freebsd-skq/share/man/man9/disk.9

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.Dd September 26, 2003
.Dt DISK 9
.Os
.Sh NAME
.Nm disk
.Nd Kernel disk storage API
.Sh SYNOPSIS
.In geom/geom_disk.h
.Ft void
.Fo disk_create
.Fa "int unit"
.Fa "struct disk *disk"
.Fa "int flags"
.Fa "void *unused"
.Fa "void *unused2"
.Fc
.Ft void
.Fn disk_destroy "struct disk *disk"
.Sh 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
.Xr GEOM 4 ,
and
.Xr devfs 5 .
.Pp
Each disk device is described by a
.Vt "struct disk"
structure, which contains a variety of parameters for the disk device,
function pointers 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 statistics.
Because of storage driver framework private data stored in
.Vt "struct disk" ,
instances of the structure should be allocated out of writable, pre-zero'd
memory.
.Pp
Public fields in the structure will generally be assumed not to change once
the structure is submitted to
.Fn disk_create ,
and so no explicit locking is employed; drivers that change the values of
any of these fields do so at their own risk.
.Pp
Memory associated with the
.Vt "struct disk"
is owned by the device driver, but should not be released until after
the completion of a call to
.Fn disk_destroy .
.Ss Descriptive Fields
.Pp
The following fields identify the disk device described by the structure
instance, and must be filled in prior to submitting the structure to
.Fn disk_create :
.Bl -tag -width XXX
.It Vt u_int Va d_flags
Optional flags indicating to the storage framework what optional features
or descriptions the storage device driver supports.
Currently supported flags are
.Dv DISKFLAG_NOGIANT
(maintained by device driver),
.Dv DISKFLAG_OPEN
(maintained by storage framework),
and
.Dv DISKFLAG_CANDELETE
(maintained by device driver).
.Pp
.It Vt "const char *" Va d_name
Holds the name of the storage device class, e.g.,
.Dq ahd .
This value typically uniquely identifies a particular driver device,
and must not conflict with devices serviced by other device drivers.
.It Vt u_int Va d_unit
Holds the instance of the storage device class, e.g.,
.Dq 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
.Va d_name
and
.Va d_unit
values will uniquely identify a disk storage device.
.El
.Ss Disk Device Methods
The following fields identify various disk device methods, if implemented:
.Bl -tag -width XXX
.It Vt "disk_open_t *" Va d_open
Invoked when the disk device is opened.
.It Vt "disk_close_t *" Va d_close
Invoked when the disk device is closed.
.It Vt "disk_strategy_t *" Va d_strategy
Invoked when a new
.Vt struct bio
is to be initiated on the disk device.
.It Vt "disk_ioctl_t *" Va d_ioctl
Invoked when a I/O control operation is initiated on the disk device.
.It Vt "dumper_t *" Va d_dump
Invoked when a kernel crash dump is performed on the disk device.
.El
.Ss Media Properties
The following fields identify the size, layout, and other media properties
of the disk device.
.Bl -tag -width XXX
.It Vt u_int Va d_sectorsize
The sectorsize of the disk device.
.It Vt off_t Va d_mediasize
The size of the disk device in bytes.
.It Vt u_int Va d_fwsectors
The number of sectors advertised on the disk device by the firmware or
BIOS.
.It Vt u_int Va d_fwheads
The number of heads advertised on the disk device by the firmeware or
BIOS.
.It Vt u_int Va d_maxsize
The maximum I/O request the disk device supports.
.It Vt u_int Va d_stripeoffset
If the disk device supports an optimal stripe size and offset, such as
a RAID device, it may advertise that offset using this field.
.It Vt u_int Va d_stripesize
If the disk device supports an optimal stripe size and offset, such as
a RAID device, it may advertise that size using this field.
.El
.Ss Driver Private Data
This field may be used by the device driver to store a pointer to
private data to implement the disk service.
.Bl -tag -width XXX
.It Vt "void *" Va d_drv1
Private data pointer.
.El
.Sh SEE ALSO
.Xr GEOM 4 ,
.Xr devfs 5
.Sh AUTHORS
This manual page was written by
.An Robert Watson .