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Annotation of 40BSD/sys/h/buf.h, revision 1.1

1.1     ! root        1: /*     buf.h   4.1     11/9/80 */
        !             2: 
        !             3: /*
        !             4:  * Each buffer in the pool is usually doubly linked into 2 lists:
        !             5:  * the device with which it is currently associated (always)
        !             6:  * and also on a list of blocks available for allocation
        !             7:  * for other use (usually).
        !             8:  * The latter list is kept in last-used order, and the two
        !             9:  * lists are doubly linked to make it easy to remove
        !            10:  * a buffer from one list when it was found by
        !            11:  * looking through the other.
        !            12:  * A buffer is on the available list, and is liable
        !            13:  * to be reassigned to another disk block, if and only
        !            14:  * if it is not marked BUSY.  When a buffer is busy, the
        !            15:  * available-list pointers can be used for other purposes.
        !            16:  * Most drivers use the forward ptr as a link in their I/O
        !            17:  * active queue.
        !            18:  * A buffer header contains all the information required
        !            19:  * to perform I/O.
        !            20:  * Most of the routines which manipulate these things
        !            21:  * are in bio.c.
        !            22:  */
        !            23: struct buf
        !            24: {
        !            25:        int     b_flags;                /* see defines below */
        !            26:        struct  buf *b_forw;            /* headed by d_tab of conf.c */
        !            27:        struct  buf *b_back;            /*  "  */
        !            28:        struct  buf *av_forw;           /* position on free list, */
        !            29:        struct  buf *av_back;           /*     if not BUSY*/
        !            30:        dev_t   b_dev;                  /* major+minor device name */
        !            31:        unsigned b_bcount;              /* transfer count */
        !            32:        union {
        !            33:            caddr_t b_addr;             /* low order core address */
        !            34:            int *b_words;               /* words for clearing */
        !            35:            struct filsys *b_filsys;    /* superblocks */
        !            36:            struct dinode *b_dino;      /* ilist */
        !            37:            daddr_t *b_daddr;           /* indirect block */
        !            38:        } b_un;
        !            39:        daddr_t b_blkno;                /* block # on device */
        !            40:        char    b_xmem;                 /* high order core address */
        !            41:        char    b_error;                /* returned after I/O */
        !            42:        short   b_hlink;                /* hash links for buffer cache */
        !            43:        unsigned int b_resid;           /* words not transferred after error */
        !            44:        struct  proc  *b_proc;          /* process doing physical or swap I/O */
        !            45: };
        !            46: 
        !            47: #ifdef KERNEL
        !            48: extern struct buf buf[];               /* The buffer pool itself */
        !            49: extern struct buf swbuf[];             /* swap I/O headers */
        !            50: extern struct buf bfreelist;           /* head of available list */
        !            51: extern struct buf bswlist;             /* head of free swap header list */
        !            52: extern struct buf *bclnlist;           /* head of cleaned page list */
        !            53: 
        !            54: struct buf *alloc();
        !            55: struct buf *baddr();
        !            56: struct buf *getblk();
        !            57: struct buf *geteblk();
        !            58: struct buf *bread();
        !            59: struct buf *breada();
        !            60: 
        !            61: unsigned minphys();
        !            62: #endif
        !            63: 
        !            64: #define        NSWBUF  48                      /* number of swap I/O headers */
        !            65: 
        !            66: /*
        !            67:  * These flags are kept in b_flags.
        !            68:  */
        !            69: #define        B_WRITE  0x0000 /* non-read pseudo-flag */
        !            70: #define        B_READ          0x0001  /* read when I/O occurs */
        !            71: #define        B_DONE          0x0002  /* transaction finished */
        !            72: #define        B_ERROR         0x0004  /* transaction aborted */
        !            73: #define        B_BUSY          0x0008  /* not on av_forw/back list */
        !            74: #define        B_PHYS          0x0010  /* physical IO */
        !            75: #define        B_MAP           0x0020  /* UNIBUS map allocated */
        !            76: #define        B_WANTED        0x0040  /* issue wakeup when BUSY goes off */
        !            77: #define        B_AGE           0x0080  /* delayed write for correct aging */
        !            78: #define        B_ASYNC         0x0100  /* don't wait for I/O completion */
        !            79: #define        B_DELWRI        0x0200  /* write at exit of avail list */
        !            80: #define        B_TAPE          0x0400  /* this is a magtape (no bdwrite) */
        !            81: #define        B_UAREA         0x0800  /* add u-area to a swap operation */
        !            82: #define        B_PAGET         0x1000  /* page in/out of page table space */
        !            83: #define        B_DIRTY         0x2000  /* dirty page to be pushed out async */
        !            84: #define        B_PGIN          0x4000  /* pagein op, so swap() can count it */
        !            85: #define        B_CACHE         0x8000  /* did bread find us in the cache ? */
        !            86: 
        !            87: /*
        !            88:  * special redeclarations for
        !            89:  * the head of the queue per
        !            90:  * device driver.
        !            91:  */
        !            92: #define        b_actf          av_forw
        !            93: #define        b_actl          av_back
        !            94: #define        b_active        b_bcount
        !            95: #define        b_errcnt        b_resid
        !            96: #define        b_pfcent        b_resid

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