+--------------------------+ | CS 318 | | PROJECT 2: USER PROGRAMS | | DESIGN DOCUMENT | +--------------------------+ ---- GROUP ---- >> Fill in the names and email addresses of your group members. FirstName LastName FirstName LastName FirstName LastName ---- PRELIMINARIES ---- >> If you have any preliminary comments on your submission, notes for the >> TAs, or extra credit, please give them here. >> Please cite any offline or online sources you consulted while >> preparing your submission, other than the Pintos documentation, course >> text, lecture notes, and course staff. ARGUMENT PASSING ================ ---- DATA STRUCTURES ---- >> A1: Copy here the declaration of each new or changed `struct' or >> `struct' member, global or static variable, `typedef', or >> enumeration. Identify the purpose of each in 25 words or less. ---- ALGORITHMS ---- >> A2: Briefly describe how you implemented argument parsing. How do >> you arrange for the elements of argv[] to be in the right order? >> How do you avoid overflowing the stack page? ---- RATIONALE ---- >> A3: Why does Pintos implement strtok_r() but not strtok()? >> A4: In Pintos, the kernel separates commands into a executable name >> and arguments. In Unix-like systems, the shell does this >> separation. Identify at least two advantages of the Unix approach. SYSTEM CALLS ============ ---- DATA STRUCTURES ---- >> B1: Copy here the declaration of each new or changed `struct' or >> `struct' member, global or static variable, `typedef', or >> enumeration. Identify the purpose of each in 25 words or less. >> B2: Describe how file descriptors are associated with open files. >> Are file descriptors unique within the entire OS or just within a >> single process? ---- ALGORITHMS ---- >> B3: Describe your code for reading and writing user data from the >> kernel. >> B4: Suppose a system call causes a full page (4,096 bytes) of data >> to be copied from user space into the kernel. What is the least >> and the greatest possible number of inspections of the page table >> (e.g. calls to pagedir_get_page()) that might result? What about >> for a system call that only copies 2 bytes of data? Is there room >> for improvement in these numbers, and how much? >> B5: Briefly describe your implementation of the "wait" system call >> and how it interacts with process termination. >> B6: Any access to user program memory at a user-specified address >> can fail due to a bad pointer value. Such accesses must cause the >> process to be terminated. System calls are fraught with such >> accesses, e.g. a "write" system call requires reading the system >> call number from the user stack, then each of the call's three >> arguments, then an arbitrary amount of user memory, and any of >> these can fail at any point. This poses a design and >> error-handling problem: how do you best avoid obscuring the primary >> function of code in a morass of error-handling? Furthermore, when >> an error is detected, how do you ensure that all temporarily >> allocated resources (locks, buffers, etc.) are freed? In a few >> paragraphs, describe the strategy or strategies you adopted for >> managing these issues. Give an example. ---- SYNCHRONIZATION ---- >> B7: The "exec" system call returns -1 if loading the new executable >> fails, so it cannot return before the new executable has completed >> loading. How does your code ensure this? How is the load >> success/failure status passed back to the thread that calls "exec"? >> B8: Consider parent process P with child process C. How do you >> ensure proper synchronization and avoid race conditions when P >> calls wait(C) before C exits? After C exits? How do you ensure >> that all resources are freed in each case? How about when P >> terminates without waiting, before C exits? After C exits? Are >> there any special cases? ---- RATIONALE ---- >> B9: Why did you choose to implement access to user memory from the >> kernel in the way that you did? >> B10: What advantages or disadvantages can you see to your design >> for file descriptors? >> B11: The default tid_t to pid_t mapping is the identity mapping. >> If you changed it, what advantages are there to your approach? SURVEY QUESTIONS ================ Answering these questions is optional, but it will help us improve the course in future quarters. Feel free to tell us anything you want--these questions are just to spur your thoughts. You may also choose to respond anonymously in the course evaluations at the end of the quarter. >> In your opinion, was this assignment, or any one of the three problems >> in it, too easy or too hard? Did it take too long or too little time? >> Did you find that working on a particular part of the assignment gave >> you greater insight into some aspect of OS design? >> Is there some particular fact or hint we should give students in >> future quarters to help them solve the problems? Conversely, did you >> find any of our guidance to be misleading? >> Do you have any suggestions for the TAs to more effectively assist >> students, either for future quarters or the remaining projects? >> Any other comments?