CSE451 Introduction to Operating Systems Spring 2008

1. CSE451 Introduction to Operating Systems Spring 2008 Tour of the Windows NT File Systems Gary Kimura & Mark Zbikowski

2. History • Portable System Group formed November 1988 • Started with five software engineers • Later became Windows NT • FAT for NT was written in early 1989 • Supported DOS disk format • Entirely new code base and programming model • FASTFAT started in late 1989 (two person effort) • Other file systems done by the Core NT group were • HPFS, NTFS, CDFS, NPFS • FS development was done concurrently with kernel development • A lot of cooperative design between the file systems, I/O system, Memory Management, and the Cache manager

3. Fat on-disk Structure • Boot sector, followed by reserved sector Area • File Allocation Table (FAT) • 12, 16, and 32 bit FAT • Clusters size • Typically two copies of FAT • Root Directory • Fixed size • 32 byte Directory Entries (dirent) • 8.3 names • Data area • Once only for file data, later expanded to include subdirectories

4. 1.44 MB Floppy format • Number of sectors = 0xB40 (2,880) • Sector size = 0x200 (512) • Number of Fats = 0x2, Sectors per Fat = 0x9 • Root directory Size = 0xE (14) sectors, 0xE0 (224) entries • Layout • Sector 0x0: boot sector • Sector 0x1: start of first FAT • Sector 0xA: start of second FAT • Sector 0x13: start of root directory • Sector 0x21: start of data area • Disk Edit utility to help in your project • Added to the project4 directory (copy everything to your vhd)

5. I/O – FS Interface • Layering of drivers (file systems, disks, etc.) • All orchestrated by the I/O System • Driver Objects (one per file system). Each driver “registers” with the I/O system, see DriverEntry(…) in FatInit.c • Device Objects (one per volume). Created when a new volume is mounted, see FatMountVolume(…) in Fsctrl.c • File Objects (one per CreateFile call). See FatCommonCreate(…) in create.c • I/O Call Driver model using I/O Request Packets (IRP) • IRP Stack locations (see “inc\ddk\wdm.h”) • Major and minor functions • IoCallDriver(…) and IoCompleteRequest(…) • File Object • FsContext and FsContext2

6. Windows FS Architecture • Data Structure Layout • Mimics as much as practical the on-disk directory/file hierarchy • Keeps in memory the opened files and directories • Volume Control Block (VCB) • File Control Block (FCB) and Directory Control Block (DCB) • Context Control Block (CCB) • All rooted in FatData (See FatStruc.h)

7. Windows FS Architecture (Continued) • FSD/FSP Model • User Thread versus Worker Thread • Driven off of IRP Major Function • See DriverEntry(…) in FatInit.c • Fat Common Routines • Everything looks like a file • FatReadVolumeFile(…) • Some things to watch out for • Kernel Stack Space Limitation • Being able to wait for I/O • Recursive routines

8. Cache/MM Interaction • Virtual caching • Memory Mapped Files • Fast read and fast write • Ancillary file system data also cached • Borrowing a pin and unpin logic from databases • Noncached I/O • Where the actual read/write to disk occur • Synchronous and Asynchronous I/O • See read.c, write,c and deviosup.c

9. CreateFile Operation • Some of the main files and functions to look at • Create.c and dirsup.c • FatFsdCreate • FatCommonCreate • FatCreateNewFile • FatCreateNewDirent • FatConstructDirent

10. Programming Style • Engineering practices • Comments • Indentation • Variable names • Project 4 description has a synopsis of each source file