source: rtems/cpukit/libfs/src/dosfs/fat_file.c @ c735cd5

/**
 * @file
 *
 * @brief General operations on "fat-file"
 * @ingroup libfs_ff Fat File
 */

/*
 * Copyright (C) 2001 OKTET Ltd., St.-Petersburg, Russia
 * Author: Eugeny S. Mints <Eugeny.Mints@oktet.ru>
 *
 */

#define MSDOS_TRACE 1

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

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

#include <rtems/libio_.h>

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

static inline void
_hash_insert(rtems_chain_control *hash, uint32_t   key1, uint32_t   key2,
             fat_file_fd_t *el);

static inline void
_hash_delete(rtems_chain_control *hash, uint32_t   key1, uint32_t   key2,
             fat_file_fd_t *el);

static inline int
_hash_search(
    const fat_fs_info_t                   *fs_info,
    rtems_chain_control                   *hash,
    uint32_t                               key1,
    uint32_t                               key2,
    fat_file_fd_t                                          **ret
);

static off_t
fat_file_lseek(
    fat_fs_info_t                         *fs_info,
    fat_file_fd_t                         *fat_fd,
    uint32_t                               file_cln,
    uint32_t                              *disk_cln
);

/* fat_file_open --
 *     Open fat-file. Two hash tables are accessed by key
 *     constructed from cluster num and offset of the node (i.e.
 *     files/directories are distinguished by location on the disk).
 *     First, hash table("vhash") consists of fat-file descriptors corresponded
 *     to "valid" files is accessed. Search is made by 2 fields equal to key
 *     constructed. If descriptor is found in the "vhash" - return it.
 *     Otherwise search is made in hash table("rhash") consits of fat-file
 *     descriptors corresponded to "removed-but-still-open" files with the
 *     same keys.
 *     If search failed, new fat-file descriptor is added to "vhash"
 *     with both key fields equal to constructed key. Otherwise new fat-file
 *     descriptor is added to "vhash" with first key field equal to key
 *     constructed and the second equal to an unique (unique among all values
 *     of second key fields) value.
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     pos      - cluster and offset of the node
 *     fat_fd   - placeholder for returned fat-file descriptor
 *
 * RETURNS:
 *     RC_OK and pointer to opened descriptor on success, or -1 if error
 *     occured (errno set appropriately)
 */
int
fat_file_open(
    fat_fs_info_t                         *fs_info,
    fat_dir_pos_t                         *dir_pos,
    fat_file_fd_t                        **fat_fd
    )
{
    int            rc = RC_OK;
    fat_file_fd_t *lfat_fd = NULL;
    uint32_t       key = 0;

    /* construct key */
    key = fat_construct_key(fs_info, &dir_pos->sname);

    /* access "valid" hash table */
    rc = _hash_search(fs_info, fs_info->vhash, key, 0, &lfat_fd);
    if ( rc == RC_OK )
    {
        /* return pointer to fat_file_descriptor allocated before */
        (*fat_fd) = lfat_fd;
        lfat_fd->links_num++;
        return rc;
    }

    /* access "removed-but-still-open" hash table */
    rc = _hash_search(fs_info, fs_info->rhash, key, key, &lfat_fd);

    lfat_fd = (*fat_fd) = (fat_file_fd_t*)malloc(sizeof(fat_file_fd_t));
    if ( lfat_fd == NULL )
        rtems_set_errno_and_return_minus_one( ENOMEM );

    memset(lfat_fd, 0, sizeof(fat_file_fd_t));

    lfat_fd->links_num = 1;
    lfat_fd->flags &= ~FAT_FILE_REMOVED;
    lfat_fd->map.last_cln = FAT_UNDEFINED_VALUE;

    lfat_fd->dir_pos = *dir_pos;

    if ( rc != RC_OK )
        lfat_fd->ino = key;
    else
    {
        lfat_fd->ino = fat_get_unique_ino(fs_info);

        if ( lfat_fd->ino == 0 )
        {
            free((*fat_fd));
            /*
             * XXX: kernel resource is unsufficient, but not the memory,
             * but there is no suitable errno :(
             */
            rtems_set_errno_and_return_minus_one( ENOMEM );
        }
    }
    _hash_insert(fs_info->vhash, key, lfat_fd->ino, lfat_fd);

