Homework 2

Tom Kelliher, CS 311

30 points, due Feb. 15

1. This problem is based on Programming Problem 2.27 in the textbook. From your Linux account, download the file fileCopy.c from the class web site and compile it:

   gcc -o fileCopy fileCopy.c
   

   Using strace, generate a system call trace file:

   strace -o trace ./fileCopy
   

   The trace will be stored in the file trace. I would suggest simply using filecopy.c as the source file.

   Answer the eight questions posed in fileCopy.c.

2. To get an idea of how an operating system's system calls interact with user programs and device interrupt handlers, you're going to implement, in pseudo-code, four short system calls and two short interrupt handlers. This small ``system'' uses a pool of buffers to perform I/O between application programs, an input device, and an output device.

   The buffers in the buffer pool are in one of three states at any point in time:

   1. INFULL -- input buffer full and available to be returned to the user on request.

   2. OUTFULL -- output buffer full and waiting to be output to the I/O device when ready.

   3. EMPTY -- empty buffer available for either input or output.

   These states can be implemented as separate linked lists, which you can initialize and manipulate using, at the pseudo-code level, the functions you implemented in Project 0.

   There are four system calls that are invoked by the user to accomplish I/O:

   1. bufptr Gbufin() -- returns a pointer to the beginning of the next full input buffer from INFULL. This should block if INFULL is empty.

   2. Rbufin(bufptr) -- places the buffer pointed to by bufptr back into EMPTY.

   3. bufptr Gbufout -- returns a pointer to the beginning of an empty buffer from EMPTY into which the user places data to be output. This should block if EMPTY is empty.

   4. Rbufout(bufptr) -- places the full output buffer pointed to by bufptr onto the end of OUTFULL.

   In addition, there are two interrupt handlers, one for input and one for output:

   1. IHinput -- called when an input operation has been completed.

   2. IHoutput -- called when an output operation has been completed.

   The diagram below illustrates how a buffer can move between these different states, and the role of the system software described above.

   

Tom Kelliher