add new useful constants

[unix-history] / usr / src / sys / ufs / ffs / fs.h

/*	fs.h	4.6	83/01/02	*/

/*
 * 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, which in turn
 * describes the cylinder groups.  The super-block is critical
 * data and is replicated in each cylinder group to protect against
 * catastrophic loss.  This is done at mkfs time and the critical
 * super-block data does not change, so the copies need not be
 * referenced further unless disaster strikes.
 *
 * For file system fs, the offsets of the various blocks of interest
 * are given in the super block as:
 *	[fs->fs_sblkno]		Super-block
 *	[fs->fs_cblkno]		Cylinder group block
 *	[fs->fs_iblkno]		Inode blocks
 *	[fs->fs_dblkno]		Data blocks
 * The beginning of cylinder group cg in fs, is given by
 * the ``cgbase(fs, cg)'' macro.
 *
 * The first boot and super blocks are given in absolute disk addresses.
 */
#define BBSIZE		8192
#define SBSIZE		8192
#define	BBLOCK		((daddr_t)(0))
#define	SBLOCK		((daddr_t)(BBLOCK + BBSIZE / DEV_BSIZE))

/*
 * Addresses stored in inodes are capable of addressing fragments
 * of `blocks'. File system blocks of at most size MAXBSIZE can 
 * be optionally broken into 2, 4, or 8 pieces, each of which is
 * addressible; these pieces may be DEV_BSIZE, or some multiple of
 * a DEV_BSIZE unit.
 *
 * Large files consist of exclusively large data blocks.  To avoid
 * undue wasted disk space, the last data block of a small file may be
 * allocated as only as many fragments of a large block as are
 * necessary.  The file system format retains only a single pointer
 * to such a fragment, which is a piece of a single large block that
 * has been divided.  The size of such a fragment is determinable from
 * information in the inode, using the ``blksize(fs, ip, lbn)'' macro.
 *
 * The file system records space availability at the fragment level;
 * to determine block availability, aligned fragments are examined.
 *
 * The root inode is the root of the file system.
 * Inode 0 can't be used for normal purposes and
 * historically bad blocks were linked to inode 1,
 * thus the root inode is 2. (inode 1 is no longer used for
 * this purpose, however numerous dump tapes make this
 * assumption, so we are stuck with it)
 * The lost+found directory is given the next available
 * inode when it is created by ``mkfs''.
 */
#define	ROOTINO		((ino_t)2)	/* i number of all roots */
#define LOSTFOUNDINO	(ROOTINO + 1)

/*
 * MINFREE gives the minimum acceptable percentage of file system
 * blocks which may be free. If the freelist drops below this level
 * only the superuser may continue to allocate blocks. This may
 * be set to 0 if no reserve of free blocks is deemed necessary,
 * however severe performance degredations will be observed if the
 * file system is run at greater than 90% full; thus the default
 * value of fs_minfree is 10%.
 *
 * Empirically the best trade-off between block fragmentation and
 * overall disk utilization at a loading of 90% comes with a
 * fragmentation of 4, thus the default fragment size is a fourth
 * of the block size.
 */
#define MINFREE		10
#define DESFRAG		4

/*
 * Under current technology, most 300MB disks have 32 sectors and
 * 16 tracks, thus these are the defaults used for fs_nsect and 
 * fs_ntrak respectively.
 */
#define DFLNSECT	32
#define DFLNTRAK	16

/*
 * Cylinder group related limits.
 *
 * For each cylinder we keep track of the availability of blocks at different
 * rotational positions, so that we can lay out the data to be picked
 * up with minimum rotational latency.  NRPOS is the number of rotational
 * positions which we distinguish.  With NRPOS 8 the resolution of our
 * summary information is 2ms for a typical 3600 rpm drive.
 *
 * ROTDELAY gives the minimum number of milliseconds to initiate
 * another disk transfer on the same cylinder. It is used in
 * determining the rotationally optimal layout for disk blocks
 * within a file; the default of fs_rotdelay is 2ms.
 */
#define	NRPOS		8	/* number distinct rotational positions */
#define ROTDELAY	2

/*
 * Each file system has a number of inodes statically allocated.
 * We allocate one inode slot per NBPI bytes, expecting this
 * to be far more than we will ever need.
 *
 * MAXIPG bounds the number of inodes per cylinder group, and
 * is needed only to keep the structure simpler by having the
 * only a single variable size element (the free bit map).
 *
 * N.B.: MAXIPG must be a multiple of INOPB(fs).
 */
#define	NBPI		2048
#define	MAXIPG		2048	/* max number inodes/cyl group */