    /*
     * other fields of fat-file descriptor will be initialized on upper
     * level
     */

    return RC_OK;
}


/* fat_file_reopen --
 *     Increment by 1 number of links
 *
 * PARAMETERS:
 *     fat_fd - fat-file descriptor
 *
 * RETURNS:
 *     RC_OK
 */
int
fat_file_reopen(fat_file_fd_t *fat_fd)
{
    fat_fd->links_num++;
    return RC_OK;
}

int
fat_file_update(fat_fs_info_t *fs_info, fat_file_fd_t *fat_fd)
{
    int ret_rc = RC_OK;

    /*
     * if fat-file descriptor is not marked as "removed", synchronize
     * size, first cluster number, write time and date fields of the file
     */
    if (!FAT_FILE_IS_REMOVED(fat_fd) && FAT_FILE_HAS_META_DATA_CHANGED(fat_fd))
    {
        int rc;

        rc = fat_file_write_first_cluster_num(fs_info, fat_fd);
        if (rc != RC_OK)
            ret_rc = rc;

        rc = fat_file_write_file_size(fs_info, fat_fd);
        if (rc != RC_OK)
            ret_rc = rc;

        rc = fat_file_write_time_and_date(fs_info, fat_fd);
        if (rc != RC_OK)
            ret_rc = rc;
    }

    return ret_rc;
}

/* fat_file_close --
 *     Close fat-file. If count of links to fat-file
 *     descriptor is greater than 1 (i.e. somebody esle holds pointer
 *     to this descriptor) just decrement it. Otherwise
 *     do the following. If this descriptor corresponded to removed fat-file
 *     then free clusters contained fat-file data, delete descriptor from
 *     "rhash" table and free memory allocated by descriptor. If descriptor
 *     correspondes to non-removed fat-file and 'ino' field has value from
 *     unique inode numbers pool then set count of links to descriptor to zero
 *     and leave it in hash, otherwise delete descriptor from "vhash" and free
 *     memory allocated by the descriptor
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     fat_fd   - fat-file descriptor
 *
 * RETURNS:
 *     RC_OK, or -1 if error occured (errno set appropriately)
 */
int
fat_file_close(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd
    )
{
    int            rc = RC_OK;

    /*
     * if links_num field of fat-file descriptor is greater than 1
     * decrement only the count of links
     */
    if (fat_fd->links_num > 1)
    {
        fat_fd->links_num--;
    }
    else
    {
        uint32_t key = fat_construct_key(fs_info, &fat_fd->dir_pos.sname);

        fat_file_update(fs_info, fat_fd);

        if (fat_fd->flags & FAT_FILE_REMOVED)
        {
            rc = fat_file_truncate(fs_info, fat_fd, 0);
            if (rc == RC_OK)
            {
                _hash_delete(fs_info->rhash, key, fat_fd->ino, fat_fd);

                if (fat_ino_is_unique(fs_info, fat_fd->ino))
                    fat_free_unique_ino(fs_info, fat_fd->ino);

                free(fat_fd);
            }
        }
        else
        {
            if (fat_ino_is_unique(fs_info, fat_fd->ino))
            {
                fat_fd->links_num = 0;
            }
            else
            {
                _hash_delete(fs_info->vhash, key, fat_fd->ino, fat_fd);
                free(fat_fd);
            }
        }
    }

