source: soft/giet_vm/giet_fat32/fat32.c @ 561

//////////////////////////////////////////////////////////////////////////////////
// File     : fat32.c 
// Date     : 01/09/2013
// Authors  : Marco Jankovic, Cesar Fuguet & Alain Greiner
// Copyright (c) UPMC-LIP6
//////////////////////////////////////////////////////////////////////////////////
// The fat.h and fat_common.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.
//////////////////////////////////////////////////////////////////////////////////
// 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.
// 3. This FAT32 library uses a FAT cache whose storage capacity is one
//    sector (512 bytes = 128 cluster indexes in FAT)
//////////////////////////////////////////////////////////////////////////////////

#include <giet_config.h>
#include <hard_config.h>
#include <fat32.h>
#include <utils.h>
#include <vmem.h>
#include <bdv_driver.h>
#include <hba_driver.h>
#include <sdc_driver.h>
#include <rdk_driver.h>
#include <mmc_driver.h>
#include <tty0.h>

//////////////////////////////////////////////////////////////////////////////////
//      Global variable : internal FAT representation
//////////////////////////////////////////////////////////////////////////////////

extern fat32_fs_t _fat;

extern unsigned int _ptabs_vaddr[GIET_NB_VSPACE_MAX][X_SIZE][Y_SIZE];
  
//////////////////////////////////////////////////////////////////////////////
// This function computes the memory buffer physical address, and calls 
// the proper IOC driver depending on the subtype (BDV / HBA / SDC /RDK). 
// The use_irq argument allows to activate the descheduling mode, if it 
// supported by the IOC driver subtype
//////////////////////////////////////////////////////////////////////////////
// Return 0 in case of success, return -1 in case of error
//////////////////////////////////////////////////////////////////////////////
static
int _fat_ioc_access( unsigned int use_irq,
                     unsigned int to_mem,
                     unsigned int lba,
                     unsigned int buf_vaddr,
                     unsigned int count ) 
{
    // compute memory buffer physical address
    unsigned int       flags;         // for _v2p_translate
    unsigned long long buf_paddr;     // buffer physical address 

    if ( ((_get_mmu_mode() & 0x4) == 0 ) || USE_IOC_RDK )  // identity
    {
        buf_paddr = (unsigned long long)buf_vaddr;
    }
    else                                // V2P translation required
    {
        buf_paddr = _v2p_translate( buf_vaddr , &flags );
    }

#if (GIET_DEBUG_FAT > 1)
unsigned int procid  = _get_procid();
unsigned int x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);
_printf("\n[DEBUG FAT] P[%d,%d,%d] enters _fat_ioc_access() at cycle %d\n"
        "  to_mem = %d / vaddr = %x / paddr = %l / sectors = %d / lba = %x\n",
        x, y , p, _get_proctime(), to_mem, buf_vaddr, buf_paddr, count, lba );
#endif


#if GIET_NO_HARD_CC     // L1 cache inval (virtual addresses)
    if ( to_mem ) _dcache_buf_invalidate( buf_vaddr, count<<9 );
#endif


#if   ( USE_IOC_BDV )   // call the proper driver
    return( _bdv_access( use_irq , to_mem , lba , buf_paddr , count ) ); 
#elif ( USE_IOC_HBA )
    return( _hba_access( use_irq , to_mem , lba , buf_paddr , count ) );
#elif ( USE_IOC_SPI )
    return( _sdc_access( use_irq , to_mem , lba , buf_paddr , count ) );
#elif ( USE_IOC_RDK )
    return( _rdk_access( use_irq , to_mem , lba , buf_paddr , count ) );
#else
    _printf("\n[FAT ERROR] in _fat_ioc_access() : no IOC driver\n");
    _exit();
#endif

}  // end _fat_ioc_access()


//////////////////////////////////////////////////////////////////////////////////
// This function displays the content of the FAT cache
//////////////////////////////////////////////////////////////////////////////////
#if (GIET_DEBUG_FAT > 1)
static
void _display_fat_cache()
{
    unsigned int line;
    unsigned int word;
    unsigned int temp[9];

    temp[8] = 0;

