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Annotation of 42BSD/sys/h/fs.h, revision 1.1

1.1     ! root        1: /*     fs.h    6.1     83/07/29        */
        !             2: 
        !             3: /*
        !             4:  * Each disk drive contains some number of file systems.
        !             5:  * A file system consists of a number of cylinder groups.
        !             6:  * Each cylinder group has inodes and data.
        !             7:  *
        !             8:  * A file system is described by its super-block, which in turn
        !             9:  * describes the cylinder groups.  The super-block is critical
        !            10:  * data and is replicated in each cylinder group to protect against
        !            11:  * catastrophic loss.  This is done at mkfs time and the critical
        !            12:  * super-block data does not change, so the copies need not be
        !            13:  * referenced further unless disaster strikes.
        !            14:  *
        !            15:  * For file system fs, the offsets of the various blocks of interest
        !            16:  * are given in the super block as:
        !            17:  *     [fs->fs_sblkno]         Super-block
        !            18:  *     [fs->fs_cblkno]         Cylinder group block
        !            19:  *     [fs->fs_iblkno]         Inode blocks
        !            20:  *     [fs->fs_dblkno]         Data blocks
        !            21:  * The beginning of cylinder group cg in fs, is given by
        !            22:  * the ``cgbase(fs, cg)'' macro.
        !            23:  *
        !            24:  * The first boot and super blocks are given in absolute disk addresses.
        !            25:  */
        !            26: #define BBSIZE         8192
        !            27: #define SBSIZE         8192
        !            28: #define        BBLOCK          ((daddr_t)(0))
        !            29: #define        SBLOCK          ((daddr_t)(BBLOCK + BBSIZE / DEV_BSIZE))
        !            30: 
        !            31: /*
        !            32:  * Addresses stored in inodes are capable of addressing fragments
        !            33:  * of `blocks'. File system blocks of at most size MAXBSIZE can 
        !            34:  * be optionally broken into 2, 4, or 8 pieces, each of which is
        !            35:  * addressible; these pieces may be DEV_BSIZE, or some multiple of
        !            36:  * a DEV_BSIZE unit.
        !            37:  *
        !            38:  * Large files consist of exclusively large data blocks.  To avoid
        !            39:  * undue wasted disk space, the last data block of a small file may be
        !            40:  * allocated as only as many fragments of a large block as are
        !            41:  * necessary.  The file system format retains only a single pointer
        !            42:  * to such a fragment, which is a piece of a single large block that
        !            43:  * has been divided.  The size of such a fragment is determinable from
        !            44:  * information in the inode, using the ``blksize(fs, ip, lbn)'' macro.
        !            45:  *
        !            46:  * The file system records space availability at the fragment level;
        !            47:  * to determine block availability, aligned fragments are examined.
        !            48:  *
        !            49:  * The root inode is the root of the file system.
        !            50:  * Inode 0 can't be used for normal purposes and
        !            51:  * historically bad blocks were linked to inode 1,
        !            52:  * thus the root inode is 2. (inode 1 is no longer used for
        !            53:  * this purpose, however numerous dump tapes make this
        !            54:  * assumption, so we are stuck with it)
        !            55:  * The lost+found directory is given the next available
        !            56:  * inode when it is created by ``mkfs''.
        !            57:  */
        !            58: #define        ROOTINO         ((ino_t)2)      /* i number of all roots */
        !            59: #define LOSTFOUNDINO   (ROOTINO + 1)
        !            60: 
        !            61: /*
        !            62:  * Cylinder group related limits.
        !            63:  *
        !            64:  * For each cylinder we keep track of the availability of blocks at different
        !            65:  * rotational positions, so that we can lay out the data to be picked
        !            66:  * up with minimum rotational latency.  NRPOS is the number of rotational
        !            67:  * positions which we distinguish.  With NRPOS 8 the resolution of our
        !            68:  * summary information is 2ms for a typical 3600 rpm drive.
        !            69:  */
        !            70: #define        NRPOS           8       /* number distinct rotational positions */
        !            71: 
        !            72: /*
        !            73:  * MAXIPG bounds the number of inodes per cylinder group, and
        !            74:  * is needed only to keep the structure simpler by having the
        !            75:  * only a single variable size element (the free bit map).
        !            76:  *
        !            77:  * N.B.: MAXIPG must be a multiple of INOPB(fs).
