Summary of HDIO_ ioctl calls¶

Edward A. Falk <efalk@google.com>

November, 2004

This document attempts to describe the ioctl(2) calls supported by the HD/IDE layer. These are by-and-large implemented (as of Linux 2.6) in drivers/ide/ide.c and drivers/block/scsi_ioctl.c

ioctl values are listed in <linux/hdreg.h>. As of this writing, they are as follows:

ioctls that pass argument pointers to user space:

HDIO_GETGEO get device geometry

HDIO_GET_UNMASKINTR get current unmask setting

HDIO_GET_MULTCOUNT get current IDE blockmode setting

HDIO_GET_QDMA get use-qdma flag

HDIO_SET_XFER set transfer rate via proc

HDIO_OBSOLETE_IDENTITY OBSOLETE, DO NOT USE

HDIO_GET_KEEPSETTINGS get keep-settings-on-reset flag

HDIO_GET_32BIT get current io_32bit setting

HDIO_GET_NOWERR get ignore-write-error flag

HDIO_GET_DMA get use-dma flag

HDIO_GET_NICE get nice flags

HDIO_GET_IDENTITY get IDE identification info

HDIO_GET_WCACHE get write cache mode on|off

HDIO_GET_ACOUSTIC get acoustic value

HDIO_GET_ADDRESS get sector addressing mode

HDIO_GET_BUSSTATE get the bus state of the hwif

HDIO_TRISTATE_HWIF execute a channel tristate

HDIO_DRIVE_RESET execute a device reset

HDIO_DRIVE_TASKFILE execute raw taskfile

HDIO_DRIVE_TASK execute task and special drive command

HDIO_DRIVE_CMD execute a special drive command

HDIO_DRIVE_CMD_AEB HDIO_DRIVE_TASK

ioctls that pass non-pointer values:

HDIO_SET_MULTCOUNT change IDE blockmode

HDIO_SET_UNMASKINTR permit other irqs during I/O

HDIO_SET_KEEPSETTINGS keep ioctl settings on reset

HDIO_SET_32BIT change io_32bit flags

HDIO_SET_NOWERR change ignore-write-error flag

HDIO_SET_DMA change use-dma flag

HDIO_SET_PIO_MODE reconfig interface to new speed

HDIO_SCAN_HWIF register and (re)scan interface

HDIO_SET_NICE set nice flags

HDIO_UNREGISTER_HWIF unregister interface

HDIO_SET_WCACHE change write cache enable-disable

HDIO_SET_ACOUSTIC change acoustic behavior

HDIO_SET_BUSSTATE set the bus state of the hwif

HDIO_SET_QDMA change use-qdma flag

HDIO_SET_ADDRESS change lba addressing modes

HDIO_SET_IDE_SCSI Set scsi emulation mode on/off

HDIO_SET_SCSI_IDE not implemented yet

The information that follows was determined from reading kernel source code. It is likely that some corrections will be made over time.

General:

Unless otherwise specified, all ioctl calls return 0 on success and -1 with errno set to an appropriate value on error.

Unless otherwise specified, all ioctl calls return -1 and set errno to EFAULT on a failed attempt to copy data to or from user address space.

Unless otherwise specified, all data structures and constants are defined in <linux/hdreg.h>

HDIO_GETGEO

get device geometry

usage:

struct hd_geometry geom;

ioctl(fd, HDIO_GETGEO, &geom);

inputs:

none

outputs:

hd_geometry structure containing:

heads	number of heads
sectors	number of sectors/track
cylinders	number of cylinders, mod 65536
start	starting sector of this partition.

error returns:

EINVAL

if the device is not a disk drive or floppy drive, or if the user passes a null pointer

notes:

Not particularly useful with modern disk drives, whose geometry is a polite fiction anyway. Modern drives are addressed purely by sector number nowadays (lba addressing), and the drive geometry is an abstraction which is actually subject to change. Currently (as of Nov 2004), the geometry values are the “bios” values – presumably the values the drive had when Linux first booted.

In addition, the cylinders field of the hd_geometry is an unsigned short, meaning that on most architectures, this ioctl will not return a meaningful value on drives with more than 65535 tracks.

