UCDavis, ecs150 Fall 2006 11/20/2006ecs150, Fall 20061 Operating System ecs150 Fall 2006 : Operating...

11/20/2006 ecs150, Fall 2006 1

UCDavis, ecs150Fall 2006

ecs150 Fall 2006:Operating SystemOperating System#5: File Systems(chapters: 6.4~6.7, 8)

Dr. S. Felix Wu

Computer Science Department

University of California, Davishttp://www.cs.ucdavis.edu/~wu/

[email protected]

11/20/2006 ecs150, Fall 2006 2


File System AbstractionFile System Abstraction

Files Directories

11/20/2006 ecs150, Fall 2006 3


System-call interfaceActive file entries

VNODE Layer or VFS

Local naming (UFS)

FFS

Buffer cache

Block or character device driver

Hardware

11/20/2006 ecs150, Fall 2006 4


11/20/2006 ecs150, Fall 2006 5


11/20/2006 ecs150, Fall 2006 6


11/20/2006 ecs150, Fall 2006 7


dirp = opendir(const char *filename);struct dirent *direntp = readdir(dirp);

struct dirent {ino_t d_ino;char d_name[NAME_MAX+1];

};

directory

direntinode

file_name

file

file

file

direntinode

file_name

direntinode

file_name

11/20/2006 ecs150, Fall 2006 8


Local versus RemoteLocal versus Remote

System Call Interface V-node Local versus remote

– NFS or i-node– Stackable File System

Hard-disk blocks

11/20/2006 ecs150, Fall 2006 9


File-System StructureFile-System Structure File structure

– Logical storage unit– Collection of related information

File system resides on secondary storage (disks).

File system organized into layers. File control block – storage structure

consisting of information about a file.

11/20/2006 ecs150, Fall 2006 10

UCDavis, ecs150Fall 2006 File File Disk Disk

separate the disk into blocks separate the file into blocks as well paging from file to disk

blocks: 4 - 7- 2- 10- 12

How to represent the file??How to link these 5 pages together??

11/20/2006 ecs150, Fall 2006 11


Bit torrent piecesBit torrent pieces

1 big file (X Gigabytes) with a number of pieces (5%) already in (and sharing with others).

How much disk space do we need at this moment?

11/20/2006 ecs150, Fall 2006 12

UCDavis, ecs150Fall 2006 Hard DiskHard Disk

Track, Sector, Head– Track + Heads Cylinder

Performance– seek time– rotation time– transfer time

LBA– Linear Block Addressing

11/20/2006 ecs150, Fall 2006 13

UCDavis, ecs150Fall 2006 File File Disk blocks Disk blocks

fileblock

0

4

fileblock

1

7

fileblock

2

2

fileblock

3

10

0file

block4

12

What are the disadvantages?1. disk access can be slow for “random access”.2. How big is each block? 64 bytes? 68 bytes?

11/20/2006 ecs150, Fall 2006 14


Kernel Hacking SessionKernel Hacking Session

This Friday from 7:30 p.m. until midnight.. 3083 Kemper

– Bring your laptop– And bring your mug…

11/20/2006 ecs150, Fall 2006 15

UCDavis, ecs150Fall 2006 A File SystemA File System

partition partition partition

i-list directory and data blockssb

i-node i-node ……. i-node

d

11/20/2006 ecs150, Fall 2006 16


One Logical File One Logical File Physical Disk Blocks Physical Disk Blocks

efficient representation & access

11/20/2006 ecs150, Fall 2006 17

UCDavis, ecs150Fall 2006 An i-nodeAn i-node

Typical:each block 8K or 16K bytes

??? entries inone disk block

A file

11/20/2006 ecs150, Fall 2006 18


inode (index node) structureinode (index node) structure meta-data of the file.