    /*
     * flush any modified "cached" buffer back to disk
     */
    rc = fat_buf_release(fs_info);

    return rc;
}

/* fat_file_read --
 *     Read 'count' bytes from 'start' position from fat-file. This
 *     interface hides the architecture of fat-file, represents it as
 *     linear file
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     fat_fd   - fat-file descriptor
 *     start    - offset in fat-file (in bytes) to read from
 *     count    - count of bytes to read
 *     buf      - buffer provided by user
 *
 * RETURNS:
 *     the number of bytes read on success, or -1 if error occured (errno
 *     set appropriately)
 */
ssize_t
fat_file_read(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd,
    uint32_t                              start,
    uint32_t                              count,
    uint8_t                              *buf
)
{
    int            rc = RC_OK;
    ssize_t        ret = 0;
    uint32_t       cmpltd = 0;
    uint32_t       cur_cln = 0;
    uint32_t       cl_start = 0;
    uint32_t       save_cln = 0;
    uint32_t       ofs = 0;
    uint32_t       save_ofs;
    uint32_t       sec = 0;
    uint32_t       byte = 0;
    uint32_t       c = 0;

    /* it couldn't be removed - otherwise cache update will be broken */
    if (count == 0)
        return cmpltd;

    /*
     * >= because start is offset and computed from 0 and file_size
     * computed from 1
     */
    if ( start >= fat_fd->fat_file_size )
        return FAT_EOF;

    if ((count > fat_fd->fat_file_size) ||
        (start > fat_fd->fat_file_size - count))
        count = fat_fd->fat_file_size - start;

    if ((FAT_FD_OF_ROOT_DIR(fat_fd)) &&
        (fs_info->vol.type & (FAT_FAT12 | FAT_FAT16)))
    {
        sec = fat_cluster_num_to_sector_num(fs_info, fat_fd->cln);
        sec += (start >> fs_info->vol.sec_log2);
        byte = start & (fs_info->vol.bps - 1);

        ret = _fat_block_read(fs_info, sec, byte, count, buf);
        if ( ret < 0 )
            return -1;

        return ret;
    }

    cl_start = start >> fs_info->vol.bpc_log2;
    save_ofs = ofs = start & (fs_info->vol.bpc - 1);

    rc = fat_file_lseek(fs_info, fat_fd, cl_start, &cur_cln);
    if (rc != RC_OK)
        return rc;

    while (count > 0)
    {
        c = MIN(count, (fs_info->vol.bpc - ofs));

        sec = fat_cluster_num_to_sector_num(fs_info, cur_cln);
        sec += (ofs >> fs_info->vol.sec_log2);
        byte = ofs & (fs_info->vol.bps - 1);

        ret = _fat_block_read(fs_info, sec, byte, c, buf + cmpltd);
        if ( ret < 0 )
            return -1;

        count -= c;
        cmpltd += c;
        save_cln = cur_cln;
        rc = fat_get_fat_cluster(fs_info, cur_cln, &cur_cln);
        if ( rc != RC_OK )
            return rc;

        ofs = 0;
    }

    /* update cache */
    /* XXX: check this - I'm not sure :( */
    fat_fd->map.file_cln = cl_start +
                           ((save_ofs + cmpltd - 1) >> fs_info->vol.bpc_log2);
    fat_fd->map.disk_cln = save_cln;

    return cmpltd;
}

/* fat_is_fat12_or_fat16_root_dir --
 *     Returns true for FAT12 root directories respectively FAT16
 *     root directories. Returns false for everything else.
 *
 *  PARAMETERS:
 *      fat_fd        - fat-file descriptor
 *      volume_type   - type of fat volume: FAT_FAT12 or FAT_FAT16 or FAT_FAT32
 *
 *  RETURNS:
 *      true if conditions for FAT12 root directory or FAT16 root directory
 *      match, false if not
 */
static bool
 fat_is_fat12_or_fat16_root_dir (const fat_file_fd_t *fat_fd,
                                 const uint8_t volume_type)
{
    return (FAT_FD_OF_ROOT_DIR(fat_fd)) && (volume_type & (FAT_FAT12 | FAT_FAT16));
}

