Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | This is the implementation of the SystemV/Coherent filesystem for Linux. |
2 | It grew out of separate filesystem implementations | |
3 | ||
4 | Xenix FS Doug Evans <dje@cygnus.com> June 1992 | |
5 | SystemV FS Paul B. Monday <pmonday@eecs.wsu.edu> March-June 1993 | |
6 | Coherent FS B. Haible <haible@ma2s2.mathematik.uni-karlsruhe.de> June 1993 | |
7 | ||
8 | and was merged together in July 1993. | |
9 | ||
10 | These filesystems are rather similar. Here is a comparison with Minix FS: | |
11 | ||
12 | * Linux fdisk reports on partitions | |
13 | - Minix FS 0x81 Linux/Minix | |
14 | - Xenix FS ?? | |
15 | - SystemV FS ?? | |
16 | - Coherent FS 0x08 AIX bootable | |
17 | ||
18 | * Size of a block or zone (data allocation unit on disk) | |
19 | - Minix FS 1024 | |
20 | - Xenix FS 1024 (also 512 ??) | |
21 | - SystemV FS 1024 (also 512 and 2048) | |
22 | - Coherent FS 512 | |
23 | ||
24 | * General layout: all have one boot block, one super block and | |
25 | separate areas for inodes and for directories/data. | |
26 | On SystemV Release 2 FS (e.g. Microport) the first track is reserved and | |
27 | all the block numbers (including the super block) are offset by one track. | |
28 | ||
29 | * Byte ordering of "short" (16 bit entities) on disk: | |
30 | - Minix FS little endian 0 1 | |
31 | - Xenix FS little endian 0 1 | |
32 | - SystemV FS little endian 0 1 | |
33 | - Coherent FS little endian 0 1 | |
34 | Of course, this affects only the file system, not the data of files on it! | |
35 | ||
36 | * Byte ordering of "long" (32 bit entities) on disk: | |
37 | - Minix FS little endian 0 1 2 3 | |
38 | - Xenix FS little endian 0 1 2 3 | |
39 | - SystemV FS little endian 0 1 2 3 | |
40 | - Coherent FS PDP-11 2 3 0 1 | |
41 | Of course, this affects only the file system, not the data of files on it! | |
42 | ||
43 | * Inode on disk: "short", 0 means non-existent, the root dir ino is: | |
44 | - Minix FS 1 | |
45 | - Xenix FS, SystemV FS, Coherent FS 2 | |
46 | ||
47 | * Maximum number of hard links to a file: | |
48 | - Minix FS 250 | |
49 | - Xenix FS ?? | |
50 | - SystemV FS ?? | |
51 | - Coherent FS >=10000 | |
52 | ||
53 | * Free inode management: | |
54 | - Minix FS a bitmap | |
55 | - Xenix FS, SystemV FS, Coherent FS | |
56 | There is a cache of a certain number of free inodes in the super-block. | |
57 | When it is exhausted, new free inodes are found using a linear search. | |
58 | ||
59 | * Free block management: | |
60 | - Minix FS a bitmap | |
61 | - Xenix FS, SystemV FS, Coherent FS | |
62 | Free blocks are organized in a "free list". Maybe a misleading term, | |
63 | since it is not true that every free block contains a pointer to | |
64 | the next free block. Rather, the free blocks are organized in chunks | |
65 | of limited size, and every now and then a free block contains pointers | |
66 | to the free blocks pertaining to the next chunk; the first of these | |
67 | contains pointers and so on. The list terminates with a "block number" | |
68 | 0 on Xenix FS and SystemV FS, with a block zeroed out on Coherent FS. | |
69 | ||
70 | * Super-block location: | |
71 | - Minix FS block 1 = bytes 1024..2047 | |
72 | - Xenix FS block 1 = bytes 1024..2047 | |
73 | - SystemV FS bytes 512..1023 | |
74 | - Coherent FS block 1 = bytes 512..1023 | |
75 | ||
76 | * Super-block layout: | |
77 | - Minix FS | |
78 | unsigned short s_ninodes; | |
79 | unsigned short s_nzones; | |
80 | unsigned short s_imap_blocks; | |
