Lecture 2 Stat system call

1
Lecture 2Stat system call
CSCE 510 Systems Programming

• Topics
• Course Pragmatics
• What is systems software?
• Unix History
• C/C history
• Primitive Unix I/O
• Unix I/O system Calls
• Open File Structure
• String library

August 23, 2005
2
Overview

• Last Time
• Standard I/O struct _iobuf
• I/O system calls
• Readings
• Unix I/O system Calls
• Open File Structure
• String library
• Next Time
• The Stat Structure
• Handouts
• C Reference Card

3
Hole.c

• include ltsys/types.hgt
• include ltsys/stat.hgt
• include ltfcntl.hgt
• include "ourhdr.h"
• char buf1 "abcdefghij"
• char buf2 "ABCDEFGHIJ"
• int
• main(void)
• int fd
• if ( (fd creat("file.hole", FILE_MODE)) lt 0)
• err_sys("creat error")
• if (write(fd, buf1, 10) ! 10)
• err_sys("buf1 write error")
• / offset now 10 /

if (lseek(fd, 400000, SEEK_SET)
-1) err_sys("lseek error") / offset now
40000 / if (write(fd, buf2, 10) !
10) err_sys("buf2 write error") exit(0) vo
id err_sys(const char msg, ...)
fprintf(stderr, "ERROR s", msg) exit(1)
4
The string library

• /usr/include/string.h
• strings in C
• strlen
• strcmp
• strncmp
• strcat
• strncat
• strcpy
• strchr
• strstr
• strpbrk
• strspn
• strcspan
• strtok
• strerror

5
The string library

• Strings in C
• char p
• /usr/include/string.h

• strlen
• strcmp
• strncmp
• strcat
• strncat
• strcpy
• strchr
• strstr
• strpbrk
• strspn
• strcspan
• strtok
• strerror

6
getchar macro

• define getc(p) \
• (--(p)-gt_cnt lt 0 ? __filbuf(p)
  (int)(p)-gt_ptr)

7
File Sharing
8
Dup and dup2

• DUP(2) Linux Programmer's
  Manual
• NAME
• dup, dup2 - duplicate a file descriptor
• SYNOPSIS
• include ltunistd.hgt
• int dup(int oldfd)
• int dup2(int oldfd, int newfd)

9
Lseek

• include lt sys/types gt
• include lt unistd.h gt
• off_t lseek(int filedes, off_t offset, int
  start_flag)
• SEEK_SET(0)
• SEEK_CUR(1)
• SEEK_END(2)

10
Stat Structure

• include lt sys/stat.h gt
• struct stat
• dev_t st_dev / file system ID /
• ino_t st_ino / the inode number /
• mode_t st_mode / permissions and type
  information/
• nlink_t st_nlink / number of links /
• uid_t st_uid / File owner user ID /
• gid_t st_gid / File group ID /
• dev_t st_rdev / Major and minor device
  numbers /
• off_t st_size / size in bytes /
• time_t st_atime / last access time /
• time_t st_mtime / last modification time /
• time_t st_ctime / last status change time /
  
• long st_blksize / best I/O block size /
• long st_blocks / number of 512-byte blocks'
  /

11
st_mode

• st_mode - information on file type and
  permissions

12
File types

• regular file
• directory
• symbolic link
• character device file
• block device file
• FIFO
• socket

13

• mode 32 bits -
• define _S_IFMT 0170000 / Octal number type of
  file /
• define _S_IFREG 0100000 / regular sync with
  S_IFREG /

14
File type Testing macros

• File type Testing macros from stdio.h
• define S_ISDIR( mode ) (((mode) _S_IFMT)
  _S_IFDIR)

15
File Permissions

• File Permissions
• User, group, others
• 3 bits for each read, write, execute (rwx)
• ls -l
• chmod command

16
Mode Testing definitions

• Mode Testing definitions / file modes /
• define S_IRWXU 00700 / read, write, execute
  owner /
• define S_IRUSR 00400 / read permission owner
  /
• define S_IWUSR 00200 / write permission owner
  /
• define S_IXUSR 00100 / execute permission
  owner ...
• define S_ISUID 0004000 / set user id on
  execution /
• define S_ISGID 0002000 / set group id on
  execution /

17
The stat, fstat lstat system calls

• int stat(const path, struct stat buf) - get
  statistics on this file
• int fstat(int fd, struct stat buf) - a version
  of stat for open files
• int lstat(const path, struct stat buf) - a
  version of stat that does not follow symbolic
  links
• Command line arguments website/C-Intro/printargs.c
  

18
filetype.c

• ...
• struct stat buf
• char ptr
• for (i 1 i lt argc i)
• printf("s ", argvi)
• if (lstat(argvi, buf) lt 0)
• err_ret("lstat error")
• continue
• if (S_ISREG(buf.st_mode)) ptr "regular"

19
Inode information

• All of the stat structure info
• Disk block addresses
• Original Unix File system Disk Block Pointers
• 10 direct pointers
• single indirect pointer
• double indirect pointer
• triple indirect pointer

20
HW 1 Due Thursday 500PM

• Create a file with a hole in it and check the
  file size with "ls -s".
• Get a copy of hole.c, compile and run it.
• cp /class/csci510/Examples/hole.c . // copy files
  
• cp /class/csci510/Examples/ourhdr.h .
• cc o genHole hole.c // Compile the program
• ./genHole // Create the file file.hole
• Use man to see what "ls -s" tells you.
• Use "ls -s file.hole.
• Use "cp file.hole file2" to create another copy
  and then use "ls -s file2".
• Login to a solaris machine (e.g. coosawhatchee)
  and repeat compile, create and copy to create
  file3
• Use "wc" (wordcount) on these files.