source: soft/giet_vm/giet_fat32/fat32.c @ 412

//////////////////////////////////////////////////////////////////////////////////
// File     : fat32.c 
// Date     : 01/09/2013
// Authors  : Marco Jankovic, Cesar Fuguet & Alain Greiner
// Copyright (c) UPMC-LIP6
//////////////////////////////////////////////////////////////////////////////////
// The fat32.h and fat32.c files define a library of access functions
// to a FAT32 disk on a block device. It is intended to be used
// by the GIET_VM nano-kernel for both the boot code and the kernel code.
// This code uses functions defined in the utils.c and drivers.c files.
//////////////////////////////////////////////////////////////////////////////////
// Implementation notes:
// 1. the "lba" (Logical Block Address) is the physical sector index on
//    the block device. The physical sector size is supposed to be 512 bytes.
// 2. the "cluster" variable is actually a cluster index. A cluster contains
//    typically 8 sectors (4K bytes) and the cluster index is a 32 bits word.
// 2. This FAT32 library uses a FAT cache whose storage capacity is one
//    sector (512 bytes, or 128 cluster indexes in FAT)
// 3. This FAT32 library can be used in four modes: BOOT_PA/BOOT_VA/KERNEL/USER
//    defining different behaviours for the IOC driver.
//////////////////////////////////////////////////////////////////////////////////

#include <giet_config.h>
#include <fat32.h>
#include <tty_driver.h>
#include <ioc_driver.h>
#include <utils.h>

//////////////////////////////////////////////////////////////////////////////////
//      Global variable used by all FAT access functions
//////////////////////////////////////////////////////////////////////////////////

__attribute__((section (".fatdata"))) 
fat32_fs_t fat __attribute__((aligned(512)));

//////////////////////////////////////////////////////////////////////////////////
// This function displays the content of the FAT cache
//////////////////////////////////////////////////////////////////////////////////
void display_fat_cache()
{
    unsigned int line;
    unsigned int word;
    unsigned int temp[9];

    temp[8] = 0;

    _printf("\n*********************** fat_cache_lba = %x *****************************\n",
            fat.cache_lba );

    for ( line=0 ; line<16 ; line++ )
    {
        // display line index
        _printf( "%x : ", line );

        // display data hexa
        for ( word=0 ; word<8 ; word++ )
        {
            unsigned int byte  = (line<<5) + (word<<2);
            unsigned int hexa  = (fat.fat_cache[byte  ]<<24) |
                                 (fat.fat_cache[byte+1]<<16) |
                                 (fat.fat_cache[byte+2]<< 8) |
                                 (fat.fat_cache[byte+3]);
            _printf("%x | ", hexa );

            // prepare display ascii
            temp[word] = fat.fat_cache[byte]         |
                         (fat.fat_cache[byte+1]<<8)  |
                         (fat.fat_cache[byte+2]<<16) |
                         (fat.fat_cache[byte+3]<<24) ;
        }
        
        // display data ascii 
        _printf( (char*)temp );
        _printf("\n");
    }
    _printf("**************************************************************************\n");
} // end display_fat_cache()  

//////////////////////////////////////////////////////////////////////////////////
// This function returns the length of a FAT field. This field is identified
// man by an (offset,length) mnemonic defined in fat32.h file.
//////////////////////////////////////////////////////////////////////////////////
static inline int get_length( int offset, 
                              int length)
{
    return length;
}

//////////////////////////////////////////////////////////////////////////////
// Write one 32 bits word "value" in a char[] buffer. 
// This field is defined by the offset and size arguments.
//////////////////////////////////////////////////////////////////////////////
static void write_entry( unsigned int   offset,
                         unsigned int   size,
                         char*          buffer,
                         unsigned int   value )
{
    unsigned int turn = 0;
    unsigned int res  = value;
    unsigned int mask = 0x000000ff;

    while( turn != size - 1 )
    {
        buffer[ offset + turn ] = res & mask;
        res = res >> 8;
        turn++;
    }
    buffer[offset + turn] = res & mask;
}

//////////////////////////////////////////////////////////////////////////////
// Read one 32 bits word in a char[] buffer, taking endianness into account. 
// This field is defined by the offset and size arguments.
//////////////////////////////////////////////////////////////////////////////
static unsigned int read_entry( unsigned int   offset,
                                unsigned int   size,
                                char*          buffer,
                                unsigned int   little_indian )
{
    unsigned int turn;
    unsigned int res  = 0;
    unsigned int mask = 0x000000ff;

    if( little_indian )
    {
        turn = size;
        while( turn != 1 )
        {
            res = res | (buffer[offset + (turn-1)] & mask);
            res = res << 8;
            turn--;
        }
        res = (buffer[offset + (turn-1)] & mask) | res;
    }
    else
    {
        turn = 0;
        while( turn != size - 1 )
        {

            res = res  | (buffer[ offset + turn ] & mask );
            res = res << 8;
            turn++;
        }
        res = res | (buffer[offset + turn] & mask);
    }
    return res;
}

//////////////////////////////////////////////////////////////////////////////////
// This function retuns the cluster index from the lba of a DATA sector.
// The lba must be larger than the lba of the first DATA sector.
// The DATA region indexing starts a cluster 2.
//////////////////////////////////////////////////////////////////////////////////
static inline unsigned int lba_to_cluster( unsigned int lba )                   
{
   if (lba < fat.data_lba ) return 0;

   return ( (lba - fat.data_lba) / fat.sectors_per_cluster) + 2; 
}

//////////////////////////////////////////////////////////////////////////////////
// This function retuns the lba of first sector in DATA region 
// from the cluster index. The cluster index must be larger than 2. 
//////////////////////////////////////////////////////////////////////////////////
static inline unsigned int cluster_to_lba( unsigned int cluster )       
{
   if ( cluster < 2 ) return 0; 

   return  (fat.sectors_per_cluster * (cluster - 2)) + fat.data_lba;
}

///////////////////////////////////////////////////////////////////////////////// 
// This function search the FAT (using the FAT cache), and returns 
// the next cluster index from the current cluster index in the FAT.
// remark: a sector of FAT contains 128 cluster indexes.
/////////////////////////////////////////////////////////////////////////////////
static unsigned int get_next_cluster_id( unsigned int mode,
                                         unsigned int cluster )
{
    // compute lba of the sector containing the cluster index
    unsigned int lba = fat.fat_lba + (cluster / 128);

    if ( lba == fat.cache_lba )      // hit in cache
    {
        return read_entry( ((cluster % 128) * 4), 
                           4, 
                           fat.fat_cache,
                           1 );
    }
    else                                  // miss in cache
    {
        // we cannot access fat in user mode
        if( mode == IOC_USER_MODE ) mode = IOC_KERNEL_MODE;
        
        // access fat
        if( _ioc_read( 0,                 // channel
                       mode,              // mode for IOC driver
                       lba,               // sector index 
                       fat.fat_cache,     // fat cache
                       1 ) )              // one sector
        {
            _printf("[FAT_ERROR] in get_next cluster_id() "
                    "cannot read block %x\n", lba );
            return 1;
        }
        fat.cache_lba = lba;

        return read_entry( ((cluster % 128) * 4), 
                           4, 
                           fat.fat_cache,
                           1 );
    }
}

//////////////////////////////////////////////////////
static inline unsigned char to_upper(unsigned char c)
{
   if (c >= 'a' && c <= 'z') return (c & ~(0x20));
   else                      return c;
}