/* fat_file_write_fat32_or_non_root_dir --
 *     Execute fat file write for FAT32 respectively for non-root
 *     directories of FAT12 or FAT16
 *
 * PARAMETERS:
 *     fs_info          - FS info
 *     fat_fd           - fat-file descriptor
 *     start            - offset(in bytes) to write from
 *     count            - count
 *     buf              - buffer provided by user
 *     file_cln_initial - initial current cluster number of the file
 *
 * RETURNS:
 *     number of bytes actually written to the file on success, or -1 if
 *     error occured (errno set appropriately)
 */
static ssize_t
 fat_file_write_fat32_or_non_root_dir(
     fat_fs_info_t                        *fs_info,
     fat_file_fd_t                        *fat_fd,
     const uint32_t                        start,
     const uint32_t                        count,
     const uint8_t                        *buf,
     const uint32_t                        file_cln_initial)
{
    int            rc = RC_OK;
    uint32_t       cmpltd = 0;
    uint32_t       cur_cln = 0;
    uint32_t       save_cln = 0; /* FIXME: This might be incorrect, cf. below */
    uint32_t       start_cln = start >> fs_info->vol.bpc_log2;
    uint32_t       ofs_cln = start - (start_cln << fs_info->vol.bpc_log2);
    uint32_t       ofs_cln_save = ofs_cln;
    uint32_t       bytes_to_write = count;
    uint32_t       file_cln_cnt;
    ssize_t        ret;
    uint32_t       c;
    bool           overwrite_cluster = false;

    rc = fat_file_lseek(fs_info, fat_fd, start_cln, &cur_cln);
    if (RC_OK == rc)
    {
        file_cln_cnt = cur_cln - fat_fd->cln;
        while (   (RC_OK == rc)
               && (bytes_to_write > 0))
        {
            c = MIN(bytes_to_write, (fs_info->vol.bpc - ofs_cln));

            if (file_cln_initial < file_cln_cnt)
                overwrite_cluster = true;

            ret = fat_cluster_write(fs_info,
                                      cur_cln,
                                      ofs_cln,
                                      c,
                                      &buf[cmpltd],
                                      overwrite_cluster);
            if (0 > ret)
              rc = -1;

            if (RC_OK == rc)
            {
                ++file_cln_cnt;
                bytes_to_write -= ret;
                cmpltd += ret;
                save_cln = cur_cln;
                if (0 < bytes_to_write)
                  rc = fat_get_fat_cluster(fs_info, cur_cln, &cur_cln);

                ofs_cln = 0;
            }
        }

        /* update cache */
        /* XXX: check this - I'm not sure :( */
        fat_fd->map.file_cln = start_cln +
                               ((ofs_cln_save + cmpltd - 1) >> fs_info->vol.bpc_log2);
        fat_fd->map.disk_cln = save_cln;
    }

    if (RC_OK != rc)
      return rc;
    else
      return cmpltd;
}

/* fat_file_write --
 *     Write 'count' bytes of data from user supplied buffer to fat-file
 *     starting at offset 'start'. This interface hides the architecture
 *     of fat-file, represents it as linear file
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     fat_fd   - fat-file descriptor
 *     start    - offset(in bytes) to write from
 *     count    - count
 *     buf      - buffer provided by user
 *
 * RETURNS:
 *     number of bytes actually written to the file on success, or -1 if
 *     error occured (errno set appropriately)
 */
ssize_t
fat_file_write(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd,
    uint32_t                              start,
    uint32_t                              count,
    const uint8_t                        *buf
    )
{
    int            rc = RC_OK;
    ssize_t        ret;
    uint32_t       cmpltd = 0;
    uint32_t       byte;
    uint32_t       c = 0;
    bool           zero_fill = start > fat_fd->fat_file_size;
    uint32_t       file_cln_initial = fat_fd->map.file_cln;
    uint32_t       cln;


    if ( count == 0 )
        return cmpltd;

    if (start >= fat_fd->size_limit)
        rtems_set_errno_and_return_minus_one(EFBIG);

    if (count > fat_fd->size_limit - start)
        count = fat_fd->size_limit - start;

    rc = fat_file_extend(fs_info, fat_fd, zero_fill, start + count, &c);
    if (RC_OK == rc)
    {
        /*
         * check whether there was enough room on device to locate
         * file of 'start + count' bytes
         */
        if (c != (start + count))
            count = c - start;