    _puts("\n*********************** fat_cache_lba = ");
    _putx( _fat.cache_lba );
    _puts(" *****************************\n");

    for ( line = 0 ; line < 16 ; line++ )
    {
        // display line index 
        _putx( line );
        _puts(" : ");

        // display 8*4 bytes 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]);
            _putx( hexa );
            _puts(" | ");

            // 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 
        _puts( (char*)temp );
        _puts("\n");
    }
    _puts("***************************************************************************\n");

} // end _display_fat_cache()  
#endif

//////////////////////////////////////////////////////////////////////////////////
// This function displays the FAT descriptor.
//////////////////////////////////////////////////////////////////////////////////
#if GIET_DEBUG_FAT
static
void _fat_print()
{
    _printf("\n########################## FAT32 ################################"  
            "\nFAT initialised                  %x"
            "\nSector Size  (bytes)             %x"
            "\nSectors per cluster              %x"
            "\nFAT region first lba             %x"
            "\nData region first lba            %x"
            "\nNumber of sectors for one FAT    %x"
            "\nNumber of free clusters          %x"
            "\nLast allocated cluster           %x" 
            "\n#################################################################\n",
            _fat.initialised,
            _fat.sector_size,
            _fat.sectors_per_cluster,
            _fat.fat_lba,
            _fat.data_lba,
            _fat.fat_sectors,
            _fat.number_free_cluster,
            _fat.last_cluster_allocated );
} // end _fat_print()
#endif

//////////////////////////////////////////////////////////////////////////////////
// This function returns the length of a FAT field. This field is identified
// 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. 
// The modified field in buffer 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. 
// The analysed field in buffer 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( unsigned int use_irq,
                                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 )      // miss in fat_cache
    {
        // access fat
        if( _fat_ioc_access( use_irq,
                             1,               // read
                             lba, 
                             (unsigned int)_fat.fat_cache,
                             1 ) )            // one sector
        {
            _printf("[FAT_ERROR] in get_next_cluster_id() : cannot read block %x", 
                    lba );
            return 1;
        }
        _fat.cache_lba = lba;
    }

    unsigned int next = _read_entry( ((cluster % 128) * 4), 
                                     4, 
                                     _fat.fat_cache,
                                     1 );
#if (GIET_DEBUG_FAT > 1)
unsigned int procid  = _get_procid();
unsigned int x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);
_printf("\n[DEBUG FAT] P[%d,%d,%d] in _get_next_cluster() :  next = %x\n",
        x , y , p , next );
_display_fat_cache();
#endif

    return next;
}

//////////////////////////////////////////////////////
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 use_irq,
                            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_string[12]  = {[0 ... 10] = ' ', '\0'};     // buffer 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;                            // dir entry attribute
    unsigned int ord     = 0;                            // dir entry sequence
    unsigned int found   = 0;                            // name found
    unsigned int offset  = 0;                            // offset in fat_cache
    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 ) )
    {
    }

    // Format file_name to SFN format
    is_sfn = is_short( file_name, sfn_string );

    // access FAT
    if ( _fat_ioc_access( use_irq,
                          1,               // read
                          lba, 
                          (unsigned int)_fat.fat_cache,
                          1 ) )            // one sector
    {
        _printf("\n[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("\n[FAT ERROR] in _update_entry() : reaches end\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("\n[FAT ERROR] in _update_entry() reaches end\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_string, (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;
            }
        }
    }

    // write block to FAT
    if ( _fat_ioc_access( use_irq,
                          0,                // write
                          lba, 
                          (unsigned int)_fat.fat_cache, 
                          1 ) )             // one sector
    {
        _printf("\n[FAT ERROR] in _update_entry() cannot write sector %x\n", 
                lba );
        return 1;
    }

    return 0;
} // end _update_entry()


//////////////////////////////////////////////////////////////////////////////////
// This function update the FS_INFO block:
// 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 use_irq )
{
    unsigned int lba = _fat.fs_info_lba;

