source: mainline/uspace/srv/fs/fat/fat_ops.c@ dfddfcd

/*
 * 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 <adt/hash_table.h>
#include <adt/list.h>
#include <assert.h>
#include <fibril_sync.h>
#include <sys/mman.h>
#include <align.h>

#define FAT_NODE(node)  ((node) ? (fat_node_t *) (node)->data : NULL)
#define FS_NODE(node)   ((node) ? (node)->bp : NULL)

/** Mutex protecting the list of cached free FAT nodes. */
static FIBRIL_MUTEX_INITIALIZE(ffn_mutex);

/** List of cached free FAT nodes. */
static LIST_INITIALIZE(ffn_head);

/*
 * Forward declarations of FAT libfs operations.
 */
static int fat_root_get(fs_node_t **, dev_handle_t);
static int fat_match(fs_node_t **, fs_node_t *, const char *);
static int fat_node_get(fs_node_t **, dev_handle_t, fs_index_t);
static int fat_node_put(fs_node_t *);
static int fat_create_node(fs_node_t **, dev_handle_t, int);
static int fat_destroy_node(fs_node_t *);
static int fat_link(fs_node_t *, fs_node_t *, const char *);
static int fat_unlink(fs_node_t *, fs_node_t *, const char *);
static int fat_has_children(bool *, fs_node_t *);
static fs_index_t fat_index_get(fs_node_t *);
static size_t fat_size_get(fs_node_t *);
static unsigned fat_lnkcnt_get(fs_node_t *);
static char fat_plb_get_char(unsigned);
static bool fat_is_directory(fs_node_t *);
static bool fat_is_file(fs_node_t *node);

/*
 * Helper functions.
 */
static void fat_node_initialize(fat_node_t *node)
{
        fibril_mutex_initialize(&node->lock);
        node->bp = NULL;
        node->idx = NULL;
        node->type = 0;
        link_initialize(&node->ffn_link);
        node->size = 0;
        node->lnkcnt = 0;
        node->refcnt = 0;
        node->dirty = false;
}

static int fat_node_sync(fat_node_t *node)
{
        block_t *b;
        fat_bs_t *bs;
        fat_dentry_t *d;
        uint16_t bps;
        unsigned dps;
        int rc;
        
        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. */
        rc = _fat_block_get(&b, bs, node->idx->dev_handle, node->idx->pfc,
            (node->idx->pdi * sizeof(fat_dentry_t)) / bps, BLOCK_FLAGS_NONE);
        if (rc != EOK)
                return rc;

        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 */
        rc = block_put(b);
        return rc;
}

static int fat_node_get_new(fat_node_t **nodepp)
{
        fs_node_t *fn;
        fat_node_t *nodep;
        int rc;

        fibril_mutex_lock(&ffn_mutex);
        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 (!fibril_mutex_trylock(&nodep->lock))
                        goto skip_cache;
                idxp_tmp = nodep->idx;
                if (!fibril_mutex_trylock(&idxp_tmp->lock)) {
                        fibril_mutex_unlock(&nodep->lock);
                        goto skip_cache;
                }
                list_remove(&nodep->ffn_link);
                fibril_mutex_unlock(&ffn_mutex);
                if (nodep->dirty) {
                        rc = fat_node_sync(nodep);
                        if (rc != EOK) {
                                idxp_tmp->nodep = NULL;
                                fibril_mutex_unlock(&nodep->lock);
                                fibril_mutex_unlock(&idxp_tmp->lock);
                                free(nodep->bp);
                                free(nodep);
                                return rc;
                        }
                }
                idxp_tmp->nodep = NULL;
                fibril_mutex_unlock(&nodep->lock);
                fibril_mutex_unlock(&idxp_tmp->lock);
                fn = FS_NODE(nodep);
        } else {
skip_cache:
                /* Try to allocate a new node structure. */
                fibril_mutex_unlock(&ffn_mutex);
                fn = (fs_node_t *)malloc(sizeof(fs_node_t));
                if (!fn)
                        return ENOMEM;
                nodep = (fat_node_t *)malloc(sizeof(fat_node_t));
                if (!nodep) {
                        free(fn);
                        return ENOMEM;
                }
        }
        fat_node_initialize(nodep);
        fs_node_initialize(fn);
        fn->data = nodep;
        nodep->bp = fn;
        
