Overview. I/O Devices. Memory Access. Device Controller. Advanced Operating System Project. Device Drivers. M. Muztaba Fuad

Transcription

1 Advanced Operating System Project Device Drivers M. Muztaba Fuad Overview Basics Definitions What the OS books say? Linux way of doing things (Kernel 2.4) Check Linux Source code. Windows way of doing things Check Windows Source code (just kidding!). Write your own driver in Linux What you need to know? How to write? Things to remember Changes in Kernel 2.6 Slide 2 I/O Devices! "$# %"! &! '( ' ) * + ',+ & # - -'. / 0 ' ) *1 " ( '1 2 # 3! ' I/O devices are attached to the computer bus. Each I/O device consists of a controller subassembly to control the detailed operation of the physical device itself. Slide 3 Slide 4 Device Controller Memory Access ;:6<6= >?? QH? O FCG6? 8 RS=FC:6? 8 Q6? O FCGH? 8 RX=FC:6? 8 DLQET DLQET DE:6FCFCGH<6I J6K G6K 5H7 9LG6K G D$:6<6K? :HU U =? D$:6<6K? :HU U =? M,:HN6O P Slide 5 Conventional DMA Slide 6 1

2 B Device Addressing Device Independent I/O Driver RS=FC:6? 8 LI6IE? =7,7 Q6? O FCGH? 8 RX=FC:6? 8 QH? O FCG6? 8 RX=FC:6? 8 9L=V6O P= RS=FC:6? 8 IHI6? =7,7 9L=V6O P= LI6I$? =7,7 9L=V6O P= 9L=V6O P= 9L=V6O P= 9L=V6O P= No Standard Interface Standard Interface Conventional Memory Mapped I/O Slide 7 Slide 8 Device Manager Abstraction Device Management =%GHI,@CB Common Device Interface 9L=V6O P=,<HK =? G6P= J867,K =F <6K =? G6P= &%%$U O PG6K O :$< Q6? :6P=%77 $O U = RXGH<6G6N6=? E=? FCO <HG6U 9L? O V6=6? QH? O <6K =6? 9;? O VW=H? 9LO 7 9;? O VW=H? LG6? ICG6? =,<6K =? G6P=!" "# "! # 9;=,V6O P%= RXG6<HG6NE=? E=? FCO <HG6U DE:6<HK? :6U U =? QH? O <6K =6? D$:6<6K? :HU U =? 9LO 7 DE:H<6K? :6U U =? D$:6FCFCG6<6I J6K G6K 5H7 9LGHK G XDE:$<6K? :HU U =? Slide 9 Slide 10 I/O Strategies Direct I/O with polling The CPU is responsible for data transfer between device and primary memory. Slow data transfer. Difficult to achieve effective CPU utilization Interrupt Driven I/O The controller don t needs to be checked for status constantly. Controller interrupts the device manager to indicate when it finishes its operation. Polling I/O Read 1? =G6I,@ B 9LGHK G 9L=V6O P=,<HK =? G6P= 9L=V6O P= 9;? O VE=? '$=G6I 56<EPK O :6< (? O K =) 56<HP,K O :H< ;G6? I GH? = <6K =%? G6P= G? U DE:6FCFCGH<6I JHK G6K 567 9;G6K 9L=V6O P=XD$:$<6K :6U =? Slide 11 Slide 12 2

3 ! Interrupt Processing When the kernel receives an interrupt from a particular device, the kernel passes control to its corresponding interrupt handler Interrupt handlers do not belong to any single process context Scheduler cannot place an interrupt handler in a run queue Thus, interrupt handler cannot sleep, call the scheduler, be preempted or raise faults or exceptions As a result, most interrupt handlers are designed to execute quickly Interrupts are divided into top and bottom halves Top half sets up. Bottom half performs the operation. 9;=,V6O P%=),<6K =? G6P,= ;G6? I G6? = <6K =? G6P= 2 Interrupt Driven I/O 1 9L=V6O P= 9;? O VE=? '$=%GHI 56<$P,K O :6< (? O K = 5H<6P,K O :6< 3 4? =G6I,@CB 9LG6K G J6K G6K 5H7 $G U = D$:6FCFCG6<6I J6K GHK 567 9LG6K G 9;=,V6O P%=SDE:$<6K? :6U U =%? LG6<6IHU =? <6K =%?? 5%6K LG6<6IHU =? 8 Slide 13 Slide 14 Linux Device Driver "# $ Initial Unix implementations has the device drivers coded inside the kernel. Problems???? Module is an independent software unit that can be loaded into the kernel dynamically at run time. Helps to install new device without modifying the kernel. Kernel provides common interface for I/O system calls. Slide 15 Slide 16 Kernel Driver Initialization Device files are more than half of the size of the kernel source. fs/devices.c % Defines all the device functions /devices directory % Holds all the device driver codes /devices/char /devices/block Kernel driver initialization: start_kernel & init/main.c setup_arch ' arch/i386/kernel/setup.c Sets up system variables, such as video type, root device etc. console_init ' driver/char/tty_io.c init ' init/main.c do_basic_setup ( init/main.c» Initialize all bus sub system prepare_namespace ( init/do_mounts.c» Mount root and device file system do_initcalls ( init/main.c» All built in device driver is initialized which are registered with initcall() Slide 17 Linux Device Driver Most have been written by independent developers. Typically implemented as loadable kernel modules. Device special files Most devices are represented by device special files. Entries in the )+*,.- directory that provide access to devices. List of devices in the system can be obtained by reading the contents of )/01324)3*,.-5 26,378 Devices are grouped into classes Three classes: Character Devices Block Devices Network Devices Members of each device class perform similar functions Slide 18 3