////////////////////////////////////////////////////////////////
// This function is a filter:
// Return the c character if c is a legal short name character
// Return the '_' character if c is illegal
////////////////////////////////////////////////////////////////
static unsigned char illegal_short(unsigned char c)
{
   const unsigned char illegal_char [] =";+=[]’,\"*\\<>/?:|\0";
   short i = 0;
   while (illegal_char[i]!='\0')
   {
      if (c == illegal_char[i])
         return '_';
      i++;
   }
   return c;
}

/////////////////////////////////////////////////////////////////////////////////
// This function test if the string argument is a legal SFN (Short File Name)
// and copies this name (removing the .) in the sfn_string argument.
// Criteria for a Short File Name are:
// - separator is '.' (extension is not mandatory)
// - 1 <= name length <= 8
// - 0 <= extension length <= 3
// - no illegal character (see illega_short() function)
// Return 1 if it string is a legal SFN
// Return 0 if not legal SFN
/////////////////////////////////////////////////////////////////////////////////
static int is_short( char* string, 
                     char* sfn_string)
{
    int s_size   = 0;
    int dot_ext  = 0;       // dot offset in the filename
    int name_len = 0;       // length of file name
    int ext_len  = 0;       // length of extension
    int i        = 0;
    int sc_i     = 0;
    char ch;

    if(string[0] == '.' && string[1] == '\0')
    {
        sfn_string[0] = '.';
        return 1;
    }
    if(string[0] == '.' && string[1] == '.' && string[2] == '\0')
    {
        sfn_string[0] = '.';
        sfn_string[1] = '.';
        return 1;
    }
    sfn_string[11] = '\0';
    while (string[s_size] != '\0')
    {
        if (string[s_size] == '.')
        {
            dot_ext = s_size;
            ext_len = -1;
        }
        ext_len++;
        s_size++;
    }
    if (dot_ext != 0)
    {
        name_len = s_size - ext_len - 1;
    }
    else
    {
        name_len = s_size;
        ext_len = 0;
    }
    if ( ext_len > 3 || ( name_len > 8))
    {
        return 0;
    }
    if (dot_ext != 0)
    {
        while (i != ext_len)
        {
            ch = to_upper(string[dot_ext + 1 + i]);
            ch = illegal_short(ch);
            sfn_string[8+i] = ch;
            i++;
        } 
    }
    i = 0;
    sc_i = 0;
    while (i!= name_len)
    {
        ch = to_upper(string[i]);
        ch = illegal_short(ch);
        if (ch != '.') sfn_string[sc_i++] = ch;
        i++;
    }
    return 1;
}

///////////////////////////////////////////////////////////////////////
// This function analyses the pathname argument, from the character 
// defined by the *nb_read argument.
// It copies the found name (between '/') in the name[] buffer, 
// and updates the nb_read argument.
// Return 1 if name found, Return 0 if NUL character found, 
///////////////////////////////////////////////////////////////////////
static int get_name_from_path( char*          pathname,
                               char*          name,
                               unsigned int*  nb_read ) 
{
    if ( pathname[*nb_read] == 0 ) return 0;

    int i = (pathname[*nb_read] == '/')? (*nb_read) + 1 : *nb_read;
    int j = 0;
   
    while(pathname[i] != '/' && pathname[i] != '\0')
    {
        name[j] = pathname[i];    
        j++;
        i++;
    }
    name[j] = 0;

    if ( pathname[i] == '/' ) *nb_read += j+1;
    else                      *nb_read += j;

    return 1;
}

////////////////////////////////////////////////////////////////////////////////
static int get_name_from_short( char* dir_entry,     // input:  SFN dir_entry
                                char* entry_name )   // output: name
{
    unsigned int i   = 0;
    unsigned int length = get_length(DIR_NAME);

    while ( i < length )
    {
        entry_name[i] = dir_entry[i];
        i++;
    }
    entry_name[i] = '\0';

    return i;
}

///////////////////////////////////////////////////////////////////////////////
static int get_name_from_long( char *dir_entry,     // input : LFN dir_entry
                               char *entry_name )   // output : name
{
    unsigned int   entry_name_offset   = 0;
    unsigned int   dir_entry_offset    = get_length(LDIR_ORD);
    unsigned int   l_name_1            = get_length(LDIR_NAME_1);
    unsigned int   l_name_2            = get_length(LDIR_NAME_2);
    unsigned int   l_name_3            = get_length(LDIR_NAME_3);
    unsigned int   l_attr              = get_length(LDIR_ATTR);
    unsigned int   l_type              = get_length(LDIR_TYPE);
    unsigned int   l_chksum            = get_length(LDIR_CHKSUM);
    unsigned int   l_rsvd              = get_length(LDIR_RSVD);

    unsigned int j            = 0;
    unsigned int eof          = 0;

    while ( (dir_entry_offset != DIR_ENTRY_SIZE)  && (!eof) )
    {
        while (j != l_name_1 && !eof )
        {
            if ( (dir_entry[dir_entry_offset] == 0x00) || 
                 (dir_entry[dir_entry_offset] == 0xFF) )
            {
                eof = 1;
                continue;
            }
            entry_name[entry_name_offset] = dir_entry[dir_entry_offset];
            dir_entry_offset += 2;
            j += 2;
            entry_name_offset++;
        }

        dir_entry_offset += (l_attr + l_type + l_chksum);
        j = 0;

        while (j != l_name_2 && !eof )
        {
            if ( (dir_entry[dir_entry_offset] == 0x00) || 
                 (dir_entry[dir_entry_offset] == 0xFF) )
            {
                eof = 1;
                continue;
            }
            entry_name[entry_name_offset] = dir_entry[dir_entry_offset];
            dir_entry_offset += 2;
            j += 2;
            entry_name_offset++;
        }

        dir_entry_offset += l_rsvd;
        j = 0;

        while (j != l_name_3 && !eof )
        {
            if ( (dir_entry[dir_entry_offset] == 0x00) || 
                 (dir_entry[dir_entry_offset] == 0xFF) )
            {
                eof = 1;
                continue;
            }
            entry_name[entry_name_offset] = dir_entry[dir_entry_offset];
            dir_entry_offset += 2;
            j += 2;
            entry_name_offset++;
        }
    }
    entry_name[entry_name_offset] = '\0';

    return entry_name_offset;
} // end get_name_from_long()

//////////////////////////////////////////////////////////////////////////////////////
// This function update a DIR_ENTRY, write a new value into a specific field 
// (ex : DIR_FILE_SIZE, when we want update the file size after a fat_write)
// Return 0 in case of success, > 0 if failure.
//////////////////////////////////////////////////////////////////////////////////////
// TODO : make this function less complex
//////////////////////////////////////////////////////////////////////////////////////
static inline unsigned int update_entry( unsigned int fd_id, 
                                         unsigned int field,
                                         unsigned int size,
                                         unsigned int value )
{
    char dir_entry[32];   // buffer to store a full directory_entry
    char name_entry[14];  // buffer to store a 13 characters (partial) name
    char file_name[256];  // buffer to store the name (not pathname) of the file
    char sfn[12]            = {[0 ... 10] = ' ', '\0'};      // buffer for a Short File Name

    unsigned int lba       = fat.fd[fd_id].lba_dir_entry;    // Lba of file dir_entry
    unsigned int is_sfn;         
    unsigned int attr      = 0;                              // directory entry attribute
    unsigned int ord       = 0;                              // directory entry sequence
    unsigned int found     = 0;                              // name found
    unsigned int offset    = 0;
    unsigned int i         = 0;
    unsigned int nb_read   = 0;

    for ( i = 0 ; i < 32 ; i++ ) dir_entry[i]  = 0;
    for ( i = 0 ; i < 14 ; i++ ) name_entry[i] = 0;
    
