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# Constants and Defined Types

This section covers constants and types defined for use by kernel drivers and modules.

## Constants

### Current Driver API Version

Declared in: <drivers/Drivers.h>

The `B_CUR_DRIVER_API_VERSION` constant indicates what version of the driver API your driver will be built to.

See also: "Symbols Drivers Export"

### Driver Control Opcodes

Declared in: <drivers/Drivers.h>

Constant | Meaning
`B_GET_DEVICE_SIZE` | Returns a size_t indicating the device size in bytes.
`B_SET_DEVICE_SIZE` | Sets the device size to the value pointed to by data.
`B_SET_NONBLOCKING_IO` | Sets the device to use nonblocking I/O.
`B_SET_BLOCKING_IO` | Sets the device to use blocking I/O.
`B_GET_READ_STATUS` | Returns `true` if the device can read without blocking, otherwise `false` .
`B_GET_WRITE_STATUS` | Returns `true` if the device can write without blocking, otherwise `false` .
`B_GET_GEOMETRY` | Fills out the specified device_geometry structure to describe the device.
`B_GET_DRIVER_FOR_DEVICE` | Returns the path of the driver executable handling the device.
`B_GET_PARTITION_INFO` | Returns a partition_info structure for the device.
`B_SET_PARTITION` | Creates a user-defined partition. data points to a partition_info structure.
`B_FORMAT_DEVICE` | Formats the device. data should point to a boolean value. If this is `true` , the device is formatted low-level. If it's `false` , <<<unclear>>>
`B_EJECT_DEVICE` | Ejects the device.
`B_GET_ICON` | Fills out the specified device_icon structure to describe the device's icon.
`B_GET_BIOS_GEOMETRY` | Fills out a device_geometry structure to describe the device as the BIOS sees it.
`B_GET_MEDIA_STATUS` | Gets the status of the media in the device by placing a status_t at the location pointed to by data.
`B_LOAD_MEDIA` | Loads the media, if this is supported. <<<what does that mean?>>>
`B_GET_BIOS_DRIVE_ID` | Returns the BIOS ID for the device.
`B_SET_UNINTERRUPTABLE_IO` | Prevents control-C from interrupting I/O.
`B_SET_INTERRUPTABLE_IO` | Allows control-C to interrupt I/O.
`B_FLUSH_DRIVE_CACHE` | Flushes the drive's cache.
`B_GET_NEXT_OPEN_DEVICE` | Iterates through open devices; data points to an `open_device_iterator` .
`B_ADD_FIXED_DRIVER` | For internal use only.
`B_REMOVE_FIXED_DRIVER` | For internal use only.
`B_AUDIO_DRIVER_BASE` | Base for codes in audio_driver.h.
`B_MIDI_DRIVER_BASE` | Base for codes in midi_driver.h.
`B_JOYSTICK_DRIVER_BASE` | Base for codes in joystick.h.
`B_GRAPHIC_DRIVER_BASE` | Base for codes in graphic_driver.h.
`B_DEVICE_OP_CODES_END` | End of Be-defined control IDs.

`B_GET_MEDIA_STATUS` can return the following values:

## Defined Types

### device_geometry

Declared in: <drivers/Drivers.h>

typedef struct { uint32 `bytes_per_sector` ; uint32 `sectors_per_track` ; uint32 `cylinder_count` ; uint32 `head_count` ; uchar `device_type` ; bool `removable` ; bool `read_only` ; bool `write_once` ; } `device_geometry`

The device_geometry structure is returned by the `B_GET_GEOMETRY` driver control function. Its fields are:

- bytes_per_sector indicates how many bytes each sector of the disk contains.

- sectors_per_track indicates how many sectors each disk track contains.

- cylinder_count indicates the number of cylinders the disk contains.

- head_count indicates how many heads the disk has.

- device_type specifies the type of device; there's a list of device type definitions below.

- removable is `true` if the device's media can be removed from the drive, and is `false` otherwise.

