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LMP1: I/O and Filesystems ========================= Welcome to LMP1, the first long MP. LMP1 is the first stage of a project aimed at creating a simple yet functional networked filesystem. In this MP, you will learn about and use POSIX file system calls, while subsequent LMPs will introduce memory management, messaging, and networking functionality. If you implement all parts of this MP correctly, you will be able to reuse your code for future MPs. This first LMP concentrates on the file I/O portion of the project. Specifically, you will implement a custom filesystem and test its performance using a filesystem benchmark. A benchmark is an application used to test the performance of some aspect of the system. We will be using Bonnie, a real filesystem benchmark, to test various performance aspects of the filesystem we implement. LMP1 consists of four steps: 1. Read the code; run the Bonnie benchmark and the LMP1 test suite. 2. Implement Test Suite 1 functionality, encompassing basic file I/O operations. 3. Implement Test Suite 2-4 functionality (directory operations, file creation/deletion, and recursive checksumming). 4. Modify Bonnie to use your client-server file I/O methods. Code structure -------------- The code for this project is structured according to the client-server model. The client code (filesystem benchmark) will interact with the server (filesystem) only through interface functions defined in fileio.h: int file_read(char *path, int offset, void *buffer, size_t bufbytes); int file_info(char *path, void *buffer, size_t bufbytes); int file_write(char *path, int offset, void *buffer, size_t bufbytes); int file_create(char *path,char *pattern, int repeatcount); int file_remove(char *path); int dir_create(char *path); int dir_list(char *path,void *buffer, size_t bufbytes); int file_checksum(char *path); int dir_checksum(char *path); These functions represent a simple interface to our filesystem. In Steps 2 and 3 of this MP, you will write the code for functions implementing this interface, replacing the stub code in fileio.c. In Step 4, you will modify a Bonnie method to use this interface, rather than calling the normal POSIX I/O functions directly. The purpose of Step 4 is to help test our implementation. Step 1: Understanding the code ------------------------------ 1. Compile the project, execute Bonnie and the test framework. Note: you may need to add execute permissions to the .sh files using the command "chmod +x *.sh". Try the following: make ./lmp1 (this runs the Bonnie benchmark - it may take a little while) ./lmp1 -test suite1 (run Test Suite 1 - this has to work for stage1) make test (run all tests - this has to work for stage2) 2. Read through the provided .c and .h files and understand how this project is organized: bonnie.c - a version of the filesystem benchmark fileio.c - file I/O functions to be implemented fileio.h - declaration of file I/O functions restart.c - restart library (available for use in fileio.c) restart.h - declaration of restart library functions util.c - useful utility functions util.h - declaration of useful utility functions and macros In particular, pay close attention to the comments in fileio.h and bonnieb.c. You should understand what each of the following functions in bonnie.c does before undertaking the remainder of the MP: fill_file_char() file_read_rewrite() file_read_rewrite_block() fill_file_block() fill_read_getc() file_read_chunk() newfile() Step 2: Basic I/O operations ---------------------------- Implement file_read, file_write and file_info operations in fileio.c. If done correctly, your code should pass all suite1 tests: ./lmp1 -test suite1 Running tests... 1.read ::pass 2.info ::pass 3.write ::pass Test Results:3 tests,3 passed,0 failed. IMPORTANT: fileio.c is the only file you should modify for this step. Step 3: More filesystem operations ---------------------------------- Implement file and directory operations for suite2 (dir_create and dir_list), suite3 (file_create and file_remove), and suite4 (file_checksum and dir_checksum). You can test each operation and test suite individually: ./lmp1 -test dirlist ./lmp1 -test suite2 All tests should now pass: make test Running tests... 1.read ::pass 2.info ::pass 3.write ::pass 4.dirlist ::pass 5.dircreate ::pass 6.remove ::pass 7.create ::pass 8.filechecksum ::pass 9.dirchecksum ::pass Test Results:9 tests,9 passed,0 failed. Step 4: Performance testing --------------------------- In this step, we will change parts of Bonnie to use our filesystem interface. Make the function file_read_rewrite_block() in bonnie.c to call your fileio.c functions instead of POSIX I/O operations. When answering the questions below, use this modified version of bonnie.c. Before making this change, it's a good idea to write pseudocode comments for what each part of file_read_rewrite_block() does, so that you understand the code and can perform the change correctly. There may not be an exact one-to-one correspondence between our filesystem interface and the POSIX commands. Note: In future LMPs, we will be using the fileio.h interface in a similar manner, but we will call the functions remotely, via a message queue. Questions --------- Q1. Briefly explain what the following code from bonnie.c does: if ((words = read(fd, (char *) buf, Chunk)) == -1) ... Q2. Is the above an example of a block read or a character read? What is the value of the variable 'words' if the read succeeds? Fails? Q3. Explain the meaning of the flag value (O_CREAT | O_WRONLY | O_APPEND) for the POSIX function open(). Q4. Run Bonnie. What is being measured by each test function? Q5. Look at the summary results from the Bonnie run in Q4. Does Bonnie measure latency, throughput or something else? Justify your answer. Q6. Compare character reads with block reads using Bonnie. Which is faster? Why do you think this is the case? Q7. Copy and paste the performance measures output when running Bonnie benchmarks in a local directory and again in an NFS-mounted directory. Is one kind of disk access noticeably slower over the network, or are all tests significantly slower? Your home directory may be an NFS mount, whereas /tmp and /scratch are local disks. To test your code in /tmp, do the following: mkdir /tmp/your_username cp lmp1 /tmp/your_username cd /tmp/your_username ./lmp1 (record the output) cd rm -fr /tmp/your_username Q8. How does Bonnie handle incomplete reads, e.g., due to interruptions from signals? Justify why Bonnie's approach is good or bad for a filesystem benchmark program. Q9. By now you should be very familiar with the self-evaluation test harness we provide for the MPs. Examine the function test_file_read() in lmp1_tests.c, which tests your file_read() function from Step 2. What does this test check for, specifically? You may want to copy and paste the code for this function in your answer, and annotate each quit_if or group of related quit_ifs with a comment.

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