    // Get the name of the file.
    while ( get_name_from_path( fat.fd[fd_id].name, file_name, &nb_read ) )
    {
    }

    // Check if file_name is short
    is_sfn = is_short( file_name, sfn );

    if ( _ioc_read( 0,               // channel
                    IOC_KERNEL_MODE, // mode for IOC driver
                    lba,             // sector index 
                    fat.fat_cache,   // buffer address
                    1 ) )            // one sector
    {
        _printf("[FAT ERROR] in update_entry() cannot read sector %x\n", lba );
        return 1;
    }
    fat.cache_lba = lba;

    // - the offset increment is an integer number of directory entry (32 bytes)
    // - the exit condition is success (name found) or failure (end of directory) 
    while ( !found )
    {
        attr = read_entry( DIR_ATTR, fat.fat_cache + offset, 0 );
        ord  = read_entry( LDIR_ORD, fat.fat_cache + offset, 0 );

        if ( is_sfn == 1 )                                     // searched name is short
        {
            if      ( (ord != FREE_ENTRY ) &&
                    (ord != NO_MORE_ENTRY) &&
                    (attr == ATTR_LONG_NAME_MASK) )    // LFN entry : skipped
            {
                offset     = offset + ((ord & 0xF) * DIR_ENTRY_SIZE);
                continue;
            }
            else if ( (attr != ATTR_LONG_NAME_MASK) && 
                    (ord  != FREE_ENTRY) && 
                    (ord  != NO_MORE_ENTRY ) )         // SFN entry : checked
            {
                memcpy( dir_entry, fat.fat_cache + offset, DIR_ENTRY_SIZE );    
            }
            else if (ord == NO_MORE_ENTRY )            // end of directory : return
            {
                _printf("[FAT ERROR] in update_entry() : reaches end of directory\n");
                return 1;
            }
            else                                                                           // free entry : skipped
            {
                offset = offset + DIR_ENTRY_SIZE;
                continue;
            }
        }
        else                                           // searched name is long
        {
            if      ( (attr == ATTR_LONG_NAME_MASK) && 
                    (ord != FREE_ENTRY) &&
                    (ord != NO_MORE_ENTRY) )           // LFN entry : checked
            {
                memcpy( dir_entry, fat.fat_cache + offset, DIR_ENTRY_SIZE );    
            }
            else if ( (attr != ATTR_LONG_NAME_MASK) && 
                    (ord  != FREE_ENTRY) && 
                    (ord  != NO_MORE_ENTRY))               // SFN entry : skipped
            {
                offset = offset + DIR_ENTRY_SIZE;
                continue;
            }
            else if (ord == NO_MORE_ENTRY )                        // end of directory : return
            {
                _printf("[FAT ERROR] in update_entry() reaches end of directory\n");
                return 1;
            }
            else                                       // free entry : skipped
            {
                offset = offset + DIR_ENTRY_SIZE;
                continue;
            }
        }

        // testing the name extracted from dir entry

        if ( is_sfn == 1 )                             // searched name is short
        {
            get_name_from_short( dir_entry, name_entry );

            if ( _strncmp( (char*)sfn, (char*)name_entry, 13 ) == 0 )
            {
                write_entry(offset + field, size, fat.fat_cache, value);
                found = 1;
            }
            else                                                                       // no matching : skip
            {
                offset = offset + DIR_ENTRY_SIZE;
            }
        }
        else                                           // searched name is long
        {
            get_name_from_long( dir_entry, name_entry );

            unsigned shift = ((ord & 0xf) - 1) * 13;
            if ( _strncmp( (char*)(file_name + shift), (char*)name_entry, 13 ) == 0 )
            {
                if ( (ord & 0xf) == 1 )
                {
                    offset = offset + DIR_ENTRY_SIZE;
                    write_entry(offset + field, size, fat.fat_cache, value);
                    found = 1;
                }
                offset = offset + DIR_ENTRY_SIZE;
                continue;
            }
            else                                                                       // no matching : skip
            {
                offset = offset + ((ord & 0xf) * DIR_ENTRY_SIZE) + DIR_ENTRY_SIZE;
            }
        }
    }

    return _ioc_write( 0,                // channel
                       IOC_KERNEL_MODE,  // mode
                       lba,              // sector index
                       fat.fat_cache,    // source buffer
                       1 );              // one sector
}
//////////////////////////////////////////////////////////////////////////////////
// This function update FS_INFO:
// last cluster allocated and number of free cluster. 
// Return 0 in case of success, > 0 if failure.
//////////////////////////////////////////////////////////////////////////////////
static inline unsigned int update_fs_info( )
{
    unsigned int lba = fat.fs_info_lba;

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Enter update_fs_info()\n");
#endif

    if ( lba == fat.cache_lba )            // hit cache
    {
        write_entry( FS_FREE_CLUSTER     , fat.fat_cache, fat.number_free_cluster );
        write_entry( FS_FREE_CLUSTER_HINT, fat.fat_cache, fat.last_cluster_allocated );
    }
    else                                   // miss cache
    {
        if ( _ioc_read( 0,                 // channel
                        IOC_KERNEL_MODE,   // mode for IOC driver
                        lba,               // sector index 
                        fat.fat_cache,     // source buffer
                        1 ) )              // one sector
        {
            _printf("[FAT_ERROR] in update_fat() cannot read block %x\n", lba );
            return 1;
        }
        fat.cache_lba = lba;
        write_entry( FS_FREE_CLUSTER     , fat.fat_cache, fat.number_free_cluster );
        write_entry( FS_FREE_CLUSTER_HINT, fat.fat_cache, fat.last_cluster_allocated );
    }
    return _ioc_write( 0,                // channel
                       IOC_KERNEL_MODE,  // mode    
                       lba,              // sector index
                       fat.fat_cache,    // source buffer
                       1 );              // one sector
}

//////////////////////////////////////////////////////////////////////////////////
// This function update FAT, write a new value into cluster index.
// Used by the function _fat_allocate to update the chaining of clusters.
// Return 0 in case of success, > 0 if failure.
//////////////////////////////////////////////////////////////////////////////////
static inline unsigned int update_fat( unsigned int cluster, 
                                       unsigned int value  )
{
    unsigned int lba = fat.fat_lba + (cluster / 128);

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Enter update_fat() : cluster = %x / value = %x\n",
        cluster, value );
#endif

    if ( lba == fat.cache_lba )            // hit cache
    {
        write_entry( ((cluster % 128) << 2), 4, fat.fat_cache, value );
    }
    else                                   // miss cache
    {
        if ( _ioc_read( 0,                 // channel
                        IOC_KERNEL_MODE,   // mode for IOC driver
                        lba,               // sector index 
                        fat.fat_cache,     // source buffer
                        1 ) )              // one sector
        {
            _printf("[FAT_ERROR] in update_fat() cannot read block %x\n");
            return 1;
        }
        fat.cache_lba = lba;
        write_entry( ((cluster % 128) << 2), 4, fat.fat_cache, value );
    }
    return _ioc_write( 0,                // channel
                       IOC_KERNEL_MODE,  // mode      
                       lba,              // sector indexs
                       fat.fat_cache,    // source buffer 
                       1 );              // one sector
}

