ARM-Linux驱动--MTD驱动分析(二)

1. device_unregister(&mtd->r(&mtd->dev);//移除MTD设备
3. idr_remove(&mtd_idr,mtd->index);//移除mtd的id号并释放已分配的内存
5. module_put(THIS_MODULE);
6. ret=0;
7. }
9. out_error:
10. mutex_unlock(&mtd_table_mutex);
11. returnret;
12. }

4、register_mtd_user函数

1. /**
2. *register_mtd_user-registerauserofMTDdevices.
3. *@new:pointertonotifierinfostructure
4. *
5. *Registersapairofcallbacksfunctiontobecalleduponaddition
6. *orremovalofMTDdevices.Causestheaddcallbacktobeimmediately
7. *invokedforeachMTDdevicecurrentlypresentinthesystem.
8. */
9. //MTD原始设备使用者注册MTD设备（具体的字符设备或块设备）
10. //参数是新的mtd通知器，将其加入mtd_notifiers队列，然后
11. voidregister_mtd_user(structmtd_notifier*new)
12. {
13. structmtd_info*mtd;
15. mutex_lock(&mtd_table_mutex);
17. //将new->list头插mtd_notifiers入链表
18. list_add(&new->list,&mtd_notifiers);
20. __module_get(THIS_MODULE);
22. //对每个MTD原始设备执行add函数
23. mtd_for_each_device(mtd)
24. new->add(mtd);
26. mutex_unlock(&mtd_table_mutex);
27. }

5、unregister_mtd_user函数

1. /**
2. *unregister_mtd_user-unregisterauserofMTDdevices.
3. *@old:pointertonotifierinfostructure
4. *
5. *Removesacallbackfunctionpairfromthelistofuserstobe
6. *notifieduponadditionorremovalofMTDdevices.Causesthe
7. *removecallbacktobeimmediatelyinvokedforeachMTDdevice
8. *currentlypresentinthesystem.
9. */
10. //删除MTD设备。
11. //通知所有该MTD原始设备的MTD设备执行remove()函数，将被删除的MTD设备的通知器从mtd_notifier队列中删除
12. intunregister_mtd_user(structmtd_notifier*old)
13. {
14. structmtd_info*mtd;
16. mutex_lock(&mtd_table_mutex);
18. module_put(THIS_MODULE);
20. //通知所有该MTD原始设备的MTD设备执行remove()函数
21. mtd_for_each_device(mtd)
22. old->remove(mtd);
24. //将被删除的MTD设备的通知器从mtd_notifier队列中删除
25. list_del(&old->list);
26. mutex_unlock(&mtd_table_mutex);
27. return0;
28. }

6、获取MTD设备的操作指针，只是参数不同，一个是按照设备地址，另一个是安装设备的名称来获取MTD设备的操作地址

struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)

struct mtd_info *get_mtd_device_nm(const char *name)

下面现分析第一个函数

1. /**
2. *get_mtd_device-obtainavalidatedhandleforanMTDdevice
3. *@mtd:lastknownaddressoftherequiredMTDdevice
4. *@num:internaldevicenumberoftherequiredMTDdevice
5. *
6. *GivenanumberandNULLaddress,returnthenumthentryinthedevice
7. *table,ifany.Givenanaddressandnum==-1,searchthedevicetable
8. *foradevicewiththataddressandreturnifitsstillpresent.Given
9. *both,returnthenumthdriveronlyifitsaddressmatches.Return
10. *errorcodeifnot.
11. */
12. //根据设备地址来获取MTD设备的操作地址
13. structmtd_info*get_mtd_device(structmtd_info*mtd,intnum)
14. {
15. structmtd_info*ret=NULL,*other;
16. interr=-ENODEV;
18. //给mtd_table加锁，以便互斥访问
19. mutex_lock(&mtd_table_mutex);
21. if(num==-1){//num=-1&&链表不空，则返回mtd的地址
22. mtd_for_each_device(other){
23. if(other==mtd){
24. ret=mtd;
25. break;
26. }
27. }
28. }elseif(num>=0){//num>=0，查找第num个设备，若不空，返回地址，若为空，返回NULL
29. ret=idr_find(&mtd_idr,num);
30. if(mtd&&mtd!=ret)
31. ret=NULL;
32. }
34. if(!ret){
35. ret=ERR_PTR(err);
36. gotoout;
37. }
39. err=__get_mtd_device(ret);
40. //错误处理
41. if(err)
42. ret=ERR_PTR(err);
43. out:
44. mutex_unlock(&mtd_table_mutex);//解锁互斥信号量
45. returnret;
46. }
49. int__get_mtd_device(structmtd_info*mtd)
50. {
51. interr;
53. if(!try_module_get(mtd->owner))
54. return-ENODEV;
56. if(mtd->get_device){
58. err=mtd->get_device(mtd);
60. if(err){
61. module_put(mtd->owner);
62. returnerr;
63. }
64. }
65. mtd->usecount++;//增加该MTD原始设备的使用者计数器
66. return0;
67. }

第二个函数

1. /**
2. *get_mtd_device_nm-obtainavalidatedhandleforanMTDdeviceby
3. *devicename
4. *@name:MTDdevicenametoopen
5. *
6. *ThisfunctionreturnsMTDdevicedescriptionstructureincaseof
7. *successandanerrorcodeincaseoffailure.
8. */
9. //通过设备名来获得相应的MTD原始设备的操作地址
10. //该函数和上面的函数类似，不过就是通过循环比较MTD设备的name字段来返回
11. structmtd_info*get_mtd_device_nm(constchar*name)
12. {
13. interr=-ENODEV;
14. structmtd_info*mtd=NULL,*other;
16. mutex_lock(&mtd_table_mutex);
18. mtd_for_each_device(other){
19. if(!strcmp(name,other->name)){
20. mtd=other;
21. break;
22. }
23. }
25. if(!mtd)
26. gotoout_unlock;
28. if(!try_module_get(mtd->if(