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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_gone(struct disk *disk);

     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 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.

     GEOM has the ownership of struct disk, and drivers must allocate storage
     for it with the disk_alloc() function, fill in the fields and call
     disk_create() when the device is ready to service requests.  disk_gone()
     orphans all of the providers associated with the drive, setting an error
     condition of ENXIO in each one.  In addition, it prevents a re-taste on
     last close for writing if an error condition has been set in the
     provider.  After calling disk_destroy(), the device driver is not allowed
     to access 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 device 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),
             DISKFLAG_CANDELETE (maintained by device driver), and
             DISKFLAG_CANFLUSHCACHE (maintained by device driver).

     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 reasons these
             operations should not be able to affect other devices than the
             one on which they are performed.

     dumper_t * d_dump
             Optional: if configured with dumpon(8), this function 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 request.  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 universally 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.

     char d_ident[DISK_IDENT_SIZE]
             This field can and should be used to store disk’s serial number.

   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.