File System FAQ

Fs_init() vs. fs_mkfs() What need to be done where: FS_init() takes care of system wise FS related initialization (Related to the running system). FS_mkfs() is doing the initialization of the FS itself. (Related to the specifics of FS on disk) How to tell: Think what will happen if you have two disks in your system (How you separate work)

Fs_init() vs. fs_mkfs() (cont.) When to init file descriptor table. When to set bitmaps and inodes to be free. When to initialize currentInode (correspond to “/”)

Directory structure Disk layout vs memory layout: common.h typedef struct { char name[MAX_NAME]; int inodeNo; char dummy[DIRECTORY_ENTR Y_SIZE - MAX_NAME - 4]; } dirEntry; #define MAX_NAME 32 #define MAX_INODE_DIGITS 31 #define DIRECTORY_ENTRY_SI ZE (MAX_NAME+MAX_INO DE_DIGITS+1) #define INVALID -1

Inode contents Opens: To keep track of concurrent opens for this file. (No need to put them on disk) Links: To keep track of number of hard links.

Fs_lseek() semantic. Our fs_lseek() only takes two arguments fd, offset Unix lseek() takes three fd, offset, whence Whence: SEEK_SET, SEEK_CUR, SEEK_END So our fs_lseek() will assume one of them SEEK_SET, if you prefer other, put that in your README file. What if lseek() want to seek after end of file?

Pathname (Absolute pathname?) Do we need to support absolute pathname Eg: When I am in “/foo”, do I need to support: chdir /bar/tmp/ You do not need to do that for this project. (Otherwise, you would have to support absolute pathname everywhere: open, link, mkdir… etc)

Remove directory Do I need to support removing directory that are not empty? Ie: Remove all the subdirectories and files contained in the parent directory when removing parent directory? No. Just return error when the directory to be removed is not empty.

Treat directory as file? What does it mean; why? If you treat directory as file, then you can use your existing function to handle file I/O to do directory manipulation. (Avoid duplicate efforts internally.) Say if you want to implement indirect blocks (both for file and directory) If you treat directory same as file, then you would not need to worry about indirect blocks when you are working on the directory.

Can I modify fs_fsck and others Yes. If you have different disk layout or assumptions than ours. (But make sure you still have a correct fs_fsck! Also document them in README.) Also if you implement extra credits, you would have to make fs_fsck correct as well.

Synchronous operation Can I cache directory, inode, bitmap … etc to speed up FS? Yes. But for this project, your first priority is to make it correct. (ie, if power failure occurs, your FS should still be in consistent state.) So better make them synchronous. If you make them work, you can get extra credit!!

Want some more for Christmas?! If you think you have fancy ideas to improve our FS, you can get extra credits. Please me on what you want to do and we can discuss them. Potential ideas: (Other than on web) Implement buffer cache (1 credit?) Implement write ahead log (2 credits?) Implement a good automated test suite using “expect”? (1 credit?)