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264 lines
8.1 KiB
264 lines
8.1 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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================== |
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SystemV Filesystem |
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================== |
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It implements all of |
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- Xenix FS, |
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- SystemV/386 FS, |
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- Coherent FS. |
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To install: |
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* Answer the 'System V and Coherent filesystem support' question with 'y' |
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when configuring the kernel. |
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* To mount a disk or a partition, use:: |
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mount [-r] -t sysv device mountpoint |
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The file system type names:: |
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-t sysv |
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-t xenix |
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-t coherent |
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may be used interchangeably, but the last two will eventually disappear. |
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Bugs in the present implementation: |
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- Coherent FS: |
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- The "free list interleave" n:m is currently ignored. |
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- Only file systems with no filesystem name and no pack name are recognized. |
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(See Coherent "man mkfs" for a description of these features.) |
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- SystemV Release 2 FS: |
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The superblock is only searched in the blocks 9, 15, 18, which |
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corresponds to the beginning of track 1 on floppy disks. No support |
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for this FS on hard disk yet. |
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These filesystems are rather similar. Here is a comparison with Minix FS: |
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* Linux fdisk reports on partitions |
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- Minix FS 0x81 Linux/Minix |
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- Xenix FS ?? |
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- SystemV FS ?? |
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- Coherent FS 0x08 AIX bootable |
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* Size of a block or zone (data allocation unit on disk) |
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- Minix FS 1024 |
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- Xenix FS 1024 (also 512 ??) |
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- SystemV FS 1024 (also 512 and 2048) |
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- Coherent FS 512 |
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* General layout: all have one boot block, one super block and |
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separate areas for inodes and for directories/data. |
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On SystemV Release 2 FS (e.g. Microport) the first track is reserved and |
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all the block numbers (including the super block) are offset by one track. |
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* Byte ordering of "short" (16 bit entities) on disk: |
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- Minix FS little endian 0 1 |
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- Xenix FS little endian 0 1 |
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- SystemV FS little endian 0 1 |
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- Coherent FS little endian 0 1 |
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Of course, this affects only the file system, not the data of files on it! |
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* Byte ordering of "long" (32 bit entities) on disk: |
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- Minix FS little endian 0 1 2 3 |
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- Xenix FS little endian 0 1 2 3 |
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- SystemV FS little endian 0 1 2 3 |
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- Coherent FS PDP-11 2 3 0 1 |
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Of course, this affects only the file system, not the data of files on it! |
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* Inode on disk: "short", 0 means non-existent, the root dir ino is: |
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================================= == |
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Minix FS 1 |
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Xenix FS, SystemV FS, Coherent FS 2 |
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================================= == |
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* Maximum number of hard links to a file: |
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=========== ========= |
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Minix FS 250 |
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Xenix FS ?? |
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SystemV FS ?? |
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Coherent FS >=10000 |
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=========== ========= |
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* Free inode management: |
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- Minix FS |
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a bitmap |
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- Xenix FS, SystemV FS, Coherent FS |
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There is a cache of a certain number of free inodes in the super-block. |
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When it is exhausted, new free inodes are found using a linear search. |
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* Free block management: |
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- Minix FS |
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a bitmap |
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- Xenix FS, SystemV FS, Coherent FS |
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Free blocks are organized in a "free list". Maybe a misleading term, |
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since it is not true that every free block contains a pointer to |
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the next free block. Rather, the free blocks are organized in chunks |
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of limited size, and every now and then a free block contains pointers |
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to the free blocks pertaining to the next chunk; the first of these |
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contains pointers and so on. The list terminates with a "block number" |
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0 on Xenix FS and SystemV FS, with a block zeroed out on Coherent FS. |
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* Super-block location: |
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=========== ========================== |
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Minix FS block 1 = bytes 1024..2047 |
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Xenix FS block 1 = bytes 1024..2047 |
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SystemV FS bytes 512..1023 |
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Coherent FS block 1 = bytes 512..1023 |
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=========== ========================== |
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* Super-block layout: |