        *nodepp = nodep;
        return EOK;
}

/** Internal version of fat_node_get().
 *
 * @param idxp          Locked index structure.
 */
static int fat_node_get_core(fat_node_t **nodepp, 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;
        int rc;

        if (idxp->nodep) {
                /*
                 * We are lucky.
                 * The node is already instantiated in memory.
                 */
                fibril_mutex_lock(&idxp->nodep->lock);
                if (!idxp->nodep->refcnt++) {
                        fibril_mutex_lock(&ffn_mutex);
                        list_remove(&idxp->nodep->ffn_link);
                        fibril_mutex_unlock(&ffn_mutex);
                }
                fibril_mutex_unlock(&idxp->nodep->lock);
                *nodepp = idxp->nodep;
                return EOK;
        }

        /*
         * We must instantiate the node from the file system.
         */
        
        assert(idxp->pfc);

        rc = fat_node_get_new(&nodep);
        if (rc != EOK)
                return rc;

        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. */
        rc = _fat_block_get(&b, bs, idxp->dev_handle, idxp->pfc,
            (idxp->pdi * sizeof(fat_dentry_t)) / bps, BLOCK_FLAGS_NONE);
        if (rc != EOK) {
                (void) fat_node_put(FS_NODE(nodep));
                return rc;
        }

        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.
                 */
                uint16_t clusters;
                rc = fat_clusters_get(&clusters, bs, idxp->dev_handle,
                    uint16_t_le2host(d->firstc));
                if (rc != EOK) {
                        (void) fat_node_put(FS_NODE(nodep));
                        return rc;
                }
                nodep->size = bps * spc * clusters;
        } 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;

        rc = block_put(b);
        if (rc != EOK) {
                (void) fat_node_put(FS_NODE(nodep));
                return rc;
        }

        /* Link the idx structure with the node structure. */
        nodep->idx = idxp;
        idxp->nodep = nodep;

        *nodepp = nodep;
        return EOK;
}

/*
 * FAT libfs operations.
 */

int fat_root_get(fs_node_t **rfn, dev_handle_t dev_handle)
{
        return fat_node_get(rfn, dev_handle, 0);
}

int fat_match(fs_node_t **rfn, fs_node_t *pfn, const char *component)
{
        fat_bs_t *bs;
        fat_node_t *parentp = FAT_NODE(pfn);
        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;
        int rc;

        fibril_mutex_lock(&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++) {
                rc = fat_block_get(&b, bs, parentp, i, BLOCK_FLAGS_NONE);
                if (rc != EOK) {
                        fibril_mutex_unlock(&parentp->idx->lock);
                        return rc;
                }
                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:
                                /* miss */
                                rc = block_put(b);
                                fibril_mutex_unlock(&parentp->idx->lock);
                                *rfn = NULL;
                                return rc;
                        default:
                        case FAT_DENTRY_VALID:
                                fat_dentry_name_get(d, name);
                                break;
                        }
                        if (fat_dentry_namecmp(name, component) == 0) {
                                /* hit */
                                fat_node_t *nodep;
                                /*
                                 * 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);
                                fibril_mutex_unlock(&parentp->idx->lock);
                                if (!idx) {
                                        /*
                                         * Can happen if memory is low or if we
                                         * run out of 32-bit indices.
                                         */
                                        rc = block_put(b);
                                        return (rc == EOK) ? ENOMEM : rc;
                                }
                                rc = fat_node_get_core(&nodep, idx);
                                fibril_mutex_unlock(&idx->lock);
                                if (rc != EOK) {
                                        (void) block_put(b);
                                        return rc;
                                }
                                *rfn = FS_NODE(nodep);
                                rc = block_put(b);
                                if (rc != EOK)
                                        (void) fat_node_put(*rfn);
                                return rc;
                        }
                }
                rc = block_put(b);
                if (rc != EOK) {
                        fibril_mutex_unlock(&parentp->idx->lock);
                        return rc;
                }
        }

        fibril_mutex_unlock(&parentp->idx->lock);
        *rfn = NULL;
        return EOK;
}

