4. Reading code in MP

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4. Reading code in MP

제 13 강 : Reading Code in Modular Process(MP)

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Modular Programming ...• Solves

– Faster compile– Many people can edit

• New Problems– Inter-dependency between files (eg define - use)– Which information - which file?– Change a file – what next?– N people update a.c simultaneously?– Debugging?

src

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src

include sysvmnet

sys.h inode.h user.h driver.c stream.c hd.cvm.h file.h error.h intrp.c signal.c strategy.ccdev.h bdev.h type.h read.c write.c sleep.cinit.h flt.h mount.h nfs.c super.c win.cobj.h text.h abs.h ftp.c telnet.c fill.c . . . . . . . .

. . . . .

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#include "user.h"#include "sys.h"#include "type.h"

int sys_read (pst)struct buf *pst;{char ps[MAX];int index;

while (i ... ){ ... }

Reading Codes . . . read.c src

sysvm

net

sys.h inode.h user.h driver.c stream.c hd.cvm.h file.h error.h intrp.c signal.c strategy.ccdev.h bdev.h type.h read.c write.c sleep.cinit.h flt.h mount hnfs.c super.c win.cobj.h text.h abs.h ftp.c telnet.c fill.c . . . . . . . .

. . . . .

ex cd linux-practice/srccd lions/usr/syslscd kenvi fio.c

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#include "user.h"#include "sys.h"#include "type.h"

int sys_read (pst) struct buf *pst; {char ps[MAX];int index;

while ((index < MAX ) && (read (temp) != LEVEL) ) {. . . .

}

Reading Codes . . . read.c

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#include "user.h"#include "sys.h"#include "type.h"

int sys_read (pst) --------------- who calls this?struct buf *pst; ------- what is “buf”?{char ps[MAX];int index;

while ((index < MAX ) && (read (temp) != LEVEL) ) {. . . .

------------ where is read()? what does it perform?}

Reading Codes . . . read.c

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src

include sys vm net

sys.h inode.h user.h driver.c stream.c hd.cvm.h file.h error.h intrp.c signal.c strategy.ccdev.h bdev.h type.h read.c write.c sleep.cinit.h flt.h mount.h nfs.c super.c win.cobj.h text.h abs.h ftp.c telnet.c fill.c . . . . . . . .

. . . . .

Where do I find “read()" ?

Reading Codes

Manual or automatic search?

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Where is getc() function? (1/5)grep

• Character String Search Command command string file

grep read *.c

Output: eg function (1), calls(30),

comments(100) ex cd linux-practice/src

cd lions/usr/sys/kengrep read *.c | more #--- find read() function

#--- too many lines

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Where is getc() function? (2/5)

Regular Expression• Previous approach: too much output • Find out exact location where function is

defined: eg Find the line where function read()

begins

Regular Expression

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Skip RE if you already know

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finding exact location of a function definition

egreturn type space function name para

comment

[ C syntax ]– return type alphabets [a-Z]*– space bar | tab [\b \t]*– function name alphabet + any char [a-Z] .*– parameters ( expression )

int read (parameters); /* sys call */

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---- Regular Expression: Metacharacters ----

. Any single char

[ ] any single char from this set [abc] [a-z] [a-zA-Z]+ one or more repetition of preceding item (.+ [a-z]+)* zero or more repetition of preceding item (.* [a-z]*)

[^ ] negate the set (“caret”) ([^0-9] – any char except digit)

[ \t] tab[ \b] blank

^ BOL$ EOL

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---- RE Examples ----

. Any char

[ ] a char from this set[^ ] negate the set

+ one or more repeat* zero or more repeat

[ \t] tab[ \b] blank

^ BOL$ EOL

. a b c d O

.* O a aa aaa abc

.+ a aa aaa abc

a a ( 一般 search : no meta-char)

abc abc ( 一般 search :no

meta-char )

ab+ ab abb abbb

ab* a ab abb abbb

ab. abc abd abf

abc+ abc abccc abccccc

ab[1-3] ab1 ab2 ab3

ab[1-3]+ ab11 ab1233

a[1-5]b[6-9] a1b6 a5b7

c[^a-Z]+ c1 c23 c243

Strings in the target fileRE

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grep---regular expression

• grep ^[a-Z]* [ ]*read( *.c search in all .c files

left-parenthesis

match “read” string space-or-tab

zero-or-more-repetition-of-previous-char any-alphabet-charbeginning-of-new-line

New line, function type, function_name ( The target pattern

type space name para

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Escape – “Don’t handle this part”

