fs.h

<B>Digital的Unix操作系统VAX 4.2源码</B>

/* @(#)fs.h	4.1	(ULTRIX)	7/2/90 */

/************************************************************************
 *									*
 *			Copyright (c) 1984, 1986 by			*
 *		Digital Equipment Corporation, Maynard, MA		*
 *			All rights reserved.				*
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 *   This software is furnished under a license and may be used and	*
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 *   software  or  any  other copies thereof may not be provided or	*
 *   otherwise made available to any other person.  No title to and	*
 *   ownership of the software is hereby transferred.			*
 *									*
 *   This software is  derived  from  software  received  from  the	*
 *   University    of   California,   Berkeley,   and   from   Bell	*
 *   Laboratories.  Use, duplication, or disclosure is  subject  to	*
 *   restrictions  under  license  agreements  with  University  of	*
 *   California and with AT&T.						*
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 *   The information in this software is subject to change  without	*
 *   notice  and should not be construed as a commitment by Digital	*
 *   Equipment Corporation.						*
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 *   Digital assumes no responsibility for the use  or  reliability	*
 *   of its software on equipment which is not supplied by Digital.	*
 *									*
 ************************************************************************/

/* ------------------------------------------------------------------------
 * Modification History: /sys/h/fs.h
 *
 * 14 Jun 89 -- prs
 *	Added clean byte timeout logic.
 *
 * 28 Mar 88 -- prs
 *	Changed value of FS_CLEAN to be product release number.
 *	This value should change with each new release of ULTRIX,
 *	to guarantee file systems will be checked across releases.
 *
 * 06 Nov 84 -- jrs
 *	Add new Berkeley macro definitions
 *	Derived from 4.2BSD, labeled:
 *		fs.h 6.2	84/09/28
 *
 *	11-Sep-84 Stephen Reilly
 * 001- Added new structure for the disk partitioning scheme
 *
 *	fs.h	6.1	83/07/29
 * -----------------------------------------------------------------------
 */

/*
 * 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)

/*
 * 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.
 */
#define	NRPOS		8	/* number distinct rotational positions */

/*
 * 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	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	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 500
#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 */
};

#define PT_MAGIC	0x032957	/* Partition magic number */
#define PT_VALID	1		/* Indicates if struct is valid */
 
/*
 * Structure that is used to determine the partitioning of the disk.
 * It's location is at the end of the superblock area.
 * The reason for both the cylinder offset and block offset
 * is that some of the disk drivers (most notably the uda 
 * driver) require the block offset rather than the cyl.
 * offset.
 */
struct pt {
	long	pt_magic;	/* magic no. indicating part. info exits */
	int	pt_valid;	/* set by driver if pt is current */
	struct  pt_info {
		int	pi_nblocks;	/* no. of sectors for the partition */
		daddr_t	pi_blkoff;	/* block offset for start of part. */
	} pt_part[8];
};

/*
 * 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 */
/* these are configuration parameters */
	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 */
/* these fields can be computed from the others */
	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 */
/* these are configuration parameters */
	long	fs_maxcontig;		/* max number of contiguous blks */
	long	fs_maxbpg;		/* max number of blks per cyl group */
/* these fields can be computed from the others */
	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 */