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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_fat.c

 * @brief   Functions that manipulate the File Allocation Tables.

 */

#include "fat_fat.h"

#include "fat_dentry.h"

#include "fat.h"

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

#include <libfs.h>

#include <libblock.h>

#include <errno.h>

#include <byteorder.h>

#include <align.h>

#include <assert.h>

#include <futex.h>

/**

 * The fat_alloc_lock futex protects all copies of the File Allocation Table

 * during allocation of clusters. The lock does not have to be held durring

 * deallocation of clusters.

 */  

static futex_t fat_alloc_lock = FUTEX_INITIALIZER;

/** Walk the cluster chain.

 *

 * @param bs        Buffer holding the boot sector for the file.

 * @param dev_handle    Device handle of the device with the file.

 * @param firstc    First cluster to start the walk with.

 * @param penult    If non-NULL, output argument hodling the

 *          the penultimate cluster visited.

 * @param ult       If non-NULL, output argument holding the

 *          ultimate cluster visited.

 * @param max_clusters  Maximum number of clusters to visit.   

 *

 * @return      Number of clusters seen during the walk.

 */

uint16_t

fat_cluster_walk(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,

    fat_cluster_t *penult, fat_cluster_t *ult, uint16_t max_clusters)

{

    block_t *b;

    unsigned bps;

    unsigned rscnt;     /* block address of the first FAT */

    uint16_t clusters = 0;

    fat_cluster_t clst = firstc;

    bps = uint16_t_le2host(bs->bps);

    rscnt = uint16_t_le2host(bs->rscnt);

    if (firstc == FAT_CLST_RES0) {

        /* No space allocated to the file. */

        if (ult)

            *ult = firstc;

        return 0;

    }

    /* At this point, the meaning of penult is not well-defined. */

    if (penult)

        *penult = FAT_CLST_RES0;

    while (clst < FAT_CLST_LAST1 && clusters < max_clusters) {

        unsigned fsec;  /* sector offset relative to FAT1 */

        unsigned fidx;  /* FAT1 entry index */

        assert(clst >= FAT_CLST_FIRST);

        if (penult)

            *penult = clst; /* remember the penultimate cluster */

        fsec = (clst * sizeof(fat_cluster_t)) / bps;

        fidx = clst % (bps / sizeof(fat_cluster_t));

        /* read FAT1 */

        b = block_get(dev_handle, rscnt + fsec);

        clst = uint16_t_le2host(((fat_cluster_t *)b->data)[fidx]);

        assert(clst != FAT_CLST_BAD);

        block_put(b);

        clusters++;

    }

    if (ult)

        *ult = clst;

    return clusters;

}

/** Read block from file located on a FAT file system.

 *

 * @param bs        Buffer holding the boot sector of the file system.

 * @param dev_handle    Device handle of the file system.

 * @param firstc    First cluster used by the file. Can be zero if the file

 *          is empty.

 * @param offset    Offset in blocks.

 *

 * @return      Block structure holding the requested block.

 */

block_t *

_fat_block_get(fat_bs_t *bs, dev_handle_t dev_handle, fat_cluster_t firstc,

    off_t offset)

{

    block_t *b;

    unsigned bps;

    unsigned rscnt;     /* block address of the first FAT */

    unsigned rde;

    unsigned rds;       /* root directory size */

    unsigned sf;

    unsigned ssa;       /* size of the system area */

    unsigned clusters, max_clusters;

    fat_cluster_t lastc, clst = firstc;

    bps = uint16_t_le2host(bs->bps);

    rscnt = uint16_t_le2host(bs->rscnt);

    rde = uint16_t_le2host(bs->root_ent_max);

    sf = uint16_t_le2host(bs->sec_per_fat);

    rds = (sizeof(fat_dentry_t) * rde) / bps;

    rds += ((sizeof(fat_dentry_t) * rde) % bps != 0);

    ssa = rscnt + bs->fatcnt * sf + rds;

    if (firstc == FAT_CLST_ROOT) {

        /* root directory special case */

        assert(offset < rds);

        b = block_get(dev_handle, rscnt + bs->fatcnt * sf + offset);

        return b;

    }

    max_clusters = offset / bs->spc;

    clusters = fat_cluster_walk(bs, dev_handle, firstc, NULL, &lastc,

        max_clusters);

    assert(clusters == max_clusters);

    b = block_get(dev_handle, ssa + (lastc - FAT_CLST_FIRST) * bs->spc +

        offset % bs->spc);

    return b;

}

/** Fill the gap between EOF and a new file position.