– di_mode 02– di_nlinks 02– di_uid 02– di_gid 02– di_size 04– di_addr 39– di_gen 01– di_atime 04– di_mtime 04– di_ctime 04

11/20/2006 ecs150, Fall 2006 19



VNODE Layer or VFS

Local naming (UFS)

FFS

Buffer cache


Hardware

11/20/2006 ecs150, Fall 2006 20


11/20/2006 ecs150, Fall 2006 21





d

11/20/2006 ecs150, Fall 2006 22


11/20/2006 ecs150, Fall 2006 23


125 struct ufs2_dinode {126 u_int16_t di_mode; /* 0: IFMT, permissions; see below. */127 int16_t di_nlink; /* 2: File link count. */128 u_int32_t di_uid; /* 4: File owner. */ 129 u_int32_t di_gid; /* 8: File group. */ 130 u_int32_t di_blksize; /* 12: Inode blocksize. */ 131 u_int64_t di_size; /* 16: File byte count. */ 132 u_int64_t di_blocks; /* 24: Bytes actually held. */ 133 ufs_time_t di_atime; /* 32: Last access time. */ 134 ufs_time_t di_mtime; /* 40: Last modified time. */ 135 ufs_time_t di_ctime; /* 48: Last inode change time. */ 136 ufs_time_t di_birthtime; /* 56: Inode creation time. */ 137 int32_t di_mtimensec; /* 64: Last modified time. */ 138 int32_t di_atimensec; /* 68: Last access time. */ 139 int32_t di_ctimensec; /* 72: Last inode change time. */ 140 int32_t di_birthnsec; /* 76: Inode creation time. */ 141 int32_t di_gen; /* 80: Generation number. */ 142 u_int32_t di_kernflags; /* 84: Kernel flags. */ 143 u_int32_t di_flags; /* 88: Status flags (chflags). */ 144 int32_t di_extsize; /* 92: External attributes block. */ 145 ufs2_daddr_t di_extb[NXADDR];/* 96: External attributes block. */ 146 ufs2_daddr_t di_db[NDADDR]; /* 112: Direct disk blocks. */ 147 ufs2_daddr_t di_ib[NIADDR]; /* 208: Indirect disk blocks. */ 148 int64_t di_spare[3]; /* 232: Reserved; currently unused */ 149 };

11/20/2006 ecs150, Fall 2006 24

UCDavis, ecs150Fall 2006166 struct ufs1_dinode {

167 u_int16_t di_mode; /* 0: IFMT, permissions; see below. */ 168 int16_t di_nlink; /* 2: File link count. */ 169 union { 170 u_int16_t oldids[2]; /* 4: Ffs: old user and group ids. */ 171 } di_u; 172 u_int64_t di_size; /* 8: File byte count. */ 173 int32_t di_atime; /* 16: Last access time. */ 174 int32_t di_atimensec; /* 20: Last access time. */ 175 int32_t di_mtime; /* 24: Last modified time. */ 176 int32_t di_mtimensec; /* 28: Last modified time. */ 177 int32_t di_ctime; /* 32: Last inode change time. */ 178 int32_t di_ctimensec; /* 36: Last inode change time. */ 179 ufs1_daddr_t di_db[NDADDR]; /* 40: Direct disk blocks. */ 180 ufs1_daddr_t di_ib[NIADDR]; /* 88: Indirect disk blocks. */ 181 u_int32_t di_flags; /* 100: Status flags (chflags). */ 182 int32_t di_blocks; /* 104: Blocks actually held. */ 183 int32_t di_gen; /* 108: Generation number. */ 184 u_int32_t di_uid; /* 112: File owner. */ 185 u_int32_t di_gid; /* 116: File group. */ 186 int32_t di_spare[2]; /* 120: Reserved; currently unused */ 187 };

11/20/2006 ecs150, Fall 2006 25


Bittorrent piecesBittorrent pieces

File size: 10 GBPieces downloaded: 512 MBHow much disk space do we need?

11/20/2006 ecs150, Fall 2006 26


#include <stdio.h>#include <stdlib.h>

intmain(void){ FILE *f1 = fopen("./sss.txt", "w"); int i;

for (i = 0; i < 1000; i++) { fseek(f1, rand(), SEEK_SET); fprintf(f1, "%d%d%d%d", rand(), rand(), rand(), rand()); if (i % 100 == 0) sleep(1); } fflush(f1);}

# ./t# ls –l ./sss.txt

11/20/2006 ecs150, Fall 2006 27


11/20/2006 ecs150, Fall 2006 28


11/20/2006 ecs150, Fall 2006 29


11/20/2006 ecs150, Fall 2006 30

UCDavis, ecs150Fall 2006 An i-nodeAn i-node

Typical:each block 1K


A file

11/20/2006 ecs150, Fall 2006 31


i-nodei-node

How many disk blocks can a FS have? How many levels of i-node indirection will be

necessary to store a file of 2G bytes? (I.e., 0, 1, 2 or 3) What is the largest possible file size in i-node? What is the size of the i-node itself for a file of 10GB

with only 512 MB downloaded?

