{

	fat_node_t *parentp = (fat_node_t *)prnt;

	fat_node_t *childp = (fat_node_t *)chld;

	fat_bs_t *bs;

	fat_dentry_t *d;

	uint16_t bps;

	block_t *b;

	futex_down(&parentp->lock);

	futex_down(&childp->lock);

	assert(childp->lnkcnt == 1);

	futex_down(&childp->idx->lock);

	bs = block_bb_get(childp->idx->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	b = _fat_block_get(bs, childp->idx->dev_handle, childp->idx->pfc,

	    (childp->idx->pdi * sizeof(fat_dentry_t)) / bps,

	    BLOCK_FLAGS_NONE);

	d = (fat_dentry_t *)b->data +

	    (childp->idx->pdi % (bps / sizeof(fat_dentry_t)));

	/* mark the dentry as not-currently-used */

	d->name[0] = FAT_DENTRY_ERASED;

	b->dirty = true;		/* need to sync block */

	block_put(b);

	/* remove the index structure from the position hash */

	fat_idx_hashout(childp->idx);

	/* clear position information */

	childp->idx->pfc = FAT_CLST_RES0;

	childp->idx->pdi = 0;

	futex_up(&childp->idx->lock);

	childp->lnkcnt = 0;

	childp->dirty = true;

	futex_up(&childp->lock);

	futex_up(&parentp->lock);

	return EOK;

}

void *fat_match(void *prnt, const char *component)

{

	fat_bs_t *bs;

	fat_node_t *parentp = (fat_node_t *)prnt;

	char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];

	unsigned i, j;

	unsigned bps;		/* bytes per sector */

	unsigned dps;		/* dentries per sector */

	unsigned blocks;

	fat_dentry_t *d;

	block_t *b;

	futex_down(&parentp->idx->lock);

	bs = block_bb_get(parentp->idx->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	dps = bps / sizeof(fat_dentry_t);

	blocks = parentp->size / bps;

	for (i = 0; i < blocks; i++) {

		b = fat_block_get(bs, parentp, i, BLOCK_FLAGS_NONE);

		for (j = 0; j < dps; j++) { 

			d = ((fat_dentry_t *)b->data) + j;

			switch (fat_classify_dentry(d)) {

			case FAT_DENTRY_SKIP:

			case FAT_DENTRY_FREE:

				continue;

			case FAT_DENTRY_LAST:

				block_put(b);

				futex_up(&parentp->idx->lock);

				return NULL;

			default:

			case FAT_DENTRY_VALID:

				fat_dentry_name_get(d, name);

				break;

			}

			if (fat_dentry_namecmp(name, component) == 0) {

				/* hit */

				void *node;

				/*

				 * Assume tree hierarchy for locking.  We

				 * already have the parent and now we are going

				 * to lock the child.  Never lock in the oposite

				 * order.

				 */

				fat_idx_t *idx = fat_idx_get_by_pos(

				    parentp->idx->dev_handle, parentp->firstc,

				    i * dps + j);

				futex_up(&parentp->idx->lock);

				if (!idx) {

					/*

					 * Can happen if memory is low or if we

					 * run out of 32-bit indices.

					 */

					block_put(b);

					return NULL;

				}

				node = fat_node_get_core(idx);

				futex_up(&idx->lock);

				block_put(b);

				return node;

			}

		}

		block_put(b);

	}

	futex_up(&parentp->idx->lock);

	return NULL;

}

fs_index_t fat_index_get(void *node)

{

	fat_node_t *fnodep = (fat_node_t *)node;

	if (!fnodep)

		return 0;

	return fnodep->idx->index;

}

size_t fat_size_get(void *node)

{

	return ((fat_node_t *)node)->size;

}

unsigned fat_lnkcnt_get(void *node)

{

	return ((fat_node_t *)node)->lnkcnt;

}

bool fat_has_children(void *node)

{

	fat_bs_t *bs;

	fat_node_t *nodep = (fat_node_t *)node;

	unsigned bps;

	unsigned dps;

	unsigned blocks;

	block_t *b;

	unsigned i, j;

	if (nodep->type != FAT_DIRECTORY)

		return false;

	futex_down(&nodep->idx->lock);

	bs = block_bb_get(nodep->idx->dev_handle);

	bps = uint16_t_le2host(bs->bps);

	dps = bps / sizeof(fat_dentry_t);

	blocks = nodep->size / bps;

	for (i = 0; i < blocks; i++) {

		fat_dentry_t *d;

		b = fat_block_get(bs, nodep, i, BLOCK_FLAGS_NONE);

		for (j = 0; j < dps; j++) {

			d = ((fat_dentry_t *)b->data) + j;

			switch (fat_classify_dentry(d)) {

			case FAT_DENTRY_SKIP:

			case FAT_DENTRY_FREE:

				continue;

			case FAT_DENTRY_LAST:

				block_put(b);

				futex_up(&nodep->idx->lock);

				return false;

			default:

			case FAT_DENTRY_VALID:

				block_put(b);

				futex_up(&nodep->idx->lock);

				return true;