 *

 * @param bs        Buffer holding the boot sector for nodep.

 * @param nodep     FAT node with the gap.

 * @param mcl       First cluster in an independent cluster chain that will

 *          be later appended to the end of the node's own cluster

 *          chain. If pos is still in the last allocated cluster,

 *          this argument is ignored.

 * @param pos       Position in the last node block.

 */

void fat_fill_gap(fat_bs_t *bs, fat_node_t *nodep, fat_cluster_t mcl, off_t pos)

{

    uint16_t bps;

    unsigned spc;

    block_t *b;

    off_t o, boundary;

    bps = uint16_t_le2host(bs->bps);

    spc = bs->spc;

    boundary = ROUND_UP(nodep->size, bps * spc);

    /* zero out already allocated space */

    for (o = nodep->size - 1; o < pos && o < boundary;

        o = ALIGN_DOWN(o + bps, bps)) {

        b = fat_block_get(bs, nodep, o / bps);

        memset(b->data + o % bps, 0, bps - o % bps);

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

        block_put(b);

    }

    if (o >= pos)

        return;

    /* zero out the initial part of the new cluster chain */

    for (o = boundary; o < pos; o += bps) {

        b = _fat_block_get(bs, nodep->idx->dev_handle, mcl,

            (o - boundary) / bps);

        memset(b->data, 0, min(bps, pos - o));

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

        block_put(b);

    }

}

/** Mark cluster in one instance of FAT.

 *

 * @param bs        Buffer holding the boot sector for the file system.

 * @param dev_handle    Device handle for the file system.

 * @param fatno     Number of the FAT instance where to make the change.

 * @param clst      Cluster which is to be marked.

 * @param value     Value mark the cluster with.

 */

void

fat_mark_cluster(fat_bs_t *bs, dev_handle_t dev_handle, unsigned fatno,

    fat_cluster_t clst, fat_cluster_t value)

{

    block_t *b;

    uint16_t bps;

    uint16_t rscnt;

    uint16_t sf;

    fat_cluster_t *cp;

    bps = uint16_t_le2host(bs->bps);

    rscnt = uint16_t_le2host(bs->rscnt);

    sf = uint16_t_le2host(bs->sec_per_fat);

    assert(fatno < bs->fatcnt);

    b = block_get(dev_handle, rscnt + sf * fatno +

        (clst * sizeof(fat_cluster_t)) / bps);

    cp = (fat_cluster_t *)b->data + clst % (bps / sizeof(fat_cluster_t));

    *cp = host2uint16_t_le(value);

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

    block_put(b);

}

/** Replay the allocatoin of clusters in all shadow instances of FAT.

 *

 * @param bs        Buffer holding the boot sector of the file system.

 * @param dev_handle    Device handle of the file system.

 * @param lifo      Chain of allocated clusters.

 * @param nclsts    Number of clusters in the lifo chain.

 */

void fat_alloc_shadow_clusters(fat_bs_t *bs, dev_handle_t dev_handle,

    fat_cluster_t *lifo, unsigned nclsts)

{

    uint8_t fatno;

    unsigned c;

    for (fatno = FAT1 + 1; fatno < bs->fatcnt; fatno++) {

        for (c = 0; c < nclsts; c++) {

            fat_mark_cluster(bs, dev_handle, fatno, lifo[c],

                c == 0 ? FAT_CLST_LAST1 : lifo[c - 1]);

        }

    }

}

/** Allocate clusters in FAT1.

