Reminder. COP4600 Discussion 9 Assignment4. Discussion 8 Recap. Question-1(Segmentation) Question-2(I-node) Question-1(Segmentation) 10/24/2010

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1 COP4600 Discussion 9 Assignment4 TA: Huafeng Jin hj0@cise.ufl.edu Reminder Homework3 is due today at midnight will be posted soon, please prepare for it Discussion 8 Recap Segmentation Segmentation vs. paging (dynamic vs. fixed) Segmentation with paging (seg. no. + page no. + offset) File System (basic unit: block) File System Implementation (contiguous) FAT (File Allocation Table: entry for each block) I-node (direct, single/double/triple indirect address) File Directory (file hierarchy) with I-node (directory block + i-node) Question-1(Segmentation) We have: Total 16 pages Each segment has at most 4 pages Page size is 2KB How many bits are used for segmentation no.? How many bits are used for page no.? What is the MULTICS virtual address for 9000? Fork() Implementation (Delay the copy of space) Question-1(Segmentation) We have: Total 16 pages Each segment has at most 4 pages Page size is 2KB How many bits are used for segmentation no.? How many bits are used for page no.? What is the MULTICS virtual address for 9000? Answer: 2 bits for segmentation no. (4 segments) 2 bits for page no. (4 pages/segment) Offset: 9000%2KB = 9000%2048 = 808 Seg. no. : 1, Page no. : 0, Offset: 808 Question-2(I-node) Each I-node block can hold: 12 direct addresses 1 single indirect address 1 double indirect address 1 triple indirect address Block size is 2KB, and a block address takes 32 bits. What is the largest file size using this i-node? 1

2 Question-2(I-node) Each I-node block can hold: 12 direct addresses 1 single indirect address 1 double indirect address 1 triple indirect address Block size is 2KB, and a block address takes 32 bits. What is the largest file size using this i-node? Answer: One block can hold 2KB/32bits = 2048/4 = 512 addresses. N = 512 Total # blocks: 12 + N + N 2 + N 3 = 134,480,396 Max file size: 134, * 2KB = 256.5GB Question-2(I-node) Each I-node block can hold: 12 direct addresses 1 single indirect address 1 double indirect address 1 triple indirect address Block size is 2KB, and a block address takes 32 bits. What is the largest file size using this i-node? Answer: Triple indirection is powerful enough One block can hold 2KB/32bits = 2048/4 = 512 addresses. N = 512 Total # blocks: 12 + N + N 2 + N 3 = 134,480,396 Max file size: 134, * 2KB = 256.5GB Hard link and symbolic link: A special file used in file sharing Hard Link: Make all directory entries that share a file point to the i-node of the file and keep a link counter in the i-node. counter: 2 2

3 Symbolic Link: Create a new i-node for the link and store the full path of the shared file in the i-node of the symbolic link. New i-node: \-B-B-? Hard Link: Symbolic Link: What happens if we delete the shared file? Hard Link: Only decrements the counter, file still exist Delete the file when counter = 0 Symbolic Link: Delete the file Symbolic link becomes dangle. Assignment4 Description : Make changes to the File System simulator to include hard link and symbolic link. C Version: Provided: FileSystem.c, Block.c, Block.h Java Version: Provided: Block.java, AddressBlock.java, DataBlock.java, DirectoryBlock.java, Inode.java, FileSystem.java Both versions are the same. Run the simulator Compile the simulator: C: Java: gcc *.c javac *.java Run the simulator: Type help to find out the available commands > //input command here > 3

4 Commands Supported What you need to do Command help pwd touch filename cp filename1 filename2 more filename rmfilename stat filename mkdir dirname ls cd dirname up exit Description Print out all the commands Print current directory Create a file under current directory Copy file1 to file2 Print out contents of file Delete the file Print out block#, link# for a file Create a directory Print out all the files in the current directory Changes to a subdirectory Changes to the parent directory Terminates the simulator Implement 3 more commands: ln source_file_name hardlink_name ln -s source_file_name symbolic_link_name stat -L file_name Changes to 4 existing commands to support hard/symbolic links: rm filename more filename cp filename1 filename2 cd dirname Three New Commands ln source_file_name hardlink_name Create a hard link Directory block: Add a new entry (hardlink_name, inode# of source_file_name) to current directory s directory block. Inode: Increments the count in the inode of source_file_name. ln -s source_file_name symbolic_link_name Create a symbolic link Data block: Create new data block(s) to hold the name of source file. Inode: Create a new inode with address of the data block. Directory block:add a new entry (symbolic_link_name, inode# of new inode) to the current directory s directory block. Three New Commands stat -L file_name Print out status of symbolic link with file_name If file_name is a symbolic link, then follow the link and print out the source file s status. ln Command Hard Link: Symbolic Link: Four Existing Commands rm filename Decrements link count for a file If count = 0, then delete the file more filename If file: display the file contents If link: if does not exist (symbolic link), then msg cp filename1 filename2 If filename2 is a link, then overwrite the source file of the link. cd dirname If a symbolic link to a directory, then change current directory to the source directory. 4

5 Notes The names: File/directory names are all immediate names (no path). This means refer to a file/directory under the current directory. Four existing commands: Only change behavior when name is a hard/symbolic link, otherwise they do not change. Sample Output Type help to find out the available commands > mkdir Creates a new directory under root directory. InodeNo: 1 > touch Creates an empty file under root. InodeNo: 2 > cp temp f2 Creates a new file f2 under root and copy temp to f2. temp is a file under the simulator folder. InodeNo: 3 f2 Lists all the files/directories under current directory (root). stat Regular file InodeNo: 2 # of data blocks 1 Print out status of directory ln f2 hf2 Creates a hard link hf2 to f2 under root directory. Doesn t create a new inode. f2 hf2 > stat hf2 Hardlink InodeNo: 3 # of data blocks 1 Prints out status of hf2. Actually the status of f2. > ln -s s Creates a symbolic link s to under root directory. InodeNo: 4 (creates a new inode) f2 hf2 s > stat s SymLink InodeNo: 4 # of data blocks 1 Prints out status of s. Actually the status of. > cd s Changes the current directory to the source of s (). 5

6 > up Changes the current directory to the parent directory (root). > more hf2 a b c d Prints out the source file of hf2 (f2). > rm f2 Decrements the link count of f2 (2 1). hf2 s Lists all the files/directories under current directory (root). > more hf2 a b c d Prints out hf2 (f2 still exists, rm only decrements the count). > more s s is a link to a directory! Cannot print out a directory. > exit Terminates the program. Simulator Structure Main function/method: Both C and Java versions: while(true/1){ Parse input processcommand(); } Process Command: List of if-else switches for each command. Blocks Four kinds of blocks: Data Block (file) Each data block can hold at most 20 bytes Directory Block (directory) I-node I-node is a special block that contains addresses of blocks. Address Block (I-node indirections) 6

7 Blocks C Version: Block is a union of Inode, address block, directory block, and data block structs. Java Version: Block is a parent class of Inode, address block, directory block, and data block classes. Basic Operations Block operations: Creates a new block: AddressBlock, Inode, DataBlock, DirectoryBlock Gets a block Gets block number Sets block number Adds an entry to DirectoryBlock Basic Operations C Version: Defined in Block.h Java Version: Defined in Block.java Recap Any Questions? 7