GIET-VM / FAT32 Handler
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GIET-VM / FAT32 Handler
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Kernel FAT32 access functions
- 1) int _fat_init( unsigned int use_irq )
- 2) int _fat_open( unsigned int use_irq , char* pathname , …
- 3) int _fat_read( unsigned int use_irq , unsigned int fd_id , …
- 4) int _fat_write( unsigned int use_irq , unsigned int fd_id , …
- 5) int _fat_fstat( unsigned int fd_id )
- 6) int _fat_close( unsigned int fd_id )
- 7) int _fat_ioc_access( unsigned int use_irq , unsigned int …
- User FAT32 access functions
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Kernel FAT32 access functions
The fat32.c and fat32.h files define the data structures and functions that are used to access a FAT32 file system stored on a mass storage block device (such as the BDV, HBA, SDC, or RDK peripherals).
All the block device peripherals support a polling mode on the peripheral status register to detect the completion of a read or write access to the device, but some peripheral (BDV and HBA) support a descheduling mode for the calling task, with an interrupt to signal transfer completion.
The GIET-VM handler supports the 4 peripheral types (only one type in a given platform), and most of the FAT access functions support a specific argument to activate the descheduling/IRQ mode when it is supported by the hardware. As a general rule the GIET-VM boot-loader uses only the polling mode, and the GIET-VM kernel uses the descheduling + IRQ mode to handle the user system calls.
All these functions are prefixed by _ to remind that they can only be executed by a processor in kernel mode.
Kernel FAT32 access functions
1) int _fat_init( unsigned int use_irq )
This function initialises the kernel _fat structure describing the FAT32 file system, including the set of open files, and the FAT cache (only one single 512 bytes block at the moment). The use_irq argument define the requested access mode (polling / descheduling), but both the GIET-VM boot-loader and the GIET-VM kernel use the polling mode for FAT initialisation. Return 0 in case of success, exit if error.
2) int _fat_open( unsigned int use_irq , char* pathname , unsigned int create )
This function open a file, register it in the set of open files, and return a file descriptor index (fd_id) that must be used by all other access functions.
- use_irq : Boolean => request to use the descheduling mode when non zero.
- pathname : file absolute path name from the root directory.
- create : Boolean => request to create the file if it does not exist (Not supported yet).
Returns fd_id if success, returns -1 if file not found).
3) int _fat_read( unsigned int use_irq , unsigned int fd_id , void* buffer , unsigned int count , unsigned int offset )
This function transfer an integer number of blocks from an open file (identified by the fd_id) to a memory buffer, after checking the arguments. If the number of requested sectors exceeds the file size, this number of loaded sectors is reduced.
- use_irq : Boolean => request to use the descheduling mode when non zero.
- fd_id : file descriptor index
- buffer : memory buffer virtual base address
- count : number of blocks to transfer
- offset : number of blocks to skip in file
Returns number of sectors transfered if success, returns -1 if error.
4) int _fat_write( unsigned int use_irq , unsigned int fd_id , void* buffer , unsigned int count , unsigned int offset )
This function transfer an integer number of blocks from a memory buffer to an open file (identified by the fd_id), after checking the arguments. It allocates new clusters on the block device if (offset + count) is larger than the current file size.
- use_irq : Boolean => request to use the descheduling mode when non zero.
- fd_id : file descriptor index
- buffer : memory buffer virtual base address
- count : number of blocks to transfer
- offset : number of blocks to skip in file
Returns number of sectors written if success, returns -1 if error.
5) int _fat_fstat( unsigned int fd_id )
Return the file size (bytes) for a file identified by the fd_id.
6) int _fat_close( unsigned int fd_id )
This function removes a file identified by the fd_id from the set of open files.
7) int _fat_ioc_access( unsigned int use_irq , unsigned int to_mem , unsigned int lba , unsigned int buf_vaddr , unsigned int count )
This function is acting as a generic block device driver: all the previous functions use this last function to access the available block device, depending on the USE_IOC_BDV / USE_IOC_HBA / USE_IOC_SDC / USE_IOC_RDK flags defined in the hard_config.h file. It computes the buffer physical address, and check access rights.
- use_irq : Boolean => request to use the descheduling mode when non zero.
- to_mem : Boolean => to memory transfer when non zero.
- lba : first block index on the block device.
- buf_vaddr : memory buffer virtual base address
- count : number of blocks to transfer
Returns 0 if success, returns -1 if error.
User FAT32 access functions
These functions are used by the kernel to handle the user system calls. They should be modified to respect the UNIX specification.