CS Week 12. Lab 4 - Introduction. Teaching Assistant Henrique Potter

Transcription

1 CS 1550 Week 12 Lab 4 - Introduction Teaching Assistant Henrique Potter

2 Lab 4 Bigger Files for xv6 Reuse xv6 qemu Changing how xv6 organizes file blocks in the inode

3 Lab 4 Bigger Files for xv6 Current implementation limit files to 72 KB Disk Sectors 0 xv6 Can only map 140 sectors

4 Lab 4 Bigger Files for xv6 Current implementation limit files to 72 KB Disk Sectors bytes

5 Lab 4 Bigger Files for xv6 Current implementation limit files to 72 KB Disk Sectors bytes bytes 140

6 Lab 4 Bigger Files for xv6 Current implementation limit files to 72 KB Disk Sectors bytes bytes We want it to be able to map more then 140 sectors/ blocks.

7 Lab 4 Bigger Files for xv6 This limit is based in the current implementation of direct and indirect references you can use in the inode.

8 Lab 4 Bigger Files for xv6 This limit is based in the current implementation of direct and indirect references you can use in the inode. We can modify xv6 to be able to map bigger files by adding a double indirect reference in its inode.

9 Lab 4 Bigger Files for xv6 This limit is based in the current implementation of direct and indirect references you can use in the inode. We can modify xv6 to be able to map bigger files by adding a double indirect reference in its inode. xv6 also uses the Unix Fast File System (FFS) or (UFS)

10 Lab 4 xv6 Unix Fast File System inode meta Every file have an inode that holds its meta

11 Lab 4 xv6 Unix Fast File System inode meta Every file have an inode that holds its meta It also maps where to find in disk the blocks of that compose that file

12 Lab 4 xv6 Unix Fast File System inode meta some_file.some_extesion

13 Lab 4 xv6 Unix Fast File System inode meta.. some_file.some_extesion

14 Lab 4 xv6 Unix Fast File System inode meta.. some_file.some_extesion Saved as blocks of 512 bytes. (each block is a disk sector)

15 Lab 4 xv6 Unix Fast File System inode meta Direct pointers

16 Lab 4 xv6 Unix Fast File System inode meta. Direct pointers

17 Lab 4 xv6 Unix Fast File System inode meta Direct pointers. Referred in the lab 4 description as the disk sectors

18 Lab 4 xv6 Unix Fast File System inode meta Direct pointers single indirect.

19 Lab 4 xv6 Unix Fast File System Another table of pointers to actual addresses in disk inode meta Direct pointers single indirect.

20 Lab 4 xv6 Unix Fast File System In xv6 you can have 12 direct pointers In xv6 this guy holds 128 blocks inode meta Direct pointers single indirect.

21 Lab 4 xv6 Unix Fast File System inode meta Direct pointers. The lab task is to increase is to add a double indirect block single indirect

22 Lab 4 xv6 Unix Fast File System inode meta Direct pointers single indirect double indirect Each pointer will point to a table of single indirect pointers.

23 Lab 4 xv6 Unix Fast File System inode meta Direct pointers single indirect double indirect And each pointer from this table table to actual physical blocks.

24 Lab 4 xv6 Unix Fast File System inode meta Direct pointers single indirect double indirect And each pointer from this table table to actual physical blocks..

25 Lab 4 xv6 Unix Fast File System inode meta Direct pointers single indirect double indirect triple indirect...

26 Lab 4 xv6 Unix Fast File System Lab 4 goal inode meta Direct pointers single indirect double indirect.. It will allow us to map files up to 8.5 MB

27 Lab 4 Bigger Files for xv6 Important xv6 files for this lab are: fs.h defines the number of direct blocks fs.c bmap() file.h inode struct

28 Lab 4 Bigger Files for xv6 qemu optimizations Modify the xv6 makefile CPUS := 1 QEMUESTRA = -snapshot

29 Lab 4 Bigger Files for xv6 qemu optimizations Modify the xv6 makefile CPUS := 1 QEMUESTRA = -snapshot Param.h FSSIZE = 20000

30 Lab 4 Bigger Files for xv6 qemu optimizations Modify the xv6 makefile CPUS := 1 QEMUESTRA = -snapshot Param.h FSSIZE = Copy big.c (course web lab description) Will attempt to create a big and will how many sectors it could use to create it

31 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done

32 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done In the bmap() from the fs.c file if((addr = a[bn]) == 0){ a[bn] = addr = balloc(ip->dev); log_write(bp); }

33 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done In the bmap() from the fs.c file if((addr = a[bn]) == 0){ a[bn] = addr = balloc(ip->dev); log_write(bp); } Blocks are not immediately written to disk

34 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done In the end_op(void) from the log.c file

35 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done In the end_op(void) from the log.c file commit(); At the end of all FS system calls end_op is called and commits all pending disk writes

36 Lab 4 Bigger Files for xv6 Writes to disk are delayed and will be written in batch once disk operations are done In the commit(void) from the log.c file commit() { if (log.lh.n > 0) write_head(); // Write header to disk -- the real commit }

37 CS 1550 Lab 4 Due: Monday, November 30, Late: Wednesday, December 2, 10% reduction per late day

38 CS 1550 Week 12 Lab 4 Teaching Assistant Henrique Potter