The start field is unsigned long, meaning that it will not contain a meaningful value for disks over 219 Gb in size.

HDIO_GET_UNMASKINTR

get current unmask setting

usage:

long val;

ioctl(fd, HDIO_GET_UNMASKINTR, &val);

inputs:: none
outputs:: The value of the drive’s current unmask setting

HDIO_SET_UNMASKINTR

permit other irqs during I/O

usage:

unsigned long val;

ioctl(fd, HDIO_SET_UNMASKINTR, val);

inputs:

New value for unmask flag

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_GET_MULTCOUNT

get current IDE blockmode setting

usage:

long val;

ioctl(fd, HDIO_GET_MULTCOUNT, &val);

inputs:: none
outputs:: The value of the current IDE block mode setting. This controls how many sectors the drive will transfer per interrupt.

HDIO_SET_MULTCOUNT

change IDE blockmode

usage:

int val;

ioctl(fd, HDIO_SET_MULTCOUNT, val);

inputs:

New value for IDE block mode setting. This controls how many sectors the drive will transfer per interrupt.

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range supported by disk.
EBUSY Controller busy or blockmode already set.
EIO Drive did not accept new block mode.

notes:

Source code comments read:

This is tightly woven into the driver->do_special cannot
touch.  DON'T do it again until a total personality rewrite
is committed.

If blockmode has already been set, this ioctl will fail with -EBUSY

HDIO_GET_QDMA

get use-qdma flag

Not implemented, as of 2.6.8.1

HDIO_SET_XFER

set transfer rate via proc

Not implemented, as of 2.6.8.1

HDIO_OBSOLETE_IDENTITY

OBSOLETE, DO NOT USE

Same as HDIO_GET_IDENTITY (see below), except that it only returns the first 142 bytes of drive identity information.

HDIO_GET_IDENTITY

get IDE identification info

usage:

unsigned char identity[512];

ioctl(fd, HDIO_GET_IDENTITY, identity);

inputs:

none

outputs:

ATA drive identity information. For full description, see the IDENTIFY DEVICE and IDENTIFY PACKET DEVICE commands in the ATA specification.

error returns:

EINVAL Called on a partition instead of the whole disk device
ENOMSG IDENTIFY DEVICE information not available

notes:

Returns information that was obtained when the drive was probed. Some of this information is subject to change, and this ioctl does not re-probe the drive to update the information.

This information is also available from /proc/ide/hdX/identify

HDIO_GET_KEEPSETTINGS

get keep-settings-on-reset flag

usage:

long val;

ioctl(fd, HDIO_GET_KEEPSETTINGS, &val);

inputs:: none
outputs:: The value of the current “keep settings” flag
notes:: When set, indicates that kernel should restore settings after a drive reset.

HDIO_SET_KEEPSETTINGS

keep ioctl settings on reset

usage:

long val;

ioctl(fd, HDIO_SET_KEEPSETTINGS, val);

inputs:

New value for keep_settings flag

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_GET_32BIT

get current io_32bit setting

usage:

long val;

ioctl(fd, HDIO_GET_32BIT, &val);

inputs:: none
outputs:: The value of the current io_32bit setting
notes:: 0=16-bit, 1=32-bit, 2,3 = 32bit+sync

HDIO_GET_NOWERR

get ignore-write-error flag

usage:

long val;

ioctl(fd, HDIO_GET_NOWERR, &val);

inputs:: none
outputs:: The value of the current ignore-write-error flag

HDIO_GET_DMA

get use-dma flag

usage:

long val;

ioctl(fd, HDIO_GET_DMA, &val);

inputs:: none
outputs:: The value of the current use-dma flag

HDIO_GET_NICE

get nice flags

usage:

long nice;

ioctl(fd, HDIO_GET_NICE, &nice);

inputs:

none

outputs:

The drive’s “nice” values.

notes:

Per-drive flags which determine when the system will give more bandwidth to other devices sharing the same IDE bus.

See <linux/hdreg.h>, near symbol IDE_NICE_DSC_OVERLAP.