        /* for the root directory of FAT12 and FAT16 we need this special handling */
        if (fat_is_fat12_or_fat16_root_dir(fat_fd, fs_info->vol.type))
        {
            cln = fat_fd->cln;
            cln += (start >> fs_info->vol.bpc_log2);
            byte = start & (fs_info->vol.bpc -1);

            ret = fat_cluster_write(fs_info,
                                      cln,
                                      byte,
                                      count,
                                      buf,
                                      false);
            if (0 > ret)
              rc = -1;
            else
              cmpltd = ret;
        }
        else
        {
            ret = fat_file_write_fat32_or_non_root_dir(fs_info,
                                                       fat_fd,
                                                       start,
                                                       count,
                                                       buf,
                                                       file_cln_initial);
            if (0 > ret)
              rc = -1;
            else
              cmpltd = ret;
        }
    }
    if (RC_OK != rc)
        return rc;
    else
        return cmpltd;
}

/* fat_file_extend --
 *     Extend fat-file. If new length less than current fat-file size -
 *     do nothing. Otherwise calculate necessary count of clusters to add,
 *     allocate it and add new clusters chain to the end of
 *     existing clusters chain.
 *
 * PARAMETERS:
 *     fs_info    - FS info
 *     fat_fd     - fat-file descriptor
 *     new_length - new length
 *     a_length   - placeholder for result - actual new length of file
 *
 * RETURNS:
 *     RC_OK and new length of file on success, or -1 if error occured (errno
 *     set appropriately)
 */
int
fat_file_extend(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd,
    bool                                  zero_fill,
    uint32_t                              new_length,
    uint32_t                             *a_length
    )
{
    int            rc = RC_OK;
    uint32_t       chain = 0;
    uint32_t       bytes2add = 0;
    uint32_t       cls2add = 0;
    uint32_t       old_last_cl;
    uint32_t       last_cl = 0;
    uint32_t       bytes_remain = 0;
    uint32_t       cls_added;
    ssize_t        bytes_written;

    *a_length = new_length;

    if (new_length <= fat_fd->fat_file_size)
        return RC_OK;

    if ((FAT_FD_OF_ROOT_DIR(fat_fd)) &&
        (fs_info->vol.type & (FAT_FAT12 | FAT_FAT16)))
        rtems_set_errno_and_return_minus_one( ENOSPC );

    bytes_remain = (fs_info->vol.bpc -
                   (fat_fd->fat_file_size & (fs_info->vol.bpc - 1))) &
                   (fs_info->vol.bpc - 1);

    bytes2add = new_length - fat_fd->fat_file_size;

    if (bytes2add > bytes_remain)
        bytes2add -= bytes_remain;
    else
        bytes2add = 0;

    if (zero_fill && bytes_remain > 0) {
        uint32_t start = fat_fd->fat_file_size;
        uint32_t cl_start = start >> fs_info->vol.bpc_log2;
        uint32_t ofs = start & (fs_info->vol.bpc - 1);
        uint32_t cur_cln;

        rc = fat_file_lseek(fs_info, fat_fd, cl_start, &cur_cln);
        if (rc != RC_OK)
            return rc;

        bytes_written = fat_cluster_set (fs_info, cur_cln, ofs, bytes_remain, 0);
        if (bytes_remain != bytes_written)
            return -1;
    }

    /*
     * if in last cluster allocated for the file there is enough room to
     * handle extention (hence we don't need to add even one cluster to the
     * file ) - return
     */
    if (bytes2add == 0)
        return RC_OK;

    cls2add = ((bytes2add - 1) >> fs_info->vol.bpc_log2) + 1;

    rc = fat_scan_fat_for_free_clusters(fs_info, &chain, cls2add,
                                        &cls_added, &last_cl, zero_fill);

