PEMP ESD2531. I/O and File System. Session Speaker. Deepak V. M.S Ramaiah School of Advanced Studies - Bengaluru

Transcription

1 I/O and File System Session Speaker Deepak V. 1

2 Session Objectives To understand the concepts of Basic I/O, Standard I/O and formatted I/O in VxWorks VxWorks support for File system types Creating a dosfs File System 2

3 Session Topics Memory Management Creating Memory Partitions Managing Memory Partitions I/O Basic I/O Buffered I/O Standard I/O Formatted I/O File system Creating a dosfs File System Disk Organization CD-ROM File System: cdromfs 3

4 I/O System Interface 4

5 VxWorks I/O System Is designed to present a simple, device independent interface to Character-oriented devices such as terminals or communications lines Random -access block devices such as disks Virtual devices such as intertask pipes and sockets Monitor and control devices such as digital and analog I/O devices Network devices that give access to remote devices 5

6 Overview of the VxWorks I/O System 6

7 Driver Installation A device driver must be installed in the I/O system Then VxWorks can call driver-specific routines when generic routines are called: e.g. calling xxread( ) when read( ) is called on an XX device Installation done automatically for VxWorks drivers included in VxWorks image: ttydrv( ) pipedrv( ) Must call driver s xxdrv( ) routine before using a third party driver 7

8 Device Creation Each device driver has a device creation routine: Pipes Created at your request with pipedevcreate( ) Serial devices Created automatically at system start up (via ttydevcreate( )) Remote file systems See Network Basics chapter Local file systems See Local File Systems chapter Third-party devices xxdevcreate( ) These routines each initialize instances of a particular device type 8

9 Basic I/O Basic I/O is the lowest level of I/O in VxWorks. The basic I/O interface is source-compatible with the I/O primitives in the standard C library Basic I/O Routines Call Description creat( ) Creates a file delete( ) Deletes a file open( ) Opens a file (Optionally, creates a file.) close( ) Closes a file read( ) Reads a previously created or opened file write( ) Writes to a previously created or opened file ioctl( ) Performs special control functions on files 9

10 Standard Input, Output and Error The first three file descriptors are predefined by the system and are never reassigned by the system These three file descriptors (0-2) are never returned by creat( ) or open( ) By default, these are directed to the console at system start-up Global assignments may be changed using void ioglobalstdset (stdfd, newfd) Example: fd = open ( columbia:/vx/errlog, O_RDWR, 0); ioglobalstdset (STD_ERR, fd); Redirect I/O on a per-task basis with void iotaskstdset (taskid, stdfd, newfd) 10

11 Accessing Files int open (name, flags, mode) name Name of file to open flags Specifies type of access: O_RDONLY Open file for reading only O_WRONLY Open file for writing only O_RDWR Reading and writing O_TRUNC Truncate file on open O_CREAT Create file if it doesn t exist mode Permissions used when creating a file in an NFS file system Returns file descriptor on success, otherwise ERROR 11

12 creat and delete creat( ) routine similar to open( ), but for new files on a file system device The arguments to creat( ) are similar to those of open( ) except that the filename specifies the name of the new file rather than an existing one; the creat( ) routine returns an fd identifying the new file fd = creat ("name", flag); The delete( ) routine deletes a named file on a file-oriented device: delete ("name"); 12

13 Examining the File Descriptor Table -> iosfdshow fd name drv 3 /tyco/0 1 4 (socket) 3 10 /pipe/dream 2 12 /pipe/cleaner 2 13

14 Read/Write int read (fd, buffer, nbytes) int write (fd, buffer, nbytes) fd File descriptor returned by open( ) or creat( ) buffer Address of buffer. Will be filled on a read, copied to device on write nbytes Maximum number of bytes to read/write Returns the number of bytes read/written or ERROR if unsuccessful 14

15 ioctl The ioctl( ) routine is an open-ended mechanism for performing any I/O functions that do not fit the other basic I/O calls int ioctl (fd, command, arg) fd File descriptor returned from open( ) or creat( ) command Integer identifying some driver-specific command. Symbolic constants typically used arg Type and value depends on command Driver manual pages lists valid ioctl commands for that driver 15