//////////////////////////////////////////////////////////////////////////////////
// This function allocate a count number of cluster to a file by calling the
// update_fat function that takes care to update the chaining of clusters.
// return 0 if success, -1 if failure
//////////////////////////////////////////////////////////////////////////////////
static inline int _fat_allocate( unsigned int fd_id, 
                                 unsigned int count )
{
    unsigned int next_cluster        = fat.fd[fd_id].first_cluster;   // Get the first cluster of file
    unsigned int cluster_to_allocate = count;                         // Number of cluster to allocate

    unsigned int last_cluster_file;                                   // Last cluster of the file (EOC)

    unsigned int free_cluster = fat.last_cluster_allocated + 1;       // First free cluster

    // Check if free_cluster is really free (must be true)
    if ( get_next_cluster_id( IOC_KERNEL_MODE, free_cluster ) != FREE_CLUSTER)
    {
        _printf("\n[FAT ERROR] in _fat_allocate() : first free_cluster not free\n");
        return -1;
    }
    // Check if FAT contains enough cluster free for this allocation
    if ( count > fat.number_free_cluster )
    {
        _printf("\n[FAT ERROR] in _fat_allocate() : Not enough free cluster(s)\n");
        return -1;
    }

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Enter in _fat_allocate() for file %d\n", fd_id );
#endif

    // Get the last cluster allocated for the file (seek END_OF_CHAIN_CLUSTER).
    do{
        last_cluster_file = next_cluster;
        next_cluster      = get_next_cluster_id( IOC_KERNEL_MODE, next_cluster );
    }while ( next_cluster < END_OF_CHAIN_CLUSTER );

    // Loop on the number of cluster needed to be allocated
    while ( cluster_to_allocate > 0 )
    {

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] cluster to update = %x / free cluster = %x / clusters required = %d\n",
        last_cluster_file, free_cluster, cluster_to_allocate );
#endif

        // update, in the FAT, the value of last cluster allocated by the index
        // of free cluster.
        if ( update_fat( last_cluster_file, free_cluster ) )
        {
            _printf("\n[FAT ERROR] in _fat_allocate() : update fat failed\n");
            return -1;
        }

        cluster_to_allocate = cluster_to_allocate - 1;
        // Last cluster allocated is then free_cluster
        last_cluster_file = free_cluster;

        // Last cluster to allocate done, then we must close the chain of clusters
        if ( cluster_to_allocate == 0 )
        {
            // update, in the FAT, the value of the last cluster allocated by
            // END_OF_CHAIN_CLUSTER
            if ( update_fat( last_cluster_file, END_OF_CHAIN_CLUSTER ) )
            {
                _printf("\n[FAT ERROR] in _fat_allocate() : update fat failed\n");
                return -1;
            }
        }

        free_cluster = free_cluster + 1;

        // Check if free_cluster is really free (must be true)
        if ( get_next_cluster_id( IOC_KERNEL_MODE, free_cluster ) != FREE_CLUSTER)
        {
            _printf("\n[FAT ERROR] in _fat_allocate() : free_cluster not free\n");
            return -1;
        }
    }

    // Update field number_free_cluster and last_cluster_allocated 
    // of structure fat for next fat_allocate
    fat.last_cluster_allocated = last_cluster_file;
    fat.number_free_cluster    = fat.number_free_cluster - count;

    if ( update_fs_info() )
    {
        _printf("\n[FAT ERROR] in _fat_allocate() : update fs_info failed\n");
        return -1;
    }

    return 0;
}

///////////////////////////////////////////////////////////////////////////////
// This function returns the cluster index from a (32 bytes) directory entry
///////////////////////////////////////////////////////////////////////////////
static inline unsigned int read_cluster( char* buf )                 
{
   unsigned int cluster = read_entry( DIR_FST_CLUS_HI, buf, 1 ) << 16;
   cluster = cluster | read_entry( DIR_FST_CLUS_LO, buf, 1 );
   return cluster;
} 


////////////////////////////////////////////////////////////////////////////////////////
// This function read the blocks defined by the cluster index argument, in a data 
// region containing a directory to search the name of a file/firectory, 
// and returns the cluster index of the file/directory when the name has been found.
// Return cluster index if name found / Return -1 if not found,
////////////////////////////////////////////////////////////////////////////////////////
static int scan_directory( unsigned int   mode,            // mode for IOC driver
                           unsigned int   cluster,         // cluster containing dir_entry 
                           char*          file_name,       // searched file/directory name
                           unsigned int*  file_size,       // file size
                           unsigned int*  lba_dir_entry )  // lba of dir_entry
{

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] enters _scan_directory() for dir/file %s\n", file_name );
#endif

    char dir_entry[32];   // buffer to store a full directory_entry
    char name_entry[14];  // buffer to store a 13 characters (partial) name

    char sfn[12]            = {[0 ... 10] = ' ', '\0'};   // buffer for a Short File Name
    unsigned int  is_sfn    = is_short(file_name, sfn);   // if file_name is short, sfn = 1     
    unsigned int  offset    = 0;                          // byte offset in block
    unsigned int  block_id  = fat.sectors_per_cluster;   // sector index initialisation       
    unsigned int  lba       = cluster_to_lba(cluster);    
    unsigned int  attr      = 0;                          // directory entry attribute
    unsigned int  ord       = 0;                          // directory entry sequence
    unsigned int  found     = 0;                          // name found
    unsigned int  i;

    for( i = 0 ; i < 32 ; i++ ) dir_entry[i]  = 0;
    for( i = 0 ; i < 14 ; i++ ) name_entry[i] = 0;

    // load first cluster sector from DATA region into FAT cache
    // other sectors will be loaded inside loop as required
    if( _ioc_read( 0,               // channel
                   mode,            // mode for IOC driver
                   lba,             // sector index 
                   fat.fat_cache,   // buffer address
                   1 ) )            // one sector
    {
        _printf("[FAT ERROR] in scan directory() cannot read sector %x\n", lba );
        return -1;
    }

    fat.cache_lba = lba;

#if ( GIET_DEBUG_FAT > 1 )
display_fat_cache();
#endif

    // in this loop we scan all names in directory identified by cluster: 
    // - the offset increment is an integer number of directory entry (32 bytes)
    // - the exit condition is success (name found) or failure (end of directory) 
    while( 1 )
    {
        // load a new sector if required
        if (offset >= 512)              
        {
            if ( block_id )           // not a new cluster
            {
                lba += 1;
                block_id --;
            }
            else                                          // get next cluster
            {
                cluster = get_next_cluster_id( mode, cluster );

                if ( cluster >= END_OF_CHAIN_CLUSTER  ) return END_OF_CHAIN_CLUSTER;

                lba      = cluster_to_lba(cluster);
                block_id = fat.sectors_per_cluster;
            }
            if( _ioc_read( 0,               // channel
                           mode,            // mode for IOC driver
                           lba,             // sector index 
                           fat.fat_cache,   // buffer address
                           1 ) )            // one sector
            {
                _printf("[FAT ERROR] in scan directory() cannot read sector %x\n", lba );
                return -1;
            }
            fat.cache_lba = lba;
            block_id--;
            offset = offset % 512;
        }