4 Linux Device Driver Major and minor identification numbers Used by device drivers to identify their devices Devices that are assigned the same major identification number are controlled by the same driver Minor identification numbers enable the system to distinguish between devices of the same class /usr/src/linux/documentation/devices.txt brw-rw root disk 3, 1 May hda1 brw-rw root disk 3, 2 May hda2 brw-rw root disk 3, 3 May hda3 crw root root 4, 0 Jan tty0 crw root root 4, 1 Oct 31 14:55 tty1 crw-r--r-- 1 root root 10, 135 Jan rtc Linux Device Driver Device special files are accessed via the virtual file system System calls pass to the VFS, which in turn issues calls to device drivers Most drivers implement common file operations such as, and To support tasks such as ejecting a CD-ROM tray or retrieving status information from a printer, Linux provides the system call Slide 19 Slide 20 I/O Interface Layers Character Device I/O Transmits data as a stream of bytes Represented by a structure that contains the driver name and a pointer to the driver s file_operations structure Maintains the operations supported by the device driver All registered drivers are referenced by a vector (major number) The file_operations structure Stores functions called by the VFS when a system call accesses a device special file! " # $ % & '(%() * + #,(-(. "(# $ % & '(%() * + #,(-(. chardevs / 0(132 /30:132 ;<7 = > / / ? Slide A Slide 22 Block Device I/O Block I/O subsystem Complex then character device Buffering Caching Direct I/O and so on. Represented by block_device_operations Different than file_operations Extra operations for caching, buffering and queue management When data from a block device is requested, kernel first searches page cache If found, data is copied to the process s address space Otherwise, typically added to a request queue Direct I/O Enables driver to bypass kernel caches when accessing devices Some times, need to provide advanced algorithms for certain devices Optimizing moving head storage Slide 23 Network I/O Network Device I/O Accessed via the IPC subsystem s socket interface. Network traffic can arrive at any time. The C DFEG and HIC J K D operations of a device special file are not sufficient to access data from network devices Kernel uses L DK M G DN<J OD structures to describe network devices No P Q R S3TUWVSX YZ Q UW[\ structure Packet processing Complex. Depends on different issues. Slide 24 4

5 Unified Device Model Attempts to simplify device management in the kernel Relates device classes to system buses Helps support hot-swappable devices Power management UDM defines structures to represent devices, device drivers, device classes, buses Kernel Module A new kernel module can be added on the fly While the OS is still running. No need to re-compile the kernel. They are not user program. Some times they are also called Loadable Kernel Modules Several types of kernel module: Device Drivers Virtual terminals Interpreters Only be controlled by super user. All installed modules: /lib/modules/kernel_version Slide 25 Slide 26 Modules! "!#$!% 9 : & '& ( )+*,-./ & 5( 03 D : ; ;: 6 / 07'.8) *,-+. / 012 < 9 ACB ACB. '304+& 5( 0 3 Slide 27 Slide 28 Windows Device Driver Windows Device Driver Organized into device driver stack. Device driver with different level of services. Device Object Stores data for device Driver Object Pointers to common driver routines Plug and Play (PnP) Dynamically add new hardware devices Slide 29 Slide 30 5