16 ioctl( ) Examples To set the baud rate of a serial device: status = ioctl (fd, FIOBAUDRATE, baudrate); To find the number of messages in a pipe: status = ioctl (fd, FIONMSGS, &nmsgs); To get/set your current file offset: status = ioctl (fd, FIOSEEK, newoffset) position = ioctl (fd, FIOWHERE, 0) 16

17 Buffered I/O: stdio The VxWorks I/O library provides a buffered I/O package that is compatible with the UNIX and Windows stdio package, and provides full ANSI C support Configure VxWorks with the ANSI Standard component bundle to provide buffered I/O support NOTE: The implementation of printf( ), sprintf( ), and sscanf( ), traditionally considered part of the stdio package, is part of a different package in VxWorks These routines are discussed in Other Formatted I/O 17

18 Standard I/O Functions ansistdio functions include: fopen( ) opens a stream to a device or file fclose( ) closes a stream fread( ) reads data into an array fwrite( ) writes data to a stream getc( ) gets next character from a stream putc( ) puts a character to a stream ungetc( ) returns character to input stream 18

19 Other ANSI Libraries Manual Page Header File Description Examples ansictype ctype.h Character isdigit( ) testing and isalpha( ) conversion toupper( ) ansistring string.h String strlen( ) manipulation strcat( ) strcpy( ) ansistdarg stdarg.h Variable va_start( ) number of var_arg( ) arguments va_end( ) ansistdlib stdlib.h Standard atoi( ) conversion atof( ) routines rand( ) 19

20 Formatted I/O fiolib contains routines for non-buffered formatted I/O Includes printf( ) and sprintf( ) which are normally part of stdio fiolib allows ansistdio to be excluded without losing functionality 20

21 Special Cases Printf( ), sprintf( ), and sscanf( ) uses a self-contained, formatted, non-buffered interface to the I/O system in the library fiolib Additional routines: Printerr( ) and fdprintf( ) routine printerr( ) is analogous to printf( ) but outputs formatted strings to the standard error fd (2) The routine fdprintf( ) outputs formatted strings to a specified fd 21

22 File System 22

23 Introduction to VxWorks File System VxWorks uses a standard I/O interface between the file system and the device driver which allows multiple file systems, of the same or different types, to operate within a single VxWorks system. Write own file system for VxWorks, and freely mix file systems and device drivers dosfs: rawfs: tapefs: CdromFs: TSFS (Target Server File System) VxWorks also provides support for flash memory devices through the optional product TrueFFS 23

24 Introduction to VxWorks File System dosfs: Designed for real-time use of block devices (disks) and compatible with the MS-DOS file system rawfs: Provides a simple raw file system that essentially treats an entire disk as a single large file tapefs: Designed for tape devices that do not use a standard file or directory structure on tape. Essentially treats the tape volume as a raw device in which the entire volume is a large file CdromFs: Allows applications to read data from CD-ROMs formatted according to the ISO 9660 standard file system TSFS (Target Server File System) : Uses the Tornado target server to provide the target with access to files on the host system 24

25 MS-DOS-Compatible File System: dosfs The primary features are: Hierarchical files and directories A choice of contiguous or non-contiguous files on a per-file basis. Compatibility with widely available storage and retrieval media (diskettes, hard drives, and so on) The ability to boot VxWorks from a dosfs file system Support for FAT12, FAT16, and FAT32 file allocation table types For API reference information about dosfs, see the entries for dosfslib and dosfsfmtlib, as well as the cbiolib, dcachecbio, and dpartcbio 25

26 Creating a dosfs File System Step 1: Configure the Kernel Step 2: Initialize the dosfs File System Step 3: Create the Block Device Step 4: Create a Disk Cache Creating a disk cache is optional Disk cache is intended only for rotational media Step 5: Create the Partition for Use Step 6: Create a dosfs Device Step 7: Format the Volume Step 8: Check the Disk Volume Integrity Step 9: Mount the Disk 26