        // analyse a directory entry (pointed by fat.fat_cache + offset)
        if ( !found )
        { 
            attr = read_entry( DIR_ATTR, fat.fat_cache + offset, 0);   
            ord  = read_entry( LDIR_ORD, fat.fat_cache + offset, 0);

            if ( is_sfn == 1 )                            // searched name is short
            {
                if      ( (ord != FREE_ENTRY ) &&
                          (ord != NO_MORE_ENTRY) &&
                          (attr == ATTR_LONG_NAME_MASK) )    // LFN entry : skipped
                {
                                        offset     = offset + ((ord & 0xF) * DIR_ENTRY_SIZE);
                    continue;
                }
                else if ( (attr != ATTR_LONG_NAME_MASK) && 
                          (ord  != FREE_ENTRY) && 
                          (ord  != NO_MORE_ENTRY ) )         // SFN entry : checked
                {
                    memcpy( dir_entry, fat.fat_cache + offset, DIR_ENTRY_SIZE );    
                    offset = offset + DIR_ENTRY_SIZE;
                }
                else if (ord == NO_MORE_ENTRY )              // end of directory : return
                {
                    return END_OF_CHAIN_CLUSTER;
                }
                else                                                                         // free entry : skipped
                {
                    offset = offset + DIR_ENTRY_SIZE;
                    continue;
                }
            }
            else                                      // searched name is long
            {
                if( (attr == ATTR_LONG_NAME_MASK) && 
                    (ord != FREE_ENTRY) &&
                    (ord != NO_MORE_ENTRY) )                 // LFN entry : checked
                {
                    memcpy( dir_entry, fat.fat_cache + offset, DIR_ENTRY_SIZE );    
                    offset = offset + DIR_ENTRY_SIZE;
                }
                else if( (attr != ATTR_LONG_NAME_MASK) && 
                         (ord  != FREE_ENTRY) && 
                         (ord  != NO_MORE_ENTRY))                        // SFN entry : skipped
                {
                    offset = offset + DIR_ENTRY_SIZE;
                    continue;
                }
                else if (ord == NO_MORE_ENTRY )                          // end of director : return
                {
                    return END_OF_CHAIN_CLUSTER;
                }
                else                                           // free entry : skipped
                {
                    offset = offset + DIR_ENTRY_SIZE;
                    continue;
                }
            }

            // testing the name extracted from dir entry
            if ( is_sfn == 1 )                            // searched name is short
            {
                get_name_from_short( dir_entry, name_entry );

                if ( _strncmp( (char*)sfn, (char*)name_entry, 13 ) == 0 )
                {
                    *file_size = read_entry( DIR_FILE_SIZE , dir_entry, 1 );
                    *lba_dir_entry = lba;
                    return read_cluster( dir_entry );
                }
            }
            else                                         // searched name is long
            {
                get_name_from_long( dir_entry, name_entry );

                unsigned shift = ((ord & 0xf) - 1) * 13;
                if ( _strncmp( (char*)(file_name + shift), (char*)name_entry, 13 ) == 0 )
                {
                    if( (ord & 0xf) == 1 )  found = 1;
                    continue;
                }
                else                                                                 // no matching : skip
                {
                    offset = offset + ((ord & 0xf) * DIR_ENTRY_SIZE);
                }
            }
        } 
        else    // file found
        {
            memcpy( dir_entry, fat.fat_cache + offset, DIR_ENTRY_SIZE );    
            offset     = offset + DIR_ENTRY_SIZE;
            *file_size = read_entry( DIR_FILE_SIZE, dir_entry, 1 );
            *lba_dir_entry = lba;

            return read_cluster( dir_entry );
        }
    }
    return -1;
} // end scan_directory()


//////////////////////////////////////////////////////////////////////
// This function create a new entry in a directory identified 
// by "dir_cluster". The name is defined by "name".
// The type (dir/file) is defined by "is_file".
// Returns cluster index if success, Returns -1 if error.
//////////////////////////////////////////////////////////////////////
static int fat_create( char*           name,
                       unsigned int    is_file,
                       unsigned int    dir_cluster )
{
    _printf("\n[FAT ERROR] _fat_create() not implemented\n");
    return 0;
}  //end _fat_create()



////////////// Extern functions //////////////////////////////////////////

//////////////////////////////////////////////////////////////////////////
// This function initializes the FAT structure, including the
// files descriptors array, from informations found in the boot record.
//////////////////////////////////////////////////////////////////////////
// Return 0 if success, Return -1 if failure 
//////////////////////////////////////////////////////////////////////////
int _fat_init( unsigned int mode )   // mode for IOC driver
{
    unsigned int   n;

#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int cid     = procid / NB_PROCS_MAX;
unsigned int lpid    = procid % NB_PROCS_MAX;
unsigned int x       = cid >> Y_WIDTH;
unsigned int y       = cid & ((1<<Y_WIDTH) - 1);

_printf("\n[FAT DEBUG] Processor[%d,%d,%d] enters _fat_init()\n",
        x, y, lpid );
#endif
    
    // load Boot Record (VBR) into fat cache
    if ( _ioc_read( 0,                   // channel
                    mode,                // mode for IOC driver
                    0,                   // sector index
                    fat.fat_cache,       // buffer address
                    1 ) )                // one sector
    {
        _printf("\n[FAT ERROR] in _fat_init() cannot load VBR\n");
        return -1;
    }
    fat.cache_lba = 0;

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Boot Sector Loaded\n");
#endif

    // checking various FAT32 assuptions from boot sector
    if( read_entry( BPB_BYTSPERSEC, fat.fat_cache, 1 ) != 512 )
    {
        _printf("\n[FAT ERROR] The sector size must be 512 bytes\n");
        return -1;  
    }
    if( read_entry( BPB_NUMFATS, fat.fat_cache, 1 ) != 1 )
    {
        _printf("\n[FAT ERROR] The number of FAT copies in FAT region must be 1\n");
        return -1;  
    }
    if( (read_entry( BPB_FAT32_FATSZ32, fat.fat_cache, 1 ) & 0xF) != 0 )
    {
        _printf("\n[FAT ERROR] The FAT region in FAT32 must be multiple of 32 sectors\n");
        return -1;  
    }
    if( read_entry( BPB_FAT32_ROOTCLUS, fat.fat_cache, 1 ) != 2 )
    {
        _printf("\n[FAT ERROR] The first cluster index must be 2\n");
        return -1;  
    }
    // FS Info always in sector 1
    fat.fs_info_lba         = read_entry( BPB_FAT32_FSINFO, fat.fat_cache, 1 );

    // initialise fat descriptor from VBR
    fat.sectors_per_cluster = read_entry( BPB_SECPERCLUS, fat.fat_cache, 1 );
    fat.sector_size         = read_entry( BPB_BYTSPERSEC, fat.fat_cache, 1 );
    fat.cluster_size        = fat.sectors_per_cluster * 512;
    fat.fat_sectors         = read_entry( BPB_FAT32_FATSZ32, fat.fat_cache, 1 );
    fat.fat_lba             = read_entry( BPB_RSVDSECCNT, fat.fat_cache, 1 );
    fat.data_lba            = fat.fat_lba + fat.fat_sectors;
    fat.fat_lock.value      = 0;
    fat.initialised         = FAT_INITIALISED;

