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ecs150 Fall 2007 : Operating System #5: File Systems (chapters: 6.4~6.7, 8) PowerPoint Presentation
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ecs150 Fall 2007 : Operating System #5: File Systems (chapters: 6.4~6.7, 8). Dr. S. Felix Wu Computer Science Department University of California, Davis http://www.cs.ucdavis.edu/~wu/ sfelixwu@gmail.com. File System Abstraction. Files Directories. System-call interface.

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ecs150 Fall 2007 : Operating System #5: File Systems (chapters: 6.4~6.7, 8)


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    1. ecs150 Fall 2007:Operating System#5: File Systems(chapters: 6.4~6.7, 8) Dr. S. Felix Wu Computer Science Department University of California, Davis http://www.cs.ucdavis.edu/~wu/ sfelixwu@gmail.com ecs150, Fall 2007

    2. File System Abstraction • Files • Directories ecs150, Fall 2007

    3. System-call interface Active file entries VNODE Layer or VFS Local naming (UFS) FFS Buffer cache Block or character device driver Hardware ecs150, Fall 2007

    4. ecs150, Fall 2007

    5. ecs150, Fall 2007

    6. ecs150, Fall 2007

    7. dirp = opendir(const char *filename); struct dirent *direntp = readdir(dirp); struct dirent { ino_t d_ino; char d_name[NAME_MAX+1]; }; directory dirent inode file_name dirent inode file_name dirent inode file_name file file file ecs150, Fall 2007

    8. Local versus Remote • System Call Interface • V-node • Local versus remote • NFS or i-node • Stackable File System • Hard-disk blocks ecs150, Fall 2007

    9. File-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. ecs150, Fall 2007

    10. File  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?? ecs150, Fall 2007

    11. Bit 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? ecs150, Fall 2007

    12. Hard Disk • Track, Sector, Head • Track + Heads  Cylinder • Performance • seek time • rotation time • transfer time • LBA • Linear Block Addressing ecs150, Fall 2007

    13. File  Disk blocks 0 file block 0 file block 1 file block 2 file block 3 file block 4 4 7 2 10 12 • What are the disadvantages? • disk access can be slow for “random access”. • How big is each block? 64 bytes? 68 bytes? ecs150, Fall 2007

    14. Kernel Hacking Session • This Friday from 7:30 p.m. until midnight.. • 3083 Kemper • Bring your laptop • And bring your mug… ecs150, Fall 2007

    15. A File System partition partition partition b s i-list directory and data blocks d i-node i-node ……. i-node ecs150, Fall 2007

    16. One Logical File  Physical Disk Blocks efficient representation & access ecs150, Fall 2007

    17. An i-node A file ??? entries in one disk block Typical: each block 8K or 16K bytes ecs150, Fall 2007

    18. inode (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 ecs150, Fall 2007

    19. System-call interface Active file entries VNODE Layer or VFS Local naming (UFS) FFS Buffer cache Block or character device driver Hardware ecs150, Fall 2007

    20. ecs150, Fall 2007

    21. A File System partition partition partition b s i-list directory and data blocks d i-node i-node ……. i-node ecs150, Fall 2007

    22. ecs150, Fall 2007

    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 }; ecs150, Fall 2007

    24. 166 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 }; ecs150, Fall 2007

    25. Bittorrent pieces File size: 10 GB Pieces downloaded: 512 MB How much disk space do we need? ecs150, Fall 2007

    26. #include <stdio.h> #include <stdlib.h> int main (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 ecs150, Fall 2007

    27. ecs150, Fall 2007

    28. ecs150, Fall 2007

    29. ecs150, Fall 2007

    30. An i-node A file ??? entries in one disk block Typical: each block 1K ecs150, Fall 2007

    31. i-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? ecs150, Fall 2007

    32. Answer • 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! ecs150, Fall 2007

    33. Answer: Lower Bound • How many pointers? • 512MB divided by the block size (1K) • 512K pointers times 8 (4) bytes = 4 (2) MB ecs150, Fall 2007

    34. Bittorrent pieces File size: 10 GB Pieces downloaded: 512 MB How much disk space do we need? ecs150, Fall 2007

    35. Answer: Upper Bound • In the worst case, EVERY indirection block has at least one entry! • How many indirection blocks? • Single: 1 block • Double: 1 + 28 • Tripple: 1 + 28 + 216 • Total ~ 216 blocks times 1K = 64 MB • 214 times 1K = 16MB (ufs2 inode) ecs150, Fall 2007

    36. Answer (4) • 2 MB ~ 64 MB ufs1 • 4 MB ~ 16 MB ufs2 • Answer: sss.txt ~17 MB • ~16 MB (inode indirection blocks) • 1000 writes times 1K ~ 1MB ecs150, Fall 2007

    37. An i-node A file ??? entries in one disk block Typical: each block 1K ecs150, Fall 2007

    38. A File System partition partition partition b s i-list directory and data blocks d i-node i-node ……. i-node ecs150, Fall 2007

    39. FFS and UFS • /usr/src/sys/ufs/ffs/* • Higher-level: directory structure • Soft updates & Snapshot • /usr/src/sys/ufs/ufs/* • Lower-level: buffer, i-node ecs150, Fall 2007

    40. # of i-nodes • UFS1: pre-allocation • 3% of HD, about < 25% used. • UFS2: dynamic allocation • Still limited # of i-nods ecs150, Fall 2007

    41. di_size vs. di_blocks • ??? ecs150, Fall 2007

    42. One Logical File  Physical Disk Blocks efficient representation & access ecs150, Fall 2007

    43. di_size vs. di_blocks • Logical • Physical • fstat • du ecs150, Fall 2007

    44. Extended 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 ecs150, Fall 2007

    45. 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. ecs150, Fall 2007

    46. A File System partition partition partition b s i-list directory and data blocks d i-node i-node ……. i-node ecs150, Fall 2007

    47. struct dirent { ino_t d_ino; char d_name[NAME_MAX+1]; }; struct stat {… short nlinks; …}; directory dirent inode file_name dirent inode file_name dirent inode file_name file file file ecs150, Fall 2007

    48. ecs150, Fall 2007

    49. root wheel . 2 directory / 2 drwxr-xr-x .. 2 Apr 1 2004 usr 4 3 vmunix 5 root wheel . 4 drwxr-xr-x directory /usr .. 2 4 Apr 1 2004 bin 7 root wheel foo 6 rwxr-xr-x 5 file /vmunix Apr 15 2004 text data kirk staff 6 rw-rw-r-- file /usr/foo Hello World! Jan 19 2004 root wheel . 7 7 drwxr-xr-x .. 4 directory /usr/bin Apr 1 2004 ex 9 8 groff 10 bin bin vi 9 file /usr/bin/vi 9 rwxr-xr-x text data Apr 15 2004 ecs150, Fall 2007

    50. What is the difference? • ln –s /usr/src/sys/sys/proc.h ppp.h • ln /usr/src/sys/sys/proc.h ppp.h ecs150, Fall 2007