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AIX Version 4 Files Reference
omd Special File
Purpose
Provides access to the read/write optical
device driver.
Description
The omd special file provides block
and character (raw) access to disks in the read/write optical drive.
The r prefix on a special file name
means that the drive is accessed as a raw device rather than a block device.
Performing raw I/O with an optical disk requires that all data transfers be in
multiples of the optical-disk logical block length. Also, all lseek subroutines that are made to the raw read/write optical device driver must
set the file offset pointer to a value that is a multiple of the specified
logical block size.
Read/Write Optical Device Driver
Read/write optical disks, used in
read/write optical drives, are media that provide storage for large amounts of
data. Block access to optical disks is achieved through the special files
/dev/omd0, /dev/omd1, ... /dev/omdn. Character
access is provided through the special files /dev/romd0,
/dev/romd1, ... /dev/romdn.
When a read/write optical disk is ejected from
the drive for a mounted read/write optical file system, the files on the
optical disk can no longer be accessed. Before attempting to access these files
again, perform the following steps for a file system mounted from the
read/write optical disk:
- Stop processes that have files open on the
file system.
- Move processes that have current directories
on the file system.
- Unmount the file system.
- Remount the file system after reinserting the
media.
If these actions do not work, perform a forced
unmount of the file system; then, remount the file system.
Note: Reinserting the
read/write optical disk will not fix the problem. Stop all
InfoExplorer processes (graphical and ASCII), and then forcibly
unmount the file system. Then remount the file system. After performing this
procedure, you can restart InfoExplorer and any man commands.
Device-Dependent Subroutines
Most read/write optical operations are
implemented using the open, read, write, and close
subroutines. However, for some purposes, use of the openx (extended)
subroutine is required.
The openx Subroutine
The openx subroutine is supported
to provide additional functions to the open sequence. Appropriate
authority is required for execution. If an attempt is made to run the
openx subroutine without the proper authority, the subroutine returns a
value of -1 and sets the errno global variable to a value of
EPERM.
The ioctl Subroutine
The ioctl subroutine IOCINFO
operation returns the devinfo structure defined in the
/usr/include/sys/devinfo.h file. The IOCINFO operation is the only
operation defined for all device drivers that use the ioctl subroutine.
Other ioctl operations are specific for the type of device driver.
Diagnostic mode is not required for the IOCINFO operation.
Error Conditions
Possible errno values for
ioctl, open, read, and write subroutines when using
the omd special file include:
EACCES |
Indicates one of the following circumstances:
- An attempt was made to open a device
currently open in Diagnostic or Exclusive Access mode.
- An attempt was made to open a Diagnostic mode
session on a device already open.
- The user attempted a subroutine other than an
ioctl or close subroutine while in Diagnostic mode.
- A DKIOCMD operation was attempted on a
device not in Diagnostic mode.
- A DKFORMAT operation was attempted on a
device not in Exclusive Access mode.
|
EBUSY |
Indicates one of the following circumstances:
- The target device is reserved by another
initiator.
- An attempt was made to open a session in
Exclusive Access mode on a device already opened.
|
EFAULT |
Indicates an illegal user address. |
EFORMAT |
Indicates the target device has unformatted media or media in an
incompatible format. |
EINVAL |
Indicates one of the following circumstances:
- The read or write subroutine
supplied an nbyte parameter that is not an even multiple of the block
size.
- A sense data buffer length of greater than 255
bytes is not valid for a DKIOWRSE or DKIORDSE ioctl
subroutine operation.
- The data buffer length exceeded the maximum
defined in the devinfo structure for a DKIORDSE, DKIOWRSE,
or DKIOCMD ioctl subroutine operation.
- An unsupported ioctl subroutine
operation was attempted.
- An attempt was made to configure a device that
is still open.
- An illegal configuration command has been
given.
- A DKPMR (Prevent Media Removal),
DKAMR (Allow Media Removal), or DKEJECT (Eject Media) command was
sent to a device that does not support removable media.
- A DKEJECT (Eject Media) command was
sent to a device that currently has its media locked in the drive.
|
EIO |
Indicates one of the following circumstances:
- The target device cannot be located or is
not responding.
- The target device has indicated an unrecovered
hardware error.
|
EMEDIA |
Indicates one of the following circumstances:
- The target device has indicated an
unrecovered media error.
- The media was changed.
|
EMFILE |
Indicates an open operation was attempted for an adapter that
already has the maximum permissible number of opened devices. |
ENODEV |
Indicates one of the following circumstances:
- An attempt was made to access an undefined
device.
- An attempt was made to close an undefined
device.
|
ENOTREADY |
Indicates no read/write optical disk is in the drive. |
ENXIO |
Indicates one of the following circumstances:
- The ioctl subroutine supplied an
invalid parameter.
- A read or write operation was
attempted beyond the end of the physical volume.
|
EPERM |
Indicates the attempted subroutine requires appropriate
authority. |
ESTALE |
Indicates a read-only optical disk was ejected (without first being
closed by the user) and then either reinserted or replaced with a second
disk. |
ETIMEDOUT |
Indicates an I/O operation has exceeded the given timer value. |
EWRPROTECT |
Indicates one of the following circumstances:
- An open operation requesting
read/write mode was attempted on read-only media.
- A write operation was attempted to
read-only media.
|
Implementation Specifics
The scdisk SCSI Device Driver provides
more information about implementation specifics.
The omd special file is part of Base
Operating System (BOS) Runtime.
Files
/dev/romd0,
/dev/romd1,..., /dev/romdn |
Provides character access to the read/write optical device driver. |
/dev/omd0,
/dev/omd1,..., /dev/omdn |
Provides block access to the read/write optical device driver. |
Related Information
Special Files Overview.
scdisk SCSI Device Driver.
The close subroutine, ioctl subroutine,
lseek subroutine,
open subroutine, read subroutine, write subroutine.
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