/** Instantiate a FAT in-core node. */
int fat_node_get(fs_node_t **rfn, dev_handle_t dev_handle, fs_index_t index)
{
        fat_node_t *nodep;
        fat_idx_t *idxp;
        int rc;

        idxp = fat_idx_get_by_index(dev_handle, index);
        if (!idxp) {
                *rfn = NULL;
                return EOK;
        }
        /* idxp->lock held */
        rc = fat_node_get_core(&nodep, idxp);
        fibril_mutex_unlock(&idxp->lock);
        if (rc == EOK)
                *rfn = FS_NODE(nodep);
        return rc;
}

int fat_node_put(fs_node_t *fn)
{
        fat_node_t *nodep = FAT_NODE(fn);
        bool destroy = false;

        fibril_mutex_lock(&nodep->lock);
        if (!--nodep->refcnt) {
                if (nodep->idx) {
                        fibril_mutex_lock(&ffn_mutex);
                        list_append(&nodep->ffn_link, &ffn_head);
                        fibril_mutex_unlock(&ffn_mutex);
                } 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;
                }
        }
        fibril_mutex_unlock(&nodep->lock);
        if (destroy) {
                free(nodep->bp);
                free(nodep);
        }
        return EOK;
}

int fat_create_node(fs_node_t **rfn, 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 rc;
                /* populate the new cluster with unused dentries */
                rc = fat_zero_cluster(bs, dev_handle, mcl);
                if (rc != EOK) {
                        (void) fat_free_clusters(bs, dev_handle, mcl);
                        return rc;
                }
        }

        rc = fat_node_get_new(&nodep);
        if (rc != EOK) {
                (void) fat_free_clusters(bs, dev_handle, mcl);
                return rc;
        }
        rc = fat_idx_get_new(&idxp, dev_handle);
        if (rc != EOK) {
                (void) fat_free_clusters(bs, dev_handle, mcl);  
                (void) fat_node_put(FS_NODE(nodep));
                return rc;
        }
        /* idxp->lock held */
        if (flags & L_DIRECTORY) {
                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;

        fibril_mutex_unlock(&idxp->lock);
        *rfn = FS_NODE(nodep);
        return EOK;
}

int fat_destroy_node(fs_node_t *fn)
{
        fat_node_t *nodep = FAT_NODE(fn);
        fat_bs_t *bs;
        bool has_children;
        int rc;

        /*
         * 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.
         */
        rc = fat_has_children(&has_children, fn);
        if (rc != EOK)
                return rc;
        assert(!has_children);

        bs = block_bb_get(nodep->idx->dev_handle);
        if (nodep->firstc != FAT_CLST_RES0) {
                assert(nodep->size);
                /* Free all clusters allocated to the node. */
                rc = fat_free_clusters(bs, nodep->idx->dev_handle,
                    nodep->firstc);
        }

        fat_idx_destroy(nodep->idx);
        free(nodep->bp);
        free(nodep);
        return rc;
}

int fat_link(fs_node_t *pfn, fs_node_t *cfn, const char *name)
{
        fat_node_t *parentp = FAT_NODE(pfn);
        fat_node_t *childp = FAT_NODE(cfn);
        fat_dentry_t *d;
        fat_bs_t *bs;
        block_t *b;
        unsigned i, j;
        uint16_t bps;
        unsigned dps;
        unsigned blocks;
        fat_cluster_t mcl, lcl;
        int rc;

