source: mainline/uspace/srv/fs/fat/fat_idx.c@ 9a5ccfb3

/*
 * 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;
}