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- Minix FS:: |
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unsigned short s_ninodes; |
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unsigned short s_nzones; |
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unsigned short s_imap_blocks; |
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unsigned short s_zmap_blocks; |
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unsigned short s_firstdatazone; |
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unsigned short s_log_zone_size; |
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unsigned long s_max_size; |
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unsigned short s_magic; |
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- Xenix FS, SystemV FS, Coherent FS:: |
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unsigned short s_firstdatazone; |
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unsigned long s_nzones; |
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unsigned short s_fzone_count; |
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unsigned long s_fzones[NICFREE]; |
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unsigned short s_finode_count; |
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unsigned short s_finodes[NICINOD]; |
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char s_flock; |
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char s_ilock; |
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char s_modified; |
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char s_rdonly; |
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unsigned long s_time; |
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short s_dinfo[4]; -- SystemV FS only |
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unsigned long s_free_zones; |
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unsigned short s_free_inodes; |
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short s_dinfo[4]; -- Xenix FS only |
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unsigned short s_interleave_m,s_interleave_n; -- Coherent FS only |
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char s_fname[6]; |
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char s_fpack[6]; |
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then they differ considerably: |
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Xenix FS:: |
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char s_clean; |
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char s_fill[371]; |
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long s_magic; |
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long s_type; |
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SystemV FS:: |
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long s_fill[12 or 14]; |
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long s_state; |
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long s_magic; |
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long s_type; |
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Coherent FS:: |
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unsigned long s_unique; |
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Note that Coherent FS has no magic. |
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* Inode layout: |
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- Minix FS:: |
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unsigned short i_mode; |
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unsigned short i_uid; |
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unsigned long i_size; |
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unsigned long i_time; |
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unsigned char i_gid; |
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unsigned char i_nlinks; |
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unsigned short i_zone[7+1+1]; |
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- Xenix FS, SystemV FS, Coherent FS:: |
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unsigned short i_mode; |
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unsigned short i_nlink; |
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unsigned short i_uid; |
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unsigned short i_gid; |
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unsigned long i_size; |
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unsigned char i_zone[3*(10+1+1+1)]; |
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unsigned long i_atime; |
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unsigned long i_mtime; |
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unsigned long i_ctime; |
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* Regular file data blocks are organized as |
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- Minix FS: |
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- 7 direct blocks |
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- 1 indirect block (pointers to blocks) |
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- 1 double-indirect block (pointer to pointers to blocks) |
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- Xenix FS, SystemV FS, Coherent FS: |
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- 10 direct blocks |
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- 1 indirect block (pointers to blocks) |
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- 1 double-indirect block (pointer to pointers to blocks) |
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- 1 triple-indirect block (pointer to pointers to pointers to blocks) |
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=========== ========== ================ |
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Inode size inodes per block |
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=========== ========== ================ |
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Minix FS 32 32 |
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Xenix FS 64 16 |
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SystemV FS 64 16 |
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Coherent FS 64 8 |
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=========== ========== ================ |
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* Directory entry on disk |
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- Minix FS:: |
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unsigned short inode; |
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char name[14/30]; |
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- Xenix FS, SystemV FS, Coherent FS:: |
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unsigned short inode; |
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char name[14]; |
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=========== ============== ===================== |
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Dir entry size dir entries per block |
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=========== ============== ===================== |
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Minix FS 16/32 64/32 |
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Xenix FS 16 64 |
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SystemV FS 16 64 |
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Coherent FS 16 32 |
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=========== ============== ===================== |
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* How to implement symbolic links such that the host fsck doesn't scream: |
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- Minix FS normal |
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- Xenix FS kludge: as regular files with chmod 1000 |
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- SystemV FS ?? |
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- Coherent FS kludge: as regular files with chmod 1000 |
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Notation: We often speak of a "block" but mean a zone (the allocation unit) |
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and not the disk driver's notion of "block".
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