HDIO_SET_NICE

set nice flags

usage:

unsigned long nice;

...
ioctl(fd, HDIO_SET_NICE, nice);

inputs:

bitmask of nice flags.

outputs:

none

error returns:

EACCES Access denied: requires CAP_SYS_ADMIN
EPERM Flags other than DSC_OVERLAP and NICE_1 set.
EPERM DSC_OVERLAP specified but not supported by drive

notes:

This ioctl sets the DSC_OVERLAP and NICE_1 flags from values provided by the user.

Nice flags are listed in <linux/hdreg.h>, starting with IDE_NICE_DSC_OVERLAP. These values represent shifts.

HDIO_GET_WCACHE

get write cache mode on|off

usage:

long val;

ioctl(fd, HDIO_GET_WCACHE, &val);

inputs:: none
outputs:: The value of the current write cache mode

HDIO_GET_ACOUSTIC

get acoustic value

usage:

long val;

ioctl(fd, HDIO_GET_ACOUSTIC, &val);

inputs:: none
outputs:: The value of the current acoustic settings
notes:: See HDIO_SET_ACOUSTIC

HDIO_GET_ADDRESS

usage:

long val;

ioctl(fd, HDIO_GET_ADDRESS, &val);

inputs:

none

outputs:

The value of the current addressing mode:

0	28-bit
1	48-bit
2	48-bit doing 28-bit
3	64-bit

HDIO_GET_BUSSTATE

get the bus state of the hwif

usage:

long state;

ioctl(fd, HDIO_SCAN_HWIF, &state);

inputs:

none

outputs:

Current power state of the IDE bus. One of BUSSTATE_OFF, BUSSTATE_ON, or BUSSTATE_TRISTATE

error returns:

EACCES Access denied: requires CAP_SYS_ADMIN

HDIO_SET_BUSSTATE

set the bus state of the hwif

usage:

int state;

...
ioctl(fd, HDIO_SCAN_HWIF, state);

inputs:

Desired IDE power state. One of BUSSTATE_OFF, BUSSTATE_ON, or BUSSTATE_TRISTATE

outputs:

none

error returns:

EACCES Access denied: requires CAP_SYS_RAWIO
EOPNOTSUPP Hardware interface does not support bus power control

HDIO_TRISTATE_HWIF

execute a channel tristate

Not implemented, as of 2.6.8.1. See HDIO_SET_BUSSTATE

HDIO_DRIVE_RESET

execute a device reset

usage:

int args[3]

...
ioctl(fd, HDIO_DRIVE_RESET, args);

inputs:

none

outputs:

none

error returns:

EACCES Access denied: requires CAP_SYS_ADMIN
ENXIO No such device: phy dead or ctl_addr == 0
EIO I/O error: reset timed out or hardware error

notes:

Execute a reset on the device as soon as the current IO operation has completed.

Executes an ATAPI soft reset if applicable, otherwise executes an ATA soft reset on the controller.

HDIO_DRIVE_TASKFILE

execute raw taskfile

Note:: If you don’t have a copy of the ANSI ATA specification handy, you should probably ignore this ioctl.

Execute an ATA disk command directly by writing the “taskfile” registers of the drive. Requires ADMIN and RAWIO access privileges.

usage:

struct {

  ide_task_request_t req_task;
  u8 outbuf[OUTPUT_SIZE];
  u8 inbuf[INPUT_SIZE];
} task;
memset(&task.req_task, 0, sizeof(task.req_task));
task.req_task.out_size = sizeof(task.outbuf);
task.req_task.in_size = sizeof(task.inbuf);
...
ioctl(fd, HDIO_DRIVE_TASKFILE, &task);
...

inputs:

(See below for details on memory area passed to ioctl.)

io_ports[8] values to be written to taskfile registers

hob_ports[8] high-order bytes, for extended commands.

out_flags flags indicating which registers are valid

in_flags flags indicating which registers should be returned

data_phase see below

req_cmd command type to be executed

out_size size of output buffer

outbuf buffer of data to be transmitted to disk

inbuf buffer of data to be received from disk (see [1])

outputs:

io_ports[] values returned in the taskfile registers

hob_ports[] high-order bytes, for extended commands.

