Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 264 insertions, 0 deletions

diff --git a/Documentation/filesystems/sysv-fs.rst b/Documentation/filesystems/sysv-fs.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+SystemV Filesystem
+==================
+
+It implements all of
+  - Xenix FS,
+  - SystemV/386 FS,
+  - Coherent FS.
+
+To install:
+
+* Answer the 'System V and Coherent filesystem support' question with 'y'
+  when configuring the kernel.
+* To mount a disk or a partition, use::
+
+    mount [-r] -t sysv device mountpoint
+
+  The file system type names::
+
+               -t sysv
+               -t xenix
+               -t coherent
+
+  may be used interchangeably, but the last two will eventually disappear.
+
+Bugs in the present implementation:
+
+- Coherent FS:
+
+  - The "free list interleave" n:m is currently ignored.
+  - Only file systems with no filesystem name and no pack name are recognized.
+    (See Coherent "man mkfs" for a description of these features.)
+
+- SystemV Release 2 FS:
+
+  The superblock is only searched in the blocks 9, 15, 18, which
+  corresponds to the beginning of track 1 on floppy disks. No support
+  for this FS on hard disk yet.
+
+
+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".