11/20/2006 ecs150, Fall 2006 32


AnswerAnswer How many disk blocks can a FS have?

– 264 or 232: Pointer (to blocks) size is 8/4 bytes. How many levels of i-node indirection will be

necessary to store a file of 2G (231) bytes? (I.e., 0, 1, 2 or 3)– 12*210 + 28 * 210 + 28 *28 *2 10 + 28 * 28 *28 *2 10 >? 231

What is the largest possible file size in i-node?– 12*210 + 28 * 210 + 28 *28 *2 10 + 28 * 28 *28 *2 10

– 264 –1– 232 * 210

You need to consider three issues and find the minimum!

11/20/2006 ecs150, Fall 2006 33


AnswerAnswer

How many pointers?– 512MB divided by the block size (1K)– 512K pointers times 8 (4) bytes = 4 (2) MB

11/20/2006 ecs150, Fall 2006 34





d

11/20/2006 ecs150, Fall 2006 35


FFS and UFSFFS and UFS

/usr/src/sys/ufs/ffs/*– Higher-level: directory structure– Soft updates & Snapshot

/usr/src/sys/ufs/ufs/*– Lower-level: buffer, i-node

11/20/2006 ecs150, Fall 2006 36


# of i-nodes# of i-nodes

UFS1: pre-allocation– 3% of HD, about < 25% used.

UFS2: dynamic allocation– Still limited # of i-nods

11/20/2006 ecs150, Fall 2006 37


di_size vs. di_blocksdi_size vs. di_blocks

???

11/20/2006 ecs150, Fall 2006 38


One Logical File One Logical File Physical Disk Blocks Physical Disk Blocks

efficient representation & access

11/20/2006 ecs150, Fall 2006 39


di_size vs. di_blocksdi_size vs. di_blocks

Logical Physical

fstat du

11/20/2006 ecs150, Fall 2006 40


Extended Attributes in UFS2Extended Attributes in UFS2 Attributes associated with the File

– di_extb[2]; – two blocks, but indirection if needed.

Format– Length 4– Name Space 1– Content Pad Length 1– Name Length 1– Name mod 8– Content variable

Applications: ACL, Data Labelling

11/20/2006 ecs150, Fall 2006 41


Some thoughts….Some thoughts…. What can you do with “extended attributes”? How to design/implement?

– Should/can we do it “Stackable File Systems”?– Otherwise, the program to manipulate the EA’s

will have to be very UFS2-dependent or FiST with an UFS2 optimization option.

Are there any counter examples?– security and performance considerations.

11/20/2006 ecs150, Fall 2006 42


11/20/2006 ecs150, Fall 2006 43


11/20/2006 ecs150, Fall 2006 44

UCDavis, ecs150Fall 2006 struct dirent {

ino_t d_ino;char d_name[NAME_MAX+1];

};

struct stat {…short nlinks;

…};

directory

direntinode

file_name

file

file

file

direntinode

file_name

direntinode

file_name

11/20/2006 ecs150, Fall 2006 45





d

11/20/2006 ecs150, Fall 2006 46


ln –s /usr/src/sys/sys/proc.h ppp.h ln /usr/src/sys/sys/proc.h ppp.h

11/20/2006 ecs150, Fall 2006 47


File System Buffer CacheFile System Buffer Cacheapplication: read/write files

OS: translate file to disk blocks

...buffer cache ...maintains

controls disk accesses: read/write blocks

hardware:

Any problems?