/*
 * MINBSIZE is the smallest allowable block size.
 * In order to insure that it is possible to create files of size
 * 2^32 with only two levels of indirection, MINBSIZE is set to 4096.
 * MINBSIZE must be big enough to hold a cylinder group block,
 * thus changes to (struct cg) must keep its size within MINBSIZE.
 * MAXCPG is limited only to dimension an array in (struct cg);
 * it can be made larger as long as that structures size remains
 * within the bounds dictated by MINBSIZE.
 * Note that super blocks are always of size MAXBSIZE,
 * and that MAXBSIZE must be >= MINBSIZE.
 */
#define MINBSIZE	4096
#define	DESCPG		16	/* desired fs_cpg */
#define	MAXCPG		32	/* maximum fs_cpg */

/*
 * The path name on which the file system is mounted is maintained
 * in fs_fsmnt. MAXMNTLEN defines the amount of space allocated in 
 * the super block for this name.
 * The limit on the amount of summary information per file system
 * is defined by MAXCSBUFS. It is currently parameterized for a
 * maximum of two million cylinders.
 */
#define MAXMNTLEN 512
#define MAXCSBUFS 32

/*
 * Per cylinder group information; summarized in blocks allocated
 * from first cylinder group data blocks.  These blocks have to be
 * read in from fs_csaddr (size fs_cssize) in addition to the
 * super block.
 *
 * N.B. sizeof(struct csum) must be a power of two in order for
 * the ``fs_cs'' macro to work (see below).
 */
struct csum {
	long	cs_ndir;	/* number of directories */
	long	cs_nbfree;	/* number of free blocks */
	long	cs_nifree;	/* number of free inodes */
	long	cs_nffree;	/* number of free frags */
};

/*
 * Super block for a file system.
 */
#define	FS_MAGIC	0x011954
struct	fs
{
	struct	fs *fs_link;		/* linked list of file systems */
	struct	fs *fs_rlink;		/*     used for incore super blocks */
	daddr_t	fs_sblkno;		/* addr of super-block in filesys */
	daddr_t	fs_cblkno;		/* offset of cyl-block in filesys */
	daddr_t	fs_iblkno;		/* offset of inode-blocks in filesys */
	daddr_t	fs_dblkno;		/* offset of first data after cg */
	long	fs_cgoffset;		/* cylinder group offset in cylinder */
	long	fs_cgmask;		/* used to calc mod fs_ntrak */
	time_t 	fs_time;    		/* last time written */
	long	fs_size;		/* number of blocks in fs */
	long	fs_dsize;		/* number of data blocks in fs */
	long	fs_ncg;			/* number of cylinder groups */
	long	fs_bsize;		/* size of basic blocks in fs */
	long	fs_fsize;		/* size of frag blocks in fs */
	long	fs_frag;		/* number of frags in a block in fs */
	long	fs_minfree;		/* minimum percentage of free blocks */
	long	fs_rotdelay;		/* num of ms for optimal next block */
	long	fs_rps;			/* disk revolutions per second */
	long	fs_bmask;		/* ``blkoff'' calc of blk offsets */
	long	fs_fmask;		/* ``fragoff'' calc of frag offsets */
	long	fs_bshift;		/* ``lblkno'' calc of logical blkno */
	long	fs_fshift;		/* ``numfrags'' calc number of frags */
	long	fs_maxcontig;		/* max number of contiguous blks */
	long	fs_maxbpg;		/* max number of blks per cyl group */
	long	fs_fragshift;		/* block to frag shift */
	long	fs_fsbtodb;		/* fsbtodb and dbtofsb shift constant */
	long	fs_sbsize;		/* actual size of super block */
	long	fs_csmask;		/* csum block offset */
	long	fs_csshift;		/* csum block number */
	long	fs_nindir;		/* value of NINDIR */
	long	fs_inopb;		/* value of INOPB */
	long	fs_nspf;		/* value of NSPF */
	long	fs_sparecon[6];		/* reserved for future constants */
/* sizes determined by number of cylinder groups and their sizes */
	daddr_t fs_csaddr;		/* blk addr of cyl grp summary area */
	long	fs_cssize;		/* size of cyl grp summary area */
	long	fs_cgsize;		/* cylinder group size */
/* these fields should be derived from the hardware */
	long	fs_ntrak;		/* tracks per cylinder */
	long	fs_nsect;		/* sectors per track */
	long  	fs_spc;   		/* sectors per cylinder */
/* this comes from the disk driver partitioning */
	long	fs_ncyl;   		/* cylinders in file system */
/* these fields can be computed from the others */
	long	fs_cpg;			/* cylinders per group */
	long	fs_ipg;			/* inodes per group */
	long	fs_fpg;			/* blocks per group * fs_frag */
/* this data must be re-computed after crashes */
	struct	csum fs_cstotal;	/* cylinder summary information */
/* these fields are cleared at mount time */
	char   	fs_fmod;    		/* super block modified flag */
	char   	fs_clean;    		/* file system is clean flag */
	char   	fs_ronly;   		/* mounted read-only flag */
	char   	fs_flags;   		/* currently unused flag */
	char	fs_fsmnt[MAXMNTLEN];	/* name mounted on */
/* these fields retain the current block allocation info */
	long	fs_cgrotor;		/* last cg searched */
	struct	csum *fs_csp[MAXCSBUFS];/* list of fs_cs info buffers */
	long	fs_cpc;			/* cyl per cycle in postbl */
	short	fs_postbl[MAXCPG][NRPOS];/* head of blocks for each rotation */
	long	fs_magic;		/* magic number */
	u_char	fs_rotbl[1];		/* list of blocks for each rotation */
/* actually longer */
};

