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 5.11) drivers/ata/libata-scsi.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_32BIT
get current io_32bit setting
HDIO_GET_IDENTITY
get IDE identification info
HDIO_DRIVE_TASKFILE
execute raw taskfile
HDIO_DRIVE_TASK
execute task and special drive command
HDIO_DRIVE_CMD
execute a special drive command
ioctls that pass non-pointer values:
HDIO_SET_32BIT
change io_32bit flags
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_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_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_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_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