File Processing : File Organization and File Systems

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File Processing File Organization and File
Systems

• 2008, Spring
• Pusan National University
• Ki-Joune Li

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

• Fixed Size
• 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

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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

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Delimiters
Record
Record

Record
Record
Record

Record

• Difficult to handle deletions and insertions

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Slotted Page

• 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.

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Reserved Space
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Overflow Area
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Binary Large Object Block (BLOB)

• If size (field) gt 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
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File System

• Example
• fdopen(data.txt,O_RDONLY,0)
• Nbytesread(fd,buf,100)
• ? How to process these functions in OS ?

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i (index)node information about file
Name
Type directory, data, special
Permission
Ownership
Last updated date/time
Created date/time
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i-node Pointer to data block
Attributes
Pointers to data block (0-9 up to 40K bytes)
Single direct Pointer
Double direct Pointer
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Block configuration for i-node
Boot Block
0
Reserved Block
Super Block
1
User space
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Implementation of File Hierarchy
i-node for root directory
i-node for /usr
i-node for /usr/lik
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FAT (File Allocation Table)

• DOS or MS-Windows 98
• Same purpose of i-node in UNIX

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fdopen(data.txt,O_RDONLY,0)Nbytesread(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 OpenFileTablefd.offset
• OpenFileTablefd.offset 100