Lecture 3 CSCE 510 - the Stat structure

• Omitted Last time
  • O_RDONLY, O_WRONLY, O_RDWR
  • O_CREAT, O_EXCL, O_TRUNC
• Error Last Time seek constants reveresed?

  #include < sys/types >
  #include < unistd.h >
  off_t lseek(int filedes, off_t offset, int start_flag);
  
  SEEK_SET(=0)
  SEEK_CUR(=1)
  SEEK_END(=2)
  

• Stat Structure < sys/stat.h > revisited

  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' */
  };
  

• st_mode - information on file type and permissions
• filetypes
  • regular file
  • directory
  • symbolic link
  • character device file
  • block device file
  • FIFO
  • socket
• mode 32 bits -
  • #define _S_IFMT 0170000 /* Octal number type of file; */
  • #define _S_IFREG 0100000 /* regular; sync with S_IFREG */
• File type Testing macros from stdio.h

  #define S_ISDIR( mode )         (((mode) & _S_IFMT) == _S_IFDIR)
  

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

• 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
• filetype.c

    ...
    struct stat   buf;
    char          *ptr;
    
    for (i = 1; i < argc; i++) {
      printf("%s: ", argv[i]);
      if (lstat(argv[i], &buf) < 0) {
        err_ret("lstat error");
        continue;
      }
      if      (S_ISREG(buf.st_mode))      ptr = "regular";
    ...        
  

• 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
• Assuming 32 bit words, 24 bit disk block pointers and 512 byte blocks what is the largest possible file using the original Unix Scheme?
• AR - archive and library maintainer
  • Why is it needed?
  • Syntax: ar -option [ posname ] archive file1 ...fileN
• man 5 ar

       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_name[16];
               char   ar_date[12];
               char   ar_uid[6];
               char   ar_gid[6];
               char   ar_mode[8];
               char   ar_size[10];
               char   ar_fmag[2];
       };
  

• AR options
• suboptions
• File Times
  • st_atime "last access time" (ls -ul)
  • st_mtime "last modification time"
  • st_ctime "last inode change time" chmod, chown, (ls -cl)
  • int utime(const *path, struct utimbuf *times)

    time_t  time in seconds since 00:00:00 GMT, January 1, 1970
    
    /usr/include/time.h 
    
    struct  utimbuf  {
                 time_t  actime;    /* access time */
                 time_t  modtime;   /* modification time */
         };
    
    

  [Readings:]

  [Assignment:]

  Program 1 due Sept 14 - AR
  

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