    // initialise file descriptor array
    for( n = 0 ; n < GIET_OPEN_FILES_MAX ; n++ ) fat.fd[n].used = 0;

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] FS_INFO Sector = %x\n", fat.fs_info_lba );
#endif

    // load FS_INFO into fat cache
    if ( _ioc_read( 0,                  // channel
                    mode,               // mode for IOC driver
                    fat.fs_info_lba,    // sector index 
                    fat.fat_cache,      // buffer address
                    1 ) )               // one sector
    { 
        _printf("\n[FAT ERROR] in _fat_init() cannot load FS_INFO Sector\n"); 
        return -1;
    }
    fat.cache_lba = fat.fs_info_lba;

    fat.number_free_cluster    = read_entry( FS_FREE_CLUSTER     , fat.fat_cache, 1);
    fat.last_cluster_allocated = read_entry( FS_FREE_CLUSTER_HINT, fat.fat_cache, 1);


#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] initialises FAT descriptor\n", x, y, lpid );
_fat_print();
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] exit _fat_init()\n", x, y, lpid );
#endif

    return 0;
}  // end _fat_init()

/////////////////
void _fat_print()
{
    _printf("\n########################## FAT32 ################################");  
    _printf("\nFAT initialised                  %x", fat.initialised );
    _printf("\nSector Size  (bytes)             %x", fat.sector_size );
    _printf("\nSectors per cluster              %x", fat.sectors_per_cluster );
    _printf("\nFAT region first lba             %x", fat.fat_lba );
    _printf("\nData region first lba            %x", fat.data_lba );
    _printf("\nNumber of sectors for one FAT    %x", fat.fat_sectors );
    _printf("\nNumber of free clusters          %x", fat.number_free_cluster );
    _printf("\nLast allocated cluster           %x", fat.last_cluster_allocated );
    _printf("\n#################################################################\n");
}

///////////////////////////////////////////////////////////////////////////////
// This function checks that the kernel FAT structure has been initialised.
// It makes the FAT initialisation if it is the first open request. 
// This function searches a file identified by the "pathname" argument.
// It starts from root (cluster 2) to scan successively each subdirectory.
// When the file is not found, but the path is found, and "creat" is set,
// a new file is created and introduced in the directory.
// Finally, it sets a new open file in the file descriptors array.
// The same file can be open several times by differents tasks.
///////////////////////////////////////////////////////////////////////////////
// Returns file descriptor index if success, returns -1 if error.
///////////////////////////////////////////////////////////////////////////////
int _fat_open( unsigned     mode,
               char*        pathname,
               unsigned int creat )
{
    char                 name[256];        // buffer for one name in pathname
    unsigned int         nb_read;              // number of characters written in name[] 
    unsigned int         cluster;          // current cluster index when scanning FAT
    unsigned int         dir_cluster;      // previous cluster index when scanning FAT
    unsigned int         fd_id;            // index when scanning file descriptors array
    unsigned int         file_size = 0;    // number of bytes
    unsigned int         last_name = 0;    // directory containing file name is reached
    unsigned int         lba       = 0;    // lba of dir_entry for this file
    
#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int cid     = procid / NB_PROCS_MAX;
unsigned int lpid    = procid % NB_PROCS_MAX;
unsigned int x       = cid >> Y_WIDTH;
unsigned int y       = cid & ((1<<Y_WIDTH) - 1);

_printf("\n[FAT DEBUG] Processor[%d,%d,%d] enters _fat_open() for file %s\n",
        x, y, lpid, pathname );
#endif

    // checking arguments
    if ( creat )
    {
        _printf("[FAT ERROR] in _fat_open() : create not supported yet\n");
        return -1;
    }

    // takes the FAT lock for exclusive access
    _get_lock( &fat.fat_lock );

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] takes the FAT lock\n",
        x, y, lpid );
#endif

    // FAT initialisation if required
    if( fat.initialised != FAT_INITIALISED )
    {
        if ( _fat_init( mode ) )
        {
            _printf("[FAT ERROR] in _fat_open() : Cannot initialize FAT descriptor\n");
            _release_lock( &fat.fat_lock );
            return -1;
        }
    }
 
    // Scan the directories, starting from the root directory (cluster 2)
    // - The get_name_from_path() function extracts (successively) 
    //   each directory name from the pathname, and store it in name[] buffer
    // - The scan_directory() function scan one (or several) cluster(s) containing 
    //   a directory looking for name[], and return the cluster index
    //   corresponding to the directory/file found.
    nb_read     = 0;
    cluster     = 2;
    last_name   = 0;
    while ( get_name_from_path( pathname, name, &nb_read) )
    {

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] search dir/file : %s\n",
        x, y, lpid, name );
#endif

        // test if we reach the last name (file name)
        if( pathname[nb_read] == 0 )  
        {
            last_name   = 1;
            dir_cluster = cluster;
        }

        // scan current directory
        cluster  = scan_directory( mode, cluster, name, &file_size, &lba );

        if( cluster == END_OF_CHAIN_CLUSTER && last_name && creat )
        {
            cluster = fat_create( name, 1, dir_cluster );
        }
        else if ( cluster == END_OF_CHAIN_CLUSTER )
        {
            _printf("\n[FAT ERROR] in _fat_open() cannot found %s\n", name );

            // release FAT lock
            _release_lock( &fat.fat_lock );

            return -1;
        }
    }

    // check the next value for cluster index found
    unsigned next = get_next_cluster_id( mode, cluster );

    if ( (next != BAD_CLUSTER) && (next != FREE_CLUSTER) )
    {
        // Search an empty slot scanning open file descriptors array
        fd_id = 0;
        while ( fat.fd[fd_id].used != 0 && fd_id < GIET_OPEN_FILES_MAX )
        {
            fd_id++;
        }

        // set file descriptor if found empty slot
        if ( fd_id < GIET_OPEN_FILES_MAX )
        {
            fat.fd[fd_id].used          = 1;
            fat.fd[fd_id].first_cluster = cluster;
            fat.fd[fd_id].file_size     = file_size;
            fat.fd[fd_id].lba_dir_entry = lba;
            _strcpy( fat.fd[fd_id].name, pathname );

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] open file %s with fd = %d\n",
        x, y, lpid, pathname, fd_id );
#endif

            // release FAT lock
            _release_lock( &fat.fat_lock );

            return fd_id;
        }
        else
        {
            _printf("\n[FAT ERROR] in _fat_open() for file %s : fd array full\n",
                    pathname );

            // release FAT lock
            _release_lock( &fat.fat_lock );

            return -1;
        }
    }
    else
    {
        _printf("\n[FAT ERROR] in _fat_open() for file %s : bad cluster\n",
                pathname );

        // release FAT lock
        _release_lock( &fat.fat_lock );

        return -1;
    }
} // end _fat_open()

///////////////////////////////////////////////////////////////////////////////
// For an open file, identified by the file descriptor index, transfer 
// an integer number of sectors from block device to a memory buffer.
// If the number of requested sectors exceeds the file size, it is reduced.
///////////////////////////////////////////////////////////////////////////////
// Returns number of sectors transfered if success, < 0 if error.
///////////////////////////////////////////////////////////////////////////////
int _fat_read( unsigned int mode,       // mode for IOC driver
               unsigned int fd_id,      // file descriptor
               void*        buffer,     // target buffer base address
               unsigned int count,      // number of sector to read
               unsigned int offset )    // nuber of sectors to skip in file
{
    unsigned int spc = fat.sectors_per_cluster;

    unsigned int file_size;         // number of bytes in file
    unsigned int file_sectors;      // number of sectors in file
    unsigned int total_sectors;     // actual number of sectors to be transfered
    unsigned int cluster;           // cluster index 
    unsigned int clusters_to_skip;  // number of clusters to skip because offset
    unsigned int sectors_to_skip;   // number of sectors to skip in first iteration

