--- /dev/null
+.. 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".
+++ /dev/null
-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".
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