(1) user sees shell prompt(2) types command, say, grep [a-Z]* read( *.c(3) shell reads input (line edit)

– (Meaning of *’s are different)• grep’s interpretation of * (0 or more repetition)• sh’s interpretation of * (all .c files under cwd)

– (1st *) is for grep (child process)– (2nd *) is for sh (current process)– escape – “Current process should not handle this part”

(4) Escaped parts are un-touched by current process

grep ‘ [a-Z]* read(’ *.c shell

grep

RE for grep

[a-Z]* read(’

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Shell Escape• Escape a single char (\ -- back slash)

– echo * vs echo \*

• Escape string ( ‘ ‘ -- single quote), – echo ‘this part is not for shell’

• Escape string ( “ ” -- double quote), except– echo “this part not for shell except $PATH”– echo “Today is `date`”– A few exceptions such as:

($) variable expansion (``) command substitution (see

next)

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Command substitution ( ` ` back-quote)1. execute inside ` `2. substitute command arg by output from

` `

eg echo date; echo `date`

– mail `cat name_file` name_file:bob jim

– mail bob jim dan dan

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shell escape exerciseecho date

echo `date`

echo *echo \*

echo ‘PATH is $PATH’echo “PATH is $PATH”

echo ‘Today is `date`’echo “Today is `date`”

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---- Regular Expression ----

. Any char

[ ] a char from this set[^ ] negate the set

+ one or more repetetion* zero or more repetetion

[ \t] tab[ \b] blank

^ BOL$ EOL

In Linux: -E should be used (grep -E …) -[ ] type blank as it is (not [\b]) -\{ escape needed for { e.g. grep -E “struct[ ]+buf[ ]+\{” -f file_name containing RE pattern

Used in many commands vi, sh, perl, sed, awk minor differences …

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To find MAX• char ps[MAX]; --- It must be a C constant

looking for #define MAX

123 RE ^#define[ ]+MAX [ ]

+[0-9]+To find buf

• struct buf *pst; --- It must be a C struct

looking for struct buf { RE ^struct[ ]+ buf[ ]*\{

See next page for this

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ex cd cd lions/usr/sys/ken

(1) to find struct buf

grep –E ‘struct[ ]+buf[ ]*’ *.c

(2) to find macro MAX

grep –E ‘#define[ ]+MAX[ ]+’ *.c

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Where is read() function?find

• What if many directories? – Run grep many times (each dir)?

• find: traverse all nodes in a sub-tree • find /x -print

– Visit each file under /x and print its pathname

• find / -name ‘a.out’ -print– all files with name a.out (why single quote here?)

• find . -size +12 -print– size 12 blocks

• find / -mtime 7 -print– not modified for a week

src

bobdan

jim

ex find /^c

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Where is read() function?find

• find /x -exec wc {} \; for this pathname (file)

end of this command (wc)– Visit each file under /x and – perform given command (wc) for the current given

file

• find /x -exec cat {} \;– Visit each file under /x and – cat each current given file

• find / -name ‘a.out’ -exec rm {} \;

src

bobdan

jim

** locate command find is slow locate builds DB fast search

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• find / -type d -user root -print– !: negate– O: or– conatenation: and

• find /x -exec grep read {} \;• find /x -exec grep “^[a-Z]*[ ]+read\(” {} \;• find /x -exec grep -f use_file {} \; use_file: ^[a-Z]*[ ]+read\(

• FIND: find /x -exec grep “^[a-Z]*[ ]+$1\(” {} \; FIND getc

src

bobdan

jim

2 conditions

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ex cd cd lions/usr/sys/ken

#----- to find definition struct “inode” #----- but it is not here in ken/

cd .. #--- to lions/usr/sys #--- visit every file below #--- and check definition of

inode#--- use grep command

find . -exec grep -E “struct[ ]+inode[ ]*” {} \;

lions/src/usr/sys

kendmr buf.h ino.h