    // arguments checking
    if ( fd_id >= GIET_OPEN_FILES_MAX )
    { 
        _printf("\n[FAT ERROR] in _fat_read() : illegal file descriptor index\n");
        return -1;
    }
    if ( fat.fd[fd_id].used != 1 )
    {
        _printf("\n[FAT ERROR] in _fat_read() : file not open\n");
        return -1;
    }
    if ( ((unsigned int)buffer & 0x1FF) != 0 )
    {
        _printf("\n[FAT ERROR] in _fat_read() : memory buffer not sector aligned\n");
        return -1;
    }

    // compute file size as a number of sectors 
    file_size    = fat.fd[fd_id].file_size;
    if ( file_size & 0x1FF ) file_sectors = (file_size >> 9) + 1;
    else                     file_sectors = (file_size >> 9); 

    if ( offset >= file_sectors )
    {
        _printf("\n[FAT ERROR] offset larger than number of sectors\n");
        return -1;
    }

    // compute total number of sectors to read
    if ( file_sectors < (offset + count) ) total_sectors = file_sectors - offset;
    else                                   total_sectors = count;

    // compute clusters and sectors to be skipped
    clusters_to_skip = offset / spc;
    sectors_to_skip  = offset % spc;
    
    // get first cluster index 
    cluster = fat.fd[fd_id].first_cluster;

#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int cid     = procid / NB_PROCS_MAX;
unsigned int lpid    = procid % NB_PROCS_MAX;
unsigned int x       = cid >> Y_WIDTH;
unsigned int y       = cid & ((1<<Y_WIDTH) - 1);

_printf("\n[FAT DEBUG] Processor[%d,%d,%d] enters _fat_read() for file %s\n"
        " - buffer vbase    = %x\n"
        " - skipped sectors = %x\n"
        " - read sectors    = %x\n"
        " - first cluster   = %x\n"
        " - skiped clusters = %x\n",
        x, y, lpid, fat.fd[fd_id].name, 
        (unsigned int)buffer, offset, count, cluster, clusters_to_skip );   
#endif

    // compute index of first cluster to be loaded
    // as we may need to scan the FAT, we use the kernel mode
    while ( clusters_to_skip )
    {
        cluster = get_next_cluster_id( IOC_KERNEL_MODE, cluster );
        clusters_to_skip--;
    }

    // variables used in the loop on clusters
    int             todo_sectors;   // number of sectors still to be loaded
    unsigned int    lba;            // first sector index on device
    unsigned int    iter_sectors;   // number of sectors to load in iteration
    char*           dst;            // pointer on target buffer

    // initialize these variables for the first iteration 
    todo_sectors  = total_sectors;
    dst           = (char*)buffer;
    lba           = cluster_to_lba(cluster) + sectors_to_skip;
    if( total_sectors < (spc - sectors_to_skip) ) iter_sectors = total_sectors;
    else                                          iter_sectors = spc - sectors_to_skip; 

    // loop on the clusters: one IOC access per cluster
    while ( todo_sectors > 0 )
    {

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] makes an IOC read "
        " for cluster %x : buf = %x / lba = %x / sectors = %d\n",
        x, y, lpid, cluster, (unsigned int)dst, lba, iter_sectors );
#endif

        if( _ioc_read( 0,                 // channel
                       mode,              // mode for IOC driver
                       lba,               // first sector index 
                       dst,               // buffer address
                       iter_sectors ) )   // number of sectors
        {
            _printf("\n[FAT ERROR] in _fat_read() cannot load block %x\n", lba );
            return -1;
        }
         
        // update variables for next iteration
        cluster      = get_next_cluster_id( mode, cluster );
        todo_sectors = todo_sectors - iter_sectors;
        dst          = dst + (iter_sectors << 9);
        lba          = cluster_to_lba(cluster);
        if ( todo_sectors > spc ) iter_sectors = spc;
        else                      iter_sectors = todo_sectors;
    }
         
    // returns number of sectors actually transfered
    return total_sectors;

}  // end _fat_read() 

///////////////////////////////////////////////////////////////////////////////
// For an open file, identified by the file descriptor index, transfer 
// an integer number of sectors from a memory buffer to block device.
// Allocate new clusters if the offset+count larger than current file size,
// but the offset should be smaller than the current file size...
// - fat    : pointer on FAT 
// - mode   : mode for the IOC driver
// - fd_id  : open file descriptor index  
// - buffer : base address of the memory buffer (must be sector aligned)
// - offset : number of sectors to skip in file
// - count  : number of sectors to be written.
///////////////////////////////////////////////////////////////////////////////
// Returns number of sectors written if success, < 0 if error.
///////////////////////////////////////////////////////////////////////////////
int _fat_write( unsigned int mode,       // mode for IOC driver
                unsigned int fd_id,      // file descriptor
                void*        buffer,     // target buffer base address
                unsigned int count,      // number of sector to write
                unsigned int offset )    // nuber of sectors to skip in file
{

    unsigned int spc = fat.sectors_per_cluster;

    unsigned int file_size;         // number of bytes in file
    unsigned int file_sectors;      // number of sectors in file
    unsigned int cluster;           // cluster index 
    unsigned int clusters_to_skip;  // number of clusters to skip because offset
    unsigned int sectors_to_skip;   // number of sectors to skip in first iteration
    unsigned int allocate;          // need allocate or not
    unsigned int current_cluster;   // number of cluster allocated to the file
    unsigned int required_cluster;  // number of cluster needed for the write

    // compute file size as a number of sectors 
    file_size    = fat.fd[fd_id].file_size;
    if ( file_size & 0x1FF ) file_sectors = (file_size >> 9) + 1;
    else                     file_sectors = (file_size >> 9); 

    // Compute the number of clusters occupied by the file
    current_cluster = file_sectors / spc;

    // Compute the number of clusters that will occupy the file (after fat_write)
    required_cluster = (count + offset) / spc;

    // Check if we need to allocate new cluster(s) for the file  
    allocate = ( required_cluster > current_cluster );

#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int cid     = procid / NB_PROCS_MAX;
unsigned int lpid    = procid % NB_PROCS_MAX;
unsigned int x       = cid >> Y_WIDTH;
unsigned int y       = cid & ((1<<Y_WIDTH) - 1);

_printf("\n[FAT DEBUG] Processor[%d,%d,%d] enters _fat_write() for file %s\n",
        " - buffer vbase    = %x\n"
        " - skipped sectors = %x\n"
        " - write sectors   = %x\n" 
        " - file sectors    = %x\n" 
        " - need allocate   = %d\n", 
        x, y, lpid, fat.fd[fd_id].name, (unsigned int)buffer, 
        offset, count, file_sectors, allocate );
#endif

