fs(4) UNIX System V(UFS) fs(4)
NAME
fs (ufs) - format of ufs file system volume
SYNOPSIS
#include <sys/param.h>
#include <sys/types.h>
#include <sys/fs/ufsfs.h>
DESCRIPTION
Each disk drive contains some number of file systems. A file system
consists of a number of cylinder groups. Each cylinder group has inodes
and data.
A file system is described by its super-block, and by the information in
the cylinder group blocks. The super-block is critical data and is
replicated before each cylinder group block to protect against
catastrophic loss. This is done at mkfs time; the critical super-block
data does not change, so the copies need not normally be referenced
further.
/*
* Super block for a file system.
*/
#define FSMAGIC 0x011954
#define FSACTIVE 0x5e72d81a/* fsstate: mounted */
#define FSOKAY 0x7c269d38/* fsstate: clean */
#define FSBAD 0xcb096f43/* fsstate: bad root */
struct fs {
struct fs *fslink;/* linked list of file systems */
struct fs *fsrlink;/* used for incore super blocks */
daddrt fssblkno;/* addr of super-block in filesys */
daddrt fscblkno;/* offset of cyl-block in filesys */
daddrt fsiblkno;/* offset of inode-blocks in filesys */
daddrt fsdblkno;/* offset of first data after cg */
long fscgoffset;/* cylinder group offset in cylinder */
long fscgmask;/* used to calc mod fsntrak */
timet fstime;/* last time written */
long fssize;/* number of blocks in fs */
long fsdsize;/* number of data blocks in fs */
long fsncg;/* number of cylinder groups */
long fsbsize;/* size of basic blocks in fs */
long fsfsize;/* size of frag blocks in fs */
long fsfrag;/* number of frags in a block in fs */
/* these are configuration parameters */
long fsminfree;/* minimum percentage of free blocks */
long fsrotdelay;/* num of ms for optimal next block */
long fsrps;/* disk revolutions per second */
/* these fields can be computed from the others */
long fsbmask;/* ``blkoff'' calc of blk offsets */
long fsfmask;/* ``fragoff'' calc of frag offsets */
long fsbshift;/* ``lblkno'' calc of logical blkno */
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long fsfshift;/* ``numfrags'' calc number of frags */
/* these are configuration parameters */
long fsmaxcontig;/* max number of contiguous blks */
long fsmaxbpg;/* max number of blks per cyl group */
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/* these fields can be computed from the others */
long fsfragshift;/* block to frag shift */
long fsfsbtodb;/* fsbtodb and dbtofsb shift constant */
long fssbsize;/* actual size of super block */
long fscsmask;/* csum block offset */
long fscsshift;/* csum block number */
long fsnindir;/* value of NINDIR */
long fsinopb;/* value of INOPB */
long fsnspf;/* value of NSPF */
long fsoptim;/* optimization preference, see below */
long fsstate;/* file system state */
long fssparecon[2];/* reserved for future constants */
/* a unique id for this filesystem (currently unused and unmaintained) */
long fsid[2];/* file system id */
/* sizes determined by number of cylinder groups and their sizes */
daddrt fscsaddr;/* blk addr of cyl grp summary area */
long fscssize;/* size of cyl grp summary area */
long fscgsize;/* cylinder group size */
/* these fields should be derived from the hardware */
long fsntrak;/* tracks per cylinder */
long fsnsect;/* sectors per track */
long fsspc;/* sectors per cylinder */
/* this comes from the disk driver partitioning */
long fsncyl;/* cylinders in file system */
/* these fields can be computed from the others */
long fscpg;/* cylinders per group */
long fsipg;/* inodes per group */
long fsfpg;/* blocks per group * fsfrag */
/* this data must be re-computed after crashes */
struct csum fscstotal;/* cylinder summary information */
/* these fields are cleared at mount time */
char fsfmod;/* super block modified flag */
char fsclean;/* file system is clean flag */
char fsronly;/* mounted read-only flag */
char fsflags;/* currently unused flag */
char fsfsmnt[MAXMNTLEN];/* name mounted on */
/* these fields retain the current block allocation info */
long fscgrotor;/* last cg searched */
struct csum *fscsp[MAXCSBUFS];/* list of fscs info buffers */
long fscpc;/* cyl per cycle in postbl */
short fspostbl[MAXCPG][NRPOS];/* head of blocks for each rotation */
long fsmagic;/* magic number */
uchar fsrotbl[1];/* list of blocks for each rotation */
};
/*
* Cylinder group block for a file system.
*/
#define CGMAGIC 0x090255
struct cg {
struct cg *cglink;/* linked list of cyl groups */
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struct cg *cgrlink;/* used for incore cyl groups */
timet cgtime;/* time last written */
long cgcgx;/* we are the cgx'th cylinder group */
short cgncyl;/* number of cyl's this cg */
short cgniblk;/* number of inode blocks this cg */
long cgndblk;/* number of data blocks this cg */
struct csum cgcs;/* cylinder summary information */
long cgrotor;/* position of last used block */
long cgfrotor;/* position of last used frag */
long cgirotor;/* position of last used inode */
long cgfrsum[MAXFRAG];/* counts of available frags */
long cgbtot[MAXCPG];/* block totals per cylinder */
short cgb[MAXCPG][NRPOS];/* positions of free blocks */
char cgiused[MAXIPG/NBBY];/* used inode map */
long cgmagic;/* magic number */
uchar cgfree[1];/* free block map */
};
SEE ALSO
ufs-specific inode(4)
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