Block Device Drivers

Block device drivers have these properties:

  • include/nuttx/fs/fs.h. All structures and APIs needed to work with block drivers are provided in this header file.

  • struct block_operations. Each block device driver must implement an instance of struct block_operations. That structure defines a call table with the following methods:

  • int register_blockdriver(const char *path, const struct block_operations *bops, mode_t mode, void *priv);. Each block driver registers itself by calling register_blockdriver(), passing it the path where it will appear in the pseudo file system and it’s initialized instance of struct block_operations.

  • User Access. Users do not normally access block drivers directly, rather, they access block drivers indirectly through the mount() API. The mount() API binds a block driver instance with a file system and with a mountpoint. Then the user may use the block driver to access the file system on the underlying media. Example: See the cmd_mount() implementation in apps/nshlib/nsh_fscmds.c.

  • Accessing a Character Driver as a Block Device. See the loop device at drivers/loop.c. Example: See the cmd_losetup() implementation in apps/nshlib/nsh_fscmds.c.

  • Accessing a Block Driver as Character Device. See the Block-to-Character (BCH) conversion logic in drivers/bch/. Example: See the cmd_dd() implementation in apps/nshlib/nsh_ddcmd.c.

  • Examples. drivers/loop.c, drivers/mmcsd/mmcsd_spi.c, drivers/ramdisk.c, etc.