????????????
???????豸??blockdevice??
????--- ??????????????????????豸?????????豸???д???????е????????????????????????????????????????????????д???豸??????豸????????????????
????????豸??Character device??
????---????????????????豸?????????豸???д?????????е????????Щ????????????γ?????????????????????????????????????豸???д???????
????????(Sectors)???κο??豸??????????????????λ???????1?????????С?512byte???????豸?????
??????  (Blocks)????Linux?????????????????????????????λ???????1??????1????????????ɡ?????Linux???????????
??????(Segments)????????????????ɡ???Linux??????????????????????????????????
????????Ρ??顢??????????????￡?

???????豸??????????

???????豸???????Linux???????????????????
???????豸????????Linux?У?????????豸??????????(I/O)??????????????豸?????????????????????request?????????????????Щ?????豸????????????????????????????????е???????ЩI/O?????????????У???????????У?????????????request_queue????????????????豸????Щ???????????????????????????????????????????Ч??????????????е?I/O???????????????????  I/O ??????????????????????????????й????? I/O  ?????乤?????????豸????????У??????????е?????????????????????????????豸??
?????????(Generic Block Layer)????????????I/O?????????????????????????????????????????У?????????bio????????????I/O????
????Linux???????gendisk??????壬????????????????????豸???????????????????????з??????gendisk???????????????豸??file_operations????????????????block_device_operations???塣
????IO?????????????????????豸??????Ч??????????????????????е????????????????磺д??????????Ч?????????????????豸????????????????????????????I/O?????????????????????????????????????????к??????????Ч?????????????????????????????I/O??????????????????????elevator algorithm????????????I/O???????ɡ??????????????????????????????
????1 noop????????FIFO?????????????????????
????2 anticipatory?????I/O????????????????????????
????3 Deadline?????anticipatory?????и????????????????
????4 Cfq?????????I/O?????????????
????PS?????IO?????????????????????????????????????????????á?
????????(Mapping Layer)??????????????????????????豸??????
????VFS??????????????????????????????????????????????????ext2??FAT??NFS???豸?????
???????????(Caches):??????????????????????С?
????????????
????block_device:      ????????????????????????????????豸???
????gendisk:               ??????????????generic hard disk??????
????hd_struct:             ??????????е???????
????bio:                        ??????????????????????????????driver
????request:                ?????????????????б?????????д????
????request_queue:  ???????????request??????????????????дBIO?γ???С?