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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_idx.c

 * @brief   Layer for translating FAT entities to VFS node indices.

 */

#include "fat.h"

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

#include <errno.h>

#include <string.h>

#include <libadt/hash_table.h>

#include <libadt/list.h>

#include <assert.h>

#include <futex.h>

/** Each instance of this type describes one interval of freed VFS indices. */

typedef struct {

    link_t      link;

    fs_index_t  first;

    fs_index_t  last;

} freed_t;

/**

 * Each instance of this type describes state of all VFS indices that

 * are currently unused.

 */

typedef struct {

    link_t      link;

    dev_handle_t    dev_handle;

    /** Next unassigned index. */

    fs_index_t  next;

    /** Number of remaining unassigned indices. */

    uint64_t    remaining;

    /** Sorted list of intervals of freed indices. */

    link_t      freed_head;

} unused_t;

static LIST_INITIALIZE(unused_head);

/** Global hash table of all used fat_idx_t structures. */

static hash_table_t used_hash;

#define USED_HASH_BUCKETS_LOG   12

#define USED_HASH_BUCKETS   (1 << USED_HASH_BUCKETS_LOG)

#define USED_HASH_DH_KEY    0

#define USED_HASH_PFC_KEY   1

#define USED_HASH_PDI_KEY   2

static hash_index_t idx_hash(unsigned long key[])

{

    dev_handle_t dev_handle = (dev_handle_t)key[USED_HASH_DH_KEY];

    fat_cluster_t pfc = (fat_cluster_t)key[USED_HASH_PFC_KEY];

    unsigned pdi = (unsigned)key[USED_HASH_PDI_KEY];

    hash_index_t h;

    /*

     * The least significant half of all bits are the least significant bits

     * of the parent node's first cluster.

     *

     * The least significant half of the most significant half of all bits

     * are the least significant bits of the node's dentry index within the

     * parent directory node.

     *

     * The most significant half of the most significant half of all bits

     * are the least significant bits of the device handle.

     */

    h = pfc & ((USED_HASH_BUCKETS_LOG / 2) - 1);

    h |= (pdi & ((USED_HASH_BUCKETS_LOG / 4) - 1)) <<

        (USED_HASH_BUCKETS_LOG / 2);

    h |= (dev_handle & ((USED_HASH_BUCKETS_LOG / 4) - 1)) <<

        (3 * (USED_HASH_BUCKETS_LOG / 4));

    return h;

}

static int idx_compare(unsigned long key[], hash_count_t keys, link_t *item)

{

    dev_handle_t dev_handle = (dev_handle_t)key[USED_HASH_DH_KEY];

    fat_cluster_t pfc = (fat_cluster_t)key[USED_HASH_PFC_KEY];

    unsigned pdi = (unsigned)key[USED_HASH_PDI_KEY];

    fat_idx_t *fidx = list_get_instance(item, fat_idx_t, uh_link);

    return (dev_handle == fidx->dev_handle) && (pfc == fidx->pfc) &&

        (pdi == fidx->pdi);

}

static void idx_remove_callback(link_t *item)

{

    /* nothing to do */

}

static hash_table_operations_t used_idx_ops = {

    .hash = idx_hash,

    .compare = idx_compare,

    .remove_callback = idx_remove_callback,

};

/** Allocate a VFS index which is not currently in use. */

static bool fat_idx_alloc(dev_handle_t dev_handle, fs_index_t *index)

{

    link_t *l;

    unused_t *u;

    assert(index);

    for (l = unused_head.next; l != &unused_head; l = l->next) {

        u = list_get_instance(l, unused_t, link);

        if (u->dev_handle == dev_handle)

            goto hit;

    }

    /* dev_handle not found */

    return false;  

hit:

    if (list_empty(&u->freed_head)) {

        if (u->remaining) {

            /*

             * There are no freed indices, allocate one directly

             * from the counter.