    /* this means that low level I/O error occured */
    if (rc != RC_OK)
        return rc;

    /* this means that no space left on device */
    if ((cls_added == 0) && (bytes_remain == 0))
        rtems_set_errno_and_return_minus_one(ENOSPC);

    /*  check wether we satisfied request for 'cls2add' clusters */
    if (cls2add != cls_added)
    {
        uint32_t missing = (cls2add - cls_added) << fs_info->vol.bpc_log2;

        new_length -= bytes2add < missing ? bytes2add : missing;
    }

    if (cls_added > 0)
    {
        /* add new chain to the end of existing */
        if ( fat_fd->fat_file_size == 0 )
        {
            fat_fd->map.disk_cln = chain;
            fat_fd->map.file_cln = 0;
            fat_file_set_first_cluster_num(fat_fd, chain);
        }
        else
        {
            if (fat_fd->map.last_cln != FAT_UNDEFINED_VALUE)
            {
                old_last_cl = fat_fd->map.last_cln;
            }
            else
            {
                rc = fat_file_ioctl(fs_info, fat_fd, F_CLU_NUM,
                                    (fat_fd->fat_file_size - 1), &old_last_cl);
                if ( rc != RC_OK )
                {
                    fat_free_fat_clusters_chain(fs_info, chain);
                    return rc;
                }
            }

            rc = fat_set_fat_cluster(fs_info, old_last_cl, chain);
            if ( rc != RC_OK )
            {
                fat_free_fat_clusters_chain(fs_info, chain);
                return rc;
            }
            fat_buf_release(fs_info);
        }

        /* update number of the last cluster of the file */
        fat_fd->map.last_cln = last_cl;

        if (fat_fd->fat_file_type == FAT_DIRECTORY)
        {
            rc = fat_init_clusters_chain(fs_info, chain);
            if ( rc != RC_OK )
            {
                fat_free_fat_clusters_chain(fs_info, chain);
                return rc;
            }
        }
    }

    *a_length = new_length;
    fat_file_set_file_size(fat_fd, new_length);

    return RC_OK;
}

/* fat_file_truncate --
 *     Truncate fat-file. If new length greater than current fat-file size -
 *     do nothing. Otherwise find first cluster to free and free all clusters
 *     in the chain starting from this cluster.
 *
 * PARAMETERS:
 *     fs_info    - FS info
 *     fat_fd     - fat-file descriptor
 *     new_length - new length
 *
 * RETURNS:
 *     RC_OK on success, or -1 if error occured (errno set appropriately)
 */
int
fat_file_truncate(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd,
    uint32_t                              new_length
    )
{
    int            rc = RC_OK;
    uint32_t       cur_cln = 0;
    uint32_t       cl_start = 0;
    uint32_t       new_last_cln = FAT_UNDEFINED_VALUE;


    if ( new_length >= fat_fd->fat_file_size )
        return rc;

    assert(fat_fd->fat_file_size);

    cl_start = (new_length + fs_info->vol.bpc - 1) >> fs_info->vol.bpc_log2;

    if ((cl_start << fs_info->vol.bpc_log2) >= fat_fd->fat_file_size)
        return RC_OK;

    if (cl_start != 0)
    {
        rc = fat_file_lseek(fs_info, fat_fd, cl_start - 1, &new_last_cln);
        if (rc != RC_OK)
            return rc;

    }

    rc = fat_file_lseek(fs_info, fat_fd, cl_start, &cur_cln);
    if (rc != RC_OK)
        return rc;

    rc = fat_free_fat_clusters_chain(fs_info, cur_cln);
    if (rc != RC_OK)
        return rc;

    if (cl_start != 0)
    {
        rc = fat_set_fat_cluster(fs_info, new_last_cln, FAT_GENFAT_EOC);
        if ( rc != RC_OK )
            return rc;
        fat_fd->map.file_cln = cl_start - 1;
        fat_fd->map.disk_cln = new_last_cln;
        fat_fd->map.last_cln = new_last_cln;
    }
    return RC_OK;
}

