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.

       disk_getattr_t * d_getattr
               Optional: if this method is provided, it gives the disk driver the opportunity  to  override  the
               default  GEOM  response to BIO_GETATTR requests.  This function should return -1 if the attribute
               is not handled, 0 if the attribute is handled, or an errno to be passed to g_io_deliver().

       disk_gone_t * d_gone
               Optional: if this method is provided, it will be called after disk_gone() is  called,  once  GEOM
               has  finished  its cleanup process.  Once this callback is called, it is safe for the disk driver
               to free all of its resources, as it will not be receiving further calls from GEOM.

   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 if the d_getattr method described
               above isn't implemented, or if it does not support the GEOM::ident attribute.

       char d_descr[DISK_IDENT_SIZE]
               This field can be used to store the disk vendor and product description.

       uint16_t d_hba_vendor
               This field can be used to store the PCI vendor ID for the HBA connected to the disk.

       uint16_t d_hba_device
               This field can be used to store the PCI device ID for the HBA connected to the disk.

       uint16_t d_hba_subvendor
               This field can be used to store the PCI subvendor ID for the HBA connected to the disk.

       uint16_t d_hba_subdevice
               This field can be used to store the PCI subdevice ID for the HBA connected to the disk.

   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.

Debian                                          February 18, 2004                                        DISK(9)