			}

			block_put(b);

			futex_up(&nodep->idx->lock);

			return true;

		}

		block_put(b);

	}

	futex_up(&nodep->idx->lock);

	return false;

}

void *fat_root_get(dev_handle_t dev_handle)

{

	return fat_node_get(dev_handle, 0);

}

char fat_plb_get_char(unsigned pos)

{

	return fat_reg.plb_ro[pos % PLB_SIZE];

}

bool fat_is_directory(void *node)

{

	return ((fat_node_t *)node)->type == FAT_DIRECTORY;

}

bool fat_is_file(void *node)

{

	return ((fat_node_t *)node)->type == FAT_FILE;

}

/** libfs operations */

libfs_ops_t fat_libfs_ops = {

	.match = fat_match,

	.node_get = fat_node_get,

	.node_put = fat_node_put,

	.create = fat_create_node,

	.destroy = fat_destroy_node,

	.link = fat_link,

	.unlink = fat_unlink,

	.index_get = fat_index_get,

	.size_get = fat_size_get,

	.lnkcnt_get = fat_lnkcnt_get,

	.has_children = fat_has_children,

	.root_get = fat_root_get,

	.plb_get_char =	fat_plb_get_char,

	.is_directory = fat_is_directory,

	.is_file = fat_is_file

};

/*

 * VFS operations.

 */

void fat_mounted(ipc_callid_t rid, ipc_call_t *request)

{

	dev_handle_t dev_handle = (dev_handle_t) IPC_GET_ARG1(*request);

	fat_bs_t *bs;

	uint16_t bps;

	uint16_t rde;

	int rc;

	/* initialize libblock */

	rc = block_init(dev_handle, BS_SIZE);

	if (rc != EOK) {

		ipc_answer_0(rid, rc);

		return;

	}

	/* prepare the boot block */

	rc = block_bb_read(dev_handle, BS_BLOCK * BS_SIZE, BS_SIZE);

	if (rc != EOK) {

		block_fini(dev_handle);

		ipc_answer_0(rid, rc);

		return;

	}

	/* get the buffer with the boot sector */

	bs = block_bb_get(dev_handle);

	/* Read the number of root directory entries. */

	bps = uint16_t_le2host(bs->bps);

	rde = uint16_t_le2host(bs->root_ent_max);

	if (bps != BS_SIZE) {

		block_fini(dev_handle);

		ipc_answer_0(rid, ENOTSUP);

		return;

	}

	/* Initialize the block cache */

	rc = block_cache_init(dev_handle, bps, 0 /* XXX */);

	if (rc != EOK) {

		block_fini(dev_handle);

		ipc_answer_0(rid, rc);

		return;

	}

	rc = fat_idx_init_by_dev_handle(dev_handle);

	if (rc != EOK) {

		block_fini(dev_handle);

		ipc_answer_0(rid, rc);

		return;

	}

	/* Initialize the root node. */

	fat_node_t *rootp = (fat_node_t *)malloc(sizeof(fat_node_t));

	if (!rootp) {

		block_fini(dev_handle);

		fat_idx_fini_by_dev_handle(dev_handle);

		ipc_answer_0(rid, ENOMEM);

		return;

	}

	fat_node_initialize(rootp);

	fat_idx_t *ridxp = fat_idx_get_by_pos(dev_handle, FAT_CLST_ROOTPAR, 0);

	if (!ridxp) {

		block_fini(dev_handle);

		free(rootp);

		fat_idx_fini_by_dev_handle(dev_handle);

		ipc_answer_0(rid, ENOMEM);

		return;

	}

	assert(ridxp->index == 0);

	/* ridxp->lock held */

	rootp->type = FAT_DIRECTORY;

	rootp->firstc = FAT_CLST_ROOT;

	rootp->refcnt = 1;

	rootp->lnkcnt = 0;	/* FS root is not linked */

	rootp->size = rde * sizeof(fat_dentry_t);

	rootp->idx = ridxp;

	ridxp->nodep = rootp;

	futex_up(&ridxp->lock);

	ipc_answer_3(rid, EOK, ridxp->index, rootp->size, rootp->lnkcnt);

}

void fat_mount(ipc_callid_t rid, ipc_call_t *request)

{

	ipc_answer_0(rid, ENOTSUP);

}

void fat_lookup(ipc_callid_t rid, ipc_call_t *request)

