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Diffstat (limited to 'fs/sysv/INTRO')
| -rw-r--r-- | fs/sysv/INTRO | 182 |
1 files changed, 0 insertions, 182 deletions
diff --git a/fs/sysv/INTRO b/fs/sysv/INTRO deleted file mode 100644 index de4e4d1..0000000 --- a/fs/sysv/INTRO +++ /dev/null @@ -1,182 +0,0 @@ -This is the implementation of the SystemV/Coherent filesystem for Linux. -It grew out of separate filesystem implementations - - Xenix FS Doug Evans <dje@cygnus.com> June 1992 - SystemV FS Paul B. Monday <pmonday@eecs.wsu.edu> March-June 1993 - Coherent FS B. Haible <haible@ma2s2.mathematik.uni-karlsruhe.de> June 1993 - -and was merged together in July 1993. - -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". - - -Bruno Haible <haible@ma2s2.mathematik.uni-karlsruhe.de> |