27 1. Configuring the System Required Components INCLUDE_DOSFS_MAIN - dosfslib (2) INCLUDE_DOSFS_FAT - dosfs FAT12/16/32 FAT handler INCLUDE_CBIO - CBIO API module ONE OR BOTH THE COMPONENTS INCLUDE_DOSFS_DIR_VFAT - Microsoft VFAT direct handler INCLUDE_DOSFS_DIR_FIXED - Strict 8.3 & VxLongNames directory handler In addition, you need to include the appropriate component for your block device; for example, INCLUDE_SCSI or INCLUDE_ATA 27

28 1. Configuring the System Include Optional Components Optional dosfs components are: INCLUDE_DOSFS. usrdosfsold.c wrapper layer INCLUDE_DOSFS_FMT. dosfs2 file system formatting module INCLUDE_DOSFS_CHKDSK. file system integrity checking INCLUDE_DISK_UTIL. standard file system operations, such as ls, cd, mkdir, xcopy, and so on INCLUDE_TAR. the tar utility Optional CBIO Components INCLUDE_DISK_CACHE. CBIO API disk caching layer INCLUDE_DISK_PART. disk partition handling code INCLUDE_RAM_DISK. CBIO API RAM disk driver 28

29 1. Configuring the System Include Optional Components Optional dosfs components are: INCLUDE_DOSFS. usrdosfsold.c wrapper layer INCLUDE_DOSFS_FMT. dosfs2 file system formatting module INCLUDE_DOSFS_CHKDSK. file system integrity checking INCLUDE_DISK_UTIL. standard file system operations, such as ls, cd, mkdir, xcopy, and so on INCLUDE_TAR. the tar utility Optional CBIO Components INCLUDE_DISK_CACHE. CBIO API disk caching layer INCLUDE_DISK_PART. disk partition handling code INCLUDE_RAM_DISK. CBIO API RAM disk driver 29

30 2. Initializing the dosfs File System This happens automatically, triggered by the required dosfs components that were included in the system Initializing the file system invokes iosdrvinstall( ), which adds the driver to the I/O system driver table The driver number assigned to the dosfs file system is recorded in a global variable, dosfsdrvnum The table specifies the entry points for the dosfs file operations that are accessed by the devices using dosfs 30

31 3. Creating a Block Device To create the device, call the routine appropriate for that device driver The format for this routine is xxxdevcreate( ) where xxx represents the device driver type For example, scsiblkdevcreate( ) or atadevcreate( ) The driver routine returns a pointer to a block device descriptor structure, BLK_DEV This structure describes the physical attributes of the device and specifies the routines that the device driver provides to a file system Example: -> pata = atadevcreate (0,0,0,0) new symbol "pata" added to symbol table. pata = 0x3fff334: value = = 0x3fff344 = pata + 0x10 This step is appropriate for any BLK_DEV device; for example, flash, SCSI, and so on. For related information, see the reference entry for atadevcreate( ) 31

32 4. Creating a Disk Cache If INCLUDE_DISK_CACHE component is included in your system, use dcachedevcreate( ) to create a disk cache for each block device create an (optional) disk data cache CBIO layer atop this disc: -> pcbiocache = dcachedevcreate (pata,0,0,"ata Hard Disk Cache") new symbol "pcbiocache" added to symbol table. pcbiocache = 0x3ffdbd0: value = = 0x3fff1d8 Above, pcbiocache is a CBIO_DEV_ID, which is the handle for controlling the CBIO disk cache layer. For more information, see the reference entry for dcachedevcreate( ) 32

33 5. Creating and Using Partitions If you have included the INCLUDE_DISK_PART component in your system, you can create partitions on a disk and mount volumes atop the partitions Use the usrfdiskpartcreate( ) and dpartdevcreate( ) routines to do this -> usrfdiskpartcreate (pcbiocache, 2, 50, 0, 0) value = 0 = 0x0 For more information, see the entry for usrfdiskpartlibcbio( ) in the VxWorks Reference Manual In this step, the block device pointer pata could have been passed instead of pcbiocache Doing so would cause usrfdiskpartcreate( ) to use the BLK_DEV routines via a wrapper internally created by cbiowrapblkdev( ) 33