             */

            *index = u->next++;

            --u->remaining;

            return true;

        }

    } else {

        /* There are some freed indices which we can reuse. */

        freed_t *f = list_get_instance(u->freed_head.next, freed_t,

            link);

        *index = f->first;

        if (f->first++ == f->last) {

            /* Destroy the interval. */

            list_remove(&f->link);

            free(f);

        }

        return true;

    }

    /*

     * We ran out of indices, which is extremely unlikely with FAT16, but

     * theoretically still possible (e.g. too many open unlinked nodes or

     * too many zero-sized nodes).

     */

    return false;

}

/** If possible, coalesce two intervals of freed indices. */

static void try_coalesce_intervals(link_t *l, link_t *r, link_t *cur)

{

    freed_t *fl = list_get_instance(l, freed_t, link);

    freed_t *fr = list_get_instance(r, freed_t, link);

    if (fl->last + 1 == fr->first) {

        if (cur == l) {

            fl->last = fr->last;

            list_remove(r);

            free(r);

        } else {

            fr->first = fl->first;

            list_remove(l);

            free(l);

        }

    }

}

/** Free a VFS index, which is no longer in use. */

static void fat_idx_free(dev_handle_t dev_handle, fs_index_t index)

{

    link_t *l;

    unused_t *u;

    for (l = unused_head.next; l != &unused_head; l = l->next) {

        u = list_get_instance(l, unused_t, link);

        if (u->dev_handle == dev_handle)

            goto hit;

    }

    /* should not happen */

    assert(0);

hit:

    if (u->next == index + 1) {

        /* The index can be returned directly to the counter. */

        u->next--;

        u->remaining++;

        return;

    } else {

        /*

         * The index must be returned either to an existing freed

         * interval or a new interval must be created.

         */

        link_t *lnk;

        freed_t *n;

        for (lnk = u->freed_head.next; lnk != &u->freed_head;

            lnk = lnk->next) {

            freed_t *f = list_get_instance(lnk, freed_t, link);

            if (f->first == index + 1) {

                f->first--;

                if (lnk->prev != &u->freed_head)

                    try_coalesce_intervals(lnk->prev, lnk,

                        lnk);

                return;

            }

            if (f->last == index - 1) {

                f->last++;

                if (lnk->next != &u->freed_head)

                    try_coalesce_intervals(lnk, lnk->next,

                        lnk);

                return;

            }

            if (index > f->first) {

                n = malloc(sizeof(freed_t));

                /* TODO: sleep until allocation succeeds */

                assert(n);

                link_initialize(&n->link);

                n->first = index;

                n->last = index;

                list_insert_before(&n->link, lnk);

                return;

            }

        }

        /* The index will form the last interval. */

        n = malloc(sizeof(freed_t));

        /* TODO: sleep until allocation succeeds */

        assert(n);

        link_initialize(&n->link);

        n->first = index;

        n->last = index;

        list_append(&n->link, &u->freed_head);

    }

}

fat_idx_t *fat_idx_map(dev_handle_t dev_handle, fat_cluster_t pfc, unsigned pdi)

{

    fat_idx_t *fidx;

    link_t *l;

    unsigned long key[] = {

        [USED_HASH_DH_KEY] = dev_handle,

        [USED_HASH_PFC_KEY] = pfc,

        [USED_HASH_PDI_KEY] = pdi,

    };

    l = hash_table_find(&used_hash, key);

    if (l) {

        fidx = hash_table_get_instance(l, fat_idx_t, uh_link);

    } else {

        fidx = (fat_idx_t *) malloc(sizeof(fat_idx_t));

        if (!fidx) {

            return NULL;

        }

        if (!fat_idx_alloc(dev_handle, &fidx->index)) {

            free(fidx);

            return NULL;

        }

        link_initialize(&fidx->uh_link);

        fidx->dev_handle = dev_handle;

        fidx->pfc = pfc;

        fidx->pdi = pdi;

        fidx->nodep = NULL;

        hash_table_insert(&used_hash, key, &fidx->uh_link);

    }

    return fidx;

}