out_flags flags indicating which registers are valid (see [2])

in_flags flags indicating which registers should be returned

outbuf buffer of data to be transmitted to disk (see [1])

inbuf buffer of data to be received from disk

error returns:

EACCES CAP_SYS_ADMIN or CAP_SYS_RAWIO privilege not set.
ENOMSG Device is not a disk drive.
ENOMEM Unable to allocate memory for task
EFAULT req_cmd == TASKFILE_IN_OUT (not implemented as of 2.6.8)
EPERM

req_cmd == TASKFILE_MULTI_OUT and drive multi-count not yet set.
EIO Drive failed the command.

notes:

[1] READ THE FOLLOWING NOTES CAREFULLY. THIS IOCTL IS FULL OF GOTCHAS. Extreme caution should be used with using this ioctl. A mistake can easily corrupt data or hang the system.

[2] Both the input and output buffers are copied from the user and written back to the user, even when not used.

[3] If one or more bits are set in out_flags and in_flags is zero, the following values are used for in_flags.all and written back into in_flags on completion.

IDE_TASKFILE_STD_IN_FLAGS | (IDE_HOB_STD_IN_FLAGS << 8) if LBA48 addressing is enabled for the drive

IDE_TASKFILE_STD_IN_FLAGS if CHS/LBA28

The association between in_flags.all and each enable bitfield flips depending on endianness; fortunately, TASKFILE only uses inflags.b.data bit and ignores all other bits. The end result is that, on any endian machines, it has no effect other than modifying in_flags on completion.

[4] The default value of SELECT is (0xa0|DEV_bit|LBA_bit) except for four drives per port chipsets. For four drives per port chipsets, it’s (0xa0|DEV_bit|LBA_bit) for the first pair and (0x80|DEV_bit|LBA_bit) for the second pair.

[5] The argument to the ioctl is a pointer to a region of memory containing a ide_task_request_t structure, followed by an optional buffer of data to be transmitted to the drive, followed by an optional buffer to receive data from the drive.

Command is passed to the disk drive via the ide_task_request_t structure, which contains these fields:

io_ports[8] values for the taskfile registers

hob_ports[8] high-order bytes, for extended commands

out_flags flags indicating which entries in the io_ports[] and hob_ports[] arrays contain valid values. Type ide_reg_valid_t.

in_flags flags indicating which entries in the io_ports[] and hob_ports[] arrays are expected to contain valid values on return.

data_phase See below

req_cmd Command type, see below

out_size output (user->drive) buffer size, bytes

in_size input (drive->user) buffer size, bytes

When out_flags is zero, the following registers are loaded.

HOB_FEATURE If the drive supports LBA48

HOB_NSECTOR If the drive supports LBA48

HOB_SECTOR If the drive supports LBA48

HOB_LCYL If the drive supports LBA48

HOB_HCYL If the drive supports LBA48

FEATURE

NSECTOR

SECTOR

LCYL

HCYL

SELECT First, masked with 0xE0 if LBA48, 0xEF otherwise; then, or’ed with the default value of SELECT.

If any bit in out_flags is set, the following registers are loaded.

HOB_DATA If out_flags.b.data is set. HOB_DATA will travel on DD8-DD15 on little endian machines and on DD0-DD7 on big endian machines.

DATA If out_flags.b.data is set. DATA will travel on DD0-DD7 on little endian machines and on DD8-DD15 on big endian machines.

HOB_NSECTOR If out_flags.b.nsector_hob is set

HOB_SECTOR If out_flags.b.sector_hob is set

HOB_LCYL If out_flags.b.lcyl_hob is set

HOB_HCYL If out_flags.b.hcyl_hob is set

FEATURE If out_flags.b.feature is set

NSECTOR If out_flags.b.nsector is set

SECTOR If out_flags.b.sector is set

LCYL If out_flags.b.lcyl is set

HCYL If out_flags.b.hcyl is set

SELECT Or’ed with the default value of SELECT and loaded regardless of out_flags.b.select.

Taskfile registers are read back from the drive into {io|hob}_ports[] after the command completes iff one of the following conditions is met; otherwise, the original values will be written back, unchanged.