    // arguments checking
    if ( fd_id >= GIET_OPEN_FILES_MAX )
    { 
        _printf("\n[FAT ERROR] in _fat_write() : illegal file descriptor index\n");
        return -1;
    }
    if ( fat.fd[fd_id].used != 1 )
    {
        _printf("\n[FAT ERROR] in _fat_write() : file not open\n");
        return -1;
    }
    if ( ((unsigned int)buffer & 0x1FF) != 0 )
    {
        _printf("\n[FAT ERROR] in _fat_write() : memory buffer not sector aligned\n");
        return -1;
    }

    if ( allocate  )
    {
        if ( _fat_allocate( fd_id, (required_cluster - current_cluster) ) < 0 )
        {
            _printf("\n[FAT ERROR] in _fat_write() : fat_allocate failed\n");
            return -1;
        }
    }

    // compute clusters and sectors to be skipped
    clusters_to_skip = offset / spc;
    sectors_to_skip  = offset % spc;
    
    // get first cluster index 
    cluster = fat.fd[fd_id].first_cluster;

#if GIET_DEBUG_FAT
_printf(" - first cluster   = %x\n"
        " - skiped clusters = %x\n",
        cluster, clusters_to_skip );   
#endif

    // compute index of first cluster to be loaded
    // as we may need to scan the FAT, we use the kernel mode
    while ( clusters_to_skip )
    {
        cluster = get_next_cluster_id( IOC_KERNEL_MODE, cluster );
        clusters_to_skip--;
    }

    // variables used in the loop on clusters
    int             todo_sectors;   // number of sectors still to be loaded
    unsigned int    lba;            // first sector index on device
    unsigned int    iter_sectors;   // number of sectors to load in iteration
    char*           src;            // pointer on target buffer

    // initialize these variables for the first iteration 
    todo_sectors  = count;
    src           = (char*)buffer;
    lba           = cluster_to_lba(cluster) + sectors_to_skip;
    if( count < (spc - sectors_to_skip) ) iter_sectors = count;
    else                                  iter_sectors = spc - sectors_to_skip; 

    // loop on the clusters
    while ( todo_sectors > 0 )
    {

#if GIET_DEBUG_FAT
_printf("\n[FAT DEBUG] Processor[%d,%d,%d] makes an IOC write : "
        "buf = %x / lba = %x / sectors = %x\n",
        x, y, lpid, (unsigned int)src, lba, iter_sectors );
#endif

        if( _ioc_write( 0,                 // channel
                        mode,              // mode for IOC driver
                        lba,               // first sector index 
                        src,               // source buffer address
                        iter_sectors ) )   // number of sectors
        {
            _printf("\n[FAT ERROR] in _fat_write() cannot write block %x\n", lba );
            return -1;
        }
         
        // update variables for next iteration
        cluster      = get_next_cluster_id( mode, cluster );
        todo_sectors = todo_sectors - iter_sectors;
        src          = src + (iter_sectors << 9);
        lba          = cluster_to_lba(cluster);
        if ( todo_sectors > spc ) iter_sectors = spc;
        else                      iter_sectors = todo_sectors;
    }

    // Update structure file descriptor, field file_size with
    // the new file size if the file is bigger than the previous file
    if ( ( offset + count ) > file_sectors )
    {
        fat.fd[fd_id].file_size = (count + offset) << 9;
    }

    // Update entry of directory with the new value 
    // of file size (Field : DIR_FILE_SIZE)
    if ( update_entry(fd_id, DIR_FILE_SIZE, fat.fd[fd_id].file_size) )
    {
            _printf("\n[FAT ERROR] in _fat_write() update entry failed\n");
            return -1;
    }
         
    // returns number of sectors actually transfered
    return count;
}

/////////////////////////////////////////////////////////////////////////////////
// Return stats of a file identified by "fd". 
// (Only the file_size in sectors for this moment)
/////////////////////////////////////////////////////////////////////////////////
// Returns file size (on sectors) on success, -1 on failure.
/////////////////////////////////////////////////////////////////////////////////
int _fat_fstat( unsigned int fd_id )
{
    unsigned int file_size    = 0;
    unsigned int file_sectors = 0;

    if( (fd_id < GIET_OPEN_FILES_MAX) )
    {
        file_size = fat.fd[fd_id].file_size;

        if ( file_size & 0x1FF ) file_sectors = (file_size >> 9) + 1;
        else                     file_sectors = (file_size >> 9); 

        return file_sectors;
    }
    else
    {
        _printf("\n[FAT ERROR] in _fat_fstat() : illegal file descriptor index\n");
        return -1;
    } 
} // end _fat_fstat()

/////////////////////////////////////////////////////////////////////////////////
// Close the file identified by the file_descriptor index. 
/////////////////////////////////////////////////////////////////////////////////
// Returns 0 on success, -1 on failure.
/////////////////////////////////////////////////////////////////////////////////
int _fat_close( unsigned int fd_id )
{
    if( (fd_id < GIET_OPEN_FILES_MAX) )
    {
        fat.fd[fd_id].used = 0;
        return 0;
    }
    else
    {
        _printf("\n[FAT ERROR] in _fat_close() : illegal file descriptor index\n");
        return -1;
    } 
} // end fat_close()

/////////////////////////////////////////////////////////////////////////////////////
// The following function implement the user_level system call.
// The flags argument is nor used, as file access modes are not implemented yet.
/////////////////////////////////////////////////////////////////////////////////////
// Return the file descriptor index if success / return -1 if failure
/////////////////////////////////////////////////////////////////////////////////////
int _fat_user_open( char*  pathname,         // absolute pathname from root
                    unsigned int flags )     // unused: TODO
{
    return _fat_open( IOC_KERNEL_MODE,       // we use KERNEL_MODE, because
                      pathname,              // we need to write into FAT cache
                      0 );                   // no creation if not found
}

/////////////////////////////////////////////////////////////////////////////////////
// The following function implement the user_level system call.
// This function should be modified to respect the UNIX specification 
/////////////////////////////////////////////////////////////////////////////////////
// Return number of sectors actually transfered if success / return -1 if failure
/////////////////////////////////////////////////////////////////////////////////////
int _fat_user_read( unsigned int fd,        // file descriptor index
                    void*        buffer,    // destination buffer
                    unsigned int count,     // number of sectors to read
                    unsigned int offset )   // number of sectors to skip
{
    return _fat_read( IOC_USER_MODE,
                      fd,
                      buffer,  
                      count,  
                      offset );
}

/////////////////////////////////////////////////////////////////////////////////////
// The following function implement the user_level system call.
// This function should be modified to respect the UNIX specification. 
/////////////////////////////////////////////////////////////////////////////////////
// Return number of sectors actually transfered if success / return -1 if failure
/////////////////////////////////////////////////////////////////////////////////////
int _fat_user_write( unsigned int fd,       // file descriptor
                     void*        buffer,   // source buffer
                     unsigned int count,    // number of sectors to write
                     unsigned int offset )  // number of sectors to skip on file
{
    return _fat_write( IOC_USER_MODE,
                       fd,
                       buffer,  
                       count,  
                       offset );
}

/////////////////////////////////////////////////////////////////////////////////////
int _fat_user_lseek( unsigned int fd_id,
                     unsigned int offset,
                     unsigned int whence )
{
    _printf("[GIET ERROR] _fat_user_lseek() not implemented\n");
    _exit();
    return 0;
}


// Local Variables:
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// c-file-offsets:((innamespace . 0)(inline-open . 0))
// indent-tabs-mode: nil
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// vim: filetype=c:expandtab:shiftwidth=4:tabstop=4:softtabstop=4