-This is the implementation of the SystemV/Coherent filesystem for Linux.
It implements all of
- Xenix FS,
- SystemV/386 FS,
- Coherent FS.
-This is version beta 4.
-
To install:
* Answer the 'System V and Coherent filesystem support' question with 'y'
when configuring the kernel.
for this FS on hard disk yet.
-Please report any bugs and suggestions to
- Bruno Haible <haible@ma2s2.mathematik.uni-karlsruhe.de>
- Pascal Haible <haible@izfm.uni-stuttgart.de>
- Krzysztof G. Baranowski <kgb@manjak.knm.org.pl>
+These filesystems are rather similar. Here is a comparison with Minix FS:
+
+* Linux fdisk reports on partitions
+ - Minix FS 0x81 Linux/Minix
+ - Xenix FS ??
+ - SystemV FS ??
+ - Coherent FS 0x08 AIX bootable
+
+* Size of a block or zone (data allocation unit on disk)
+ - Minix FS 1024
+ - Xenix FS 1024 (also 512 ??)
+ - SystemV FS 1024 (also 512 and 2048)
+ - Coherent FS 512
+
+* General layout: all have one boot block, one super block and
+ separate areas for inodes and for directories/data.
+ On SystemV Release 2 FS (e.g. Microport) the first track is reserved and
+ all the block numbers (including the super block) are offset by one track.
+
+* Byte ordering of "short" (16 bit entities) on disk:
+ - Minix FS little endian 0 1
+ - Xenix FS little endian 0 1
+ - SystemV FS little endian 0 1
+ - Coherent FS little endian 0 1
+ Of course, this affects only the file system, not the data of files on it!
+
+* Byte ordering of "long" (32 bit entities) on disk:
+ - Minix FS little endian 0 1 2 3
+ - Xenix FS little endian 0 1 2 3
+ - SystemV FS little endian 0 1 2 3
+ - Coherent FS PDP-11 2 3 0 1
+ Of course, this affects only the file system, not the data of files on it!
+
+* Inode on disk: "short", 0 means non-existent, the root dir ino is:
+ - Minix FS 1
+ - Xenix FS, SystemV FS, Coherent FS 2
+
+* Maximum number of hard links to a file:
+ - Minix FS 250
+ - Xenix FS ??
+ - SystemV FS ??
+ - Coherent FS >=10000
+
+* Free inode management:
+ - Minix FS a bitmap
+ - Xenix FS, SystemV FS, Coherent FS
+ There is a cache of a certain number of free inodes in the super-block.
+ When it is exhausted, new free inodes are found using a linear search.
+
+* Free block management:
+ - Minix FS a bitmap
+ - Xenix FS, SystemV FS, Coherent FS
+ Free blocks are organized in a "free list". Maybe a misleading term,
+ since it is not true that every free block contains a pointer to
+ the next free block. Rather, the free blocks are organized in chunks
+ of limited size, and every now and then a free block contains pointers
+ to the free blocks pertaining to the next chunk; the first of these
+ contains pointers and so on. The list terminates with a "block number"
+ 0 on Xenix FS and SystemV FS, with a block zeroed out on Coherent FS.
+
+* Super-block location:
+ - Minix FS block 1 = bytes 1024..2047
+ - Xenix FS block 1 = bytes 1024..2047
+ - SystemV FS bytes 512..1023
+ - Coherent FS block 1 = bytes 512..1023
+
+* Super-block layout:
+ - Minix FS
+ unsigned short s_ninodes;
+ unsigned short s_nzones;
+ unsigned short s_imap_blocks;
+ unsigned short s_zmap_blocks;
+ unsigned short s_firstdatazone;
+ unsigned short s_log_zone_size;
+ unsigned long s_max_size;
+ unsigned short s_magic;
+ - Xenix FS, SystemV FS, Coherent FS
+ unsigned short s_firstdatazone;
+ unsigned long s_nzones;
+ unsigned short s_fzone_count;
+ unsigned long s_fzones[NICFREE];
+ unsigned short s_finode_count;
+ unsigned short s_finodes[NICINOD];
+ char s_flock;
+ char s_ilock;
+ char s_modified;
+ char s_rdonly;
+ unsigned long s_time;
+ short s_dinfo[4]; -- SystemV FS only
+ unsigned long s_free_zones;
+ unsigned short s_free_inodes;
+ short s_dinfo[4]; -- Xenix FS only
+ unsigned short s_interleave_m,s_interleave_n; -- Coherent FS only
+ char s_fname[6];
+ char s_fpack[6];
+ then they differ considerably:
+ Xenix FS
+ char s_clean;
+ char s_fill[371];
+ long s_magic;
+ long s_type;
+ SystemV FS
+ long s_fill[12 or 14];
+ long s_state;
+ long s_magic;
+ long s_type;
+ Coherent FS
+ unsigned long s_unique;
+ Note that Coherent FS has no magic.
+
+* Inode layout:
+ - Minix FS
+ unsigned short i_mode;
+ unsigned short i_uid;
+ unsigned long i_size;
+ unsigned long i_time;
+ unsigned char i_gid;
+ unsigned char i_nlinks;
+ unsigned short i_zone[7+1+1];
+ - Xenix FS, SystemV FS, Coherent FS
+ unsigned short i_mode;
+ unsigned short i_nlink;
+ unsigned short i_uid;
+ unsigned short i_gid;
+ unsigned long i_size;
+ unsigned char i_zone[3*(10+1+1+1)];
+ unsigned long i_atime;
+ unsigned long i_mtime;
+ unsigned long i_ctime;
+
+* Regular file data blocks are organized as
+ - Minix FS
+ 7 direct blocks
+ 1 indirect block (pointers to blocks)
+ 1 double-indirect block (pointer to pointers to blocks)
+ - Xenix FS, SystemV FS, Coherent FS
+ 10 direct blocks
+ 1 indirect block (pointers to blocks)
+ 1 double-indirect block (pointer to pointers to blocks)
+ 1 triple-indirect block (pointer to pointers to pointers to blocks)
+
+* Inode size, inodes per block
+ - Minix FS 32 32
+ - Xenix FS 64 16
+ - SystemV FS 64 16
+ - Coherent FS 64 8
+
+* Directory entry on disk
+ - Minix FS
+ unsigned short inode;
+ char name[14/30];
+ - Xenix FS, SystemV FS, Coherent FS
+ unsigned short inode;
+ char name[14];
+
+* Dir entry size, dir entries per block
+ - Minix FS 16/32 64/32
+ - Xenix FS 16 64
+ - SystemV FS 16 64
+ - Coherent FS 16 32
+
+* How to implement symbolic links such that the host fsck doesn't scream:
+ - Minix FS normal
+ - Xenix FS kludge: as regular files with chmod 1000
+ - SystemV FS ??
+ - Coherent FS kludge: as regular files with chmod 1000
-Bruno Haible
-<haible@ma2s2.mathematik.uni-karlsruhe.de>
+Notation: We often speak of a "block" but mean a zone (the allocation unit)
+and not the disk driver's notion of "block".
git://git.onelab.eu / linux-2.6.git / blobdiff