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File System – Unix baed

File System – Unix baed. An entry of Active File table: 1. Access Right: r/w/x 2. Process Count: no. of processes which are now referring to the file 3. Read Pointer/Write pointer: The starting points of next reading and writing, respectively.

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File System – Unix baed

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  1. File System – Unix baed

  2. An entry of Active File table: • 1. Access Right: r/w/x • 2. Process Count: no. of processes which are now referring to the file • 3. Read Pointer/Write pointer: The starting points of next reading and writing, respectively. • 4. Active i-node table entry: pointer to an active i-node • …

  3. An entry of Active i-node table: • 1. Reference Count: no. of active file table entries that are pointing to this entry • 2. Device address: address of an I/O device • 3. Owner ID • 4. Group ID • 5. Last user who reads/writes: User ID of the user who perform the last read/write.

  4. System call open(): • 1. if U-ofile is full then return (-1) • 2. if (“file name” is not in Active i-node table) read the directory entry from the i-node in disk according to “file name”; • 3. if (“file name” does not exist in the i-node table in disk) return (-1); • 4. check access right – user ID and –rwxrwxrwx; • 5. if (access deny) then return (-1); • 6. allocate a free Active i-node table entry (AITE);

  5. 7. copy directory data of underlying file to this entry; • 8. allocate a free Active File table entry (AFTE); • 9. copy directory data of underlying file to this entry; • 10. allocate a free U-ofile entry (UOE) with the lowest fd in underlying user’s PCB; • 11. connect the path UOE – AFTE – AITE;

  6. system call write (): • 1. access the AFTE according to fd specified by the user. fd is one of the arguments of the system call; • 2. check the access right; • 3. if (access deny) return (-1); • 4. write the data specified in the buffer “buf” to the file according to write pointer recorded in the user’s corresponding AFTE;

  7. system call read (): • 1. access the AFTE according to fd specified by the user. fd is one of the arguments of the system call; • 2. check the access right; • 3. if (access deny) return (-1); • 4. read the data pointed to by the user’s read pointer to the buffer “buf” specified in the arguments of the system call;

  8. system call create (): • 1. allocate a free current directory entry; • 2. fill in some data, like file name, date, time, …; • 3. write the directory entry back to disk; • 4. system call open ();

  9. system call close (fd): • 1. follow the fd specified in the argument of this system call to access the corresponding AFTE from user’s U-ofile; • 2. if ((process count--) == 0) {disconnect the connection between the AFTE and its AITE; if ((reference count--) == 0) store AITE back to i-node table in disk;}

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