81 | unsigned short s_zmap_blocks; | |
82 | unsigned short s_firstdatazone; | |
83 | unsigned short s_log_zone_size; | |
84 | unsigned long s_max_size; | |
85 | unsigned short s_magic; | |
86 | - Xenix FS, SystemV FS, Coherent FS | |
87 | unsigned short s_firstdatazone; | |
88 | unsigned long s_nzones; | |
89 | unsigned short s_fzone_count; | |
90 | unsigned long s_fzones[NICFREE]; | |
91 | unsigned short s_finode_count; | |
92 | unsigned short s_finodes[NICINOD]; | |
93 | char s_flock; | |
94 | char s_ilock; | |
95 | char s_modified; | |
96 | char s_rdonly; | |
97 | unsigned long s_time; | |
98 | short s_dinfo[4]; -- SystemV FS only | |
99 | unsigned long s_free_zones; | |
100 | unsigned short s_free_inodes; | |
101 | short s_dinfo[4]; -- Xenix FS only | |
102 | unsigned short s_interleave_m,s_interleave_n; -- Coherent FS only | |
103 | char s_fname[6]; | |
104 | char s_fpack[6]; | |
105 | then they differ considerably: | |
106 | Xenix FS | |
107 | char s_clean; | |
108 | char s_fill[371]; | |
109 | long s_magic; | |
110 | long s_type; | |
111 | SystemV FS | |
112 | long s_fill[12 or 14]; | |
113 | long s_state; | |
114 | long s_magic; | |
115 | long s_type; | |
116 | Coherent FS | |
117 | unsigned long s_unique; | |
118 | Note that Coherent FS has no magic. | |
119 | ||
120 | * Inode layout: | |
121 | - Minix FS | |
122 | unsigned short i_mode; | |
123 | unsigned short i_uid; | |
124 | unsigned long i_size; | |
125 | unsigned long i_time; | |
126 | unsigned char i_gid; | |
127 | unsigned char i_nlinks; | |
128 | unsigned short i_zone[7+1+1]; | |
129 | - Xenix FS, SystemV FS, Coherent FS | |
130 | unsigned short i_mode; | |
131 | unsigned short i_nlink; | |
132 | unsigned short i_uid; | |
133 | unsigned short i_gid; | |
134 | unsigned long i_size; | |
135 | unsigned char i_zone[3*(10+1+1+1)]; | |
136 | unsigned long i_atime; | |
137 | unsigned long i_mtime; | |
138 | unsigned long i_ctime; | |
139 | ||
140 | * Regular file data blocks are organized as | |
141 | - Minix FS | |
142 | 7 direct blocks | |
143 | 1 indirect block (pointers to blocks) | |
144 | 1 double-indirect block (pointer to pointers to blocks) | |
145 | - Xenix FS, SystemV FS, Coherent FS | |
146 | 10 direct blocks | |
147 | 1 indirect block (pointers to blocks) | |
148 | 1 double-indirect block (pointer to pointers to blocks) | |
149 | 1 triple-indirect block (pointer to pointers to pointers to blocks) | |
150 | ||
151 | * Inode size, inodes per block | |
152 | - Minix FS 32 32 | |
153 | - Xenix FS 64 16 | |
154 | - SystemV FS 64 16 | |
155 | - Coherent FS 64 8 | |
156 | ||
157 | * Directory entry on disk | |
158 | - Minix FS | |
159 | unsigned short inode; | |
160 | char name[14/30]; | |
161 | - Xenix FS, SystemV FS, Coherent FS | |
162 | unsigned short inode; | |
163 | char name[14]; | |
164 | ||
165 | * Dir entry size, dir entries per block | |
166 | - Minix FS 16/32 64/32 | |
167 | - Xenix FS 16 64 | |
168 | - SystemV FS 16 64 | |
169 | - Coherent FS 16 32 | |
170 | ||
171 | * How to implement symbolic links such that the host fsck doesn't scream: | |
172 | - Minix FS normal | |
173 | - Xenix FS kludge: as regular files with chmod 1000 | |
174 | - SystemV FS ?? | |
175 | - Coherent FS kludge: as regular files with chmod 1000 | |
176 | ||
177 | ||
178 | Notation: We often speak of a "block" but mean a zone (the allocation unit) | |
179 | and not the disk driver's notion of "block". | |
180 | ||
181 | ||
182 | Bruno Haible <haible@ma2s2.mathematik.uni-karlsruhe.de> |