11/20/2006 ecs150, Fall 2006 48


File System ConsistencyFile System Consistency

To maintain file system consistency the ordering of updates from buffer cache to disk is critical

Example:– if the directory block is written back before the

i-node and the system crashes, the directory structure will be inconsistent

11/20/2006 ecs150, Fall 2006 49


File System ConsistencyFile System Consistency File system almost always use a buffer/disk cache for

performance reasons This problem is critical especially for the blocks that

contain control information: i-node, free-list, directory blocks

Two copies of a disk block (buffer cache, disk) consistency problem if the system crashes before all the modified blocks are written back to disk

Write back critical blocks from the buffer cache to disk immediately

Data blocks are also written back periodically: sync

11/20/2006 ecs150, Fall 2006 50


Two StrategiesTwo Strategies Prevention

– Use un-buffered I/O when writing i-nodes or pointer blocks

– Use buffered I/O for other writes and force sync every 30 seconds

Detect and Fix– Detect the inconsistency

– Fix them according to the “rules”

– Fsck (File System Checker)

11/20/2006 ecs150, Fall 2006 51


File System IntegrityFile System Integrity Block consistency:

– Block-in-use table

– Free-list table

File consistency:– how many directories pointing to that i-node?

– nlink?

– three cases: D == L, L > D, D > L What to do with the latter two cases?

0 1 1 1 0 0 0 1 0 0 0 2

1 0 0 0 1 1 1 0 1 0 2 0

11/20/2006 ecs150, Fall 2006 52

UCDavis, ecs150Fall 2006 File System IntegrityFile System Integrity

File system states(a) consistent(b) missing block(c) duplicate block in free list(d) duplicate data block

11/20/2006 ecs150, Fall 2006 53


Metadata OperationsMetadata Operations

Metadata operations modify the structure of the file system– Creating, deleting, or renaming

files, directories, or special files– Directory & I-node

Data must be written to disk in such a way that the file system can be recovered to a consistent state after a system crash

11/20/2006 ecs150, Fall 2006 54


Metadata IntegrityMetadata Integrity

FFS uses synchronous writes to guarantee the integrity of metadata– Any operation modifying multiple pieces of

metadata will write its data to disk in a specific order

– These writes will be blocking Guarantees integrity and durability of

metadata updates

11/20/2006 ecs150, Fall 2006 55


Deleting a file (I)Deleting a file (I)

abc

def

ghi

i-node-1

i-node-2

i-node-3

Assume we want to delete file “def”

11/20/2006 ecs150, Fall 2006 56


Deleting a file (II)Deleting a file (II)

abc

def

ghi

i-node-1

i-node-3

Cannot delete i-node before directory entry “def”

?

11/20/2006 ecs150, Fall 2006 57


Deleting a file (III)Deleting a file (III)

Correct sequence is1. Write to disk directory block containing deleted

directory entry “def”

2. Write to disk i-node block containing deleted i-node

Leaves the file system in a consistent state

11/20/2006 ecs150, Fall 2006 58


Creating a file (I)Creating a file (I)

abc

ghi

i-node-1

i-node-3

Assume we want to create new file “tuv”

11/20/2006 ecs150, Fall 2006 59


Creating a file (II)Creating a file (II)

abc

ghi

tuv

i-node-1

i-node-3

Cannot write directory entry “tuv” before i-node

?

11/20/2006 ecs150, Fall 2006 60


Creating a file (III)Creating a file (III)

Correct sequence is1. Write to disk i-node block containing new i-node

2. Write to disk directory block containing new directory entry

Leaves the file system in a consistent state

11/20/2006 ecs150, Fall 2006 61


Synchronous UpdatesSynchronous Updates

Used by FFS to guarantee consistency of metadata:– All metadata updates are done through blocking

writes

Increases the cost of metadata updates Can significantly impact the performance

of whole file system

11/20/2006 ecs150, Fall 2006 62


11/20/2006 ecs150, Fall 2006 63


SOFT UPDATESSOFT UPDATES

Use delayed writes (write back) Maintain dependency information about

cached pieces of metadata:This i-node must be updated before/after this directory entry

Guarantee that metadata blocks are written to disk in the required order

11/20/2006 ecs150, Fall 2006 64


3 Soft Update Rules3 Soft Update Rules

Never point to a structure before it has been initialized.

Never reuse a resource before nullifying all previous pointers to it.

Never reset the old pointer to a live resource before the new pointer has been set.

11/20/2006 ecs150, Fall 2006 65


Problem #1 with S.U.Problem #1 with S.U.