6 Windows Driver Model Windows Driver Model (WDM) Bus driver Interact directly with bus (PCI, SCSI) Mandatory one bus driver per bus Provide generic functions for devices on bus Filter driver Optional Modify device actions: encryption Add features: security checks Function driver Implements main function of device Slide 31 Slide 32 Things to do Understand the device characteristic and supported commands. Map device specific operations to Linux file operation Select the device name (user interface) /dev/virtual_device Select a major and minor number (a device special file creation) for VFS interface Implement interface subroutines Compile the device driver Install the device driver module. Or Rebuild (compile) the kernel Interface between Kernel & Driver!# #! "! # %$ "!#$! & #! '!# # (#)! $! #!%*+! #!%#!,! #)$ -#)$#.*+$ /!!(0 +1!%# 2(#)! $ # #. 3# #! :);3< = Ä B8C :3< = VWẌ Y 6 CD E F Ä D.G H B: 78)9:)E I3D H ; C+G 839 C J.> :);3< = K Ä B8C :3< = K H ;3D%H ;H D 7)L 8MNF3B:3< O8)HM= > E :PNHCD :)E 7M3: Ö HA:)< L I Q 8)E 73;)F3LR:3E ST.G 839C = U Slide 33 Slide 34 file_operation Structure From the file /usr/src/linux-2.4/include/linux/fs.h 5( 3. 6 ( Z & / 0)+,8 03 7( &, '5[ 5( 3. 6 (*,-./ 0\,N] '03 ^ /,(Z Z )+(1\ / / 5 003_215( 3. 6 ( Z & / 0`\3a+/,Z Z )+( a & ' ( 2 ^ 55& X 0) (1\ ( 3. 6 ( Z & / 0`\3a 6b 73c\3a+5& X 0) ( a+/,z Z )+( \2 ^ 55& X 0) (1\3] 3& ( 0215( 3. 6 ( Z & / 0\3a 6,'5( 63b 73 \3a+5& X 0)+( a+/,z Z )+(c\2 ^ & ' (1\307-- & ( 3. 6 ( Z & / 0d\3a(e, & -f\na%z & / / -+& 3 )+( 2 ^.'5& 4'+0-& '(1\+8,/ / 2 15( 3. 6 ( Z & / 0`\3a+5( 3. 6 (8,/ / )+( 7g/ 0) 5( 3. 6 (+\2 ^ & ' (1\&, 6 ( / 215( 3. 6 (& ',- 0d\3a 5( 3. 6 ( Z & / 0\3a.'5& 4' 0-& '( a.'5& 4' 0-/, '42 ^ & ' (1\**78215( 3. 6 ( Z & / 0d\3a 5( 3. 6 (.e*)+73 07) 5( 3. 6 (+\2 ^ & ' (1\,8 0'2 15( 3. 6 (& ', -0`\3a+5( 3. 6 ( Z & / 0`\2 ^ & ' (1\Z /.5 b 2 15( 3. 6 ( Z & / 0`\2 ^ & ' (1\30/ ( 3. 6 (& ',- 0`\3a+5( 3. 6 ( Z & / 0\2 ^ & ' (1\Z 5 W ' 6 215( 3. 6 ( Z & / 0`\3a+5( 3. 6 (-+0'( 3 W \3a & ' (-7( 75 W ' 6 2 ^ & ' (1\Z 75 W ' 6 21& '( a+5( 3. 6 ( Z & / 0`\3a+& '( 2 ^ & ' (1\/, 6 _215( 3. 6 ( Z & / 0`\3a+& '( a+5( 3. 6 ( Z & / 0)+/, 6 _f\2 ^ 55& X 0) (1\ e2 15( 3. 6 (cz & / 0`\3a 6,'5(5( 3. 6 (&,(e0 6 \3a+. '5& 4' 0-/,' 43a+/,Z Z )+( \2 ^ 55& X 0) (1\3] 3& ( 0e2 15( 3. 6 ( Z & / 0`\3a 6,'5(5( 3. 6 (&,3e+0 6 \3a+. '5& 4 '+0-/, '+43a /,Z Z )+( \2 ^ 55& X 0) (1\50 ' ( 3. 6 ( Z & / 0`\3a+5( 3. 6 (8740`\3a+& '( a+5& X 0) ( a+/,z Z )+( \3a& '( 2 ^.'5& 4'+0-/,'+4 1\4 0( ).'* ) ( 3. 6 ( Z & / 0\3a.'5& 4 '0-/, '43a+. '5& 4 '+0-/, '+43a. '5& 4' 0-/,' 43a+. '5& 4 '0- /, '42 ^ h3^ Slide 35 Things to remember Careful! You are programming in kernel mode! Can t use any standard functions. Can only use kernel functions, which are the functions you can see in /proc/ksyms. Version. Compile Need to use special gcc options. Device special file mknod /dev/device_name device_type major_number minor_number Slide 36 6

7 Kernel 2.6.x Lets check our driver code Creation of Unified Device Model is one of the most important changes in 2.6 kernel. Expanded the limitation of the major number from 255 to Now more than one million sub devices per type is allowed. PnP support. Module subsystem is changed: kbuild tool. New file naming concept. Modules now has.ko extension. Slide 37 Slide 38 Loooooooong way to go.. We can propose a course on device driver as after all that we didn t touch the following: I/O Buffering I/O Caching Block devices Network devices. Module programming Stacked Modules Controller interaction Interrupt processing References OS books: Operating System Concepts by Silberschatz & Galvin Operating System by Garry Nutt. Linux Device Driver book Linux Programmer s Guide The Linux Kernel Module Programming Guide Device Driver Development for Microsoft Windows Slide 39 Slide 40 Thanks Slide 41 7