Based on kernel version 6.11
. Page generated on 2024-09-24 08:21 EST
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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". |