disk(9)

NAME

disk - kernel disk storage API

SYNOPSIS

#include <geom/geom_disk.h>
struct *disk
disk_alloc(void);
void
disk_create(struct disk *disk, int version);
void
disk_destroy(struct disk *disk);

DESCRIPTION

The disk storage API permits kernel device drivers providing

access to
disk-like storage devices to advertise the device to other

kernel components, including GEOM(4) and devfs(5).

Each disk device is described by a struct disk structure,

which contains
a variety of parameters for the disk device, function point

ers for various methods that may be performed on the device, as well as

private data
storage for the device driver. In addition, some fields are

reserved for
use by GEOM in managing access to the device and its statis

tics.

GEOM has the ownership of struct disk, and drivers must al

locate storage
for it with the disk_alloc() function, fill in the fields

and call
disk_create() when the device is ready to service requests.

After calling disk_destroy(), the device driver is not allowed to ac

cess the contents of struct disk anymore.

The disk_create() function takes a second parameter,

version, which must
always be passed DISK_VERSION. If GEOM detects that the

driver is compiled against an unsupported version, it will ignore the de

vice and print
a warning on the console.

Descriptive Fields

The following fields identify the disk device described by

the structure
instance, and must be filled in prior to submitting the

structure to
disk_create() and may not be subsequently changed:

u_int d_flags

Optional flags indicating to the storage framework

what optional
features or descriptions the storage device driver

supports.
Currently supported flags are DISKFLAG_NEEDSGIANT

(maintained by
device driver), DISKFLAG_OPEN (maintained by storage

framework),
and DISKFLAG_CANDELETE (maintained by device driv

er).

const char * d_name

Holds the name of the storage device class, e.g.,

``ahd''. This
value typically uniquely identifies a particular

driver device,
and must not conflict with devices serviced by other

device
drivers.

u_int d_unit

Holds the instance of the storage device class,

e.g., ``4''.
This namespace is managed by the device driver, and

assignment of
unit numbers might be a property of probe order, or

in some cases
topology. Together, the d_name and d_unit values

will uniquely
identify a disk storage device.

Disk Device Methods

The following fields identify various disk device methods,

if implemented:

disk_open_t * d_open

Optional: invoked when the disk device is opened.

If no method
is provided, open will always succeed.

disk_close_t * d_close

Optional: invoked when the disk device is closed.

Although an
error code may be returned, the call should always

terminate any
state setup by the corresponding open method call.

disk_strategy_t * d_strategy

Mandatory: invoked when a new struct bio is to be

initiated on
the disk device.

disk_ioctl_t * d_ioctl

Optional: invoked when an I/O control operation is

initiated on
the disk device. Please note that for security rea

sons these
operations should not be able to affect other de

vices than the
one on which they are performed.

dumper_t * d_dump

Optional: if configured with dumpon(8), this func

tion is invoked
from a very restricted system state after a kernel

panic to
record a copy of the system RAM to the disk.

Mandatory Media Properties

The following fields identify the size and granularity of

the disk
device. These fields must stay stable from return of the

drivers open
method until the close method is called, but it is perfectly

legal to
modify them in the open method before returning.

u_int d_sectorsize

The sector size of the disk device in bytes.

off_t d_mediasize

The size of the disk device in bytes.

u_int d_maxsize

The maximum supported size in bytes of an I/O re

quest. Requests
larger than this size will be chopped up by GEOM.

Optional Media Properties

These optional fields can provide extra information about

the disk
device. Do not initialize these fields if the field/concept

does not
apply. These fields must stay stable from return of the

drivers open
method until the close method is called, but it is perfectly

legal to
modify them in the open method before returning.

u_int d_fwsectors, u_int d_fwheads

The number of sectors and heads advertised on the

disk device by
the firmware or BIOS. These values are almost uni

versally bogus,
but on some architectures necessary for the correct

calculation
of disk partitioning.

u_int d_stripeoffset, u_int d_stripesize

These two fields can be used to describe the width

and location
of natural performance boundaries for most disk

technologies.
Please see src/sys/geom/notes for details.

Driver Private Data

This field may be used by the device driver to store a

pointer to private
data to implement the disk service.

void * d_drv1

Private data pointer. Typically used to store a

pointer to the
drivers softc structure for this disk device.

SEE ALSO

GEOM(4), devfs(5)

AUTHORS

This manual page was written by Robert Watson.

BSD February 18, 2004

BSD