        fibril_mutex_lock(&childp->lock);
        if (childp->lnkcnt == 1) {
                /*
                 * On FAT, we don't support multiple hard links.
                 */
                fibril_mutex_unlock(&childp->lock);
                return EMLINK;
        }
        assert(childp->lnkcnt == 0);
        fibril_mutex_unlock(&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.
         */
        
        fibril_mutex_lock(&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++) {
                rc = fat_block_get(&b, bs, parentp, i, BLOCK_FLAGS_NONE);
                if (rc != EOK) {
                        fibril_mutex_unlock(&parentp->idx->lock);
                        return rc;
                }
                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;
                        }
                }
                rc = block_put(b);
                if (rc != EOK) {
                        fibril_mutex_unlock(&parentp->idx->lock);
                        return rc;
                }
        }
        j = 0;
        
        /*
         * We need to grow the parent in order to create a new unused dentry.
         */
        if (parentp->firstc == FAT_CLST_ROOT) {
                /* Can't grow the root directory. */
                fibril_mutex_unlock(&parentp->idx->lock);
                return ENOSPC;
        }
        rc = fat_alloc_clusters(bs, parentp->idx->dev_handle, 1, &mcl, &lcl);
        if (rc != EOK) {
                fibril_mutex_unlock(&parentp->idx->lock);
                return rc;
        }
        rc = fat_zero_cluster(bs, parentp->idx->dev_handle, mcl);
        if (rc != EOK) {
                (void) fat_free_clusters(bs, parentp->idx->dev_handle, mcl);
                fibril_mutex_unlock(&parentp->idx->lock);
                return rc;
        }
        rc = fat_append_clusters(bs, parentp, mcl);
        if (rc != EOK) {
                (void) fat_free_clusters(bs, parentp->idx->dev_handle, mcl);
                fibril_mutex_unlock(&parentp->idx->lock);
                return rc;
        }
        parentp->size += bps * bs->spc;
        parentp->dirty = true;          /* need to sync node */
        rc = fat_block_get(&b, bs, parentp, i, BLOCK_FLAGS_NONE);
        if (rc != EOK) {
                fibril_mutex_unlock(&parentp->idx->lock);
                return rc;
        }
        d = (fat_dentry_t *)b->data;

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 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 */
        rc = block_put(b);
        fibril_mutex_unlock(&parentp->idx->lock);
        if (rc != EOK) 
                return rc;

        fibril_mutex_lock(&childp->idx->lock);
        
        /*
         * If possible, create the Sub-directory Identifier Entry and the
         * Sub-directory Parent Pointer Entry (i.e. "." and ".."). These entries
         * are not mandatory according to Standard ECMA-107 and HelenOS VFS does
         * not use them anyway, so this is rather a sign of our good will.
         */
        rc = fat_block_get(&b, bs, childp, 0, BLOCK_FLAGS_NONE);
        if (rc != EOK) {
                /*
                 * Rather than returning an error, simply skip the creation of
                 * these two entries.
                 */
                goto skip_dots;
        }
        d = (fat_dentry_t *)b->data;
        if (fat_classify_dentry(d) == FAT_DENTRY_LAST ||
            str_cmp(d->name, FAT_NAME_DOT) == 0) {
                memset(d, 0, sizeof(fat_dentry_t));
                str_cpy(d->name, 8, FAT_NAME_DOT);
                str_cpy(d->ext, 3, FAT_EXT_PAD);
                d->attr = FAT_ATTR_SUBDIR;
                d->firstc = host2uint16_t_le(childp->firstc);
                /* TODO: initialize also the date/time members. */
        }
        d++;
        if (fat_classify_dentry(d) == FAT_DENTRY_LAST ||
            str_cmp(d->name, FAT_NAME_DOT_DOT) == 0) {
                memset(d, 0, sizeof(fat_dentry_t));
                str_cpy(d->name, 8, FAT_NAME_DOT_DOT);
                str_cpy(d->ext, 3, FAT_EXT_PAD);
                d->attr = FAT_ATTR_SUBDIR;
                d->firstc = (parentp->firstc == FAT_CLST_ROOT) ?
                    host2uint16_t_le(FAT_CLST_RES0) :
                    host2uint16_t_le(parentp->firstc);
                /* TODO: initialize also the date/time members. */
        }
        b->dirty = true;                /* need to sync block */
        /*
         * Ignore the return value as we would have fallen through on error
         * anyway.
         */
        (void) block_put(b);
skip_dots:

