File Systems

Question 1

Attributes of a file

Answer 1

name, identifier
type
location
size
protection

Question 2

Goals of file management

Answer 2

• provide a convenient naming scheme for files
• provide uniform I/O support for variety of storage device types
• provide a standardized set of I/O interface functions
• minimize/eliminate loss or corruption of data

Question 3

typical file control block includes…

Answer 3

• file permissions
• file dates (create, access, write)
• file owner, group, ACL
• file size
• file data blocks or pointers to file data blocks

Question 4

How does contiguous allocation work? also name advantages & disadvantages

Answer 4

A contiguous array of blocks is allocated for each newly created file. A file can’t become larger than the pre-allocated space. The FS only needs to store the start block and the size of each file.
+ It allows for sequential and direct access.
- Can’t grow beyond initially reserved size

Question 5

How does chained allocation work? also name advantages & disadvantages

Answer 5

The FS stores a pointer to the first block of each file, but each block now contains a pointer to the next block that belongs to the same file.
+ no need to pre-allocate disk blocks for files
+ no external fragmentation
- only sequential access possible

Question 6

What is the idea of linked listed allocation with a file allocation table (FAT)?

Answer 6

The FAT approach is very similar to the chained allocation approach but stores the list information in a separate data structure. The entire list has to be walked to find a byte in a file, but it doesn’t require disk accesses if FAT is cached.
- the size of the FAT doesn’t depend on the number or size of files, but on the size of the hard disk

Question 7

How does indexed allocation work?

Answer 7

It groups the pointers to disk blocks occupied by a specific file together into a single data structure, the index block. There is one index block for each file. Once an index block is loaded to the main memory, it is easy to find a specific block of the file.

Question 8

What are hard links?

Answer 8

Each directory entry is a hard link; they simply map a name to an inode. They are thus implemented through the file system. Having created a file f and a link l to it, f and l are indistinguishable. Both names f and l are hard links to the file represented by the inode both of them map to.

Question 9

What are symbolic links?

Answer 9

Their content is interpreted by the VFS and consists only of the relative or absolute path to the pointed file. They are files of the type “symbolic link”.