usr/src/sys/ufs/ffs/fs.h

/* Copyright (c) 1981 Regents of the University of California */

/*      fs.h    1.9     %G%     */

/*
 * 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 and a cylinder group number cg:
 *      [BBLOCK]        Boot sector and bad block information
 *      [SBLOCK]        Super-block
 *      [CBLOCK(fs)]    Cylinder group block
 *      [IBLOCK(fs)..IBLOCK(fs)+fs.fs_ipg/INOPB(fs))
 *                      Inode blocks
 *      [IBLOCK(fs)+fs.fs_ipg/INOPB(fs)..fs.fs_fpg/fs.fs_frag)
 *                      Data blocks
 * The beginning of data blocks for cg in fs is also given by
 * the ``cgdmin(cg,fs)'' macro.
 *
 * The boot and super blocks are given in absolute disk addresses.
 */
#define BBLOCK          ((daddr_t)(0 * (MAXBSIZE / DEV_BSIZE)))
#define SBLOCK          ((daddr_t)(1 * (MAXBSIZE / DEV_BSIZE)))
/*
 * The cylinder group and inode blocks are given in file system
 * addresses, and hence must be converted to disk addresses by
 * the ``fsbtodb(fs, bno)'' macro.
 */
#define CBLOCK(fs)      ((daddr_t)(dbtofsb(fs, 2 * (MAXBSIZE / DEV_BSIZE))))
#define IBLOCK(fs)      ((daddr_t)(CBLOCK(fs) + (fs)->fs_frag))

/*
 * 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.
 *
 * 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 */

/*
 * Information per cylinder group 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 */
};

/*
 * Each file system has a number of inodes statically allocated.
 * We allocate one inode slot per NBPI data bytes, expecting this
 * to be far more than we will ever need.
 */
#define NBPI    2048

/*
 * 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 */

/*
 * Super block for a file system.
 *
 * The super block is nominally located at disk block SBLOCK.
 * Inode 0 can't be used for normal purposes,
 * 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)
 */
#define ROOTINO ((ino_t)2)      /* i number of all roots */

#define FS_MAGIC        0x110854
struct  fs
{
        long    fs_magic;               /* magic number */
        daddr_t fs_sblkno;              /* offset of super-block in filesys */
        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 */
        short   fs_minfree;             /* minimum percentage of free blocks */
        short   fs_rotdelay;            /* num of ms for optimal next block */
/* 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 */
        short   fs_ntrak;               /* tracks per cylinder */
        short   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 */
        short   fs_cpg;                 /* cylinders per group */
        short   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_ronly;               /* mounted read-only flag */
        char    fs_fsmnt[34];           /* name mounted on */
/* these fields retain the current block allocation info */
        long    fs_cgrotor;             /* last cg searched */
        struct  csum *fs_csp[NBUF];     /* list of fs_cs info buffers */
        short   fs_postbl[NRPOS];       /* head of blocks for each rotation */
        short   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))]

/*
 * Cylinder group macros to locate things in cylinder groups.
 */

/* cylinder group to disk block at very beginning */
#define cgbase(c,fs)    ((daddr_t)((fs)->fs_fpg*(c)))

/* cylinder group to spare super block address */
#define cgsblock(c,fs)  \
        (cgbase(c,fs) + dbtofsb(fs, SBLOCK))

/* convert cylinder group to index of its cg block */
#define cgtod(c,fs)     \
        (cgbase(c,fs) + CBLOCK(fs))

/* give address of first inode block in cylinder group */
#define cgimin(c,fs)    \
        (cgbase(c,fs) + IBLOCK(fs))

/* give address of first data block in cylinder group */
#define cgdmin(c,fs)    (cgimin(c,fs) + (fs)->fs_ipg / INOPF(fs))

/* turn inode number into cylinder group number */
#define itog(x,fs)      ((x)/(fs)->fs_ipg)

/* turn inode number into file system block address */
#define itod(x,fs)      ((daddr_t)(cgimin(itog(x,fs),fs)+(fs)->fs_frag*((x)%(fs)->fs_ipg/INOPB(fs))))

/* turn inode number into file system block offset */
#define itoo(x,fs)      ((x)%INOPB(fs))

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

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

/*
 * Cylinder group related limits.
 */

/*
 * 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.
 */
#define MAXIPG  2048            /* max number inodes/cyl group */

/*
 * 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)

#define CG_MAGIC        0x092752
struct  cg {
        long    cg_magic;               /* magic number */
        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 */
        short   cg_b[MAXCPG][NRPOS];    /* positions of free blocks */
        char    cg_iused[MAXIPG/NBBY];  /* used inode map */
        char    cg_free[1];             /* free block map */
/* actually longer */
};
#define cgsize(fp)      (sizeof (struct cg) + ((fp)->fs_fpg+NBBY-1)/NBBY)

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