Examples&Exercises:

• Complete the following codes if necessary, then compile and run the code.
• Analyze the code and output.

1. access: Testing File Permissions; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/check-access.c check-access.c
   • first execute with a non-existing file,
   • then create a file and change permission bits to observe the behavior of the program,
   • see the system calls by

     $ strace check-access
     

     study the output in detail.
2. fcntl: Locks and Other File Operations; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/lock-file.c lock-file.c
   • execute without supplying a filename,
   • execute in two different windows as

     $ ./lock-file supplyafile
     

3. fsync: Flushing Disk Buffers ; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/write_journal_entry.c write_journal_entry.c
   • Complete the code,
   • say you have a endless loop to produce the entries in the main function,
   • study the cases with and without fsync,
   • observe the size changes in the journal in another window,
   • can you estimate the buffer size for the without fsync case?
4. getrlimit and setrlimit: Resource Limits; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/limit-cpu.c limit-cpu.c
   • see what are other possible resource limits by

     $ man getrlimit
     $ man setrlimit
     

   • modify the code to print out these resource limits supplied as defaults,
   • interpret the output.
5. getrusage: Process Statistics; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/print-cpu-times.c print-cpu-times.c
   • Complete the code,
   • see what are other possible process statistics by (see struct rusage)

     $ man getrusage
     

   • modify the code to print out these process statistics supplied as defaults,
   • interpret the output.
6. mprotect: Setting Memory Permissions; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/mprotect.c mprotect.c
   • it is given for PROT_NONE for no memory access,
   • try the other memory protection flags PROT_READ, PROT_WRITE, and PROT_EXEC for read, write, and execute permission, respectively.
7. readlink: Reading Symbolic Links; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/print-symlink.c print-symlink.c
   • study the cases;
     • without a file,
     • with an ordinary file (not a symbolic file),
     • create a link by

       $ ln -s arealfile supplyaname
       $./print-symlink supplyaname
       

8. sysinfo: Obtaining System Statistics; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/sysinfo.c sysinfo.c
   • see what are other possible system statistics by (see struct sysinfo)

     $ man sysinfo
     

   • modify the code to print out these system statistics,
   • interpret the output.
9. Inline Assembly Code (Example); http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/bit-pos-asm.c bit-pos-asm.c, http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/bit-pos-loop.c bit-pos-loop.c
   • compile and execute as the followings

     $ gcc -O2 -o bit-pos-loop bit-pos-loop.c
     $ gcc -O2 -o bit-pos-asm bit-pos-asm.c
     $ time ./bit-pos-loop 250000000
     $ time ./bit-pos-asm 250000000
     

   • why the optimization level 2 is used?
   • try the other levels and observe the execution times,
   • analyze the results; which optimization level should be used and why?
10. TO BE GRADED; modify the code http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/lock-file.c lock-file.c such that
    • we have two processes (either two threads or a forked child),
    • these two processes have an access to same file to read and write,
    • your program should investigate the following cases;
      • one is locked the file by fcntl and the other tries to read and write,
      • one is locked the file by fcntl and the other also tries to lock the file by fcntl then attempts to read and write.
    • what are the possible outcomes and issues?
11. TO BE GRADED; modify the completed code; http://siber.cankaya.edu.tr/SystemsProgramming/cfiles/print-cpu-times.c print-cpu-times.c such that
    • we have a parent and one child,
    • get process statistics for both the parent and the child,
    • interpret the output.