Working with the Unix OS

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Interprocess Communication When processes A and B run simultaneously, a situation could arise whereby process A has locked semaphore 0 and wants to lock semaphore 1, but process B has locked semaphore 1 and wants to lock semaphore 0. Both processes sleep, unable to continue. They are deadlocked and exit only on receipt of a signal. To avoid deadlock use multiple semaphore operations simultaneously: struct sembuf psernbuf[2]; psernbuf[0].sem_nurn = 0; psernbuf[l].sem_nurn = 1; psernbuf[0].sem_op = -1; psernbuf[0].sem_op = -1; semop(semid, psernbuf, 2); ! Undo Structures for Semaphores Per process Undo Headers : ----- Undo Structures desc num value desc num value desc num value ----- ----- : desc num value ----- Each undo structure is an array of triples consisting of: - a semaphore ID, - a semaphore number in the set identified by ID, - and an adjustment value. Sequence of Undo Structures ! After first operation semaphore id semid semaphore nurn 0 adjustment 1 ! After second operation seamphore id semid semid semaphore nurn 0 1 adjustment 1 1 ! After third operation semaphore id semid semaphore nurn 0 adjustment 1 ! After fourth operation empty BERKELEY Sockets The Application Program Interface (API) is the interface to a programmer. For UNIX there is Berleley Sockets and System V Transport Layer Interface (TLI). Network I/O includes File I/O system calls: open, creat, close, read, write, & lseek ! Network I/O considerations - client or server? - connection-oriented or connectionless - process names are more important in networking - more parameters for a network connection - communication protocol record boundaries - support multiple communication protocols 163
Interprocess Communication ! Comparison of Sockets, TLI, and FIFOs Sockets TLI FIFOs Server allocate space t_alloc() create endpoint ocket ( ) t_open ( ) mknod () open() bind address bind ( ) t_bind ( ) specify queue listen() wait for connection accept() t_listen() get new fd t_open ( ) t_bind ( ) t_accept ( ) Client allocate space t_alloc() create endpoint socket() t_open() open() bind address bind() t_bind() connect to server connect() t_connect() transfer data read() read() read () write() write() write() write() recv() t_rcv() send() t_snd() datagrams recvfrom() t_rcvudata() sendto() t_sndudata() terminate close() t_close() close() shutdown() t_sndrel() | t_snddis() | | protocol\server iterative concurrent | connection-oriented eg Daytime typical 1 | connectionless typical eg TFTP | ! Socket system calls connectionoriented protocol Server socket() | bind() | listen() | accept() | Client blocks until connection from client socket() | | | connect() | | read() write() | | process request| | | | write() read() 164
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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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Processes I Process States 1. Execu
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Processes I } printf("%d %s\n", cnt
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Processes I dup (and other similar
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Processes I The u area contains - p
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Processes I The Context of a Proces
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Processes I Process Control use and
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Processes I Although the processes
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Processes I Handling Signals - proc
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Processes I USER=neville PATH=/user
Page 115 and 116: Processes I ! Shadow Password /etc/
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Page 119 and 120: Processes I F_SETFL set status flag
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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
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Page 131 and 132: Processes II } /* child */ signal (
Page 133 and 134: Processes II int readline(int fd, c
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Page 139 and 140: Processes II System V IPC - message
Page 141 and 142: Processes II int msgctl(int msqid,
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Page 145 and 146: Processes II /* client loop */ mesg
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Page 149 and 150: I/O Subsystem Terminal Drivers - In
Page 151 and 152: I/O Subsystem Canonical Mode algori
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: Interprocess Communication /* struc
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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
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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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Page 200 and 201: Unix Administration fi done echo $s
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Page 204 and 205: Unix Security Example: group name:g
Page 206 and 207: Unix Security $ crypt < exam320.Z >
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Page 212: Unix Security - repairs damaged use
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