Linux Kernel Architecture

Chapter 6: Device Drivers

Connectingthe Pieces

The previously introduced data structures —struct block_device,struct gendisk,andstruct

hd_struct— are directly connected with each other. Figure 6-10 shows how.

struct

block_device

bd_contains

bd_contains

bd_part

bd_disk

bd_part

bd_disk

bd_contains

bd_part

bd_disk

struct

gendisk

struct hd_struct

part

Figure 6-10: Connection between block devices, generic hard disks, and partitions.

For each partition of a block device that has already been opened, there is an instance ofstruct

block_device. The objects for partitions are connectedwith the object for the complete device via

bd_contains.Allblock_deviceinstances contain a link to their generic disk data structuregen_diskvia

bd_disk. Note that while there are multipleblock_deviceinstances for a partitioned disk, onegendisk

instance is sufficient.

Thegendiskinstance points to an array with pointers tohd_structs. Each represents one partition. If

ablock_devicerepresents a partition, then it contains a pointer to thehd_structin question — the

hd_structinstances are shared betweenstruct gendiskandstruct block_device.

Additionally, generic hard disks are integrated into thekobjectframework as shown in Figure 6-11. The

block subsystem is represented by theksetinstanceblock_subsystem.Theksetcontains a linked list on

which the embeddedkobjectsofeachgendiskinstance are collected.

list

kobj.parent kobj.parent

struct hd_struct

struct kset

block_subsys

entry entry

struct gendisk

embedded

kobj

Figure 6-11: Integration of generic harddisks with the generic kernel object

framework.