        childp->idx->pfc = parentp->firstc;
        childp->idx->pdi = i * dps + j;
        fibril_mutex_unlock(&childp->idx->lock);

        fibril_mutex_lock(&childp->lock);
        childp->lnkcnt = 1;
        childp->dirty = true;           /* need to sync node */
        fibril_mutex_unlock(&childp->lock);

        /*
         * Hash in the index structure into the position hash.
         */
        fat_idx_hashin(childp->idx);

        return EOK;
}

int fat_unlink(fs_node_t *pfn, fs_node_t *cfn, const char *nm)
{
        fat_node_t *parentp = FAT_NODE(pfn);
        fat_node_t *childp = FAT_NODE(cfn);
        fat_bs_t *bs;
        fat_dentry_t *d;
        uint16_t bps;
        block_t *b;
        bool has_children;
        int rc;

        if (!parentp)
                return EBUSY;
        
        rc = fat_has_children(&has_children, cfn);
        if (rc != EOK)
                return rc;
        if (has_children)
                return ENOTEMPTY;

        fibril_mutex_lock(&parentp->lock);
        fibril_mutex_lock(&childp->lock);
        assert(childp->lnkcnt == 1);
        fibril_mutex_lock(&childp->idx->lock);
        bs = block_bb_get(childp->idx->dev_handle);
        bps = uint16_t_le2host(bs->bps);

        rc = _fat_block_get(&b, bs, childp->idx->dev_handle, childp->idx->pfc,
            (childp->idx->pdi * sizeof(fat_dentry_t)) / bps,
            BLOCK_FLAGS_NONE);
        if (rc != EOK) 
                goto error;
        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 */
        rc = block_put(b);
        if (rc != EOK)
                goto error;

        /* 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;
        fibril_mutex_unlock(&childp->idx->lock);
        childp->lnkcnt = 0;
        childp->dirty = true;
        fibril_mutex_unlock(&childp->lock);
        fibril_mutex_unlock(&parentp->lock);

        return EOK;

error:
        fibril_mutex_unlock(&parentp->idx->lock);
        fibril_mutex_unlock(&childp->lock);
        fibril_mutex_unlock(&childp->idx->lock);
        return rc;
}

int fat_has_children(bool *has_children, fs_node_t *fn)
{
        fat_bs_t *bs;
        fat_node_t *nodep = FAT_NODE(fn);
        unsigned bps;
        unsigned dps;
        unsigned blocks;
        block_t *b;
        unsigned i, j;
        int rc;

        if (nodep->type != FAT_DIRECTORY) {
                *has_children = false;
                return EOK;
        }
        
        fibril_mutex_lock(&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;
        
                rc = fat_block_get(&b, bs, nodep, i, BLOCK_FLAGS_NONE);
                if (rc != EOK) {
                        fibril_mutex_unlock(&nodep->idx->lock);
                        return rc;
                }
                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:
                                rc = block_put(b);
                                fibril_mutex_unlock(&nodep->idx->lock);
                                *has_children = false;
                                return rc;
                        default:
                        case FAT_DENTRY_VALID:
                                rc = block_put(b);
                                fibril_mutex_unlock(&nodep->idx->lock);
                                *has_children = true;
                                return rc;
                        }
                }
                rc = block_put(b);
                if (rc != EOK) {
                        fibril_mutex_unlock(&nodep->idx->lock);
                        return rc;      
                }
        }