        !            78:  */
        !            79: #define        MAXIPG          2048    /* max number inodes/cyl group */
        !            80: 
        !            81: /*
        !            82:  * MINBSIZE is the smallest allowable block size.
        !            83:  * In order to insure that it is possible to create files of size
        !            84:  * 2^32 with only two levels of indirection, MINBSIZE is set to 4096.
        !            85:  * MINBSIZE must be big enough to hold a cylinder group block,
        !            86:  * thus changes to (struct cg) must keep its size within MINBSIZE.
        !            87:  * MAXCPG is limited only to dimension an array in (struct cg);
        !            88:  * it can be made larger as long as that structures size remains
        !            89:  * within the bounds dictated by MINBSIZE.
        !            90:  * Note that super blocks are always of size MAXBSIZE,
        !            91:  * and that MAXBSIZE must be >= MINBSIZE.
        !            92:  */
        !            93: #define MINBSIZE       4096
        !            94: #define        MAXCPG          32      /* maximum fs_cpg */
        !            95: 
        !            96: /*
        !            97:  * The path name on which the file system is mounted is maintained
        !            98:  * in fs_fsmnt. MAXMNTLEN defines the amount of space allocated in 
        !            99:  * the super block for this name.
        !           100:  * The limit on the amount of summary information per file system
        !           101:  * is defined by MAXCSBUFS. It is currently parameterized for a
        !           102:  * maximum of two million cylinders.
        !           103:  */
        !           104: #define MAXMNTLEN 512
        !           105: #define MAXCSBUFS 32
        !           106: 
        !           107: /*
        !           108:  * Per cylinder group information; summarized in blocks allocated
        !           109:  * from first cylinder group data blocks.  These blocks have to be
        !           110:  * read in from fs_csaddr (size fs_cssize) in addition to the
        !           111:  * super block.
        !           112:  *
        !           113:  * N.B. sizeof(struct csum) must be a power of two in order for
        !           114:  * the ``fs_cs'' macro to work (see below).
        !           115:  */
        !           116: struct csum {
        !           117:        long    cs_ndir;        /* number of directories */
        !           118:        long    cs_nbfree;      /* number of free blocks */
        !           119:        long    cs_nifree;      /* number of free inodes */
        !           120:        long    cs_nffree;      /* number of free frags */
        !           121: };
        !           122: 
        !           123: /*
        !           124:  * Super block for a file system.
        !           125:  */
        !           126: #define        FS_MAGIC        0x011954
        !           127: struct fs
        !           128: {
        !           129:        struct  fs *fs_link;            /* linked list of file systems */
        !           130:        struct  fs *fs_rlink;           /*     used for incore super blocks */
        !           131:        daddr_t fs_sblkno;              /* addr of super-block in filesys */
        !           132:        daddr_t fs_cblkno;              /* offset of cyl-block in filesys */
        !           133:        daddr_t fs_iblkno;              /* offset of inode-blocks in filesys */
        !           134:        daddr_t fs_dblkno;              /* offset of first data after cg */
        !           135:        long    fs_cgoffset;            /* cylinder group offset in cylinder */
        !           136:        long    fs_cgmask;              /* used to calc mod fs_ntrak */
        !           137:        time_t  fs_time;                /* last time written */
        !           138:        long    fs_size;                /* number of blocks in fs */
        !           139:        long    fs_dsize;               /* number of data blocks in fs */
        !           140:        long    fs_ncg;                 /* number of cylinder groups */
        !           141:        long    fs_bsize;               /* size of basic blocks in fs */
        !           142:        long    fs_fsize;               /* size of frag blocks in fs */
        !           143:        long    fs_frag;                /* number of frags in a block in fs */
        !           144: /* these are configuration parameters */
        !           145:        long    fs_minfree;             /* minimum percentage of free blocks */
        !           146:        long    fs_rotdelay;            /* num of ms for optimal next block */
        !           147:        long    fs_rps;                 /* disk revolutions per second */
        !           148: /* these fields can be computed from the others */
        !           149:        long    fs_bmask;               /* ``blkoff'' calc of blk offsets */
        !           150:        long    fs_fmask;               /* ``fragoff'' calc of frag offsets */
        !           151:        long    fs_bshift;              /* ``lblkno'' calc of logical blkno */
