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

1.1     ! root        1: /*     buf.h   6.1     83/07/29        */
        !             2: 
        !             3: /*
        !             4:  * The header for buffers in the buffer pool and otherwise used
        !             5:  * to describe a block i/o request is given here.  The routines
        !             6:  * which manipulate these things are given in bio.c.
        !             7:  *
        !             8:  * Each buffer in the pool is usually doubly linked into 2 lists:
        !             9:  * hashed into a chain by <dev,blkno> so it can be located in the cache,
        !            10:  * and (usually) on (one of several) queues.  These lists are circular and
        !            11:  * doubly linked for easy removal.
        !            12:  *
        !            13:  * There are currently three queues for buffers:
        !            14:  *     one for buffers which must be kept permanently (super blocks)
        !            15:  *     one for buffers containing ``useful'' information (the cache)
        !            16:  *     one for buffers containing ``non-useful'' information
        !            17:  *             (and empty buffers, pushed onto the front)
        !            18:  * The latter two queues contain the buffers which are available for
        !            19:  * reallocation, are kept in lru order.  When not on one of these queues,
        !            20:  * the buffers are ``checked out'' to drivers which use the available list
        !            21:  * pointers to keep track of them in their i/o active queues.
        !            22:  */
        !            23: 
        !            24: /*
        !            25:  * Bufhd structures used at the head of the hashed buffer queues.
        !            26:  * We only need three words for these, so this abbreviated
        !            27:  * definition saves some space.
        !            28:  */
        !            29: struct bufhd
        !            30: {
        !            31:        long    b_flags;                /* see defines below */
        !            32:        struct  buf *b_forw, *b_back;   /* fwd/bkwd pointer in chain */
        !            33: };
        !            34: struct buf
        !            35: {
        !            36:        long    b_flags;                /* too much goes here to describe */
        !            37:        struct  buf *b_forw, *b_back;   /* hash chain (2 way street) */
        !            38:        struct  buf *av_forw, *av_back; /* position on free list if not BUSY */
        !            39: #define        b_actf  av_forw                 /* alternate names for driver queue */
        !            40: #define        b_actl  av_back                 /*    head - isn't history wonderful */
        !            41:        long    b_bcount;               /* transfer count */
        !            42:        long    b_bufsize;              /* size of allocated buffer */
        !            43: #define        b_active b_bcount               /* driver queue head: drive active */
        !            44:        short   b_error;                /* returned after I/O */
        !            45:        dev_t   b_dev;                  /* major+minor device name */
        !            46:        union {
        !            47:            caddr_t b_addr;             /* low order core address */
        !            48:            int *b_words;               /* words for clearing */
        !            49:            struct fs *b_fs;            /* superblocks */
        !            50:            struct csum *b_cs;          /* superblock summary information */
        !            51:            struct cg *b_cg;            /* cylinder group block */
        !            52:            struct dinode *b_dino;      /* ilist */
        !            53:            daddr_t *b_daddr;           /* indirect block */
        !            54:        } b_un;
        !            55:        daddr_t b_blkno;                /* block # on device */
        !            56:        long    b_resid;                /* words not transferred after error */
        !            57: #define        b_errcnt b_resid                /* while i/o in progress: # retries */
        !            58:        struct  proc *b_proc;           /* proc doing physical or swap I/O */
        !            59:        int     (*b_iodone)();          /* function called by iodone */
        !            60:        int     b_pfcent;               /* center page when swapping cluster */
        !            61: };
        !            62: 
        !            63: #define        BQUEUES         4               /* number of free buffer queues */
        !            64: 
        !            65: #define        BQ_LOCKED       0               /* super-blocks &c */
        !            66: #define        BQ_LRU          1               /* lru, useful buffers */
        !            67: #define        BQ_AGE          2               /* rubbish */
        !            68: #define        BQ_EMPTY        3               /* buffer headers with no memory */
        !            69: 
        !            70: #ifdef KERNEL
        !            71: #define        BUFHSZ  63
        !            72: #define RND    (MAXBSIZE/DEV_BSIZE)
        !            73: #define        BUFHASH(dev, dblkno)    \
        !            74:        ((struct buf *)&bufhash[((int)(dev)+(((int)(dblkno))/RND)) % BUFHSZ])
        !            75: 
        !            76: struct buf *buf;               /* the buffer pool itself */
        !            77: char   *buffers;
        !            78: int    nbuf;                   /* number of buffer headers */
        !            79: int    bufpages;               /* number of memory pages in the buffer pool */
        !            80: struct buf *swbuf;             /* swap I/O headers */
        !            81: int    nswbuf;
        !            82: struct bufhd bufhash[BUFHSZ];  /* heads of hash lists */
        !            83: struct buf bfreelist[BQUEUES]; /* heads of available lists */
        !            84: struct buf bswlist;            /* head of free swap header list */
        !            85: struct buf *bclnlist;          /* head of cleaned page list */
        !            86: 
        !            87: struct buf *alloc();
        !            88: struct buf *realloccg();
        !            89: struct buf *baddr();
        !            90: struct buf *getblk();
        !            91: struct buf *geteblk();
        !            92: struct buf *getnewbuf();
        !            93: struct buf *bread();
        !            94: struct buf *breada();
        !            95: 
        !            96: unsigned minphys();
        !            97: #endif
        !            98: 
        !            99: /*
        !           100:  * These flags are kept in b_flags.
