1 File Processing : File Organization and File Systems 2015, Spring Pusan National University Ki-Joune Li

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

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

STEMPNU 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

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

STEMPNU 6 Slotted Page n 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. n 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. n Pointers should not point directly to record But to the entry for the record in header. n Pointers should not point directly to record But to the entry for the record in header. Pointer to Record

STEMPNU 7 Reserved Space Maximum # of Fields

STEMPNU 8 Overflow Area First field of record Rest records

STEMPNU 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 Name ID# Contiguous Reserved Block for BLOB

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

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

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

STEMPNU 13 Block configuration for i-node Boot Block Super Block 0 1 i-node 1 ~ 40 i-node 41 ~ 80 … … 2 3 Data block … … Reserved Block Given by formatting User space

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

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

STEMPNU 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