fat.c

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

/*
 * fat.c
 *
 * Low-level operations on a volume with FAT filesystem
 *
 * Copyright (C) 2001 OKTET Ltd., St.-Petersburg, Russia
 * Author: Eugeny S. Mints <[e-mail]>
 *
 * @(#) $Id: fat.c,v 1.2.2.4 2003/10/22 16:35:02 joel Exp $
 */

#if HAVE_CONFIG_H
#include "config.h"
#endif

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <assert.h>

#include <rtems/libio_.h>

#include "fat.h"
#include "fat_fat_operations.h"

/* _fat_block_read --
 *     This function reads 'count' bytes from device filesystem is mounted on,
 *     starts at 'start+offset' position where 'start' computed in sectors 
 *     and 'offset' is offset inside sector (reading may cross sectors 
 *     boundary; in this case assumed we want to read sequential sector(s))
 *
 * PARAMETERS:
 *     mt_entry - mount table entry
 *     start    - sector num to start read from
 *     offset   - offset inside sector 'start'
 *     count    - count of bytes to read
 *     buff     - buffer provided by user
 *
 * RETURNS:
 *     bytes read on success, or -1 if error occured
 *     and errno set appropriately
 */
ssize_t
_fat_block_read(
    rtems_filesystem_mount_table_entry_t *mt_entry, 
    unsigned32                            start, 
    unsigned32                            offset,
    unsigned32                            count, 
    void                                 *buff
    )
{
    int                     rc = RC_OK;
    register fat_fs_info_t *fs_info = mt_entry->fs_info;
    ssize_t                 cmpltd = 0;
    unsigned32              blk = start;
    unsigned32              ofs = offset;
    bdbuf_buffer           *block = NULL;
    unsigned32              c = 0;
  
    while (count > 0)
    {
        rc = fat_buf_access(fs_info, blk, FAT_OP_TYPE_READ, &block);
        if (rc != RC_OK)
            return -1;

        c = MIN(count, (fs_info->vol.bps - ofs));
        memcpy((buff + cmpltd), (block->buffer + ofs), c);

        count -= c;
        cmpltd += c;
        blk++;
        ofs = 0;
    }
    return cmpltd;
}

/* _fat_block_write --
 *     This function write 'count' bytes to device filesystem is mounted on, 
 *     starts at 'start+offset' position where 'start' computed in sectors 
 *     and 'offset' is offset inside sector (writing may cross sectors 
 *     boundary; in this case assumed we want to write sequential sector(s))
 *
 * PARAMETERS:
 *     mt_entry - mount table entry
 *     start    - sector num to start read from
 *     offset   - offset inside sector 'start'
 *     count    - count of bytes to write
 *     buff     - buffer provided by user
 *
 * RETURNS:
 *     bytes written on success, or -1 if error occured
 *     and errno set appropriately
 */
ssize_t
_fat_block_write(
    rtems_filesystem_mount_table_entry_t *mt_entry, 
    unsigned32                            start, 
    unsigned32                            offset,
    unsigned32                            count, 
    const void                           *buff)
{
    int            rc = RC_OK;
    fat_fs_info_t *fs_info = mt_entry->fs_info;
    ssize_t        cmpltd = 0;
    unsigned32     blk  = start;
    unsigned32     ofs = offset;
    bdbuf_buffer  *block = NULL;
    unsigned32     c = 0;
  
    while(count > 0)
    {
        c = MIN(count, (fs_info->vol.bps - ofs));

        if (c == fs_info->vol.bps)
            rc = fat_buf_access(fs_info, blk, FAT_OP_TYPE_GET, &block);
        else
            rc = fat_buf_access(fs_info, blk, FAT_OP_TYPE_READ, &block);
        if (rc != RC_OK)
            return -1;
    
        memcpy((block->buffer + ofs), (buff + cmpltd), c);

        fat_buf_mark_modified(fs_info);

        count -= c;
        cmpltd +=c;
        blk++;
        ofs = 0;
    }
    return cmpltd;
}