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

    // update FAT cache in case of miss
    if ( lba != _fat.cache_lba )
    {
        if ( _fat_ioc_access( use_irq,
                              1,                 // read
                              lba, 
                              (unsigned int)_fat.fat_cache, 
                              1 ) )              // one sector
        {
            _printf("\n[FAT_ERROR] in _update_fs_info() cannot read block\n");
            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 );
   
    // write bloc to FAT
    if ( _fat_ioc_access( use_irq,
                          0,                // write
                          lba,
                          (unsigned int)_fat.fat_cache, 
                          1 ) )             // one sector
    {
        _printf("\n[FAT_ERROR] in _update_fs_info() cannot write block\n");
        return 1;
    }

    return 0;
}  // end _update_fs_info()

//////////////////////////////////////////////////////////////////////////////////
// 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 use_irq,
                          unsigned int cluster, 
                          unsigned int value  )
{
    unsigned int lba = _fat.fat_lba + (cluster / 128);

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

    // update FAT cache in case of miss
    if ( lba != _fat.cache_lba )  
    {
        if ( _fat_ioc_access( use_irq,
                              1,                 // read
                              lba, 
                              (unsigned int)_fat.fat_cache, 
                              1 ) )              // one sector
        {
            _printf("\n[FAT_ERROR] in _update_fat() cannot read block %x\n",
                    lba );
            return 1;
        }
        _fat.cache_lba = lba;
    }

    _write_entry( ((cluster % 128) << 2), 4, _fat.fat_cache, value );

    // write bloc to FAT
    if ( _fat_ioc_access( use_irq,
                          0,                // write
                          lba,
                          (unsigned int)_fat.fat_cache,
                          1 ) )             // one sector
    {
        _printf("\n[FAT_ERROR] in _update_fat() cannot write block %x\n",
                lba );
        return 1;
    }

    return 0;
} // end update_fat()

//////////////////////////////////////////////////////////////////////////////////
// This function allocate count clusters 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 use_irq,
                   unsigned int fd_id, 
                   unsigned int count )
{
    unsigned int next_cluster = _fat.fd[fd_id].first_cluster;    // first cluster
    unsigned int cluster_to_allocate = count;                   // to allocate
    unsigned int last_cluster_file;                             // Last cluster 
    unsigned int free_cluster = _fat.last_cluster_allocated + 1; // First free 

    // Check if free_cluster is really free (must be true)
    if ( _get_next_cluster( use_irq , 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[DEBUG FAT] _fat_allocate() for fd = %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( use_irq , next_cluster );
    }
    while ( next_cluster < END_OF_CHAIN_CLUSTER );

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

#if GIET_DEBUG_FAT
_printf("\n[DEBUG FAT] cluster to update = %x / free cluster = %x / count = %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( use_irq , 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( use_irq , 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( use_irq , 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( use_irq ) )
    {
        _printf("\n[FAT ERROR] in _fat_allocate() : update fs_info failed\n");
        return -1;
    }

    return 0;
}  // end _fat_allocate()

//////////////////////////////////////////////////////////////////////////////////
// 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. 
// It returns the cluster index of the file/directory when the name has been found,
// as well as the file size, and the lba.
// We consider 3 types of directory entries:
// - SFN : directory entry associated to a Short File Name (8.3)
// - LFN : directory entry associated to a Long File Name
// - XTN : directory entry containing only a name extension for a Long File Name
// The cluster index is always stored in a SFN or LFN entry.
// Return cluster index if name found / Return -1 if not found.
//////////////////////////////////////////////////////////////////////////////////
static 
int _scan_directory( unsigned int   use_irq,         // use descheduling mode 
                     unsigned int   cluster,         // cluster of dir_entry 
                     char*          file_name,       // searched file/dir name
                     unsigned int*  file_size,       // file size
                     unsigned int*  lba_dir_entry )  // lba of dir_entry
{
    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_string[12]    = {[0 ... 10] = ' ', '\0'};  // buffer Short File Name
    unsigned int  is_sfn   = is_short(file_name, sfn_string); // file_name is short
    unsigned int  offset   = 0;                         // byte offset in block
    unsigned int  block_id = _fat.sectors_per_cluster;   // sector index 
    unsigned int  lba      = cluster_to_lba(cluster);   // lba of cluster 
    unsigned int  attr     = 0;                         // dir entry attribute
    unsigned int  ord      = 0;                         // dir entry sequence
    unsigned int  found    = 0;                         // searched name found
    unsigned int  long_name_found = 0;                  // matching XTN found
    unsigned int  searched_cluster;                     // searched cluster index