        !           152:        long    fs_fshift;              /* ``numfrags'' calc number of frags */
        !           153: /* these are configuration parameters */
        !           154:        long    fs_maxcontig;           /* max number of contiguous blks */
        !           155:        long    fs_maxbpg;              /* max number of blks per cyl group */
        !           156: /* these fields can be computed from the others */
        !           157:        long    fs_fragshift;           /* block to frag shift */
        !           158:        long    fs_fsbtodb;             /* fsbtodb and dbtofsb shift constant */
        !           159:        long    fs_sbsize;              /* actual size of super block */
        !           160:        long    fs_csmask;              /* csum block offset */
        !           161:        long    fs_csshift;             /* csum block number */
        !           162:        long    fs_nindir;              /* value of NINDIR */
        !           163:        long    fs_inopb;               /* value of INOPB */
        !           164:        long    fs_nspf;                /* value of NSPF */
        !           165:        long    fs_sparecon[6];         /* reserved for future constants */
        !           166: /* sizes determined by number of cylinder groups and their sizes */
        !           167:        daddr_t fs_csaddr;              /* blk addr of cyl grp summary area */
        !           168:        long    fs_cssize;              /* size of cyl grp summary area */
        !           169:        long    fs_cgsize;              /* cylinder group size */
        !           170: /* these fields should be derived from the hardware */
        !           171:        long    fs_ntrak;               /* tracks per cylinder */
        !           172:        long    fs_nsect;               /* sectors per track */
        !           173:        long    fs_spc;                 /* sectors per cylinder */
        !           174: /* this comes from the disk driver partitioning */
        !           175:        long    fs_ncyl;                /* cylinders in file system */
        !           176: /* these fields can be computed from the others */
        !           177:        long    fs_cpg;                 /* cylinders per group */
        !           178:        long    fs_ipg;                 /* inodes per group */
        !           179:        long    fs_fpg;                 /* blocks per group * fs_frag */
        !           180: /* this data must be re-computed after crashes */
        !           181:        struct  csum fs_cstotal;        /* cylinder summary information */
        !           182: /* these fields are cleared at mount time */
        !           183:        char    fs_fmod;                /* super block modified flag */
        !           184:        char    fs_clean;               /* file system is clean flag */
        !           185:        char    fs_ronly;               /* mounted read-only flag */
        !           186:        char    fs_flags;               /* currently unused flag */
        !           187:        char    fs_fsmnt[MAXMNTLEN];    /* name mounted on */
        !           188: /* these fields retain the current block allocation info */
        !           189:        long    fs_cgrotor;             /* last cg searched */
        !           190:        struct  csum *fs_csp[MAXCSBUFS];/* list of fs_cs info buffers */
        !           191:        long    fs_cpc;                 /* cyl per cycle in postbl */
        !           192:        short   fs_postbl[MAXCPG][NRPOS];/* head of blocks for each rotation */
        !           193:        long    fs_magic;               /* magic number */
        !           194:        u_char  fs_rotbl[1];            /* list of blocks for each rotation */
        !           195: /* actually longer */
        !           196: };
        !           197: 
        !           198: /*
        !           199:  * Convert cylinder group to base address of its global summary info.
        !           200:  *
        !           201:  * N.B. This macro assumes that sizeof(struct csum) is a power of two.
        !           202:  */
        !           203: #define fs_cs(fs, indx) \
        !           204:        fs_csp[(indx) >> (fs)->fs_csshift][(indx) & ~(fs)->fs_csmask]
        !           205: 
        !           206: /*
        !           207:  * MAXBPC bounds the size of the rotational layout tables and
        !           208:  * is limited by the fact that the super block is of size SBSIZE.
        !           209:  * The size of these tables is INVERSELY proportional to the block
        !           210:  * size of the file system. It is aggravated by sector sizes that
        !           211:  * are not powers of two, as this increases the number of cylinders
        !           212:  * included before the rotational pattern repeats (fs_cpc).
        !           213:  * Its size is derived from the number of bytes remaining in (struct fs)
        !           214:  */
        !           215: #define        MAXBPC  (SBSIZE - sizeof (struct fs))
        !           216: 
        !           217: /*
        !           218:  * Cylinder group block for a file system.