/* fat_file_ioctl --
 *     F_CLU_NUM:
 *         make mapping between serial number of the cluster in fat-file and
 *         its real number on the volume
 *
 * PARAMETERS:
 *     fat_fd     - fat-file descriptor
 *     fs_info    - FS info
 *     cmd        - command
 *     ...
 *
 * RETURNS:
 *     RC_OK on success, or -1 if error occured and errno set appropriately
 */
int
fat_file_ioctl(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd,
    int                                   cmd,
    ...)
{
    int            rc = RC_OK;
    uint32_t       cur_cln = 0;
    uint32_t       cl_start = 0;
    uint32_t       pos = 0;
    uint32_t      *ret;
    va_list        ap;

    va_start(ap, cmd);

    switch (cmd)
    {
        case F_CLU_NUM:
            pos = va_arg(ap, uint32_t);
            ret = va_arg(ap, uint32_t *);

            /* sanity check */
            if ( pos >= fat_fd->fat_file_size ) {
                va_end(ap);
                rtems_set_errno_and_return_minus_one( EIO );
            }

            if ((FAT_FD_OF_ROOT_DIR(fat_fd)) &&
                (fs_info->vol.type & (FAT_FAT12 | FAT_FAT16)))
            {
                /* cluster 0 (zero) reserved for root dir */
                *ret  = 0;
                rc = RC_OK;
                break;
            }

            cl_start = pos >> fs_info->vol.bpc_log2;

            rc = fat_file_lseek(fs_info, fat_fd, cl_start, &cur_cln);
            if ( rc != RC_OK )
                break;

            *ret = cur_cln;
            break;

        default:
            errno = EINVAL;
            rc = -1;
            break;
    }
    va_end(ap);
    return rc;
}

/* fat_file_mark_removed --
 *     Remove the fat-file descriptor from "valid" hash table, insert it
 *     into "removed-but-still-open" hash table and set up "removed" bit.
 *
 * PARAMETERS:
 *     fat_fd     - fat-file descriptor
 *     fs_info    - FS info
 *
 * RETURNS:
 *     None
 */
void
fat_file_mark_removed(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd
    )
{
    uint32_t       key = 0;

    key = fat_construct_key(fs_info, &fat_fd->dir_pos.sname);

    _hash_delete(fs_info->vhash, key, fat_fd->ino, fat_fd);

    _hash_insert(fs_info->rhash, key, fat_fd->ino, fat_fd);

    fat_fd->flags |= FAT_FILE_REMOVED;
}

/* fat_file_size --
 *     Calculate fat-file size - fat-file is nothing that clusters chain, so
 *     go through all clusters in the chain and count it. Only
 *     special case is root directory for FAT12/16 volumes.
 *     This function is used only for directories which are fat-files with
 *     non-zero length, hence 'fat_fd->cln' always contains valid data.
 *     Calculated size is stored in 'fat_file_size' field of fat-file
 *     descriptor.
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     fat_fd   - fat-file descriptor
 *
 * RETURNS:
 *     RC_OK on success, or -1 if error occured (errno set appropriately)
 */
int
fat_file_size(
    fat_fs_info_t                        *fs_info,
    fat_file_fd_t                        *fat_fd
    )
{
    int            rc = RC_OK;
    uint32_t       cur_cln = fat_fd->cln;
    uint32_t       save_cln = 0;