/* fat_cluster_read --
 *     wrapper for reading a whole cluster at once
 *
 * PARAMETERS:
 *     mt_entry - mount table entry
 *     cln      - number of cluster to read
 *     buff     - buffer provided by user
 *
 * RETURNS:
 *     bytes read on success, or -1 if error occured
 *     and errno set appropriately
 */
ssize_t 
fat_cluster_read(
    rtems_filesystem_mount_table_entry_t *mt_entry,
    unsigned32                            cln,
    void                                 *buff
    )
{
    fat_fs_info_t *fs_info = mt_entry->fs_info;
    unsigned32     fsec = 0; 
  
    fsec = fat_cluster_num_to_sector_num(mt_entry, cln); 

    return _fat_block_read(mt_entry, fsec, 0, 
                           fs_info->vol.spc << fs_info->vol.sec_log2, buff); 
}                 

/* fat_cluster_write --
 *     wrapper for writting a whole cluster at once
 *
 * PARAMETERS:
 *     mt_entry - mount table entry
 *     cln      - number of cluster to write
 *     buff     - buffer provided by user
 *
 * RETURNS:
 *     bytes written on success, or -1 if error occured
 *     and errno set appropriately
 */
ssize_t 
fat_cluster_write(
    rtems_filesystem_mount_table_entry_t *mt_entry,
    unsigned32                            cln,
    const void                           *buff
    )
{
    fat_fs_info_t *fs_info = mt_entry->fs_info;
    unsigned32     fsec = 0;
  
    fsec = fat_cluster_num_to_sector_num(mt_entry, cln); 
 
    return _fat_block_write(mt_entry, fsec, 0,
                          fs_info->vol.spc << fs_info->vol.sec_log2, buff); 
}                 

/* fat_init_volume_info --
 *     Get inforamtion about volume on which filesystem is mounted on
 *
 * PARAMETERS:
 *     mt_entry - mount table entry
 *
 * RETURNS:
 *     RC_OK on success, or -1 if error occured
 *     and errno set appropriately
 */
int
fat_init_volume_info(rtems_filesystem_mount_table_entry_t *mt_entry)
{
    int                 rc = RC_OK;
    fat_fs_info_t      *fs_info = mt_entry->fs_info;     
    register fat_vol_t *vol = &fs_info->vol;
    unsigned32          data_secs = 0;
    char                boot_rec[FAT_MAX_BPB_SIZE];
    char                fs_info_sector[FAT_USEFUL_INFO_SIZE];
    ssize_t             ret = 0;
    int                 fd;
    struct stat         stat_buf;
    int                 i = 0;

    rc = stat(mt_entry->dev, &stat_buf);
    if (rc == -1)
        return rc;

    /* rtmes feature: no block devices, all are character devices */   
    if (!S_ISCHR(stat_buf.st_mode))
        set_errno_and_return_minus_one(ENOTBLK);    

    /* check that  device is registred as block device and lock it */
    vol->dd = rtems_disk_lookup(stat_buf.st_dev);
    if (vol->dd == NULL) 
        set_errno_and_return_minus_one(ENOTBLK);
        
    vol->dev = stat_buf.st_dev;

    fd = open(mt_entry->dev, O_RDONLY);
    if (fd == -1)
    {
        rtems_disk_release(vol->dd);
        return -1;
    }    
  
    ret = read(fd, (void *)boot_rec, FAT_MAX_BPB_SIZE);
    if ( ret != FAT_MAX_BPB_SIZE )
    {
        close(fd);
        rtems_disk_release(vol->dd);
        set_errno_and_return_minus_one( EIO );
    }
    close(fd);

    vol->bps = FAT_BR_BYTES_PER_SECTOR(boot_rec);
 
    if ( (vol->bps != 512)  && 
         (vol->bps != 1024) && 
         (vol->bps != 2048) &&
         (vol->bps != 4096))
    {     
        rtems_disk_release(vol->dd);
        set_errno_and_return_minus_one( EINVAL );
    }    

