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Lecture Operating System: Chapter 06 - University of Technology
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Lecture Operating System: Chapter 06 - File Systems presented Files, Directories, File system implementation, Example file systems.
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Nội dung Text: Lecture Operating System: Chapter 06 - University of Technology
- Chapter 6
File Systems
6.1 Files
6.2 Directories
6.3 File system implementation
6.4 Example file systems
- Long-term Information Storage
• Must store large amounts of data
• Information stored must survive the
termination of the process using it
• Multiple processes must be able to access
the information concurrently
- File Naming
Typical file extensions.
- File Structure
• Three kinds of files
– byte sequence
– record sequence
– tree
- File Types
(a) An executable file (b) An archive
- File Access
• Sequential access
– read all bytes/records from the beginning
– cannot jump around, could rewind or back up
– convenient when medium was mag tape
• Random access
– bytes/records read in any order
– essential for data base systems
– read can be …
• move file marker (seek), then read or …
• read and then move file marker
- File Attributes
Possible file attributes
- File Operations
1. Create 7. Append
2. Delete 8. Seek
3. Open 9. Get attributes
4. Close 10.Set Attributes
5. Read 11.Rename
6. Write
- An Example Program Using File System Calls (1/2)
- An Example Program Using File System Calls (2/2)
- Memory-Mapped Files
(a) Segmented process before mapping files
into its address space
(b) Process after mapping
existing file abc into one segment
creating new segment for xyz
- Directories
Single-Level Directory Systems
• A single level directory system
– contains 4 files
– owned by 3 different people, A, B, and C
- Two-level Directory Systems
Letters indicate owners of the directories and files
- Hierarchical Directory Systems
A hierarchical directory system
- Path Names
A UNIX directory tree
- Directory Operations
1. Create 5. Readdir
2. Delete 6. Rename
3. Opendir 7. Link
4. Closedir 8. Unlink
- File System Implementation
A possible file system layout
- Implementing Files (1)
(a) Contiguous allocation of disk space for 7 files
(b) State of the disk after files D and E have been removed
- Implementing Files (2)
Storing a file as a linked list of disk blocks
- Implementing Files (3)
Linked list allocation using a file allocation table in RAM
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