OS Project #2:Random File Access  Random file access: using the lseek() system call to access files in UNIX. zTake arguments from the command line.  Syntax: viewfile [pos] [length]  Position the I/O head of a file starting from the position [pos] by lseek() system calls; print the contenet of the file for exactly [length] numbers of bytes using read() system calls.  NB: [pos] can be very large.

OS Project #2: cont’d 1 zUsing Makefile and make statement. zWrite a shell script to automatically test your program. zNote: Read the manuals of  read(), open(), lseek() system calls. ymake statement and Makefile syntax.  the isprint() library function for testing chars.  Hints: reference the output formats of the usual od (octal dump) command in UNIX.

OS Project #2: cont’d 2 zSample usage:  simon> viewfile sample.txt  c a t h e a d. t x t i d s  e  p s | m a i l - s " S  2e c20 6d61 696c 202d  U B M I T " s u b m i s s i o  d d f  j u p i t e r. k a i s t.  6e40 6a e 6b e  a c. k r y l l i n y a w l  e6b c 6c69 6e c  i y e l l o w. c s. n t h  696e c 6c6f 772e e6e 7468  u. e d  752e 6564

OS Project #2: cont’d 3 zSample usage:  simon> viewfile /home/mike/foo.bin  \0 \0 : D \0 \0 \0 \0 \0 \0 \0 \0 \0 \0  a  \ D 225 * 002  bc d003 a a a 2002  \n 027 \0 \ "  9402 a a f9 d422 e138  \0 \0 \b 302 \0 b \b \ \0 004  c  \0 \0 \0 \0 \n 001 \0 \0 \  a f004  \0 \0 \0 ? # \  fc9 9c23 a f003  \0 \0 \0 

z #include z off_t lseek(int fildes, off_t offset, int whence); zDESCRIPTION z The lseek() function sets the file pointer associated with z the open file descriptor specified by fildes as follows: z o If whence is SEEK_SET, the pointer is set to offset z bytes. z o If whence is SEEK_CUR, the pointer is set to its z current location plus offset. z o If whence is SEEK_END, the pointer is set to the size z of the file plus offset. z The symbolic constants SEEK_SET, SEEK_CUR, and SEEK_END are z defined in the header. lseek() - move read/write file pointer