Commit | Line | Data |
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1da177e4 LT |
1 | It implements all of |
2 | - Xenix FS, | |
3 | - SystemV/386 FS, | |
4 | - Coherent FS. | |
5 | ||
1da177e4 LT |
6 | To install: |
7 | * Answer the 'System V and Coherent filesystem support' question with 'y' | |
8 | when configuring the kernel. | |
9 | * To mount a disk or a partition, use | |
10 | mount [-r] -t sysv device mountpoint | |
11 | The file system type names | |
12 | -t sysv | |
13 | -t xenix | |
14 | -t coherent | |
15 | may be used interchangeably, but the last two will eventually disappear. | |
16 | ||
17 | Bugs in the present implementation: | |
18 | - Coherent FS: | |
19 | - The "free list interleave" n:m is currently ignored. | |
20 | - Only file systems with no filesystem name and no pack name are recognized. | |
21 | (See Coherent "man mkfs" for a description of these features.) | |
22 | - SystemV Release 2 FS: | |
23 | The superblock is only searched in the blocks 9, 15, 18, which | |
24 | corresponds to the beginning of track 1 on floppy disks. No support | |
25 | for this FS on hard disk yet. | |
26 | ||
27 | ||
3982cd99 AB |
28 | These filesystems are rather similar. Here is a comparison with Minix FS: |
29 | ||
30 | * Linux fdisk reports on partitions | |
31 | - Minix FS 0x81 Linux/Minix | |
32 | - Xenix FS ?? | |
33 | - SystemV FS ?? | |
34 | - Coherent FS 0x08 AIX bootable | |
35 | ||
36 | * Size of a block or zone (data allocation unit on disk) | |
37 | - Minix FS 1024 | |
38 | - Xenix FS 1024 (also 512 ??) | |
39 | - SystemV FS 1024 (also 512 and 2048) | |
40 | - Coherent FS 512 | |
41 | ||
42 | * General layout: all have one boot block, one super block and | |
43 | separate areas for inodes and for directories/data. | |
44 | On SystemV Release 2 FS (e.g. Microport) the first track is reserved and | |
45 | all the block numbers (including the super block) are offset by one track. | |
46 | ||
47 | * Byte ordering of "short" (16 bit entities) on disk: | |
48 | - Minix FS little endian 0 1 | |
49 | - Xenix FS little endian 0 1 | |
50 | - SystemV FS little endian 0 1 | |
51 | - Coherent FS little endian 0 1 | |
52 | Of course, this affects only the file system, not the data of files on it! | |
53 | ||
54 | * Byte ordering of "long" (32 bit entities) on disk: | |
55 | - Minix FS little endian 0 1 2 3 | |
56 | - Xenix FS little endian 0 1 2 3 | |
57 | - SystemV FS little endian 0 1 2 3 | |
58 | - Coherent FS PDP-11 2 3 0 1 | |
59 | Of course, this affects only the file system, not the data of files on it! | |
60 | ||
61 | * Inode on disk: "short", 0 means non-existent, the root dir ino is: | |
62 | - Minix FS 1 | |
63 | - Xenix FS, SystemV FS, Coherent FS 2 | |
64 | ||
65 | * Maximum number of hard links to a file: | |
66 | - Minix FS 250 | |
67 | - Xenix FS ?? | |
68 | - SystemV FS ?? | |
69 | - Coherent FS >=10000 | |
70 | ||
71 | * Free inode management: | |
72 | - Minix FS a bitmap | |
73 | - Xenix FS, SystemV FS, Coherent FS | |
74 | There is a cache of a certain number of free inodes in the super-block. | |
75 | When it is exhausted, new free inodes are found using a linear search. | |
76 | ||
77 | * Free block management: | |
78 | - Minix FS a bitmap | |
79 | - Xenix FS, SystemV FS, Coherent FS | |
80 | Free blocks are organized in a "free list". Maybe a misleading term, | |
81 | since it is not true that every free block contains a pointer to | |
82 | the next free block. Rather, the free blocks are organized in chunks | |
83 | of limited size, and every now and then a free block contains pointers | |
84 | to the free blocks pertaining to the next chunk; the first of these | |
85 | contains pointers and so on. The list terminates with a "block number" | |
86 | 0 on Xenix FS and SystemV FS, with a block zeroed out on Coherent FS. | |
87 | ||