    /* Have we requested root dir size for FAT12/16? */
    if ((FAT_FD_OF_ROOT_DIR(fat_fd)) &&
        (fs_info->vol.type & (FAT_FAT12 | FAT_FAT16)))
    {
        fat_fd->fat_file_size = fs_info->vol.rdir_size;
        return rc;
    }

    fat_fd->fat_file_size = 0;

    while ((cur_cln & fs_info->vol.mask) < fs_info->vol.eoc_val)
    {
        save_cln = cur_cln;
        rc = fat_get_fat_cluster(fs_info, cur_cln, &cur_cln);
        if ( rc != RC_OK )
            return rc;

        fat_fd->fat_file_size += fs_info->vol.bpc;
    }
    fat_fd->map.last_cln = save_cln;
    return rc;
}

/* hash support routines */

/* _hash_insert --
 *     Insert elemnt into hash based on key 'key1'
 *
 * PARAMETERS:
 *     hash - hash element will be inserted into
 *     key1 - key on which insertion is based on
 *     key2 - not used during insertion
 *     el   - element to insert
 *
 * RETURNS:
 *     None
 */
static inline void
_hash_insert(rtems_chain_control *hash, uint32_t   key1, uint32_t   key2,
             fat_file_fd_t *el)
{
    rtems_chain_append_unprotected((hash) + ((key1) % FAT_HASH_MODULE), &(el)->link);
}


/* _hash_delete --
 *     Remove element from hash
 *
 * PARAMETERS:
 *     hash - hash element will be removed from
 *     key1 - not used
 *     key2 - not used
 *     el   - element to delete
 *
 * RETURNS:
 *     None
 */
static inline void
_hash_delete(rtems_chain_control *hash, uint32_t   key1, uint32_t   key2,
             fat_file_fd_t *el)
{
    rtems_chain_extract_unprotected(&(el)->link);
}

/* _hash_search --
 *     Search element in hash. If both keys match pointer to found element
 *     is returned
 *
 * PARAMETERS:
 *     fs_info  - FS info
 *     hash     - hash element will be removed from
 *     key1     - search key
 *     key2     - search key
 *     ret      - placeholder for result
 *
 * RETURNS:
 *     0 and pointer to found element on success, -1 otherwise
 */
static inline int
_hash_search(
    const fat_fs_info_t                   *fs_info,
    rtems_chain_control                   *hash,
    uint32_t                               key1,
    uint32_t                               key2,
    fat_file_fd_t                          **ret
    )
{
    uint32_t          mod = (key1) % FAT_HASH_MODULE;
    rtems_chain_node *the_node = rtems_chain_first(hash + mod);

    for ( ; !rtems_chain_is_tail((hash) + mod, the_node) ; )
    {
        fat_file_fd_t *ffd = (fat_file_fd_t *)the_node;
        uint32_t       ck =  fat_construct_key(fs_info, &ffd->dir_pos.sname);

        if ( (key1) == ck)
        {
            if ( ((key2) == 0) || ((key2) == ffd->ino) )
            {
                *ret = (void *)the_node;
                return 0;
            }
        }
        the_node = the_node->next;
    }
    return -1;
}

static off_t
fat_file_lseek(
    fat_fs_info_t                         *fs_info,
    fat_file_fd_t                         *fat_fd,
    uint32_t                               file_cln,
    uint32_t                              *disk_cln
    )
{
    int rc = RC_OK;

    if (file_cln == fat_fd->map.file_cln)
        *disk_cln = fat_fd->map.disk_cln;
    else
    {
        uint32_t   cur_cln;
        uint32_t   count;
        uint32_t   i;

        if (file_cln > fat_fd->map.file_cln)
        {
            cur_cln = fat_fd->map.disk_cln;
            count = file_cln - fat_fd->map.file_cln;
        }
        else
        {
            cur_cln = fat_fd->cln;
            count = file_cln;
        }

        /* skip over the clusters */
        for (i = 0; i < count; i++)
        {
            rc = fat_get_fat_cluster(fs_info, cur_cln, &cur_cln);
            if ( rc != RC_OK )
                return rc;
        }

        /* update cache */
        fat_fd->map.file_cln = file_cln;
        fat_fd->map.disk_cln = cur_cln;

        *disk_cln = cur_cln;
    }
    return RC_OK;
}