Project 5 Roadmap

1
Project 5 Roadmap
2
Logical disk layout
3
Directory Entry
GOSFS_Dir_Entry
blockList10
size
filename128
acl10
data blocks
Directory
MAX_FILES_PER_DIR
Directory Block
4
Data storage Direct Mapping
Data storage Direct Mapping
GOSFS_Dir_Entry.blockList10
DISK
0
1
4KB data block
2
4KB data block
4KB data block
used
12KB file depicted
5
Data storage Single Indirect
Data storage Single Indirect
GOSFS_Dir_Entry.blockList10
DISK
0
0
1
4KB data block
2
3
4
.
4KB data block
5
6
4KB data block
7
single indirect block
8
4KB data block
9
0
0
1
2
3
4KB data block
4
.
.
40KB file depicted
.
1022
1023
6
Data storage Double Indirect
Data storage Double Indirect
GOSFS_Dir_Entry.blockList10
DISK
0
0
1
4KB data block
single indirect block
2
3
4
4KB data block
.
5
6
4KB data block
7
0
0
0
0
1
1
8
2
2
4KB data block
3
3
4
4
9
.
.
.
.
.
.
1022
1022
4KB data block
1023
1023
4136KB file depicted
single indirect block
double indirect block
7
Data storage - overview

• 0,32KB use direct mapped blocks only
• (32KB,4128KB use direct mapped blocks single
  indirect blocks
• (4128KB,32MB use direct mapped blocks single
  indirect blocks double indirect blocks

8
Format

• SYS_FORMAT
• Format(char dev, char fstype)
• Original Disk Layout
• Dont have to do it in init, will be called from
  user space
• Only for GOSFS, not for PFAT

9
Mount

• SYS_MOUNT
• vsf.c Mount(char devname, char pathPrefix,
  char fstype)
• gosfs.cGOSFS_Mount(struct Mount_Point
  mountPoint)
• Steps
• check superblock validity
• fill out mountPoint
• might consider using an instance
  (see PFAT_Instance in pfat.c)
• Make sure it works, so that we can test the rest
  of your project

10
Syscalls

• SYS_OPEN
• Open(char name, int mode)
• Not allowed for directories
• Create files when appropriate
• SYS_OPENDIRECTORY
• OpenDirectory(char path)
• Not allowed for files
• SYS_CLOSE
• Close(int fd)
• SYS_DELETE
• Delete(char path)
• If path is a non-empty directory and not empty,
  forbid !

11
Syscalls

• SYS_READ
• Read(int fd, char buffer, int length)
• Not allowed for directories
• return value
• lt0, if failure
• gt0 , bytes available
• SYS_WRITE
• Write(int fd, char buffer, int length)
• Not allowed for directories
• Grow on write - allocate blocks on the fly if
  past end of file
• Grow minimum needed a random seek to the
  middle of an empty file and a write result in
  only one allocated block
• Synchronous
• SYS_READ/SYS_WRITE increase the offset with
  bytes read/written

12
Syscalls

• SYS_READENTRY
• ReadEntry(int fd,VFS_Dir_Entry entry)
• Read and return information about a single file
  in a directory
• Advance one file entry at a time, return 1 when
  the directory ends
• Use File-gtfilePos to remember current entry
• Seek specifies number of entries to skip (i.e.
  seek(5) would then read the 5th entry)
• Not allowed for files

13
Syscalls

• SYS_STAT
• Stat(char path, VFS_File_Stat stat)
• Works on an unopened file
• Simply copy verbatim from GOSFS_Dir_Entry
• SYS_FSTAT
• FStat(int fd, VFS_File_Stat stat)
• Works on an open file
• Simply copy verbatim from GOSFS_Dir_Entry
• SYS_SEEK
• Seek(int fd, int offset)
• Implement only absolute semantics for offset
• Allowed to past end of file

14
Syscalls

• SYS_CREATEDIR
• CreateDirectory(char name)
• Should NOT go recursively
• e.g. CreateDirectory("/d/d1/d2/d3/d4)
• SYS_SYNC
• Sync(void)
• Should synchronize any outstanding data to disk

15
The Buffer Cache

• idea keep some disk blocks in memory (buffers)
  memory is much faster to read/write than disk
• buffer life cycle
• Get - Modify - Release
• bufcache.c
• Create_FS_Buffer_Cache(struct Block_Device
  dev,)
• Get_FS_Buffer()
• Modify_FS_Buffer()
• Sync_FS_Buffer()
• Release_FS_Buffer()