34 5. Display Partitions 34

35 6. Creating a dosfs Device Create a dosfs device using dosfsdevcreate( ), which calls iosdrvadd( ) internally. This step simply adds the device to the I/O system It does not invoke any I/O operations and, therefore, does not mount the disk This disk is not mounted until the first I/O operation occurs Create dosfs2 file systems atop each partition. The last argument specifies the integrated chkdsk configuration -> dosfsdevcreate ("/DOSA", dpartpartget (pcbioparts,0), 16, 0) value = 0 = 0x0 35

36 7. Formatting the Volume By calling dosfsvolformat( ) directly, specifying options for both the format ofthe FAT and the directory format (described below) By issuing the ioctl( ) FIODISKINIT command, which invokes the formatting routine with dosfslib This method uses the default volume format and parameters For more details, see the VxWorks API Reference entries for dosfsvolformat( ) and ioctl( ) The MS-DOS and dosfs file systems provide options for the format of the File Allocation Table (FAT) and the format of the directory 36

37 File Allocation Table (FAT) Formats 37

38 8. Mounting Volumes A disk volume is mounted automatically, generally during the first open( ) or creat( ) operation for a file or directory on the disk Certain ioctl( ) calls also cause the disk to be mounted File I/O Files on a dosfs file system device are created, deleted, written, and read using the standard VxWorks I/O routines: creat( ), remove( ), write( ), and read( ) File Attributes The file-attribute byte in a dosfs directory entry consists of a set of flag bits, each indicating a particular file characteristic 38

39 Flags in the File-Attribute Byte 39

40 Raw File System: rawfs VxWorks provides a minimal "file system," rawfs, for use in systems that require only the most basic disk I/O functions The rawfs file system, implemented in rawfslib, treats the entire disk volume much like a single large file rawfs file system offers advantages in size and performance if more complex functions are not required To use the rawfs file system in a VxWorks-based system, include the INCLUDE_RAWFS component in the kernel, and set the NUM_RAWFS_FILES parameter to the desired maximum open file descriptor count 40

41 Disk Organization The rawfs file system imposes no organization of the data on the disk It maintains no directory information; thus there is no division of the disk area into specific files All open( ) operations on rawfs devices specify only the device name; no additional filenames are possible The entire disk area is treated as a single file and is available to any file descriptor that is open for the device All read and write operations to the disk use a byte-offset relative to the start of the first block on the disk 41

42 CD-ROM File System: cdromfs The cdromfs library, cdromfslib, lets applications read any CD-ROM that is formatted in accordance with ISO 9660 file system standards To configure VxWorks with cdromfs, add the INCLUDE_CDROMFS component to the kernel After initializing cdromfs and mounting it on a CD-ROM block device, access data on that device using the standard POSIX I/O calls: open( ), close( ), read( ), ioctl( ), readdir( ), and stat( ) The write( ) call always returns an error For information on using cdromfs( ), see the VxWorks API Reference entry for cdromfslib 42

43 The Target Server File System: TSFS The Target Server File System (TSFS) is designed for development and diagnostic purposes It is a full-featured VxWorks file system, but the files are actually located on the host system The TSFS provides all of the I/O features of the network driver for remote file access (netdrv), without requiring any target resources The TSFS uses a WDB driver to transfer requests from the VxWorks I/O system to the target server To use the TSFS, your VxWorks-based system must be configured with the INCLUDE_WDB_TSFS component in the kernel. This creates the /tgtsvr file system 43

44 Summary I/O system Basic I/O Buffered I/O Formatted I/O The driver number assigned to the dosfs file system is recorded in a global variable, dosfsdrvnum Initializing the file system invokes iosdrvinstall( ), which adds the driver to the I/O system driver table A disk volume is mounted automatically, generally during the first open( ) or creat( ) operation for a file or directory on the disk The rawfs file system imposes no organization of the data on the disk The Target Server File System (TSFS) is designed for development and diagnostic purposes 44