chapter 39 - interlude: files and directories

Question 1

what is a file

Answer 1

linear sequence of bytes identified by an inode number

Question 2

What is a directory?

Answer 2

File mapping to inode numbers

Question 2

What is a directory tree?

Answer 2

A hierarchy starting from root /, containing nested directories and files

Question 3

what does int fd = open(“foo”, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR); do

Answer 3

• O_CREAT → create if not exist
• O_WRONLY → open for writing
• O_TRUNC → empty the file if it exists
• S_IRUSR | S_IWUSR → user can read/write
• Returns a file descriptor, placed in the process’s ofile[NOFILE] array

Question 4

What is a file descriptor?

Answer 4

integer used to access an open file

starts @ 3 - bc the 0,1,2 er reserved

Question 5

What does lseek(fd, offset, whence) do?

Answer 5

Moves the file offset

Question 6

What is stored in the Open File Table?

Answer 6

Read/write flags, inode pointer, offset, and reference count

Question 7

What happens after fork() to file descriptors?

Answer 7

Child gets copies of parent’s FDs, sharing the same offset and inode

Question 8

What does dup(fd) do?

Answer 8

Duplicates fd, both share offset, inode, and permissions

Question 9

What does fsync(fd) do?

Answer 9

Forces all dirty data for that file to disk immediately

Question 9

What does rename(“old”, “new”) do?

Answer 9

Atomically renames a file; ensures no corruption even during crashes

Question 10

What does stat() or fstat() return?

Answer 10

Metadata like inode, size, permissions, owner, and timestamps

Question 11

What does unlink() do?

Answer 11

Removes a file; deletes it once all links and open FDs are gone