826a613d3f
- 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>
265 lines
8.1 KiB
ReStructuredText
265 lines
8.1 KiB
ReStructuredText
.. 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".
|