194 lines
7.0 KiB
Groff
194 lines
7.0 KiB
Groff
.\"
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.\" Copyright (c) 2003 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 18, 2004
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.Dt DISK 9
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.Os
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.Sh NAME
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.Nm disk
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.Nd kernel disk storage API
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.Sh SYNOPSIS
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.In geom/geom_disk.h
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.Ft struct disk *
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.Fn disk_alloc void
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.Ft void
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.Fn disk_create "struct disk *disk" "int version"
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.Ft void
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.Fn disk_destroy "struct disk *disk"
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.Sh DESCRIPTION
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The disk storage API permits kernel device drivers providing access to
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disk-like storage devices to advertise the device to other kernel
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components, including
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.Xr GEOM 4
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and
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.Xr devfs 5 .
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.Pp
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Each disk device is described by a
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.Vt "struct disk"
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structure, which contains a variety of parameters for the disk device,
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function pointers for various methods that may be performed on the device,
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as well as private data storage for the device driver.
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In addition, some fields are reserved for use by GEOM in managing access
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to the device and its statistics.
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.Pp
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GEOM has the ownership of
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.Vt "struct disk" ,
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and drivers must allocate storage for it with the
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.Fn disk_alloc
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function,
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fill in the fields and call
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.Fn disk_create
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when the device is ready to service requests.
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After calling
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.Fn disk_destroy ,
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the device driver is not allowed to access the contents of
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.Vt "struct disk"
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anymore.
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.Pp
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The
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.Fn disk_create
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function
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takes a second parameter,
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.Fa version ,
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which must always be passed
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.Dv DISK_VERSION .
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If GEOM detects that the driver is compiled against an unsupported version,
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it will ignore the device and print a warning on the console.
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.Ss Descriptive Fields
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The following fields identify the disk device described by the structure
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instance, and must be filled in prior to submitting the structure to
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.Fn disk_create
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and may not be subsequently changed:
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.Bl -tag -width indent
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.It Vt u_int Va d_flags
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Optional flags indicating to the storage framework what optional features
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or descriptions the storage device driver supports.
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Currently supported flags are
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.Dv DISKFLAG_NEEDSGIANT
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(maintained by device driver),
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.Dv DISKFLAG_OPEN
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(maintained by storage framework),
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.Dv DISKFLAG_CANDELETE
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(maintained by device driver),
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and
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.Dv DISKFLAG_CANFLUSHCACHE
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(maintained by device driver).
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.It Vt "const char *" Va d_name
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Holds the name of the storage device class, e.g.,
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.Dq Li ahd .
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This value typically uniquely identifies a particular driver device,
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and must not conflict with devices serviced by other device drivers.
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.It Vt u_int Va d_unit
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Holds the instance of the storage device class, e.g.,
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.Dq Li 4 .
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This namespace is managed by the device driver, and assignment of unit
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numbers might be a property of probe order, or in some cases topology.
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Together, the
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.Va d_name
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and
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.Va d_unit
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values will uniquely identify a disk storage device.
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.El
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.Ss Disk Device Methods
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The following fields identify various disk device methods, if implemented:
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.Bl -tag -width indent
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.It Vt "disk_open_t *" Va d_open
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Optional: invoked when the disk device is opened.
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If no method is provided, open will always succeed.
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.It Vt "disk_close_t *" Va d_close
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Optional: invoked when the disk device is closed.
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Although an error code may be returned, the call should always terminate
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any state setup by the corresponding open method call.
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.It Vt "disk_strategy_t *" Va d_strategy
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Mandatory: invoked when a new
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.Vt "struct bio"
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is to be initiated on the disk device.
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.It Vt "disk_ioctl_t *" Va d_ioctl
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Optional: invoked when an I/O control operation is initiated on the disk device.
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Please note that for security reasons these operations should not
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be able to affect other devices than the one on which they are performed.
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.It Vt "dumper_t *" Va d_dump
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Optional: if configured with
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.Xr dumpon 8 ,
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this function is invoked from a very restricted system state after a
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kernel panic to record a copy of the system RAM to the disk.
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.El
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.Ss Mandatory Media Properties
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The following fields identify the size and granularity of the disk device.
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These fields must stay stable from return of the drivers open method until
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the close method is called, but it is perfectly legal to modify them in
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the open method before returning.
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.Bl -tag -width indent
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.It Vt u_int Va d_sectorsize
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The sector size of the disk device in bytes.
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.It Vt off_t Va d_mediasize
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The size of the disk device in bytes.
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.It Vt u_int Va d_maxsize
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The maximum supported size in bytes of an I/O request.
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Requests larger than this size will be chopped up by GEOM.
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.El
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.Ss Optional Media Properties
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These optional fields can provide extra information about the disk
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device.
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Do not initialize these fields if the field/concept does not apply.
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These fields must stay stable from return of the drivers open method until
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the close method is called, but it is perfectly legal to modify them in
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the open method before returning.
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.Bl -tag -width indent
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.It Vt u_int Va d_fwsectors , Vt u_int Va d_fwheads
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The number of sectors and heads advertised on the disk device by the
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firmware or BIOS.
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These values are almost universally bogus, but on some architectures
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necessary for the correct calculation of disk partitioning.
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.It Vt u_int Va d_stripeoffset , Vt u_int Va d_stripesize
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These two fields can be used to describe the width and location of
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natural performance boundaries for most disk technologies.
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Please see
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.Pa src/sys/geom/notes
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for details.
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.It Vt char Va d_ident[DISK_IDENT_SIZE]
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This field can and should be used to store disk's serial number.
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.El
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.Ss Driver Private Data
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This field may be used by the device driver to store a pointer to
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private data to implement the disk service.
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.Bl -tag -width indent
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.It Vt "void *" Va d_drv1
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Private data pointer.
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Typically used to store a pointer to the drivers
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.Vt softc
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structure for this disk device.
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.El
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.Sh SEE ALSO
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.Xr GEOM 4 ,
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.Xr devfs 5
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.Sh AUTHORS
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This manual page was written by
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.An Robert Watson .
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