Synchronous writes guaranteed that metadata operations were durable once the system call returned

Soft Updates guarantee that file system will recover into a consistent state but not necessarily the most recent one– Some updates could be lost

11/20/2006 ecs150, Fall 2006 66


We want to delete file “foo” and create new file “bar”

i-node-2 foo

NEW bar

NEW i-node-3

Block A Block B

What are the dependency relationship?

11/20/2006 ecs150, Fall 2006 67


We want to delete file “foo” and create new file “bar”

i-node-2 foo

NEW bar

NEW i-node-3

Block A Block B

Circular DependencyX-2nd Y-1st

11/20/2006 ecs150, Fall 2006 68


Problem #2 with S.U.Problem #2 with S.U.

Cyclical dependencies:– Same directory block contains entries to be

created and entries to be deleted– These entries point to i-nodes in the same block

Brainstorming:– How to resolve this issue in S.U.?

11/20/2006 ecs150, Fall 2006 69


How to update?? i-node first or director block first?

11/20/2006 ecs150, Fall 2006 70


11/20/2006 ecs150, Fall 2006 71


Solution in S.U.Solution in S.U.

Roll back metadata in one of the blocks to an earlier, safe state

(Safe state does not contain new directory entry)

def

Block A’

11/20/2006 ecs150, Fall 2006 72


Write first block with metadata that were rolled back (block A’ of example)

Write blocks that can be written after first block has been written (block B of example)

Roll forward block that was rolled back Write that block Breaks the cyclical dependency but must now

write twice block A

11/20/2006 ecs150, Fall 2006 73


Before any Write Operation

After any Write Operation

SU Dependency Checking(roll back if necessary)

SU Dependency Processing(task list updating)(roll forward if necessary)

11/20/2006 ecs150, Fall 2006 74


two most popular approaches for improving the performance of metadata operations and recovery:– Journaling – Soft Updates

Journaling systems record metadata operations on an auxiliary log

Soft Updates uses ordered writes

11/20/2006 ecs150, Fall 2006 75

UCDavis, ecs150Fall 2006 JOURNALINGJOURNALING

Journaling systems maintain an auxiliary log that records all meta-data operations

Write-ahead logging ensures that the log is written to disk before any blocks containing data modified by the corresponding operations.– After a crash, can replay the log to bring the file

system to a consistent state

11/20/2006 ecs150, Fall 2006 76


JOURNALINGJOURNALING

Log writes are performed in addition to the regular writes

Journaling systems incur log write overhead but– Log writes can be performed efficiently

because they are sequential (block operation consideration)

– Metadata blocks do not need to be written back after each update

11/20/2006 ecs150, Fall 2006 77


JOURNALINGJOURNALING

Journaling systems can provide– same durability semantics as FFS if log is

forced to disk after each meta-data operation– the laxer semantics of Soft Updates if log

writes are buffered until entire buffers are full

11/20/2006 ecs150, Fall 2006 78


Soft Updates vs. JournalingSoft Updates vs. Journaling

Advantages disadvantages

11/20/2006 ecs150, Fall 2006 79


With Soft Updates??With Soft Updates??

CPU

Do we still need “FSCK”? at boot time?

11/20/2006 ecs150, Fall 2006 80


Recover the Missing ResourcesRecover the Missing Resources

In the background, in an active FS…– We don’t want to wait for the lengthy FSCK

process to complete…

A related issue:– the virus scanning process– what happens if we get a new virus signature?

11/20/2006 ecs150, Fall 2006 81


Snapshot of the FSSnapshot of the FS

backup and restore dump reliably an active File System

– what will we do today to dump our 40GB FS “consistent” snapshots? (in the midnight…)

“background FSCK checks”

11/20/2006 ecs150, Fall 2006 82


What is a snapshot?What is a snapshot?(I mean “conceptually”.)(I mean “conceptually”.)

Freeze all activities related to the FS. Copy everything to “some space”. Resume the activities.

How do we efficiently implement this concept such that the activities will only be blocked for about 0.25 seconds, and we don’t have to buy a really big hard drive?

