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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.