source: mainline/uspace/srv/fs/fat/fat_fat.c@ 24d6efc

/*
 * 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);
}

/**
 * @}
 */