Working with the Unix OS

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145 I/O Subsystem Close only for the last close of the device - kernel searches the file table to make sure that no other processes still have the device open - several process may access the device via different file table entry - several device files may specify the same device different inodes but same device - for block devices, kernel searches the mount table to make sure that the device does not contain a mounted file system - the kernel searches the buffer cache for blocks marked "delayed write" and writes them before invoking the device close procedure. - kernel releases inode of the device file Kernel algorithms for read and write are similar to those of a regular file. The kernel can transmit data directly between address space and the device, or device drivers may buffer data internally e.g. terminal drivers use clist to buffer data. - memory mapped - status registers - programmed I/O - execute instructions - direct memory access (DMA) - used for bulk data transfer in parallel to CPU operations. - transfer data between device and user's address space faster (one less copy, no kernel buffers). ! Strategy interface To transmit data between the buffer cache and a device. The process must be locked in memory until the I/O transfer is complete. ! ioctl(fd, command, arg) Device specific ! Interrupt handlers Many physical devices can be associated with one interrupt vector entry, the driver must be able to resolve which device caused the interrupt. Disk Drivers Partitioning the disk into sections, means that some sections can be read-only, some read-write, and some unmounted (no access) Section Name Start Length Block in Blocks 0 0s0 0 64000 1 0s1 64000 192000 2 0s2 256000 256000 3 0s3 0 512000 Sections may overlap, but file systems must not. $ ls -1 Idev/dsk15 Idev/rdsk15 br------- 2 root root 0,21 Feb 12 15:40 /dev/dsk15 crw-rw--- 2 root root 7,21 May 7 09:29 /dev/rdsk15 The kernel loops internally 4 times to read 4096 bytes Programs that read and write the disk directly can destroy the consistency of the file system data. Therefore "fsck" should not run on active file system. Figure 31. Reading Disk Data - block & raw interface #include "fcntl.h" #include main() { char buf1[4096], buf2[4096]; int fdl, fd2, i; } if (((fdl =open("/dev/dsk5", O_RDONLY)) == -1) || ((fd2=open("/dev/rdsk5", O_RDONLY)) == -1)) { printf("failure on open\n"); exit(); } lseek(fdl, 8192L, 0); lseek(fd2, 8l92L, 0); if ((read(fdl, bufl, sizeof(buf1)) == -1) || (read(fd2, buf2, sizeof(buf2)) == -1)) { printf("failure on read\n"); exit(0); } for (i = 0; i < sizeof(buf1); i++) if (buf[I] != buf2[i]) { printf("different at offset %d\n", i); exit(0); } printf("reads match\n");
I/O Subsystem Terminal Drivers - Internally implement a "line discipline" which interprets the users' I/O. - In "canonical" mode, the line discipline converts the "raw" sequences typed by the user to a canonical form (what the user meant) before sending them to the user process. - In "raw" mode, the line discipline passes data between the process and the user without conversion. Functions of the Line Discipline - Parse input strings into lines. - Process "erase" (backspace-type) characters. - Process a "kill" character (all of present line). - Echo received characters. - Expand output e.g.: tab spaces - Generate signals e.g.: user hitting the interrupt key. - Allow a "raw" mode. Terminal I/O is buffered - Line disciplines manipulate "clists" (character list). Figure 32. Data Sequence and Data Flow through Line Dicsipline - Variable length linked list of CBlocks with a count of the number of characters on the list. - CBlock contains: - Pointer to next CBlock on list - Character array - Start & end offsets for data Next Start End Character Array Ptr Offset Offset 0123456 ... | 7 | 14 | garbage ... Kernel manages Clists and CBlocks - Keeps a list of free CBlocks A Cist is a variable linked list of Cblocks - Can do the following: 1. Assign a free CBlock to a driver 2. Return a CBlock to the free list 3. Retrieve first character from a Clist (null if none) 146
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UNIVERSITY OF ATHENS DEPARTMENT OF
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Figure 27. Driver Entry Points.....
