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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

1	It implements all of
2	  - Xenix FS,
3	  - SystemV/386 FS,
4	  - Coherent FS.
5	
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	
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
194	
195	
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".
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