The drive fails the command (EIO).

One or more than one bits are set in out_flags.

The requested data_phase is TASKFILE_NO_DATA.

HOB_DATA If in_flags.b.data is set. It will contain DD8-DD15 on little endian machines and DD0-DD7 on big endian machines.

DATA If in_flags.b.data is set. It will contain DD0-DD7 on little endian machines and DD8-DD15 on big endian machines.

HOB_FEATURE If the drive supports LBA48

HOB_NSECTOR If the drive supports LBA48

HOB_SECTOR If the drive supports LBA48

HOB_LCYL If the drive supports LBA48

HOB_HCYL If the drive supports LBA48

NSECTOR

SECTOR

LCYL

HCYL

The data_phase field describes the data transfer to be performed. Value is one of:

TASKFILE_IN

TASKFILE_MULTI_IN

TASKFILE_OUT

TASKFILE_MULTI_OUT

TASKFILE_IN_OUT

TASKFILE_IN_DMA

TASKFILE_IN_DMAQ == IN_DMA (queueing not supported)

TASKFILE_OUT_DMA

TASKFILE_OUT_DMAQ == OUT_DMA (queueing not supported)

TASKFILE_P_IN unimplemented

TASKFILE_P_IN_DMA unimplemented

TASKFILE_P_IN_DMAQ unimplemented

TASKFILE_P_OUT unimplemented

TASKFILE_P_OUT_DMA unimplemented

TASKFILE_P_OUT_DMAQ unimplemented

The req_cmd field classifies the command type. It may be one of:

IDE_DRIVE_TASK_NO_DATA

IDE_DRIVE_TASK_SET_XFER unimplemented

IDE_DRIVE_TASK_IN

IDE_DRIVE_TASK_OUT unimplemented

IDE_DRIVE_TASK_RAW_WRITE

[6] Do not access {in|out}_flags->all except for resetting all the bits. Always access individual bit fields. ->all value will flip depending on endianness. For the same reason, do not use IDE_{TASKFILE|HOB}_STD_{OUT|IN}_FLAGS constants defined in hdreg.h.

HDIO_DRIVE_CMD

execute a special drive command

Note: If you don’t have a copy of the ANSI ATA specification handy, you should probably ignore this ioctl.

usage:

u8 args[4+XFER_SIZE];

...
ioctl(fd, HDIO_DRIVE_CMD, args);

inputs:

Commands other than WIN_SMART:

args[0]	COMMAND
args[1]	NSECTOR
args[2]	FEATURE
args[3]	NSECTOR

WIN_SMART:

args[0]	COMMAND
args[1]	SECTOR
args[2]	FEATURE
args[3]	NSECTOR

outputs:

args[] buffer is filled with register values followed by any

data returned by the disk.

args[0] status

args[1] error

args[2] NSECTOR

args[3] undefined

args[4+] NSECTOR * 512 bytes of data returned by the command.

error returns:

EACCES Access denied: requires CAP_SYS_RAWIO
ENOMEM Unable to allocate memory for task
EIO Drive reports error

notes:

[1] For commands other than WIN_SMART, args[1] should equal args[3]. SECTOR, LCYL and HCYL are undefined. For WIN_SMART, 0x4f and 0xc2 are loaded into LCYL and HCYL respectively. In both cases SELECT will contain the default value for the drive. Please refer to HDIO_DRIVE_TASKFILE notes for the default value of SELECT.

[2] If NSECTOR value is greater than zero and the drive sets DRQ when interrupting for the command, NSECTOR * 512 bytes are read from the device into the area following NSECTOR. In the above example, the area would be args[4..4+XFER_SIZE]. 16bit PIO is used regardless of HDIO_SET_32BIT setting.

[3] If COMMAND == WIN_SETFEATURES && FEATURE == SETFEATURES_XFER && NSECTOR >= XFER_SW_DMA_0 && the drive supports any DMA mode, IDE driver will try to tune the transfer mode of the drive accordingly.

