Manual Pages  — DISK

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_add_alias() adds an alias for the disk and must be called before disk_create(), but may be called multiple times. For each alias added, a device node will be created with make_dev_alias(9) in the same way primary device nodes are created with make_dev(9) for d_name and d_unit. Care should be taken to ensure that only one driver creates aliases for any given name. disk_resize() can be called by the driver after modifying d_mediasize to notify GEOM about the disk capacity change. The flags field should be set to either M_WAITOK, or M_NOWAIT. 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.