HP-UX Reference (11i v2 04/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

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disk(7) disk(7)

size is a hardware-dependent value that can be queried with the

DIOC_DESCRIBE ioctl call, which is

described below.

In addition to reading and writing data, the character-special ﬁle interface can used to obtain device

speciﬁc information and to perform special operations. These operations are controlled through use of

ioctl calls. Details related to these ioctls are contained in

<sys/diskio.h>.

The

DIOC_DESCRIBE

ioctl can be used to obtain device speciﬁc identiﬁcation information. The infor-

mation returned includes the disk’s model identiﬁcation, the disk interface type, maximum offset address,

and the disk’s logical block size.

The

DIOC_CAPACITY

ioctl can be used to obtain the capacity of a disk device in

DEV_BSIZE units.

(

DEV_BSIZE is deﬁned in <sys/param.h>

The

DIOC_EXCLUSIVE

ioctl can be used to obtain and release exclusive access to a disk device.

Exclusive access is required for some special operations, such as media reformatting, and may be desir-

able in other circumstances. The value one speciﬁes that exclusive access is requested. The value zero

speciﬁes the exclusive access should be released. Exclusive access causes other open requests to fail.

Exclusive access can only be granted when the device is not currently opened in block-mode and there is

only one open ﬁle table entry for that disk device (the one accessible to the exclusive access requester).

ERRORS

The following errors can be returned by a disk device driver call:

[EACCES] Required permission is denied for the the device or operation.

[ENXIO] If resulting from an

open() call, this indicates there is no device at the speciﬁed

address. For other calls, this indicates the speciﬁed address is out of range or the

device can no longer be accessed.

[EINVAL] From an

open() call: the device is not a disk device. For other calls: Invalid

request or parameter. Note that for legacy, 32-bit access, this error can result when

the size of the device overﬂows the argument of the DIOC_DESCRIBE

DIOC_CAPACITY ioctls.

[EIO] I/O error (e.g., media defect or device communication problem).

WARNINGS

The interaction of block-special and character-special ﬁle access to the same

BLKDEV_IOSIZE

-sized

block is not speciﬁed, and in general is unpredictable.

On some systems, having both a mounted ﬁle system and a block special ﬁle open on the same device can

cause unpredictable results; this should be avoided if possible. This is because it may be possible for

some ﬁles to have private buffers in some systems.

Although disk devices have historically had small (typically 512-byte) block sizes, some disk devices (such

as optical disks and disk arrays) have relatively large block sizes. Applications using direct raw disk

access should use

ioctl() calls to determine appropriate I/O operation sizes and alignments.

Any disk with removable media (for example, ﬂoppy or CD-ROM) containing a mounted ﬁle system

should not be removed prior to being unmounted. Removal of disk media containing mounted ﬁle systems

is likely to result in ﬁle system errors and system panics.

DEPENDENCIES

disc3

Devices whose logical block size is less than DEV_BSIZE must be accessed on DEV_BSIZE boun-

daries and with transfer sizes that are multiples of DEV_BSIZE. Disk ‘‘sections’’ 0 (zero) and 2

(two) have exchanged meanings with HP-UX Release 10.0 and beyond. Whole disk is section 0.

AUTHOR

disk was developed by HP and AT&T.