    for (vol->sec_mul = 0, i = (vol->bps >> FAT_SECTOR512_BITS); (i & 1) == 0; 
         i >>= 1, vol->sec_mul++);
    for (vol->sec_log2 = 0, i = vol->bps; (i & 1) == 0; 
         i >>= 1, vol->sec_log2++);

    vol->spc = FAT_BR_SECTORS_PER_CLUSTER(boot_rec);
    /*
     * "sectors per cluster" of zero is invalid
     * (and would hang the following loop)
     */
    if (vol->spc == 0)
    {
        rtems_disk_release(vol->dd);
        set_errno_and_return_minus_one(EINVAL);
    }    

    for (vol->spc_log2 = 0, i = vol->spc; (i & 1) == 0; 
         i >>= 1, vol->spc_log2++);
  
    /* 
     * "bytes per cluster" value greater than 32K is invalid
     */
    if ((vol->bpc = vol->bps << vol->spc_log2) > MS_BYTES_PER_CLUSTER_LIMIT)
    {
        rtems_disk_release(vol->dd);
        set_errno_and_return_minus_one(EINVAL);
    }    

    for (vol->bpc_log2 = 0, i = vol->bpc; (i & 1) == 0; 
         i >>= 1, vol->bpc_log2++);

    vol->fats = FAT_BR_FAT_NUM(boot_rec);
    vol->fat_loc = FAT_BR_RESERVED_SECTORS_NUM(boot_rec);

    vol->rdir_entrs = FAT_BR_FILES_PER_ROOT_DIR(boot_rec);
    
    /* calculate the count of sectors occupied by the root directory */
    vol->rdir_secs = ((vol->rdir_entrs * FAT_DIRENTRY_SIZE) + (vol->bps - 1)) /
                     vol->bps;

    vol->rdir_size = vol->rdir_secs << vol->sec_log2;

    if ( (FAT_BR_SECTORS_PER_FAT(boot_rec)) != 0)
        vol->fat_length = FAT_BR_SECTORS_PER_FAT(boot_rec);
    else
        vol->fat_length = FAT_BR_SECTORS_PER_FAT32(boot_rec);
  
    vol->data_fsec = vol->fat_loc + vol->fats * vol->fat_length + 
                     vol->rdir_secs;

    /* for  FAT12/16 root dir starts at(sector) */
    vol->rdir_loc = vol->fat_loc + vol->fats * vol->fat_length;
  
    if ( (FAT_BR_TOTAL_SECTORS_NUM16(boot_rec)) != 0)
        vol->tot_secs = FAT_BR_TOTAL_SECTORS_NUM16(boot_rec);
    else
        vol->tot_secs = FAT_BR_TOTAL_SECTORS_NUM32(boot_rec);
  
    data_secs = vol->tot_secs - vol->data_fsec;
  
    vol->data_cls = data_secs / vol->spc;

    /* determine FAT type at least */
    if ( vol->data_cls < FAT_FAT12_MAX_CLN)
    {
        vol->type = FAT_FAT12;
        vol->mask = FAT_FAT12_MASK;
        vol->eoc_val = FAT_FAT12_EOC;
    }
    else 
    {
        if ( vol->data_cls < FAT_FAT16_MAX_CLN)
        {
            vol->type = FAT_FAT16;
            vol->mask = FAT_FAT16_MASK;
            vol->eoc_val = FAT_FAT16_EOC;
        }
        else
        {
            vol->type = FAT_FAT32;
            vol->mask = FAT_FAT32_MASK;
            vol->eoc_val = FAT_FAT32_EOC;
        }
    }
  
    if (vol->type == FAT_FAT32)
    {
        vol->rdir_cl = FAT_BR_FAT32_ROOT_CLUSTER(boot_rec);
      
        vol->mirror = FAT_BR_EXT_FLAGS(boot_rec) & FAT_BR_EXT_FLAGS_MIRROR;
        if (vol->mirror)
            vol->afat = FAT_BR_EXT_FLAGS(boot_rec) & FAT_BR_EXT_FLAGS_FAT_NUM;
        else
            vol->afat = 0;