        !           219:  */
        !           220: #define        CG_MAGIC        0x090255
        !           221: struct cg {
        !           222:        struct  cg *cg_link;            /* linked list of cyl groups */
        !           223:        struct  cg *cg_rlink;           /*     used for incore cyl groups */
        !           224:        time_t  cg_time;                /* time last written */
        !           225:        long    cg_cgx;                 /* we are the cgx'th cylinder group */
        !           226:        short   cg_ncyl;                /* number of cyl's this cg */
        !           227:        short   cg_niblk;               /* number of inode blocks this cg */
        !           228:        long    cg_ndblk;               /* number of data blocks this cg */
        !           229:        struct  csum cg_cs;             /* cylinder summary information */
        !           230:        long    cg_rotor;               /* position of last used block */
        !           231:        long    cg_frotor;              /* position of last used frag */
        !           232:        long    cg_irotor;              /* position of last used inode */
        !           233:        long    cg_frsum[MAXFRAG];      /* counts of available frags */
        !           234:        long    cg_btot[MAXCPG];        /* block totals per cylinder */
        !           235:        short   cg_b[MAXCPG][NRPOS];    /* positions of free blocks */
        !           236:        char    cg_iused[MAXIPG/NBBY];  /* used inode map */
        !           237:        long    cg_magic;               /* magic number */
        !           238:        u_char  cg_free[1];             /* free block map */
        !           239: /* actually longer */
        !           240: };
        !           241: 
        !           242: /*
        !           243:  * MAXBPG bounds the number of blocks of data per cylinder group,
        !           244:  * and is limited by the fact that cylinder groups are at most one block.
        !           245:  * Its size is derived from the size of blocks and the (struct cg) size,
        !           246:  * by the number of remaining bits.
        !           247:  */
        !           248: #define        MAXBPG(fs) \
        !           249:        (fragstoblks((fs), (NBBY * ((fs)->fs_bsize - (sizeof (struct cg))))))
        !           250: 
        !           251: /*
        !           252:  * Turn file system block numbers into disk block addresses.
        !           253:  * This maps file system blocks to device size blocks.
        !           254:  */
        !           255: #define fsbtodb(fs, b) ((b) << (fs)->fs_fsbtodb)
        !           256: #define        dbtofsb(fs, b)  ((b) >> (fs)->fs_fsbtodb)
        !           257: 
        !           258: /*
        !           259:  * Cylinder group macros to locate things in cylinder groups.
        !           260:  * They calc file system addresses of cylinder group data structures.
        !           261:  */
        !           262: #define        cgbase(fs, c)   ((daddr_t)((fs)->fs_fpg * (c)))
        !           263: #define cgstart(fs, c) \
        !           264:        (cgbase(fs, c) + (fs)->fs_cgoffset * ((c) & ~((fs)->fs_cgmask)))
        !           265: #define        cgsblock(fs, c) (cgstart(fs, c) + (fs)->fs_sblkno)      /* super blk */
        !           266: #define        cgtod(fs, c)    (cgstart(fs, c) + (fs)->fs_cblkno)      /* cg block */
        !           267: #define        cgimin(fs, c)   (cgstart(fs, c) + (fs)->fs_iblkno)      /* inode blk */
        !           268: #define        cgdmin(fs, c)   (cgstart(fs, c) + (fs)->fs_dblkno)      /* 1st data */
        !           269: 
        !           270: /*
        !           271:  * Macros for handling inode numbers:
        !           272:  *     inode number to file system block offset.
        !           273:  *     inode number to cylinder group number.
        !           274:  *     inode number to file system block address.
        !           275:  */
        !           276: #define        itoo(fs, x)     ((x) % INOPB(fs))
        !           277: #define        itog(fs, x)     ((x) / (fs)->fs_ipg)
        !           278: #define        itod(fs, x) \
        !           279:        ((daddr_t)(cgimin(fs, itog(fs, x)) + \
        !           280:        (blkstofrags((fs), (((x) % (fs)->fs_ipg) / INOPB(fs))))))
        !           281: 
        !           282: /*
        !           283:  * Give cylinder group number for a file system block.
        !           284:  * Give cylinder group block number for a file system block.
        !           285:  */
        !           286: #define        dtog(fs, d)     ((d) / (fs)->fs_fpg)
        !           287: #define        dtogd(fs, d)    ((d) % (fs)->fs_fpg)
        !           288: 
        !           289: /*
        !           290:  * Extract the bits for a block from a map.
        !           291:  * Compute the cylinder and rotational position of a cyl block addr.
