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OS Project #2:Random File Access

OS Project #2:Random File Access. Random file access: using the lseek() system call to access files in UNIX. Take arguments from the command line. Syntax: viewfile <filename> [pos] [length]

morgan-vazquez
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OS Project #2:Random File Access

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  1. OS Project #2:Random File Access • Random file access: using the lseek() system call to access files in UNIX. • Take arguments from the command line. • Syntax: viewfile <filename> [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.

  2. OS Project #2: cont’d 1 • Using Makefile and make statement. • Write a shell script to automatically test your program. • Note: Read the manuals of • read(), open(), lseek() system calls. • make 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.

  3. OS Project #2: cont’d 2 • Sample usage: • simon> viewfile sample.txt 200 100 • 0000200 c a t h e a d . t x t i d s • 6361 7420 6865 6164 2e74 7874 2069 6473 • 0000216 . p s | m a i l - s " S • 2e70 7320 7c20 6d61 696c 202d 7320 2253 • 0000232 U B M I T " s u b m i s s i o • 5542 4d49 5422 2073 7562 6d69 7373 696f • 0000248 n @ j u p i t e r . k a i s t . • 6e40 6a75 7069 7465 722e 6b61 6973 742e • 0000264 a c . k r y l l i n y a w l • 6163 2e6b 7220 796c 6c69 6e20 7961 776c • 0000280 i n @ y e l l o w . c s . n t h • 696e 4079 656c 6c6f 772e 6373 2e6e 7468 • 0000296 u . e d • 752e 6564

  4. OS Project #2: cont’d 3 • Sample usage: • simon> viewfile /home/mike/foo.bin 200 100 • 0000200 \0 \0 : D \0 \0 \0 \0 \0 \0 \0 \0 \0 \0 • 0000 3a44 0000 2020 0000 0000 0000 0000 • 0000216 274 020 \0 320 003 240 @ 222 003 240 D 225 * 002 • bc10 2000 d003 a040 9203 a044 952a 2002 • 0000232 224 002 240 004 224 002 @ \n 027 \0 \0 371 324 " 341 8 • 9402 a004 9402 400a 1700 00f9 d422 e138 • 0000248 003 \0 \0 \b 302 \0 b \b 200 220 \0 001 002 200 \0 004 • 0300 0008 c200 6208 8090 0001 0280 0004 • 0000264 001 \0 \0 \0 @ \0 \0 \n 001 \0 \0 \0 @ \0 360 004 • 0100 0000 4000 000a 0100 0000 4000 f004 • 0000280 001 \0 \0 \0 @ \0 ? 311 234 # 240 @ \0 360 003 • 0100 0000 4000 3fc9 9c23 a020 4000 f003 • 0000296 001 \0 \0 \0 • 0100 0000

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

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