/*
 * Convert cylinder group to base address of its global summary info.
 *
 * N.B. This macro assumes that sizeof(struct csum) is a power of two.
 */
#define fs_cs(fs, indx) \
	fs_csp[(indx) / ((fs)->fs_bsize / sizeof(struct csum))] \
	[(indx) % ((fs)->fs_bsize / sizeof(struct csum))]

/*
 * MAXBPC bounds the size of the rotational layout tables and
 * is limited by the fact that the super block is of size SBSIZE.
 * The size of these tables is INVERSELY proportional to the block
 * size of the file system. It is aggravated by sector sizes that
 * are not powers of two, as this increases the number of cylinders
 * included before the rotational pattern repeats (fs_cpc).
 * Its size is derived from the number of bytes remaining in (struct fs)
 */
#define	MAXBPC	(SBSIZE - sizeof (struct fs))

/*
 * Cylinder group block for a file system.
 */
#define	CG_MAGIC	0x090255
struct	cg {
	struct	cg *cg_link;		/* linked list of cyl groups */
	struct	cg *cg_rlink;		/*     used for incore cyl groups */
	time_t	cg_time;		/* time last written */
	long	cg_cgx;			/* we are the cgx'th cylinder group */
	short	cg_ncyl;		/* number of cyl's this cg */
	short	cg_niblk;		/* number of inode blocks this cg */
	long	cg_ndblk;		/* number of data blocks this cg */
	struct	csum cg_cs;		/* cylinder summary information */
	long	cg_rotor;		/* position of last used block */
	long	cg_frotor;		/* position of last used frag */
	long	cg_irotor;		/* position of last used inode */
	long	cg_frsum[MAXFRAG];	/* counts of available frags */
	long	cg_btot[MAXCPG];	/* block totals per cylinder */
	short	cg_b[MAXCPG][NRPOS];	/* positions of free blocks */
	char	cg_iused[MAXIPG/NBBY];	/* used inode map */
	long	cg_magic;		/* magic number */
	u_char	cg_free[1];		/* free block map */
/* actually longer */
};

/*
 * MAXBPG bounds the number of blocks of data per cylinder group,
 * and is limited by the fact that cylinder groups are at most one block.
 * Its size is derived from the size of blocks and the (struct cg) size,
 * by the number of remaining bits.
 */
#define	MAXBPG(fs) \
	(NBBY * ((fs)->fs_bsize - (sizeof (struct cg))) / (fs)->fs_frag)

/*
 * Turn file system block numbers into disk block addresses.
 * This maps file system blocks to device size blocks.
 */
#define fsbtodb(fs, b)	((b) * ((fs)->fs_fsize / DEV_BSIZE))
#define	dbtofsb(fs, b)	((b) / ((fs)->fs_fsize / DEV_BSIZE))