        !           292:  */
        !           293: #define blkmap(fs, map, loc) \
        !           294:     (((map)[loc / NBBY] >> (loc % NBBY)) & (0xff >> (NBBY - (fs)->fs_frag)))
        !           295: #define cbtocylno(fs, bno) \
        !           296:        ((bno) * NSPF(fs) / (fs)->fs_spc)
        !           297: #define cbtorpos(fs, bno) \
        !           298:        ((bno) * NSPF(fs) % (fs)->fs_nsect * NRPOS / (fs)->fs_nsect)
        !           299: 
        !           300: /*
        !           301:  * The following macros optimize certain frequently calculated
        !           302:  * quantities by using shifts and masks in place of divisions
        !           303:  * modulos and multiplications.
        !           304:  */
        !           305: #define blkoff(fs, loc)                /* calculates (loc % fs->fs_bsize) */ \
        !           306:        ((loc) & ~(fs)->fs_bmask)
        !           307: #define fragoff(fs, loc)       /* calculates (loc % fs->fs_fsize) */ \
        !           308:        ((loc) & ~(fs)->fs_fmask)
        !           309: #define lblkno(fs, loc)                /* calculates (loc / fs->fs_bsize) */ \
        !           310:        ((loc) >> (fs)->fs_bshift)
        !           311: #define numfrags(fs, loc)      /* calculates (loc / fs->fs_fsize) */ \
        !           312:        ((loc) >> (fs)->fs_fshift)
        !           313: #define blkroundup(fs, size)   /* calculates roundup(size, fs->fs_bsize) */ \
        !           314:        (((size) + (fs)->fs_bsize - 1) & (fs)->fs_bmask)
        !           315: #define fragroundup(fs, size)  /* calculates roundup(size, fs->fs_fsize) */ \
        !           316:        (((size) + (fs)->fs_fsize - 1) & (fs)->fs_fmask)
        !           317: #define fragstoblks(fs, frags) /* calculates (frags / fs->fs_frag) */ \
        !           318:        ((frags) >> (fs)->fs_fragshift)
        !           319: #define blkstofrags(fs, blks)  /* calculates (blks * fs->fs_frag) */ \
        !           320:        ((blks) << (fs)->fs_fragshift)
        !           321: 
        !           322: /*
        !           323:  * Determine the number of available frags given a
        !           324:  * percentage to hold in reserve
        !           325:  */
        !           326: #define freespace(fs, percentreserved) \
        !           327:        (blkstofrags((fs), (fs)->fs_cstotal.cs_nbfree) + \
        !           328:        (fs)->fs_cstotal.cs_nffree - ((fs)->fs_dsize * (percentreserved) / 100))
        !           329: 
        !           330: /*
        !           331:  * Determining the size of a file block in the file system.
        !           332:  */
        !           333: #define blksize(fs, ip, lbn) \
        !           334:        (((lbn) >= NDADDR || (ip)->i_size >= ((lbn) + 1) << (fs)->fs_bshift) \
        !           335:            ? (fs)->fs_bsize \
        !           336:            : (fragroundup(fs, blkoff(fs, (ip)->i_size))))
        !           337: #define dblksize(fs, dip, lbn) \
        !           338:        (((lbn) >= NDADDR || (dip)->di_size >= ((lbn) + 1) << (fs)->fs_bshift) \
        !           339:            ? (fs)->fs_bsize \
        !           340:            : (fragroundup(fs, blkoff(fs, (dip)->di_size))))
        !           341: 
        !           342: /*
        !           343:  * Number of disk sectors per block; assumes DEV_BSIZE byte sector size.
        !           344:  */
        !           345: #define        NSPB(fs)        ((fs)->fs_nspf << (fs)->fs_fragshift)
        !           346: #define        NSPF(fs)        ((fs)->fs_nspf)
        !           347: 
        !           348: /*
        !           349:  * INOPB is the number of inodes in a secondary storage block.
        !           350:  */
        !           351: #define        INOPB(fs)       ((fs)->fs_inopb)
        !           352: #define        INOPF(fs)       ((fs)->fs_inopb >> (fs)->fs_fragshift)
        !           353: 
        !           354: /*
        !           355:  * NINDIR is the number of indirects in a file system block.
        !           356:  */
        !           357: #define        NINDIR(fs)      ((fs)->fs_nindir)
        !           358: 
        !           359: #ifdef KERNEL
        !           360: struct fs *getfs();
        !           361: struct fs *mountfs();
        !           362: #endif

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