#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);

_printf("\n[DEBUG FAT] _scan_directory() : P[%d,%d,%d] enters for %s\n",
      x, y, p, file_name );
#endif

    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 sector from DATA region into FAT cache
    // other sectors will be loaded inside loop as required
    if( _fat_ioc_access( use_irq,
                         1,               // read
                         lba,
                         (unsigned int)_fat.fat_cache,
                         1 ) )            // one sector
    {
        _printf("[\nFAT 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 the directory identified by cluster index 
    // - 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 == 0 )
    {
        // 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( use_irq , cluster );

                if ( cluster >= END_OF_CHAIN_CLUSTER  ) return END_OF_CHAIN_CLUSTER;

                lba      = cluster_to_lba(cluster);
                block_id = _fat.sectors_per_cluster;
            }
            if( _fat_ioc_access( use_irq,
                                 1,               // read
                                 lba, 
                                 (unsigned int)_fat.fat_cache,
                                 1 ) )            // one sector
            {
                _printf("\n[FAT ERROR] in _scan_directory() : cannot read sector %x\n",
                        lba);
                return -1;
            }
            _fat.cache_lba = lba;
            block_id--;
            offset = offset % 512;
        }

        // store the directory entry pointed by offset in dir_entry buffer,
        // if it a possible candidate for the searched name

        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) )    // EXT entry : skipped
            {
                offset     = offset + ((ord & 0xF) * DIR_ENTRY_SIZE);
            }
            else if ( (attr != ATTR_LONG_NAME_MASK) && 
                      (ord  != FREE_ENTRY) && 
                      (ord  != NO_MORE_ENTRY ) )         // SFN entry : to be checked
            {
                memcpy( dir_entry, _fat.fat_cache + offset, DIR_ENTRY_SIZE );    

                get_name_from_short( dir_entry, name_entry );

                if ( _strncmp( (char*)sfn_string, 
                               (char*)name_entry, 13 ) == 0 )  // short name found
                {
                    found = 1;
                }
                else
                {
                    offset = offset + DIR_ENTRY_SIZE;
                }
            }
            else if (ord == NO_MORE_ENTRY )              // end of directory : return
            {
                return END_OF_CHAIN_CLUSTER;
            }
        }
        else                                      // searched name is long
        {
            if( (attr == ATTR_LONG_NAME_MASK) && 
                (ord != FREE_ENTRY) &&
                (ord != NO_MORE_ENTRY) )                 // EXT entry : to be checked
            {
                memcpy( dir_entry, _fat.fat_cache + offset, DIR_ENTRY_SIZE );

                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 )  // matching EXT
                {
                    if( (ord & 0xf) == 1 )                    // long name found 
                    {
                        long_name_found = 1;
                    }
                }
                offset = offset + DIR_ENTRY_SIZE;
            }
            else if( (attr != ATTR_LONG_NAME_MASK) && 
                     (ord  != FREE_ENTRY) && 
                     (ord  != NO_MORE_ENTRY) )
            {
                if ( long_name_found )                   // LFN entry
                {
                    memcpy( dir_entry, _fat.fat_cache + offset, DIR_ENTRY_SIZE );
                    found = 1;
                }
                else                                     // SFN entry: must be skipped
                {
                    offset = offset + DIR_ENTRY_SIZE;
                }
            }
            else if (ord == NO_MORE_ENTRY )                              // end of directory : return
            {
                return END_OF_CHAIN_CLUSTER;
            }
        }
    }  // end while

    // returns cluster index
    *file_size       = _read_entry( DIR_FILE_SIZE, dir_entry, 1 );
    *lba_dir_entry   = lba;
    searched_cluster = (_read_entry( DIR_FST_CLUS_HI, dir_entry, 1 ) << 16) |
                       (_read_entry( DIR_FST_CLUS_LO, dir_entry, 1 )      ) ;

