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docs: filesystems: convert sysv-fs.txt to ReST 

- Add a SPDX header;
- Add a document title;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add table markups;
- Add it to filesystems/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/5b96a6efba95773af439ab25a7dbe4d0edf8c867.1581955849.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab 2020-02-17 17:12:25 +01:00 committed by Jonathan Corbet
parent 86beb97670
commit 826a613d3f
2 changed files with 112 additions and 44 deletions
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1
Documentation/filesystems/index.rst
View File

@ -88,5 +88,6 @@ Documentation for filesystem implementations.
romfs
squashfs
sysfs
sysv-fs
virtiofs
vfat

155
Documentation/filesystems/sysv-fs.txt → Documentation/filesystems/sysv-fs.rst
View File

@ -1,25 +1,40 @@
.. 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
* To mount a disk or a partition, use::
mount [-r] -t sysv device mountpoint
The file system type names
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.)
(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.
@ -28,12 +43,14 @@ Bugs in the present implementation:
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)
@ -45,37 +62,51 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
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
================================= ==
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
=========== =========
Minix FS 250
Xenix FS ??
SystemV FS ??
Coherent FS >=10000
=========== =========
* Free inode management:
- Minix FS a bitmap
- 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
- 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
@ -86,13 +117,18 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
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
=========== ==========================
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
- Minix FS::
unsigned short s_ninodes;
unsigned short s_nzones;
unsigned short s_imap_blocks;
@ -101,7 +137,9 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
unsigned short s_log_zone_size;
unsigned long s_max_size;
unsigned short s_magic;
- Xenix FS, SystemV FS, Coherent FS
- Xenix FS, SystemV FS, Coherent FS::
unsigned short s_firstdatazone;
unsigned long s_nzones;
unsigned short s_fzone_count;
@ -120,23 +158,33 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
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
Xenix FS::
char s_clean;
char s_fill[371];
long s_magic;
long s_type;
SystemV FS
SystemV FS::
long s_fill[12 or 14];
long s_state;
long s_magic;
long s_type;
Coherent FS
Coherent FS::
unsigned long s_unique;
Note that Coherent FS has no magic.
* Inode layout:
- Minix FS
- Minix FS::
unsigned short i_mode;
unsigned short i_uid;
unsigned long i_size;
@ -144,7 +192,9 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
unsigned char i_gid;
unsigned char i_nlinks;
unsigned short i_zone[7+1+1];
- Xenix FS, SystemV FS, Coherent FS
- Xenix FS, SystemV FS, Coherent FS::
unsigned short i_mode;
unsigned short i_nlink;
unsigned short i_uid;
@ -155,38 +205,55 @@ These filesystems are rather similar. Here is a comparison with Minix FS:
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
* 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
- Minix FS::
unsigned short inode;
char name[14/30];
- Xenix FS, SystemV FS, Coherent FS
- 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
=========== ============== =====================
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 ??