1. File Processing : File Organization and File Systems
2018, Spring
Pusan National University
Ki-Joune Li

2. Logical Structure of File
Field
File
Field
Field
Record (Tuple)
Fixed Size Record
Record
Variable Size Record
Record
Block

3. Fixed Size Record Fixed Size Disk Address Deletion of a record
Fixed Number of Fields, and
Fixed Size of each Field
Easy to implement
Disk Address
(n-1)*srecord
Deletion of a record
Like Array but no movement
Free Record List or
Pointer to Next Record

4. Variable Length Record
Variable Length due to
Variable Number of Fields, or
Variable Size of each Field
Complicated to implement
Implementation
Delimiter (, size, or pointer)
Slotted Page
Fixed Length
Overflow Area
Reserved Space

5. Delimiters Difficult to handle deletions and insertions Delimiters
Record
Record …
Record
Record
Record …
Record
Delimiters
Pointer/Size
Difficult to handle deletions and insertions

6. Slotted Page Records can be moved around within a page
Pointer to Record
Records can be moved around within a page
to keep them contiguous with no empty space between them
entry in the header must be updated.
Pointers should not point directly to record
But to the entry for the record in header.

7. Reserved Space
Maximum # of Fields

8. Overflow Area
First field of record
Rest records

9. Binary Large Object Block (BLOB)
If size (field) > size (block)
e.g. Image or Video
BLOB : Type of field where its size is greater than block size
cf. CLOB : Text rather than binary
Name
ID#
Photo
Block size
Contiguous Reserved Block for BLOB
Name
ID#

10. File System Example fd=open(”data.txt”,O_RDONLY,0);
Nbytes=read(fd,buf,100);
 How to process these functions in OS ?

11. i (index)–node : information about file
Attributes
Pointers to data block
i-node
Data Block
Name
Type : directory, data, special
Permission
Ownership
Last updated date/time
Created date/time

12. i-node : Pointer to data block
. . .
Attributes
Pointers to data block
(0-9: up to 40K bytes)
Single direct Pointer
Pointer Block
(1024 blocks)
Double direct Pointer
Data Block
. . .

13. Block configuration for i-node
Boot Block
Reserved Block 1
Super Block
i-node 1 ~ 40
i-node 41 ~ 80 … 2 3
Given by formatting
Data block …
User space

14. Implementation of File Hierarchy
Attributes
i-node 1 1 4 7 14
Root directory block 9 6 8 . ..
bin
dev
lib
etc
usr
tmp
Attributes
i-node 6 6 1 19 30 54
Directory block for /usr . ..
lik
kimmk
parksh
Attributes
i-node 19 19 6
107
Directory block for /usr/lik . ..
data.txt
i-node for root directory
i-node for /usr
i-node for /usr/lik
Attributes
i-node 107
i-node for /usr/lik/data.txt
Data block for /usr/lik/data.txt

15. FAT (File Allocation Table)
DOS or MS-Windows 98
Same purpose of i-node in UNIX

16. fd=open(”data.txt”,O_RDONLY,0); Nbytes=read(fd,buf,100);
Step 1 : Find i-node for “data.txt” via i-node
from root or current directory
Step 2 : Check owner and access right
Step 3 : Register it to OpenFileTable
Initialize entry values : e.g. offset, mode
fd : array index of this table
Some entries : reserved for stdio, stderr, etc..
Step 4 : Check ownership and right
Step 5 : Read 100 bytes to buf
Read 100 bytes from the OpenFileTable[fd].offset
OpenFileTable[fd].offset += 100;
open
write