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Introduction to Unix ! Execution ma
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Introduction to Unix It works in th
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Introduction to Unix * matches 0 or
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Introduction to Unix vi file-name s
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Introduction to Unix 1,$s/^/>>/ 1,$
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Introduction to Unix ! Special Devi
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Introduction to Unix Working with F
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Introduction to Unix ! Communicatio
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Unix Shells 2. UNIX SHELLS Back Quo
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Unix Shells ! CASE Statement case t
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Unix Shells two lines !Y@Y@Z@Z@ZY c
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Unix Shells if $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
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External Variables A C program cons
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C Programming - Basics main.c #incl
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C Programming - Basics default: pri
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C Programming - Basics struct tnode
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Unix Tools 4. UNIX TOOLS Tools of t
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Unix Tools Korn shell ! .profile HI
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Unix Tools grep "$name" $PHONEBOOK
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Unix Tools awk '$3 > 0 { print $1,
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Unix Tools END { print max, maxline
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Unix Tools Let an example input fil
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Unix Tools Brown eqn 1 # output Jon
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Development Tools Make looks at the
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Development Tools /* compute size o
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Development Tools #endif #line cons
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Development Tools 1.1 5 lines Retri
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Development Tools In Emacs, you may
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Development Tools */ %{ #define YYS
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C Libraries 6. C LIBRARIES Input an
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C Libraries } while (!feof(fp1)) pu
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C Libraries } free(p); /* what is w
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C Libraries } if ((fp->flag&( _READ
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C Libraries /* dirwalk: apply fcn t
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C Libraries } switch (pid=fork()){
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C Libraries What is curses? - libra
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C Libraries } if ((fd=fopen(argv[1]
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Introduction to kernel 7. INTRODUCT
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82 Introduction to kernel Programs
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Introduction to kernel } { printf("
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Introduction to kernel The kernel r
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Introduction to kernel UNIX Interna
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Introduction to kernel File System
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Introduction to kernel Every proces
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Page 99 and 100: Processes I } printf("%d %s\n", cnt
Page 101 and 102: Processes I dup (and other similar
Page 103 and 104: Processes I The u area contains - p
Page 105 and 106: Processes I The Context of a Proces
Page 107 and 108: Processes I Process Control use and
Page 109 and 110: Processes I Although the processes
Page 111 and 112: Processes I Handling Signals - proc
Page 113 and 114: Processes I USER=neville PATH=/user
Page 115 and 116: Processes I ! Shadow Password /etc/
Page 117 and 118: struct timeval { long tv_sec; /* se
Page 119 and 120: Processes I F_SETFL set status flag
Page 121 and 122: Processes I process is the child pr
Page 123 and 124: Processes I Rules about sharing of
Page 125 and 126: Processes II 9. PROCESSES (II) FORK
Page 127 and 128: Processes II /* background.c */ #in
Page 129 and 130: Processes II } while (1){ printf("p
Page 131 and 132: Processes II } /* child */ signal (
Page 133 and 134: Processes II int readline(int fd, c
Page 135 and 136: Processes II { } char process_name[
Page 137 and 138: Processes II - Pipe in a single pro
Page 139 and 140: Processes II System V IPC - message
Page 141 and 142: Processes II int msgctl(int msqid,
Page 143 and 144: Processes II For every semop operat
Page 145 and 146: Processes II /* client loop */ mesg
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Page 153 and 154: I/O Subsystem Raw Mode Raw mode is
Page 155 and 156: Figure 43. Pushing a Module onto a
Page 157 and 158: Interprocess Communication } { ptra
Page 159 and 160: Interprocess Communication T ID KEY
Page 161 and 162: Interprocess Communication }; int m
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Page 165 and 166: Interprocess Communication /* struc
Page 167 and 168: Interprocess Communication ! Compar
Page 169 and 170: … connect(sockfd,(struct sockaddr
Page 171 and 172: Interprocess Communication Address
Page 173 and 174: Process Scheduling Page Tables and
Page 176 and 177: Figure 49. Tie breaker rule Process
Page 178 and 179: Process Scheduling Clock - restart
Page 180 and 181: Process Scheduling Figure 57. Mappi
Page 182 and 183: Figure 62. Sequence of Swapping Ope
Page 184 and 185: Buffer Cache The kernel takes buffe
Page 186 and 187: Buffer Cache The kernel places the
Page 188 and 189: Buffer Cache Process B will find th
Page 190 and 191: Unix Administration 14. UNIX ADMINI
Page 192 and 193: Unix Administration Example output
Page 194 and 195: Unix Administration *) IN=-mtime -2
Page 196 and 197: Unix Administration Load /Unix kern
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Unix Administration for (i=0; i&i d
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Unix Administration fi done echo $s
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Unix Administration New Software !
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Unix Security Example: group name:g
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Unix Security $ crypt < exam320.Z >
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Unix Security - exported filesystem
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Unix Security system(cmdstr); $ ech
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Unix Security - repairs damaged use
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