        !           101:  */
        !           102: #define        B_WRITE         0x000000        /* non-read pseudo-flag */
        !           103: #define        B_READ          0x000001        /* read when I/O occurs */
        !           104: #define        B_DONE          0x000002        /* transaction finished */
        !           105: #define        B_ERROR         0x000004        /* transaction aborted */
        !           106: #define        B_BUSY          0x000008        /* not on av_forw/back list */
        !           107: #define        B_PHYS          0x000010        /* physical IO */
        !           108: #define        B_XXX           0x000020        /* was B_MAP, alloc UNIBUS on pdp-11 */
        !           109: #define        B_WANTED        0x000040        /* issue wakeup when BUSY goes off */
        !           110: #define        B_AGE           0x000080        /* delayed write for correct aging */
        !           111: #define        B_ASYNC         0x000100        /* don't wait for I/O completion */
        !           112: #define        B_DELWRI        0x000200        /* write at exit of avail list */
        !           113: #define        B_TAPE          0x000400        /* this is a magtape (no bdwrite) */
        !           114: #define        B_UAREA         0x000800        /* add u-area to a swap operation */
        !           115: #define        B_PAGET         0x001000        /* page in/out of page table space */
        !           116: #define        B_DIRTY         0x002000        /* dirty page to be pushed out async */
        !           117: #define        B_PGIN          0x004000        /* pagein op, so swap() can count it */
        !           118: #define        B_CACHE         0x008000        /* did bread find us in the cache ? */
        !           119: #define        B_INVAL         0x010000        /* does not contain valid info  */
        !           120: #define        B_LOCKED        0x020000        /* locked in core (not reusable) */
        !           121: #define        B_HEAD          0x040000        /* a buffer header, not a buffer */
        !           122: #define        B_BAD           0x100000        /* bad block revectoring in progress */
        !           123: #define        B_CALL          0x200000        /* call b_iodone from iodone */
        !           124: 
        !           125: /*
        !           126:  * Insq/Remq for the buffer hash lists.
        !           127:  */
        !           128: #define        bremhash(bp) { \
        !           129:        (bp)->b_back->b_forw = (bp)->b_forw; \
        !           130:        (bp)->b_forw->b_back = (bp)->b_back; \
        !           131: }
        !           132: #define        binshash(bp, dp) { \
        !           133:        (bp)->b_forw = (dp)->b_forw; \
        !           134:        (bp)->b_back = (dp); \
        !           135:        (dp)->b_forw->b_back = (bp); \
        !           136:        (dp)->b_forw = (bp); \
        !           137: }
        !           138: 
        !           139: /*
        !           140:  * Insq/Remq for the buffer free lists.
        !           141:  */
        !           142: #define        bremfree(bp) { \
        !           143:        (bp)->av_back->av_forw = (bp)->av_forw; \
        !           144:        (bp)->av_forw->av_back = (bp)->av_back; \
        !           145: }
        !           146: #define        binsheadfree(bp, dp) { \
        !           147:        (dp)->av_forw->av_back = (bp); \
        !           148:        (bp)->av_forw = (dp)->av_forw; \
        !           149:        (dp)->av_forw = (bp); \
        !           150:        (bp)->av_back = (dp); \
        !           151: }
        !           152: #define        binstailfree(bp, dp) { \
        !           153:        (dp)->av_back->av_forw = (bp); \
        !           154:        (bp)->av_back = (dp)->av_back; \
        !           155:        (dp)->av_back = (bp); \
        !           156:        (bp)->av_forw = (dp); \
        !           157: }
        !           158: 
        !           159: /*
        !           160:  * Take a buffer off the free list it's on and
        !           161:  * mark it as being use (B_BUSY) by a device.
        !           162:  */
        !           163: #define        notavail(bp) { \
        !           164:        int x = spl6(); \
        !           165:        bremfree(bp); \
        !           166:        (bp)->b_flags |= B_BUSY; \
        !           167:        splx(x); \
        !           168: }
        !           169: 
        !           170: #define        iodone  biodone
        !           171: #define        iowait  biowait
        !           172: 
        !           173: /*
        !           174:  * Zero out a buffer's data portion.
        !           175:  */
        !           176: #define        clrbuf(bp) { \
        !           177:        blkclr(bp->b_un.b_addr, bp->b_bcount); \
        !           178:        bp->b_resid = 0; \
        !           179: }

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