11/20/2006 ecs150, Fall 2006 83


11/20/2006 ecs150, Fall 2006 84


11/20/2006 ecs150, Fall 2006 85


Copy-on-Write

11/20/2006 ecs150, Fall 2006 86

UCDavis, ecs150Fall 2006 Snapshot: a fileSnapshot: a file

Logical sizeVersus physical size

11/20/2006 ecs150, Fall 2006 87


ExampleExample

# mkdir /backups/usr/noon# mount –u –o snapshot /usr/snap.noon /usr# mdconfig –a –t vnode –u 0 –f /usr/snap.noon# mount –r /dev/md0 /backups/usr/noon

/* do whatever you want to test it */

# umount /backups/usr/noon# mdconfig –d –u 0# rm –f /usr/snap.noon

11/20/2006 ecs150, Fall 2006 88


11/20/2006 ecs150, Fall 2006 89


11/20/2006 ecs150, Fall 2006 90


#include <stdio.h>#include <stdlib.h>

intmain(void){ FILE *f1 = fopen("./sss.txt", "w"); int i;

for (i = 0; i < 1000; i++) { fseek(f1, rand(), SEEK_SET); fprintf(f1, "%d%d%d%d", rand(), rand(), rand(), rand()); if (i % 100 == 0) sleep(1); } fflush(f1);}

11/20/2006 ecs150, Fall 2006 91


ExampleExample




11/20/2006 ecs150, Fall 2006 92


11/20/2006 ecs150, Fall 2006 93


11/20/2006 ecs150, Fall 2006 94


11/20/2006 ecs150, Fall 2006 95


11/20/2006 ecs150, Fall 2006 96


11/20/2006 ecs150, Fall 2006 97


11/20/2006 ecs150, Fall 2006 98


11/20/2006 ecs150, Fall 2006 99


ExampleExample




11/20/2006 ecs150, Fall 2006 100


Copy-on-Write

11/20/2006 ecs150, Fall 2006 101


11/20/2006 ecs150, Fall 2006 102



A file

11/20/2006 ecs150, Fall 2006 103

UCDavis, ecs150Fall 2006 A Snapshot i-nodeA Snapshot i-node


A file

Not used orNot yet copy

11/20/2006 ecs150, Fall 2006 104

UCDavis, ecs150Fall 2006 Copy-on-writeCopy-on-write


A file


11/20/2006 ecs150, Fall 2006 105

UCDavis, ecs150Fall 2006 Copy-on-writeCopy-on-write


A file


11/20/2006 ecs150, Fall 2006 106


Multiple SnapshotsMultiple Snapshots

about 20 snapshots Interactions/sharing among snapshots

11/20/2006 ecs150, Fall 2006 107


Snapshot of the FSSnapshot of the FS

backup and restore dump reliably an active File System

– what will we do today to dump our 40GB FS “consistent” snapshots? (in the midnight…)

“background FSCK checks”

11/20/2006 ecs150, Fall 2006 108


11/20/2006 ecs150, Fall 2006 109


VFS: the FS SwitchVFS: the FS Switch

syscall layer (file, uio, etc.)

user space

Virtual File System (VFS)networkprotocol

stack(TCP/IP) NFS FFS LFS etc.*FS etc.

device drivers

Sun Microsystems introduced the virtual file system interface in 1985 to accommodate diverse filesystem types cleanly.

VFS allows diverse specific file systems to coexist in a file tree, isolating all FS-dependencies in pluggable filesystem modules.

VFS was an internal kernel restructuringwith no effect on the syscall interface.

Incorporates object-oriented concepts:a generic procedural interface withmultiple implementations.

Based on abstract objects with dynamicmethod binding by type...in C.Other abstract interfaces in the kernel: device drivers,

file objects, executable files, memory objects.

11/20/2006 ecs150, Fall 2006 110


vnodevnode In the VFS framework, every file or directory in active use

is represented by a vnode object in kernel memory.

syscall layer

NFS UFS

free vnodes

Each vnode has a standardfile attributes struct.

Vnode operations aremacros that vector tofilesystem-specificprocedures.

Generic vnode points atfilesystem-specific struct(e.g., inode, rnode), seenonly by the filesystem. Each specific file system

maintains a cache of its resident vnodes.