        fibril_mutex_unlock(&nodep->idx->lock);
        *has_children = false;
        return EOK;
}


fs_index_t fat_index_get(fs_node_t *fn)
{
        return FAT_NODE(fn)->idx->index;
}

size_t fat_size_get(fs_node_t *fn)
{
        return FAT_NODE(fn)->size;
}

unsigned fat_lnkcnt_get(fs_node_t *fn)
{
        return FAT_NODE(fn)->lnkcnt;
}

char fat_plb_get_char(unsigned pos)
{
        return fat_reg.plb_ro[pos % PLB_SIZE];
}

bool fat_is_directory(fs_node_t *fn)
{
        return FAT_NODE(fn)->type == FAT_DIRECTORY;
}

bool fat_is_file(fs_node_t *fn)
{
        return FAT_NODE(fn)->type == FAT_FILE;
}

/** libfs operations */
libfs_ops_t fat_libfs_ops = {
        .root_get = fat_root_get,
        .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,
        .has_children = fat_has_children,
        .index_get = fat_index_get,
        .size_get = fat_size_get,
        .lnkcnt_get = fat_lnkcnt_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);
        enum cache_mode cmode;
        fat_bs_t *bs;
        uint16_t bps;
        uint16_t rde;
        int rc;

        /* accept the mount options */
        ipc_callid_t callid;
        size_t size;
        if (!async_data_write_receive(&callid, &size)) {
                ipc_answer_0(callid, EINVAL);
                ipc_answer_0(rid, EINVAL);
                return;
        }
        char *opts = malloc(size + 1);
        if (!opts) {
                ipc_answer_0(callid, ENOMEM);
                ipc_answer_0(rid, ENOMEM);
                return;
        }
        ipcarg_t retval = async_data_write_finalize(callid, opts, size);
        if (retval != EOK) {
                ipc_answer_0(rid, retval);
                free(opts);
                return;
        }
        opts[size] = '\0';

        /* Check for option enabling write through. */
        if (str_cmp(opts, "wtcache") == 0)
                cmode = CACHE_MODE_WT;
        else
                cmode = CACHE_MODE_WB;

        /* 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);
        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 */, cmode);
        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. */
        fs_node_t *rfn = (fs_node_t *)malloc(sizeof(fs_node_t));
        if (!rfn) {
                block_fini(dev_handle);
                fat_idx_fini_by_dev_handle(dev_handle);
                ipc_answer_0(rid, ENOMEM);
                return;
        }
        fs_node_initialize(rfn);
        fat_node_t *rootp = (fat_node_t *)malloc(sizeof(fat_node_t));
        if (!rootp) {
                free(rfn);
                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) {
                free(rfn);
                free(rootp);
                block_fini(dev_handle);
                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;
        rootp->bp = rfn;
        rfn->data = rootp;
        
        fibril_mutex_unlock(&ridxp->lock);

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

void fat_mount(ipc_callid_t rid, ipc_call_t *request)
{
        libfs_mount(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
}

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);
        fs_node_t *fn;
        fat_node_t *nodep;
        fat_bs_t *bs;
        uint16_t bps;
        size_t bytes;
        block_t *b;
        int rc;

        rc = fat_node_get(&fn, dev_handle, index);
        if (rc != EOK) {
                ipc_answer_0(rid, rc);
                return;
        }
        if (!fn) {
                ipc_answer_0(rid, ENOENT);
                return;
        }
        nodep = FAT_NODE(fn);

        ipc_callid_t callid;
        size_t len;
        if (!async_data_read_receive(&callid, &len)) {
                fat_node_put(fn);
                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) async_data_read_finalize(callid, NULL, 0);
                } else {
                        bytes = min(len, bps - pos % bps);
                        bytes = min(bytes, nodep->size - pos);
                        rc = fat_block_get(&b, bs, nodep, pos / bps,
                            BLOCK_FLAGS_NONE);
                        if (rc != EOK) {
                                fat_node_put(fn);
                                ipc_answer_0(callid, rc);
                                ipc_answer_0(rid, rc);
                                return;
                        }
                        (void) async_data_read_finalize(callid, b->data + pos % bps,
                            bytes);
                        rc = block_put(b);
                        if (rc != EOK) {
                                fat_node_put(fn);
                                ipc_answer_0(rid, rc);
                                return;
                        }
                }
        } 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;