/*
 * Cylinder group macros to locate things in cylinder groups.
 * They calc file system addresses of cylinder group data structures.
 */
#define	cgbase(fs, c)	((daddr_t)((fs)->fs_fpg * (c)))
#define cgstart(fs, c) \
	(cgbase(fs, c) + (fs)->fs_cgoffset * ((c) & ~((fs)->fs_cgmask)))
#define	cgsblock(fs, c)	(cgstart(fs, c) + (fs)->fs_sblkno)	/* super blk */
#define	cgtod(fs, c)	(cgstart(fs, c) + (fs)->fs_cblkno)	/* cg block */
#define	cgimin(fs, c)	(cgstart(fs, c) + (fs)->fs_iblkno)	/* inode blk */
#define	cgdmin(fs, c)	(cgstart(fs, c) + (fs)->fs_dblkno)	/* 1st data */

/*
 * Macros for handling inode numbers:
 *     inode number to file system block offset.
 *     inode number to cylinder group number.
 *     inode number to file system block address.
 */
#define	itoo(fs, x)	((x) % INOPB(fs))
#define	itog(fs, x)	((x) / (fs)->fs_ipg)
#define	itod(fs, x) \
	((daddr_t)(cgimin(fs, itog(fs, x)) + \
	(x) % (fs)->fs_ipg / INOPB(fs) * (fs)->fs_frag))

/*
 * Give cylinder group number for a file system block.
 * Give cylinder group block number for a file system block.
 */
#define	dtog(fs, d)	((d) / (fs)->fs_fpg)
#define	dtogd(fs, d)	((d) % (fs)->fs_fpg)

/*
 * Extract the bits for a block from a map.
 * Compute the cylinder and rotational position of a cyl block addr.
 */
#define blkmap(fs, map, loc) \
    (((map)[loc / NBBY] >> (loc % NBBY)) & (0xff >> (NBBY - (fs)->fs_frag)))
#define cbtocylno(fs, bno) \
	((bno) * NSPF(fs) / (fs)->fs_spc)
#define cbtorpos(fs, bno) \
	((bno) * NSPF(fs) % (fs)->fs_nsect * NRPOS / (fs)->fs_nsect)

/*
 * The following macros optimize certain frequently calculated
 * quantities by using shifts and masks in place of divisions
 * modulos and multiplications.
 */
#define blkoff(fs, loc)		/* calculates (loc % fs->fs_bsize) */ \
	((loc) & ~(fs)->fs_bmask)
#define fragoff(fs, loc)	/* calculates (loc % fs->fs_fsize) */ \
	((loc) & ~(fs)->fs_fmask)
#define lblkno(fs, loc)		/* calculates (loc / fs->fs_bsize) */ \
	((loc) >> (fs)->fs_bshift)
#define numfrags(fs, loc)	/* calculates (loc / fs->fs_fsize) */ \
	((loc) >> (fs)->fs_fshift)
#define blkroundup(fs, size)	/* calculates roundup(size, fs->fs_bsize) */ \
	(((size) + (fs)->fs_bsize - 1) & (fs)->fs_bmask)
#define fragroundup(fs, size)	/* calculates roundup(size, fs->fs_fsize) */ \
	(((size) + (fs)->fs_fsize - 1) & (fs)->fs_fmask)

/*
 * Determining the size of a file block in the file system.
 */
#define blksize(fs, ip, lbn) \
	(((lbn) >= NDADDR || (ip)->i_size >= ((lbn) + 1) * (fs)->fs_bsize) \
	    ? (fs)->fs_bsize \
	    : (fragroundup(fs, blkoff(fs, (ip)->i_size))))
#define dblksize(fs, dip, lbn) \
	(((lbn) >= NDADDR || (dip)->di_size >= ((lbn) + 1) * (fs)->fs_bsize) \
	    ? (fs)->fs_bsize \
	    : (fragroundup(fs, blkoff(fs, (dip)->di_size))))

/*
 * Number of disk sectors per block; assumes DEV_BSIZE byte sector size.
 */
#define	NSPB(fs)	((fs)->fs_bsize / DEV_BSIZE)
#define	NSPF(fs)	((fs)->fs_fsize / DEV_BSIZE)

/*
 * INOPB is the number of inodes in a secondary storage block.
 */
#define	INOPB(fs)	((fs)->fs_bsize / sizeof (struct dinode))
#define	INOPF(fs)	((fs)->fs_fsize / sizeof (struct dinode))

/*
 * NINDIR is the number of indirects in a file system block.
 */
#define	NINDIR(fs)	((fs)->fs_bsize / sizeof (daddr_t))

#ifdef KERNEL
struct	fs *getfs();
struct	fs *mountfs();
#endif