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Annotation of researchv9/sys.vax/h/buf.h, revision 1.1

1.1     ! root        1: /*
        !             2:  * The header for buffers in the buffer pool and otherwise used
        !             3:  * to describe a block i/o request is given here.  The routines
        !             4:  * which manipulate these things are given in bio.c.
        !             5:  *
        !             6:  * Each buffer in the pool is usually doubly linked into 2 lists:
        !             7:  * hashed into a chain by <dev,blkno> so it can be located in the cache,
        !             8:  * and (usually) on (one of several) queues.  These lists are circular and
        !             9:  * doubly linked for easy removal.
        !            10:  *
        !            11:  * There are currently three queues for buffers:
        !            12:  *     one for buffers which must be kept permanently (super blocks)
        !            13:  *     one for buffers containing ``useful'' information (the cache)
        !            14:  *     one for buffers containing ``non-useful'' information
        !            15:  *             (and empty buffers, pushed onto the front)
        !            16:  * The latter two queues contain the buffers which are available for
        !            17:  * reallocation, are kept in lru order.  When not on one of these queues,
        !            18:  * the buffers are ``checked out'' to drivers which use the available list
        !            19:  * pointers to keep track of them in their i/o active queues.
        !            20:  */
        !            21: 
        !            22: /*
        !            23:  * Bufhd structures used at the head of the hashed buffer queues.
        !            24:  * We only need three words for these, so this abbreviated
        !            25:  * definition saves some space.
        !            26:  */
        !            27: struct bufhd
        !            28: {
        !            29:        long    b_flags;                /* see defines below */
        !            30:        struct  buf *b_forw, *b_back;   /* fwd/bkwd pointer in chain */
        !            31: };
        !            32: struct buf
        !            33: {
        !            34:        long    b_flags;                /* too much goes here to describe */
        !            35:        struct  buf *b_forw, *b_back;   /* hash chain (2 way street) */
        !            36:        struct  buf *av_forw, *av_back; /* position on free list if not BUSY */
        !            37: #define        b_actf  av_forw                 /* alternate names for driver queue */
        !            38: #define        b_actl  av_back                 /*    head - isn't history wonderful */
        !            39:        long    b_bcount;               /* transfer count */
        !            40: #define        b_active b_bcount               /* driver queue head: drive active */
        !            41:        short   b_error;                /* returned after I/O */
        !            42:        dev_t   b_dev;                  /* major+minor device name */
        !            43:        union {
        !            44:            caddr_t b_addr;             /* low order core address */
        !            45:            int *b_words;               /* words for clearing */
        !            46:            struct filsys *b_filsys;    /* superblocks */
        !            47:            struct dinode *b_dino;      /* ilist */
        !            48:            daddr_t *b_daddr;           /* indirect block */
        !            49:        } b_un;
        !            50:        daddr_t b_blkno;                /* block # on device */
        !            51:        long    b_resid;                /* words not transferred after error */
        !            52: #define        b_errcnt b_resid                /* while i/o in progress: # retries */
        !            53: #define        b_pfcent b_resid                /* garbage: don't ask */
        !            54:        struct  proc *b_proc;           /* proc doing physical or swap I/O */
        !            55: };
        !            56: 
        !            57: #define        BQUEUES         3               /* number of free buffer queues */
        !            58: #define        BQ_LOCKED       0               /* super-blocks &c */
        !            59: #define        BQ_LRU          1               /* lru, useful buffers */
        !            60: #define        BQ_AGE          2               /* rubbish */
        !            61: 
        !            62: #ifdef KERNEL
        !            63: struct buf *buf;               /* the buffer pool itself */
        !            64: char   *buffers;
        !            65: int    nbuf;
        !            66: struct buf *swbuf;             /* swap I/O headers */
        !            67: int    nswbuf;
        !            68: short  *swsize;
        !            69: int    *swpf;
        !            70: struct buf bfreelist[BQUEUES]; /* heads of available lists */
        !            71: struct buf bswlist;            /* head of free swap header list */
        !            72: struct buf *bclnlist;          /* head of cleaned page list */
        !            73: 
        !            74: struct buf *alloc();
        !            75: struct buf *baddr();
        !            76: struct buf *getblk();
        !            77: struct buf *geteblk();
        !            78: struct buf *bread();
        !            79: struct buf *breada();
        !            80: 
        !            81: unsigned minphys();
        !            82: #endif
        !            83: 
        !            84: /*
        !            85:  * These flags are kept in b_flags.
        !            86:  */
        !            87: #define        B_WRITE         0x000000        /* non-read pseudo-flag */
        !            88: #define        B_READ          0x000001        /* read when I/O occurs */
        !            89: #define        B_DONE          0x000002        /* transaction finished */
        !            90: #define        B_ERROR         0x000004        /* transaction aborted */
        !            91: #define        B_BUSY          0x000008        /* not on av_forw/back list */
        !            92: #define        B_PHYS          0x000010        /* physical IO */
        !            93: #define        B_HDR           0x000020        /* was B_MAP, now ioctl */
        !            94: #define        B_WANTED        0x000040        /* issue wakeup when BUSY goes off */
        !            95: #define        B_AGE           0x000080        /* delayed write for correct aging */
        !            96: #define        B_ASYNC         0x000100        /* don't wait for I/O completion */
        !            97: #define        B_DELWRI        0x000200        /* write at exit of avail list */
        !            98: #define        B_TAPE          0x000400        /* this is a magtape (no bdwrite) */
        !            99: #define        B_UAREA         0x000800        /* add u-area to a swap operation */
        !           100: #define        B_PAGET         0x001000        /* page in/out of page table space */
        !           101: #define        B_DIRTY         0x002000        /* dirty page to be pushed out async */
        !           102: #define        B_PGIN          0x004000        /* pagein op, so swap() can count it */
        !           103: #define        B_CACHE         0x008000        /* did bread find us in the cache ? */
        !           104: #define        B_INVAL         0x010000        /* does not contain valid info  */
        !           105: #define        B_LOCKED        0x020000        /* locked in core (not reusable) */
        !           106: #define        B_HEAD          0x040000        /* a buffer header, not a buffer */
        !           107: #define        B_SPARE1        0x080000
        !           108: #define        B_BAD           0x100000        /* bad block revectoring in progress */
        !           109: #define        B_SPARE2        0xe00000
        !           110: #define        B_PRI           0xff000000      /* i/o priority */
        !           111: 
        !           112: #define        B_PRISHIFT      24

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