{

	libfs_lookup(&fat_libfs_ops, fat_reg.fs_handle, rid, request);

}

void fat_read(ipc_callid_t rid, ipc_call_t *request)

{

	dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);

	fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);

	off_t pos = (off_t)IPC_GET_ARG3(*request);

	fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);

	fat_bs_t *bs;

	uint16_t bps;

	size_t bytes;

	block_t *b;

	if (!nodep) {

		ipc_answer_0(rid, ENOENT);

		return;

	}

	ipc_callid_t callid;

	size_t len;

	if (!ipc_data_read_receive(&callid, &len)) {

		fat_node_put(nodep);

		ipc_answer_0(callid, EINVAL);

		ipc_answer_0(rid, EINVAL);

		return;

	}

	bs = block_bb_get(dev_handle);

	bps = uint16_t_le2host(bs->bps);

	if (nodep->type == FAT_FILE) {

		/*

		 * Our strategy for regular file reads is to read one block at

		 * most and make use of the possibility to return less data than

		 * requested. This keeps the code very simple.

		 */

		if (pos >= nodep->size) {

			/* reading beyond the EOF */

			bytes = 0;

			(void) ipc_data_read_finalize(callid, NULL, 0);

		} else {

			bytes = min(len, bps - pos % bps);

			bytes = min(bytes, nodep->size - pos);

			b = fat_block_get(bs, nodep, pos / bps,

			    BLOCK_FLAGS_NONE);

			(void) ipc_data_read_finalize(callid, b->data + pos % bps,

			    bytes);

			block_put(b);

		}

	} else {

		unsigned bnum;

		off_t spos = pos;

		char name[FAT_NAME_LEN + 1 + FAT_EXT_LEN + 1];

		fat_dentry_t *d;

		assert(nodep->type == FAT_DIRECTORY);

		assert(nodep->size % bps == 0);

		assert(bps % sizeof(fat_dentry_t) == 0);

		/*

		 * Our strategy for readdir() is to use the position pointer as

		 * an index into the array of all dentries. On entry, it points

		 * to the first unread dentry. If we skip any dentries, we bump

		 * the position pointer accordingly.

		 */

		bnum = (pos * sizeof(fat_dentry_t)) / bps;

		while (bnum < nodep->size / bps) {

			off_t o;

			b = fat_block_get(bs, nodep, bnum, BLOCK_FLAGS_NONE);

			for (o = pos % (bps / sizeof(fat_dentry_t));

			    o < bps / sizeof(fat_dentry_t);

			    o++, pos++) {

				d = ((fat_dentry_t *)b->data) + o;

				switch (fat_classify_dentry(d)) {

				case FAT_DENTRY_SKIP:

				case FAT_DENTRY_FREE:

					continue;

				case FAT_DENTRY_LAST:

					block_put(b);

					goto miss;

				default:

				case FAT_DENTRY_VALID:

					fat_dentry_name_get(d, name);

					block_put(b);

					goto hit;

				}

			}

			block_put(b);

			bnum++;

		}

miss:

		fat_node_put(nodep);

		ipc_answer_0(callid, ENOENT);

		ipc_answer_1(rid, ENOENT, 0);

		return;

hit:

		(void) ipc_data_read_finalize(callid, name, strlen(name) + 1);

		bytes = (pos - spos) + 1;

	}

	fat_node_put(nodep);

	ipc_answer_1(rid, EOK, (ipcarg_t)bytes);

}

void fat_write(ipc_callid_t rid, ipc_call_t *request)

{

	dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);

	fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);

	off_t pos = (off_t)IPC_GET_ARG3(*request);

	fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);

	fat_bs_t *bs;

	size_t bytes;

	block_t *b;

	uint16_t bps;

	unsigned spc;

	unsigned bpc;		/* bytes per cluster */

	off_t boundary;

	int flags = BLOCK_FLAGS_NONE;

	if (!nodep) {

		ipc_answer_0(rid, ENOENT);

		return;

	}

	ipc_callid_t callid;

	size_t len;

	if (!ipc_data_write_receive(&callid, &len)) {

		fat_node_put(nodep);

		ipc_answer_0(callid, EINVAL);

		ipc_answer_0(rid, EINVAL);

		return;

	}

	bs = block_bb_get(dev_handle);

	bps = uint16_t_le2host(bs->bps);

	spc = bs->spc;

	bpc = bps * spc;

	/*

	 * In all scenarios, we will attempt to write out only one block worth

	 * of data at maximum. There might be some more efficient approaches,

	 * but this one greatly simplifies fat_write(). Note that we can afford

	 * to do this because the client must be ready to handle the return

	 * value signalizing a smaller number of bytes written. 