- read_only is `true` if the media is read-only (such as CD-ROM), or `false` if the media can be both read from and written .

- write_once is `true` if the media can only be written to once (such as CD-recordable), or `false` if there's no limit to the number of times the media can be written to.

If you need to compute the total size of the device in bytes, you can obtain this figure using the following simple formula:

       disk_size = geometry.cylinder_count * geometry.sectors_per_track *
                geometry.head_count * geometry.bytes_per_sector;

The device type returned in device_type is:

Constant | Meaning
`B_DISK` | Hard disk, floppy disk, etc.
`B_TAPE` | Tape drive
`B_PRINTER` | Printer
`B_CPU` | CPU device
`B_WORM` | Write-once, read-many device (like CD-recordable)
`B_CD` | CD-ROM
`B_SCANNER` | Scanner
`B_OPTICAL` | Optical device
`B_JUKEBOX` | Jukebox device
`B_NETWORK` | Network device

### device_hooks

Declared in: <drivers/Drivers.h>

typedef struct { device_open_hook `open` ; device_close_hook `close` ; device_free_hook `free` ; device_control_hook `control` ; device_read_hook `read` ; device_write_hook `write` ; device_select_hook `select` ; device_deselect_hook `deselect` ; device_readv_hook `readv` ; device_writev_hook `writev` ; } `device_hooks`

This structure is used by device drivers to export their function hooks to the kernel.

### device_icon

Declared in: <drivers/Drivers.h>

typedef struct { int32 `icon_size` ; void *`icon_data` ; } `device_icon`

When you want to obtain an icon for a specific device, call `ioctl()` on the open device, specifying the `B_GET_ICON` opcode. Pass in data a pointer to a device_icon structure in which icon_size indicates the size of icon you want and icon_data points to a buffer large enough to receive the icon's data.

icon_size can be either B_MINI_ICON, in which case the buffer pointed to by icon_data should be large enough to receive a 16x16 8-bit bitmap (256-byte), or B_LARGE_ICON, in which case the buffer should be large enough to receive a 32x32 8-bit bitmap (1024-byte). The most obvious way to set up this buffer would be to create a BBitmap of the appropriate size and color depth and use its buffer, like this:

       BBitmap bits(BRect(0, 0, B_MINI_ICON-1, B_MINI_ICON-1, 0, B_CMAP8));
       device_icon iconrec;

       iconrec.icon_size = B_MINI_ICON;
       iconrec.icon_data = bits.Bits();
       status_t err = ioctl(dev_fd, B_GET_ICON, &iconrec);
       if (err == B_OK) {
          /* enjoy the icon */
          ...
          view->DrawBitmap(bits);
       } else {
          /* I don't like icons anyway */
          }

### driver_path

Declared in: <drivers/Drivers.h>

typedef char `driver_path` [256];

Used by the `B_GET_DRIVER_FOR_DEVICE` control function to return the pathname of the specified device.

### open_device_iterator

Declared in: <drivers/Drivers.h>

typedef struct { uint32 `cookie` ; char `device` [256]; } `open_device_iterator`

Used by the `B_GET_NEXT_OPEN_DEVICE` control function. The first time you call this function, your open_device_iterator should have cookie initialized to 0. Then just keep calling it over and over; each time you'll get the name of the next open device. When an error is returned, you're done.

### partition_info

Declared in: <drivers/Drivers.h>

typedef struct { off_t `offset` ; off_t `size` ; int32 `logical_block_size` ; int32 `session` ; int32 `partition` ; char `device` [256]; } `partition_info`

The partition_info structure describes a disk partition, and is used by the `B_GET_PARTITION_INFO` and `B_SET_PARTITION` control commands.

The fields are:

- offset is the offset, in bytes, from the beginning of the disk to the beginning of the partition.

- size is the size, in bytes, of the partition.

- logical_block_size is the block size with which the file system was written to the partition.

- session and partition are the session and partition ID numbers for the partition.

- device is the pathname of the physical device on which the partition is located.

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