Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 182 insertions, 0 deletions

diff --git a/fs/sysv/INTRO b/fs/sysv/INTRO
new file mode 100644
index 000000000000..de4e4d17cac6
--- /dev/null
+++ b/fs/sysv/INTRO
@@ -0,0 +1,182 @@
+This is the implementation of the SystemV/Coherent filesystem for Linux.
+It grew out of separate filesystem implementations
+
+    Xenix FS      Doug Evans <dje@cygnus.com>  June 1992
+    SystemV FS    Paul B. Monday <pmonday@eecs.wsu.edu> March-June 1993
+    Coherent FS   B. Haible <haible@ma2s2.mathematik.uni-karlsruhe.de> June 1993
+
+and was merged together in July 1993.
+
+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
+
+
+Notation: We often speak of a "block" but mean a zone (the allocation unit)
+and not the disk driver's notion of "block".
+
+
+Bruno Haible  <haible@ma2s2.mathematik.uni-karlsruhe.de>