	 */ 

	bytes = min(len, bps - pos % bps);

	if (bytes == bps)

		flags |= BLOCK_FLAGS_NOREAD;

	boundary = ROUND_UP(nodep->size, bpc);

	if (pos < boundary) {

		/*

		 * This is the easier case - we are either overwriting already

		 * existing contents or writing behind the EOF, but still within

		 * the limits of the last cluster. The node size may grow to the

		 * next block size boundary.

		 */

		fat_fill_gap(bs, nodep, FAT_CLST_RES0, pos);

		b = fat_block_get(bs, nodep, pos / bps, flags);

		(void) ipc_data_write_finalize(callid, b->data + pos % bps,

		    bytes);

		b->dirty = true;		/* need to sync block */

		block_put(b);

		if (pos + bytes > nodep->size) {

			nodep->size = pos + bytes;

			nodep->dirty = true;	/* need to sync node */

		}

		ipc_answer_2(rid, EOK, bytes, nodep->size);	

		fat_node_put(nodep);

		return;

	} else {

		/*

		 * This is the more difficult case. We must allocate new

		 * clusters for the node and zero them out.

		 */

		int status;

		unsigned nclsts;

		fat_cluster_t mcl, lcl; 

		nclsts = (ROUND_UP(pos + bytes, bpc) - boundary) / bpc;

		/* create an independent chain of nclsts clusters in all FATs */

		status = fat_alloc_clusters(bs, dev_handle, nclsts, &mcl, &lcl);

		if (status != EOK) {

			/* could not allocate a chain of nclsts clusters */

			fat_node_put(nodep);

			ipc_answer_0(callid, status);

			ipc_answer_0(rid, status);

			return;

		}

		/* zero fill any gaps */

		fat_fill_gap(bs, nodep, mcl, pos);

		b = _fat_block_get(bs, dev_handle, lcl, (pos / bps) % spc,

		    flags);

		(void) ipc_data_write_finalize(callid, b->data + pos % bps,

		    bytes);

		b->dirty = true;		/* need to sync block */

		block_put(b);

		/*

		 * Append the cluster chain starting in mcl to the end of the

		 * node's cluster chain.

		 */

		fat_append_clusters(bs, nodep, mcl);

		nodep->size = pos + bytes;

		nodep->dirty = true;		/* need to sync node */

		ipc_answer_2(rid, EOK, bytes, nodep->size);

		fat_node_put(nodep);

		return;

	}

}

void fat_truncate(ipc_callid_t rid, ipc_call_t *request)

{

	dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);

	fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);

	size_t size = (off_t)IPC_GET_ARG3(*request);

	fat_node_t *nodep = (fat_node_t *)fat_node_get(dev_handle, index);

	fat_bs_t *bs;

	uint16_t bps;

	uint8_t spc;

	unsigned bpc;	/* bytes per cluster */

	int rc;

	if (!nodep) {

		ipc_answer_0(rid, ENOENT);

		return;

	}

	bs = block_bb_get(dev_handle);

	bps = uint16_t_le2host(bs->bps);

	spc = bs->spc;

	bpc = bps * spc;

	if (nodep->size == size) {

		rc = EOK;

	} else if (nodep->size < size) {

		/*

		 * The standard says we have the freedom to grow the node.

		 * For now, we simply return an error.

		 */

		rc = EINVAL;

	} else if (ROUND_UP(nodep->size, bpc) == ROUND_UP(size, bpc)) {

		/*

		 * The node will be shrunk, but no clusters will be deallocated.

		 */

		nodep->size = size;

		nodep->dirty = true;		/* need to sync node */

		rc = EOK;	

	} else {

		/*

		 * The node will be shrunk, clusters will be deallocated.

		 */

		if (size == 0) {

			fat_chop_clusters(bs, nodep, FAT_CLST_RES0);

		} else {

			fat_cluster_t lastc;

			(void) fat_cluster_walk(bs, dev_handle, nodep->firstc,

			    &lastc, (size - 1) / bpc);

			fat_chop_clusters(bs, nodep, lastc);

		}

		nodep->size = size;

		nodep->dirty = true;		/* need to sync node */

		rc = EOK;	

	}

	fat_node_put(nodep);

	ipc_answer_0(rid, rc);

	return;

}

void fat_destroy(ipc_callid_t rid, ipc_call_t *request)

{

	dev_handle_t dev_handle = (dev_handle_t)IPC_GET_ARG1(*request);

	fs_index_t index = (fs_index_t)IPC_GET_ARG2(*request);

	int rc;

	fat_node_t *nodep = fat_node_get(dev_handle, index);

	if (!nodep) {

		ipc_answer_0(rid, ENOENT);

		return;

	}

	rc = fat_destroy_node(nodep);

	ipc_answer_0(rid, rc);

}

/**