1It implements all of 2 - Xenix FS, 3 - SystemV/386 FS, 4 - Coherent FS. 5 6To 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 17Bugs 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 28These 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 196Notation: We often speak of a "block" but mean a zone (the allocation unit) 197and not the disk driver's notion of "block". 198