                        rc = fat_block_get(&b, bs, nodep, bnum,
                            BLOCK_FLAGS_NONE);
                        if (rc != EOK)
                                goto err;
                        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:
                                        rc = block_put(b);
                                        if (rc != EOK)
                                                goto err;
                                        goto miss;
                                default:
                                case FAT_DENTRY_VALID:
                                        fat_dentry_name_get(d, name);
                                        rc = block_put(b);
                                        if (rc != EOK)
                                                goto err;
                                        goto hit;
                                }
                        }
                        rc = block_put(b);
                        if (rc != EOK)
                                goto err;
                        bnum++;
                }
miss:
                rc = fat_node_put(fn);
                ipc_answer_0(callid, rc != EOK ? rc : ENOENT);
                ipc_answer_1(rid, rc != EOK ? rc : ENOENT, 0);
                return;

err:
                (void) fat_node_put(fn);
                ipc_answer_0(callid, rc);
                ipc_answer_0(rid, rc);
                return;

hit:
                (void) async_data_read_finalize(callid, name, str_size(name) + 1);
                bytes = (pos - spos) + 1;
        }

        rc = fat_node_put(fn);
        ipc_answer_1(rid, rc, (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);
        fs_node_t *fn;
        fat_node_t *nodep;
        fat_bs_t *bs;
        size_t bytes, size;
        block_t *b;
        uint16_t bps;
        unsigned spc;
        unsigned bpc;           /* bytes per cluster */
        off_t boundary;
        int flags = BLOCK_FLAGS_NONE;
        int rc;
        
        rc = fat_node_get(&fn, dev_handle, index);
        if (rc != EOK) {
                ipc_answer_0(rid, rc);
                return;
        }
        if (!fn) {
                ipc_answer_0(rid, ENOENT);
                return;
        }
        nodep = FAT_NODE(fn);
        