 *

 * This function will attempt to allocate the requested number of clusters in

 * the first FAT instance.  The FAT will be altered so that the allocated

 * clusters form an independent chain (i.e. a chain which does not belong to any

 * file yet).

 *

 * @param bs        Buffer holding the boot sector of the file system.

 * @param dev_handle    Device handle of the file system.

 * @param nclsts    Number of clusters to allocate.

 * @param mcl       Output parameter where the first cluster in the chain

 *          will be returned.

 * @param lcl       Output parameter where the last cluster in the chain

 *          will be returned.

 *

 * @return      EOK on success, a negative error code otherwise.

 */

int

fat_alloc_clusters(fat_bs_t *bs, dev_handle_t dev_handle, unsigned nclsts,

    fat_cluster_t *mcl, fat_cluster_t *lcl)

{

    uint16_t bps;

    uint16_t rscnt;

    uint16_t sf;

    block_t *blk;

    fat_cluster_t *lifo;    /* stack for storing free cluster numbers */

    unsigned found = 0; /* top of the free cluster number stack */

    unsigned b, c, cl;

    lifo = (fat_cluster_t *) malloc(nclsts * sizeof(fat_cluster_t));

    if (lifo)

        return ENOMEM;

    bps = uint16_t_le2host(bs->bps);

    rscnt = uint16_t_le2host(bs->rscnt);

    sf = uint16_t_le2host(bs->sec_per_fat);

    /*

     * Search FAT1 for unused clusters.

     */

    futex_down(&fat_alloc_lock);

    for (b = 0, cl = 0; b < sf; blk++) {

        blk = block_get(dev_handle, rscnt + b);

        for (c = 0; c < bps / sizeof(fat_cluster_t); c++, cl++) {

            fat_cluster_t *clst = (fat_cluster_t *)blk->data + c;

            if (uint16_t_le2host(*clst) == FAT_CLST_RES0) {

                /*

                 * The cluster is free. Put it into our stack

                 * of found clusters and mark it as non-free.

                 */

                lifo[found] = cl;

                *clst = (found == 0) ?

                    host2uint16_t_le(FAT_CLST_LAST1) :

                    host2uint16_t_le(lifo[found - 1]);

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

                if (++found == nclsts) {

                    /* we are almost done */

                    block_put(blk);

                    /* update the shadow copies of FAT */

                    fat_alloc_shadow_clusters(bs,

                        dev_handle, lifo, nclsts);

                    *mcl = lifo[found - 1];

                    *lcl = lifo[0];

                    free(lifo);

                    futex_up(&fat_alloc_lock);

                    return EOK;

                }

            }

        }

        block_put(blk);

    }

    futex_up(&fat_alloc_lock);

    /*

     * We could not find enough clusters. Now we need to free the clusters

     * we have allocated so far.

     */

    while (found--) {

        fat_mark_cluster(bs, dev_handle, FAT1, lifo[found],

            FAT_CLST_RES0);

    }

    free(lifo);

    return ENOSPC;

}

/** Append a cluster chain to the last file cluster in all FATs.

 *

 * @param bs        Buffer holding boot sector of the file system.

 * @param nodep     Node representing the file.

 * @param mcl       First cluster of the cluster chain to append.

 */

void fat_append_clusters(fat_bs_t *bs, fat_node_t *nodep, fat_cluster_t mcl)

{

    dev_handle_t dev_handle = nodep->idx->dev_handle;

    fat_cluster_t lcl;

    uint8_t fatno;

    if (fat_cluster_walk(bs, nodep->idx->dev_handle, nodep->firstc, &lcl,

        NULL, (uint16_t) -1) == 0) {

        /* No clusters allocated to the node yet. */

        nodep->firstc = host2uint16_t_le(mcl);

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

        return;

    }

    for (fatno = FAT1; fatno < bs->fatcnt; fatno++)

        fat_mark_cluster(bs, nodep->idx->dev_handle, fatno, lcl, mcl);

}

/**

 * @}

 */