#if GIET_DEBUG_FAT
_printf("\n[DEBUG FAT] _scan_directory() : P[%d,%d,%d] found %s"
        " : cluster = %x\n", x, y, p, file_name, searched_cluster );
#endif

    return searched_cluster;
} // 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 open
// files descriptors array and the lock protecting the FAT,
// from informations found in the boot record.
// This should be done only once.
//////////////////////////////////////////////////////////////////////////
// Return 0 if success, exit if failure 
//////////////////////////////////////////////////////////////////////////
int _fat_init( unsigned int use_irq )  
{

#if GIET_DEBUG_FAT
unsigned int procid  = _get_procid();
unsigned int x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);
_printf("\n[DEBUG FAT] P[%d,%d,%d] enters _fat_init\n",x,y,p);
#endif

    // FAT initialisation should be done only once
    if ( _fat.initialised == FAT_INITIALISED )
    {
        _printf("\n[FAT ERROR] Strange, FAT already initialised...\n");
        _exit();
    }

    // load Boot Record (VBR) into fat cache
    if ( _fat_ioc_access( use_irq,
                          1,                   // read
                          0,                   // sector index
                          (unsigned int)_fat.fat_cache,
                          1 ) )                // one sector
    {
        _printf("\n[FAT ERROR] in _fat_init() cannot load VBR\n");
        _exit();
    }
    _fat.cache_lba = 0;

#if GIET_DEBUG_FAT > 1
_printf("\n[DEBUG FAT] _fat_init() : Boot Sector Loaded\n");
_display_fat_cache();
#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");
        _exit();
    }
    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");
        _exit();
    }
    if( (_read_entry( BPB_FAT32_FATSZ32, _fat.fat_cache, 1 ) & 0xF) != 0 )
    {
        _printf("\n[FAT ERROR] The FAT region must be multiple of 32 sectors\n");
        _exit();
    }
    if( _read_entry( BPB_FAT32_ROOTCLUS, _fat.fat_cache, 1 ) != 2 )
    {
        _printf("\n[FAT ERROR] The first cluster index must be 2\n");
        _exit();
    }
    // 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.initialised         = FAT_INITIALISED;

    // initalise the lock protecting the FAT
    _spin_lock_init( &_fat.fat_lock );

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

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

    // load FS_INFO into fat cache
    if ( _fat_ioc_access( use_irq,
                          1,                  // read
                          _fat.fs_info_lba,    
                          (unsigned int)_fat.fat_cache,
                          1 ) )               // one sector
    { 
        _printf("\n[FAT ERROR] in _fat_init() cannot load FS_INFO Sector\n"); 
        _exit();
    }
    _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
_fat_print();
_printf("\n[DEBUG FAT] P[%d,%d,%d] exit _fat_init()\n", x,y,p );
#endif

    return 0;
}  // end _fat_init()

///////////////////////////////////////////////////////////////////////////////
// This function checks that the kernel FAT structure has been initialised.
// It 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 int use_irq,       // use descheduling mode if possible
               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 x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);
_printf("\n[DEBUG FAT] _fat_open() : P[%d,%d,%d] enters for path %s\n",
        x, y, p, pathname );
#endif

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

    // checking FAT initialised
    if( _fat.initialised != FAT_INITIALISED )
    {
        _printf("\n[FAT ERROR] in _fat_open() : FAT not initialised\n");
        return -1;
    }
    // takes the FAT lock for exclusive access
    _spin_lock_acquire( &_fat.fat_lock );

#if GIET_DEBUG_FAT
_printf("\n[DEBUG FAT] _fat_open() : P[%d,%d,%d] takes the FAT lock\n",
        x, y, p );
#endif
 
    // 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[DEBUG FAT] _fat_open() : P[%d,%d,%d] search file/dir %s\n",
        x, y, p, 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( use_irq , 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 );
            _spin_lock_release( &_fat.fat_lock );
            return -1;
        }
    }

#if GIET_DEBUG_FAT
_printf("\n[DEBUG FAT] P[%d,%d,%d] in _fat_open() : cluster for %s = %x\n",
       x, y, p, pathname, cluster );
#endif

