WebSVN – HelenOS – Diff – /branches/snapshot/uspace/srv/fs/fat/fat_fat.c


/*
 * 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);
}
 
/**
 * @}
 */
 
Subversion Repositories HelenOS

(root)/branches/snapshot/uspace/srv/fs/fat/fat_fat.c @ 4605 – Rev 3550 → 3551