88 | * Super-block location: | |
89 | - Minix FS block 1 = bytes 1024..2047 | |
90 | - Xenix FS block 1 = bytes 1024..2047 | |
91 | - SystemV FS bytes 512..1023 | |
92 | - Coherent FS block 1 = bytes 512..1023 | |
93 | ||
94 | * Super-block layout: | |
95 | - Minix FS | |
96 | unsigned short s_ninodes; | |
97 | unsigned short s_nzones; | |
98 | unsigned short s_imap_blocks; | |
99 | unsigned short s_zmap_blocks; | |
100 | unsigned short s_firstdatazone; | |
101 | unsigned short s_log_zone_size; | |
102 | unsigned long s_max_size; | |
103 | unsigned short s_magic; | |
104 | - Xenix FS, SystemV FS, Coherent FS | |
105 | unsigned short s_firstdatazone; | |
106 | unsigned long s_nzones; | |
107 | unsigned short s_fzone_count; | |
108 | unsigned long s_fzones[NICFREE]; | |
109 | unsigned short s_finode_count; | |
110 | unsigned short s_finodes[NICINOD]; | |
111 | char s_flock; | |
112 | char s_ilock; | |
113 | char s_modified; | |
114 | char s_rdonly; | |
115 | unsigned long s_time; | |
116 | short s_dinfo[4]; -- SystemV FS only | |
117 | unsigned long s_free_zones; | |
118 | unsigned short s_free_inodes; | |
119 | short s_dinfo[4]; -- Xenix FS only | |
120 | unsigned short s_interleave_m,s_interleave_n; -- Coherent FS only | |
121 | char s_fname[6]; | |
122 | char s_fpack[6]; | |
123 | then they differ considerably: | |
124 | Xenix FS | |
125 | char s_clean; | |
126 | char s_fill[371]; | |
127 | long s_magic; | |
128 | long s_type; | |
129 | SystemV FS | |
130 | long s_fill[12 or 14]; | |
131 | long s_state; | |
132 | long s_magic; | |
133 | long s_type; | |
134 | Coherent FS | |
135 | unsigned long s_unique; | |
136 | Note that Coherent FS has no magic. | |
137 | ||
138 | * Inode layout: | |
139 | - Minix FS | |
140 | unsigned short i_mode; | |
141 | unsigned short i_uid; | |
142 | unsigned long i_size; | |
143 | unsigned long i_time; | |
144 | unsigned char i_gid; | |
145 | unsigned char i_nlinks; | |
146 | unsigned short i_zone[7+1+1]; | |
147 | - Xenix FS, SystemV FS, Coherent FS | |
148 | unsigned short i_mode; | |
149 | unsigned short i_nlink; | |
150 | unsigned short i_uid; | |
151 | unsigned short i_gid; | |
152 | unsigned long i_size; | |
153 | unsigned char i_zone[3*(10+1+1+1)]; | |
154 | unsigned long i_atime; | |
155 | unsigned long i_mtime; | |
156 | unsigned long i_ctime; | |
157 | ||
158 | * Regular file data blocks are organized as | |
159 | - Minix FS | |
160 | 7 direct blocks | |
161 | 1 indirect block (pointers to blocks) | |
162 | 1 double-indirect block (pointer to pointers to blocks) | |
163 | - Xenix FS, SystemV FS, Coherent FS | |
164 | 10 direct blocks | |
165 | 1 indirect block (pointers to blocks) | |
166 | 1 double-indirect block (pointer to pointers to blocks) | |
167 | 1 triple-indirect block (pointer to pointers to pointers to blocks) | |
168 | ||
169 | * Inode size, inodes per block | |
170 | - Minix FS 32 32 | |
171 | - Xenix FS 64 16 | |
172 | - SystemV FS 64 16 | |
173 | - Coherent FS 64 8 | |
174 | ||
175 | * Directory entry on disk | |
176 | - Minix FS | |
177 | unsigned short inode; | |
178 | char name[14/30]; | |
179 | - Xenix FS, SystemV FS, Coherent FS | |
180 | unsigned short inode; | |
181 | char name[14]; | |
182 | ||
183 | * Dir entry size, dir entries per block | |
184 | - Minix FS 16/32 64/32 | |
185 | - Xenix FS 16 64 | |
186 | - SystemV FS 16 64 | |
187 | - Coherent FS 16 32 | |
188 | ||
189 | * How to implement symbolic links such that the host fsck doesn't scream: | |
190 | - Minix FS normal | |
191 | - Xenix FS kludge: as regular files with chmod 1000 | |
192 | - SystemV FS ?? | |
193 | - Coherent FS kludge: as regular files with chmod 1000 | |
1da177e4 | 194 | |
1da177e4 | 195 | |
3982cd99 AB |
196 | Notation: We often speak of a "block" but mean a zone (the allocation unit) |
197 | and not the disk driver's notion of "block". |