    // check the next value for cluster index found
    unsigned next = _get_next_cluster( use_irq , 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[DEBUG FAT] _fat_open() : P[%d,%d,%d] exit : fd = %d for file %s\n",
        x, y, p, fd_id, pathname );
#endif

            // release FAT lock
            _spin_lock_release( &_fat.fat_lock );

            return fd_id;
        }
        else
        {
            _printf("\n[FAT ERROR] in _fat_open() for file %s : fd array full\n", 
                    pathname );
            _spin_lock_release( &_fat.fat_lock );
            return -1;
        }
    }
    else
    {
        _printf("\n[FAT ERROR] in _fat_open() for file %s : bad cluster\n",
                pathname );
        _spin_lock_release( &_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 use_irq,    // use descheduling mode if possible
               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 x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);
_printf("\n[DEBUG FAT] _fat_read() : P[%d,%d,%d] enters for file %s\n"
        " - buffer vbase     = %x\n"
        " - skipped sectors  = %x\n"
        " - read sectors     = %x\n"
        " - first cluster    = %x\n"
        " - skipped clusters = %x\n",
        x, y, p, _fat.fd[fd_id].name, (unsigned int)buffer,
        offset, count, cluster, clusters_to_skip );
#endif

    // compute index of first cluster to be loaded
    while ( clusters_to_skip )
    {
        cluster = _get_next_cluster( use_irq , 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
    unsigned int    dst;            // pointer on target buffer

    // initialize these variables for the first iteration 
    todo_sectors  = total_sectors;
    dst           = (unsigned int)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[DEBUG FAT] _fat_read() : P[%d,%d,%d] makes an IOC read\n"
        "  cluster = %x / buffer = %x / lba = %x / sectors = %d\n",
        x, y, p, cluster, dst, lba, iter_sectors );
#endif

        if( _fat_ioc_access( use_irq,
                             1,                 // read
                             lba, 
                             dst,               // buffer address
                             iter_sectors ) )   // number of sectors
        {
            _printf("\n[FAT ERROR] in _fat_read() cannot load block %x", lba );
            return -1;
        }
         
        // update variables for next iteration
        cluster      = _get_next_cluster( use_irq , 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...
///////////////////////////////////////////////////////////////////////////////
// Returns number of sectors written if success, < 0 if error.
///////////////////////////////////////////////////////////////////////////////
int _fat_write( unsigned int use_irq,    // use descheduling mode if possible
                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 x       = procid >> (Y_WIDTH + P_WIDTH);
unsigned int y       = (procid >> P_WIDTH) & ((1<<Y_WIDTH)-1);
unsigned int p       = procid & ((1<<P_WIDTH)-1);

_printf("\n[DEBUG FAT] _fat_write() : P[%d,%d,%d] enters 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, p, _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( use_irq , fd_id, (required_cluster-current_cluster) ) )
        {
            _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("\n[DEBUG FAT] _fat_write() : P[%d,%d,%d] get cluster %x\n",
        x, y, p, cluster );
#endif

    // compute index of first cluster to be loaded
    while ( clusters_to_skip )
    {
        cluster = _get_next_cluster( use_irq , 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
    unsigned int    src;            // pointer on target buffer

    // initialize these variables for the first iteration 
    todo_sectors  = count;
    src           = (unsigned int)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[DEBUG FAT] _fat_write() : P[%d,%d,%d] makes an IOC write"
        "  cluster = %x / buffer = %x / lba = %x / sectors = %d\n",
        x, y, p, cluster, src, lba, iter_sectors );
#endif

        if( _fat_ioc_access( use_irq,
                             0,                 // write
                             lba, 
                             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( use_irq , 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( use_irq, 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;
}  // end _fat_write()

/////////////////////////////////////////////////////////////////////////////////
// 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 not 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( 1,        // use descheduling mode if possible
                      pathname, 
                      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( 1,        // use descheduling mode if possible
                      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( 1,       // use descheduling mode if possible
                       fd,
                       buffer,  
                       count,  
                       offset );
}

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


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