bus_type

相关数据结构：

struct bus_type {
 char   * name;

 struct subsystem subsys;
 struct kset  drivers;
 struct kset  devices;

 struct bus_attribute * bus_attrs;
 struct device_attribute * dev_attrs;
 struct driver_attribute * drv_attrs;

 int  (*match)(struct device * dev, struct device_driver * drv);
 int  (*hotplug) (struct device *dev, char **envp,
        int num_envp, char *buffer, int buffer_size);
 int  (*suspend)(struct device * dev, pm_message_t state);
 int  (*resume)(struct device * dev);
};

内核所支持的每一种总线类型都由一个bus_type对象表示。
bus_type中内嵌了一个subsystem - subsys。
系统中的bus_subsys子系统将所有的bus_type中的subsys集合在一起。
bus_subsys对应sysfs中的/sys/bus目录.

另外，bus_type中有两个内嵌的kset对象：devices 和 drivers。分别表示该bus上的设备和驱动。

                                                          
                            
                                                           
                                                           
                                                           
  /------------------------>       bus_type       <-------------------------\
  |                         +--------------------+                          |
  |                         |                    |                          |
  |                         |    name            |                          |
  |                         +--------------------+                          |
  |                         |            kset    |                          |
  |                         |         +--------+ |                          |
  |                         |         | subsys | |                          |
  |                         | drivers +--------+ |                          |
  |                         |         | kobj   | |                          |
  |                         |         +--------+ |                          |
  |                         |         | list   | |                          |
  |                         |         +--------+ |                          |
  |                         |         |        | |                          |
  |                         +--------------------+                          |
  |                         |            kset    |                          |
  |                         |         +--------+ |                          |
  |                         |         | subsys | |                          |
  |                         | devices +--------+ |                          |
  |                         |         | kobj   | |                          |
  |                         |         +--------+ |                          |
  |  /------------------------------->| list   |<----------------------\    |
  |  |                      |         +--------+ |                     |    |
  |  |                      |         |        | |                     |    |
  |  |                      +--------------------+                     |    |
  |  |                      |                    |                     |    |
  |  |                      |   subsys           |                     |    |
  |  |                      |                    |                     |    |
  |  |                      +--------------------+                     |    |
  |  |                      |                    |                     |    |
  |  |                      |                    |                     |    |
  |  |                      |                    |                     |    |
  |  |                                                                 |    |
  |  |                                                                 |    |
  |  |       device                                      device        |    |
  |  |   +-------------+                             +-------------+   |    |
  |  |   |    node     |                             |    node     |   |    |
  |  |   +-------------+                             +-------------+   |    |
  |  \-->|  bus_list   |<-------  ......  ---------->|  bus_list   |<--/    |
  |      +-------------+                             +-------------+        |
  |      |  driver_list|                             |  driver_list|        |
  |      +-------------+                             +-------------+        |
  |      |  children   |                             |  children   |        |
  |      +-------------+                             +-------------+        |
  |      |   parent    |                             |   parent    |        |
  |      +-------------+                             +-------------+        |
  |      |   kobj      |                             |   kobj      |        |
  |      +-------------+                             +-------------+        |
  \------|   bus       |                             |   bus       |--------/
         +-------------+                             +-------------+   
         |   driver    |                             |   driver    |   
         +-------------+                             +-------------+   
         |             |                             |             |   
                                                                       

                                                                             
                                                                             
                                                                             
                                                                             
                                                                             
   /------------------------>       bus_type       <-------------------------\
   |                         +--------------------+                          |
   |                         |                    |                          |
   |                         |    name            |                          |
   |                         +--------------------+                          |
   |                         |            kset    |                          |
   |                         |         +--------+ |                          |
   |                         |         | subsys | |                          |
   |                         | drivers +--------+ |                          |
   |                         |         | kobj   | |                          |
   |                         |         +--------+ |                          |
   |  /------------------------------->| list   |<----------------------\    |
   |  |                      |         +--------+ |                     |    |
   |  |                      |         |        | |                     |    |
   |  |                      +--------------------+                     |    |
   |  |                      |            kset    |                     |    |
   |  |                      |         +--------+ |                     |    |
   |  |                      |         | subsys | |                     |    |
   |  |                      | devices +--------+ |                     |    |
   |  |                      |         | kobj   | |                     |    |
   |  |                      |         +--------+ |                     |    |
   |  |                      |         | list   | |                     |    |
   |  |                      |         +--------+ |                     |    |
   |  |                      |         |        | |                     |    |
   |  |                      +--------------------+                     |    |
   |  |                      |                    |                     |    |
   |  |                      |   subsys           |                     |    |
   |  |                      |                    |                     |    |
   |  |                      +--------------------+                     |    |
   |  |                      |                    |                     |    |
   |  |                      |                    |                     |    |
   |  |                      |                    |                     |    |
   |  |                                                                 |    |
   |  |                                                                 |    |
   |  |                                                                 |    |
   |  |                                                                 |    |
   |  |          driver                               driver            |    |
   |  |    +------------------+                 +------------------+    |    |
   |  |    |                  |                 |                  |    |    |
   |  |    |    name          |                 |    name          |    |    |
   |  |    |                  |                 |                  |    |    |
   |  |    +------------------+                 +------------------+    |    |
   |  |    |          kset    |                 |          kset    |    |    |
   |  |    |       +--------+ |                 |       +--------+ |    |    |
   |  |    |       | parent | |                 |       | parent | |    |    |
   |  |    | kobj  +--------+ |                 | kobj  +--------+ |    |    |
   |  |    |       | kset   | |                 |       | kset   | |    |    |
   |  |    |       +--------+ |                 |       +--------+ |    |    |
   |  \----------->| entry  |<------------------------->| entry  |<-----/    |
   |       |       +--------+ |                 |       +--------+ |         |
   |       |       |        | |                 |       |        | |         |
   |       +------------------+                 +------------------+         |
   |       |                  |                 |                  |         |
   \-------|    bus           |                 |    bus           |---------/
           |                  |                 |                  |  
           +------------------+                 +------------------+  
           |                  |                 |                  |  
           |                  |                 |                  |  
           |                  |                 |                  |  
                                                                      
                          
     
函数bus_for_each_dev() 和 bus_for_each_drv()分别用于遍历bus上devices和drivers链表中的所有元素。