HDIO_DRIVE_TASK

execute task and special drive command

Note: If you don’t have a copy of the ANSI ATA specification handy, you should probably ignore this ioctl.

usage:

u8 args[7];

...
ioctl(fd, HDIO_DRIVE_TASK, args);

inputs:

Taskfile register values:

args[0]	COMMAND
args[1]	FEATURE
args[2]	NSECTOR
args[3]	SECTOR
args[4]	LCYL
args[5]	HCYL
args[6]	SELECT

outputs:

Taskfile register values:

args[0]	status
args[1]	error
args[2]	NSECTOR
args[3]	SECTOR
args[4]	LCYL
args[5]	HCYL
args[6]	SELECT

error returns:

EACCES Access denied: requires CAP_SYS_RAWIO
ENOMEM Unable to allocate memory for task
ENOMSG Device is not a disk drive.
EIO Drive failed the command.

notes:

[1] DEV bit (0x10) of SELECT register is ignored and the appropriate value for the drive is used. All other bits are used unaltered.

HDIO_DRIVE_CMD_AEB

HDIO_DRIVE_TASK

Not implemented, as of 2.6.8.1

HDIO_SET_32BIT

change io_32bit flags

usage:

int val;

ioctl(fd, HDIO_SET_32BIT, val);

inputs:

New value for io_32bit flag

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 3]
EBUSY Controller busy

HDIO_SET_NOWERR

change ignore-write-error flag

usage:

int val;

ioctl(fd, HDIO_SET_NOWERR, val);

inputs:

New value for ignore-write-error flag. Used for ignoring

WRERR_STAT

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_SET_DMA

change use-dma flag

usage:

long val;

ioctl(fd, HDIO_SET_DMA, val);

inputs:

New value for use-dma flag

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_SET_PIO_MODE

reconfig interface to new speed

usage:

long val;

ioctl(fd, HDIO_SET_PIO_MODE, val);

inputs:

New interface speed.

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 255]
EBUSY Controller busy

HDIO_SCAN_HWIF

register and (re)scan interface

usage:

int args[3]

...
ioctl(fd, HDIO_SCAN_HWIF, args);

inputs:

args[0] io address to probe

args[1] control address to probe

args[2] irq number

outputs:

none

error returns:

EACCES Access denied: requires CAP_SYS_RAWIO
EIO Probe failed.

notes:

This ioctl initializes the addresses and irq for a disk controller, probes for drives, and creates /proc/ide interfaces as appropriate.

HDIO_UNREGISTER_HWIF

unregister interface

usage:

int index;

ioctl(fd, HDIO_UNREGISTER_HWIF, index);

inputs:

index index of hardware interface to unregister

outputs:

none

error returns:

EACCES Access denied: requires CAP_SYS_RAWIO

notes:

This ioctl removes a hardware interface from the kernel.

Currently (2.6.8) this ioctl silently fails if any drive on the interface is busy.

HDIO_SET_WCACHE

change write cache enable-disable

usage:

int val;

ioctl(fd, HDIO_SET_WCACHE, val);

inputs:

New value for write cache enable

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_SET_ACOUSTIC

change acoustic behavior

usage:

int val;

ioctl(fd, HDIO_SET_ACOUSTIC, val);

inputs:

New value for drive acoustic settings

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 254]
EBUSY Controller busy

HDIO_SET_QDMA

change use-qdma flag

Not implemented, as of 2.6.8.1

HDIO_SET_ADDRESS

change lba addressing modes

usage:

int val;

ioctl(fd, HDIO_SET_ADDRESS, val);

inputs:

New value for addressing mode

0	28-bit
1	48-bit
2	48-bit doing 28-bit

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 2]
EBUSY Controller busy
EIO Drive does not support lba48 mode.

HDIO_SET_IDE_SCSI

usage:

long val;

ioctl(fd, HDIO_SET_IDE_SCSI, val);

inputs:

New value for scsi emulation mode (?)

outputs:

none

error return:

EINVAL Called on a partition instead of the whole disk device
EACCES Access denied: requires CAP_SYS_ADMIN
EINVAL value out of range [0 1]
EBUSY Controller busy

HDIO_SET_SCSI_IDE

Not implemented, as of 2.6.8.1