        ipc_callid_t callid;
        size_t len;
        if (!async_data_write_receive(&callid, &len)) {
                (void) fat_node_put(fn);
                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.
                 */
                rc = fat_fill_gap(bs, nodep, FAT_CLST_RES0, pos);
                if (rc != EOK) {
                        (void) fat_node_put(fn);
                        ipc_answer_0(callid, rc);
                        ipc_answer_0(rid, rc);
                        return;
                }
                rc = fat_block_get(&b, bs, nodep, pos / bps, flags);
                if (rc != EOK) {
                        (void) fat_node_put(fn);
                        ipc_answer_0(callid, rc);
                        ipc_answer_0(rid, rc);
                        return;
                }
                (void) async_data_write_finalize(callid, b->data + pos % bps,
                    bytes);
                b->dirty = true;                /* need to sync block */
                rc = block_put(b);
                if (rc != EOK) {
                        (void) fat_node_put(fn);
                        ipc_answer_0(rid, rc);
                        return;
                }
                if (pos + bytes > nodep->size) {
                        nodep->size = pos + bytes;
                        nodep->dirty = true;    /* need to sync node */
                }
                size = nodep->size;
                rc = fat_node_put(fn);
                ipc_answer_2(rid, rc, bytes, nodep->size);
                return;
        } else {
                /*
                 * This is the more difficult case. We must allocate new
                 * clusters for the node and zero them out.
                 */
                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 */
                rc = fat_alloc_clusters(bs, dev_handle, nclsts, &mcl, &lcl);
                if (rc != EOK) {
                        /* could not allocate a chain of nclsts clusters */
                        (void) fat_node_put(fn);
                        ipc_answer_0(callid, rc);
                        ipc_answer_0(rid, rc);
                        return;
                }
                /* zero fill any gaps */
                rc = fat_fill_gap(bs, nodep, mcl, pos);
                if (rc != EOK) {
                        (void) fat_free_clusters(bs, dev_handle, mcl);
                        (void) fat_node_put(fn);
                        ipc_answer_0(callid, rc);
                        ipc_answer_0(rid, rc);
                        return;
                }
                rc = _fat_block_get(&b, bs, dev_handle, lcl, (pos / bps) % spc,
                    flags);
                if (rc != EOK) {
                        (void) fat_free_clusters(bs, dev_handle, mcl);
                        (void) fat_node_put(fn);
                        ipc_answer_0(callid, rc);
                        ipc_answer_0(rid, rc);
                        return;
                }
                (void) async_data_write_finalize(callid, b->data + pos % bps,
                    bytes);
                b->dirty = true;                /* need to sync block */
                rc = block_put(b);
                if (rc != EOK) {
                        (void) fat_free_clusters(bs, dev_handle, mcl);
                        (void) fat_node_put(fn);
                        ipc_answer_0(rid, rc);
                        return;
                }
                /*
                 * Append the cluster chain starting in mcl to the end of the
                 * node's cluster chain.
                 */
                rc = fat_append_clusters(bs, nodep, mcl);
                if (rc != EOK) {
                        (void) fat_free_clusters(bs, dev_handle, mcl);
                        (void) fat_node_put(fn);
                        ipc_answer_0(rid, rc);
                        return;
                }
                nodep->size = size = pos + bytes;
                nodep->dirty = true;            /* need to sync node */
                rc = fat_node_put(fn);
                ipc_answer_2(rid, rc, bytes, size);
                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);
        fs_node_t *fn;
        fat_node_t *nodep;
        fat_bs_t *bs;
        uint16_t bps;
        uint8_t spc;
        unsigned bpc;   /* bytes per cluster */
        int rc;

        rc = fat_node_get(&fn, dev_handle, index);
        if (rc != EOK) {
                ipc_answer_0(rid, rc);
                return;
        }
        if (!fn) {
                ipc_answer_0(rid, ENOENT);
                return;
        }
        nodep = FAT_NODE(fn);

        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) {
                        rc = fat_chop_clusters(bs, nodep, FAT_CLST_RES0);
                        if (rc != EOK)
                                goto out;
                } else {
                        fat_cluster_t lastc;
                        rc = fat_cluster_walk(bs, dev_handle, nodep->firstc,
                            &lastc, NULL, (size - 1) / bpc);
                        if (rc != EOK)
                                goto out;
                        rc = fat_chop_clusters(bs, nodep, lastc);
                        if (rc != EOK)
                                goto out;
                }
                nodep->size = size;
                nodep->dirty = true;            /* need to sync node */
                rc = EOK;       
        }
out:
        fat_node_put(fn);
        ipc_answer_0(rid, rc);
        return;
}

void fat_close(ipc_callid_t rid, ipc_call_t *request)
{
        ipc_answer_0(rid, EOK);
}

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);
        fs_node_t *fn;
        int rc;

        rc = fat_node_get(&fn, dev_handle, index);
        if (rc != EOK) {
                ipc_answer_0(rid, rc);
                return;
        }
        if (!fn) {
                ipc_answer_0(rid, ENOENT);
                return;
        }

        rc = fat_destroy_node(fn);
        ipc_answer_0(rid, rc);
}

void fat_open_node(ipc_callid_t rid, ipc_call_t *request)
{
        libfs_open_node(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
}

void fat_stat(ipc_callid_t rid, ipc_call_t *request)
{
        libfs_stat(&fat_libfs_ops, fat_reg.fs_handle, rid, request);
}

void fat_sync(ipc_callid_t rid, ipc_call_t *request)
{
        /* Dummy implementation */
        ipc_answer_0(rid, EOK);
}

/**
 * @}
 */