= RTEMS File System =



[[TOC(TBR/UserManual/RTEMS_File_System, depth=2)]]


The RTEMS File System or RFS provides a fully featured file system that is fast and compact. The RFS interfaces to the [wiki:File_Systems#Block_Devices Block Devices API] and therefore supports all the block devices RTEMS has. It also interfaces to the RTEMS libc file system support layer. This means the POSIX interface to files in RTEMS is supported by the RFS file system.
= RFS Structure =


The RFS file system consists of superblock at the start followed by a series of groups. A group is a group of blocks.

<blockquote>
{| border="1" cellpadding="5" cellspacing="0"
|-
! style="background:#efefef;" | Superblock
|-
! align="center" | Group
|-
! align="center" | Group
|}
</blockquote>

A group is broken up into the block allocation bitmap the inode allocation bitmap, the inodes, and the data blocks.

<blockquote>
{| border="1" cellpadding="5" cellspacing="0"
|-
! align="center' | Block Bitmap
|-
! align="center" | Inode Bitmap
|-
! align="center" | Inodes
|-
! align="center" | Data Blocks
|}
</blockquote>

The block bitmap contains a single bit for every block in a group. The default format is to allocate the size of a group based on the number of bits that fit into a single block. For example a block of 1024 bytes has 8,192 bits therefore a group can have 8192 blocks including the block bitmap block. The inode bitmap has a bit for ever inode in the group. An inode is the information about a node on the disk. A node is the data that links the elements of the disk together to create directories, files, and nodes. The number of inodes in a group is format configuration parameter. The default is use 1% of the disk's blocks for inode data. Again with a 1024 byte block size there are 18 inodes per block and 1448 inodes per group.
= Using the RFS =


The easiest way to use the RFS and to play with it is to enable the shell in your application. To do this add to the file that handles your {{{condefs.h</code> defines:

 #define CONFIGURE_SHELL_COMMANDS_INIT
 #define CONFIGURE_SHELL_COMMANDS_ALL
 #define CONFIGURE_SHELL_MOUNT_RFS
 #define CONFIGURE_SHELL_DEBUGRFS
 #include <rtems/shellconfig.h>

In the main of your application start the shell then at the prompt list the devices you have. The [http://www.rtems.org/ftp/pub/rtems/people/chrisj/file-system/rfs-20100218.tar.gz RFS test application] running on a MCF5235 lists 3 block type devices:

 RTEMS SHELL (Ver.1.0-FRC):/dev/console. Feb 20 2010. 'help' to list commands.
 [/] # ls -las dev
 total 0
 0 crwxr-xr-x  1 root  root  0, 0 Jan  1 00:00 console
 0 brwxr-xr-x  1 root  root  3, 0 Jan  1 00:00 fdda
 0 brwxr-xr-x  1 root  root  4, 0 Jan  1 00:00 nvda
 0 brwxr-xr-x  1 root  root  2, 0 Jan  1 00:00 rda
 0 crwxr-xr-x  1 root  root  0, 1 Jan  1 00:00 tty01

For this example we will use the flash disk. The flash disk on the MCF5235 lives on the single flash device on the board which is shared with the boot monitor that comes with the board. We assume this is a new board so erase the flash:

 [/] # fderase /dev/fdda
 erase flash disk: /dev/fdda
 flash disk erased successful

The {{{fderase</code> command can be found in the RFS test application. Next we format the disk with the RFS format command. This command is:

<i><b>mkrfs [-v] [-s blksz] [-b grpblk] [-i grpinode] [-I] [-o %inode] dev</b></i>[[BR]]
where:
;-v : Verbose.
;-s blksize : The file system block size.
;-b grpblk : Number of blocks in a group.
;-i grpinode : Number of inodes in a group.
;-I : Initialise the inodes.
;-o %inode : The percentage of blocks allocated to inodes in a group.
;dev : The device to format.

Next we format the flash disk with the default configuration parameters then mounting it:

 [/] # mkrfs /dev/fdda
 [/] # mkdir f
 [/] # mount -t rfs /dev/fdda /f
 mounted /dev/fdda -> /f
 [/] # ls f
 [/]

To see the format of the disk run the {{{debugrfs</code> command with the {{{data</code> sub-command:

 [/] # debugrfs /f data
 RFS Filesystem Data
              flags: 00000000
             blocks: 1510
         block size: 1024
               size: 1546240
   media block size: 512
         media size: 1546240
             inodes: 1458
         bad blocks: 0
   max. name length: 512
             groups: 1
       group blocks: 8192
       group inodes: 1458
   inodes per block: 18
   blocks per block: 256
      singly blocks: 1280
     doublly blocks: 327680
  max. held buffers: 5
        blocks used: 84 (5.5%)
        inodes used: 1 (0.0%)