11/20/2006 ecs150, Fall 2006 111


vnode Operations and vnode Operations and AttributesAttributes

directories onlyvop_lookup (OUT vpp, name)vop_create (OUT vpp, name, vattr)vop_remove (vp, name)vop_link (vp, name)vop_rename (vp, name, tdvp, tvp, name)vop_mkdir (OUT vpp, name, vattr)vop_rmdir (vp, name)vop_symlink (OUT vpp, name, vattr, contents)vop_readdir (uio, cookie)vop_readlink (uio)

files onlyvop_getpages (page**, count, offset)vop_putpages (page**, count, sync, offset)vop_fsync ()

vnode attributes (vattr)type (VREG, VDIR, VLNK, etc.)mode (9+ bits of permissions)nlink (hard link count)owner user IDowner group IDfilesystem IDunique file IDfile size (bytes and blocks)access timemodify timegeneration number

generic operationsvop_getattr (vattr)vop_setattr (vattr)vhold()vholdrele()

11/20/2006 ecs150, Fall 2006 112


Network File System (NFS)Network File System (NFS)

syscall layer

UFS

NFSserver

VFS

VFS

NFSclient

UFS

syscall layer

client

user programs

network

server

11/20/2006 ecs150, Fall 2006 113


vnode Cachevnode CacheHASH(fsid, fileid)

VFS free list headActive vnodes are reference- counted by the structures that hold pointers to them.

- system open file table

- process current directory

- file system mount points

- etc.

Each specific file system maintains its own hash of vnodes (BSD).

- specific FS handles initialization

- free list is maintained by VFSvget(vp): reclaim cached inactive vnode from VFS free listvref(vp): increment reference count on an active vnodevrele(vp): release reference count on a vnode vgone(vp): vnode is no longer valid (file is removed)

11/20/2006 ecs150, Fall 2006 114


11/20/2006 ecs150, Fall 2006 115


11/20/2006 ecs150, Fall 2006 116


struct vnode {struct mtx v_interlock; /* lock for "i" things */u_long v_iflag; /* i vnode flags (see below) */int v_usecount; /* i ref count of users */long v_numoutput; /* i writes in progress */struct thread *v_vxthread; /* i thread owning VXLOCK */int v_holdcnt; /* i page & buffer references */struct buflists v_cleanblkhd; /* i SORTED clean blocklist */struct buf *v_cleanblkroot;/* i clean buf splay tree */int v_cleanbufcnt; /* i number of clean buffers */struct buflists v_dirtyblkhd; /* i SORTED dirty blocklist */struct buf *v_dirtyblkroot; /* i dirty buf splay tree */int v_dirtybufcnt;

11/20/2006 ecs150, Fall 2006 117



VNODE Layer or VFS

Local naming (UFS)

FFS

Buffer cache


Hardware

11/20/2006 ecs150, Fall 2006 118


11/20/2006 ecs150, Fall 2006 119

UCDavis, ecs150Fall 2006 How Stacking WorksHow Stacking Works

EXT2FS

US

ER

KE

RN

EL

User process

data &error codes

read()System CallInterface

File SystemInterface ext2fs_read()

ncryptfs_read()

data &error codes

NCryptfs

11/20/2006 ecs150, Fall 2006 120


FiST: File System TranslatorLanguage + compilerCode portabilityAverage code size over other stackable file-systems is reduced ten times.Average development time is reduced seven timesDevelopers need only to describe the core functionality of their file systems.Basefs = minimalist template derived from WrapfsExtending platform-specific vnode interfaces in a platform independent way.

11/20/2006 ecs150, Fall 2006 121


11/20/2006 ecs150, Fall 2006 122


Transaction-based FSTransaction-based FS

Performance versus consistency “Atomic Writes” on Multiple Blocks

– See the paper titled “Atomic Writes for Data Integrity and Consistency in Shared Storage Devices for Clusters” by Okun and Barak, FGCS, vol. 20, pages 539-547, 2004.

– Modify SCSI handling

Date post:	22-Dec-2015
Category:	Documents
View:	213 times
Download:	0 times

UCDavis, ecs150 Fall 2006 11/20/2006ecs150, Fall 20061 Operating System ecs150 Fall 2006 : Operating...

Documents