Lecture 5 Software Development under Unix

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Lecture 5Software Development under Unix

CSCE 510 Systems Programming

• Topics
• File systems revisited
• Directories
• Libraries archives
• Ar

September 1, 2005
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• Last Time
• xx
• Today
• Overview of the Compilation Process
• Files Systems revisited
• Next Time
• yy
• Handouts
• C Reference Card
• http//cm.bell-labs.com/cm/cs/who/dmr/chist.html
  (Ritchie Article on the history of C )

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File systems

• File systems
• 1.boot block
• 2.super block
• 3.inode table
• 4.data blocks

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Original Unix File system

• Disk Block Pointers
• 10 direct pointers
• single indirect pointer
• double indirect pointer
• triple indirect pointer
• Assuming 32 bit words, 24 bit disk block pointers
  and 512 byte blocks what is the largest possible
  file using the original Unix Scheme?

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Adding Directories

• Commands mkdir
• From in a program
• int mkdir ( const char path, mode_t mode )

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Directory Entries

• /usr/include/dirent.h
• struct dirent
• ino_t d_ino
• char d_nameNAME_MAX 1

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Directory functions

• DIR opendir(const char path)
• struct dirent readdir(DIR dp)
• void rewinddir(DIR dp)
• int closedir(DIR dp)
• int rmdir(const char path)
• mkdir

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File Times

• Times in stat struct of inode
• st_atime "last access time" (ls -ul)
• st_mtime "last modification time" (ls -l)
• st_ctime "last inode change time" chmod, chown,
  (ls -cl)
• time_t time in seconds since 000000 GMT, Jan
  1, 1970
• /usr/include/time.h
• struct utimbuf
• time_t actime / access time /
• time_t modtime / modification time /
• int utime(const path, struct utimbuf times) /
  set times/

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Ls1.c

• main(int argc, char argv)
• DIR dp
• struct dirent dirp
• if (argc ! 2)
• err_quit("a single argument (the
  directory name) is required")
• if ( (dp opendir(argv1)) NULL)
• err_quit("can't open ")
• while ( (dirp readdir(dp)) ! NULL)
• printf("7d\ts\n", dirp-gtd_ino,
  dirp-gtd_name)
• closedir(dp)

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AR - archive and library maintainer

• A file produced by ar has a magic string at the
  start, followed by the constituent files, each
  preceded by a file header. The magic number and
  header layout as described in the include file
  are
• struct ar_hdr
• char ar_name16
• char ar_date12
• char ar_uid6
• char ar_gid6
• char ar_mode8
• char ar_size10
• char ar_fmag2

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TSEARCH(3) Linux

• NAME
• tsearch, tfind, tdelete, twalk - manage a
  binary tree
• SYNOPSIS
• include ltsearch.hgt
• void tsearch(const void key, void
  rootp,
• int(compar)(const void ,
  const void ))
• void tfind(const void key, const void
  rootp,
• int(compar)(const void ,
  const void ))
• void tdelete(const void key, void
  rootp,
• int(compar)(const void ,
  const void ))
• void twalk(const void root,
  void(action)(const void nodep,
• const
  VISIT which,
• const
  int depth))

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• int compare(const void pa, const void pb)
• if((int )pa lt (int )pb) return
  -1
• if((int )pa gt (int )pb) return
  1
• return 0

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