usr/src/sys/sys/buf.h

/*      buf.h   4.10    81/02/27        */

/*
 * The header for buffers in the buffer pool and otherwise used
 * to describe a block i/o request is given here.  The routines
 * which manipulate these things are given in bio.c.
 *
 * Each buffer in the pool is usually doubly linked into 2 lists:
 * hashed into a chain by <dev,blkno> so it can be located in the cache,
 * and (usually) on (one of several) queues.  These lists are circular and
 * doubly linked for easy removal.
 *
 * There are currently three queues for buffers:
 *      one for buffers which must be kept permanently (super blocks)
 *      one for buffers containing ``useful'' information (the cache)
 *      one for buffers containing ``non-useful'' information
 *              (and empty buffers, pushed onto the front)
 * The latter two queues contain the buffers which are available for
 * reallocation, are kept in lru order.  When not on one of these queues,
 * the buffers are ``checked out'' to drivers which use the available list
 * pointers to keep track of them in their i/o active queues.
 */

/*
 * Bufhd structures used at the head of the hashed buffer queues.
 * We only need three words for these, so this abbreviated
 * definition saves some space.
 */
struct bufhd
{
        long    b_flags;                /* see defines below */
        struct  buf *b_forw, *b_back;   /* fwd/bkwd pointer in chain */
};
struct buf
{
        long    b_flags;                /* too much goes here to describe */
        struct  buf *b_forw, *b_back;   /* hash chain (2 way street) */
        struct  buf *av_forw, *av_back; /* position on free list if not BUSY */
#define b_actf  av_forw                 /* alternate names for driver queue */
#define b_actl  av_back                 /*    head - isn't history wonderful */
        long    b_bcount;               /* transfer count */
#define b_active b_bcount               /* driver queue head: drive active */
        short   b_error;                /* returned after I/O */
        dev_t   b_dev;                  /* major+minor device name */
        union {
            caddr_t b_addr;             /* low order core address */
            int *b_words;               /* words for clearing */
            struct filsys *b_filsys;    /* superblocks */
            struct dinode *b_dino;      /* ilist */
            daddr_t *b_daddr;           /* indirect block */
        } b_un;
        daddr_t b_blkno;                /* block # on device */
        long    b_resid;                /* words not transferred after error */
#define b_errcnt b_resid                /* while i/o in progress: # retries */
#define b_pfcent b_resid                /* garbage: don't ask */
        struct  proc *b_proc;           /* proc doing physical or swap I/O */
};

#define BQUEUES         3               /* number of free buffer queues */
#define BQ_LOCKED       0               /* super-blocks &c */
#define BQ_LRU          1               /* lru, useful buffers */
#define BQ_AGE          2               /* rubbish */

#ifdef  KERNEL
extern  struct buf *buf;                /* the buffer pool itself */
extern  char *buffers;
extern  int nbuf;
extern  struct buf *swbuf;              /* swap I/O headers */
extern  int nswbuf;
extern  struct buf bfreelist[BQUEUES];  /* heads of available lists */
extern  struct buf bswlist;             /* head of free swap header list */
extern  struct buf *bclnlist;           /* head of cleaned page list */

struct  buf *alloc();
struct  buf *baddr();
struct  buf *getblk();
struct  buf *geteblk();
struct  buf *bread();
struct  buf *breada();

unsigned minphys();
#endif

/*
 * These flags are kept in b_flags.
 */
#define B_WRITE         0x00000         /* non-read pseudo-flag */
#define B_READ          0x00001         /* read when I/O occurs */
#define B_DONE          0x00002         /* transaction finished */
#define B_ERROR         0x00004         /* transaction aborted */
#define B_BUSY          0x00008         /* not on av_forw/back list */
#define B_PHYS          0x00010         /* physical IO */
#define B_XXX           0x00020         /* was B_MAP, alloc UNIBUS on pdp-11 */
#define B_WANTED        0x00040         /* issue wakeup when BUSY goes off */
#define B_AGE           0x00080         /* delayed write for correct aging */
#define B_ASYNC         0x00100         /* don't wait for I/O completion */
#define B_DELWRI        0x00200         /* write at exit of avail list */
#define B_TAPE          0x00400         /* this is a magtape (no bdwrite) */
#define B_UAREA         0x00800         /* add u-area to a swap operation */
#define B_PAGET         0x01000         /* page in/out of page table space */
#define B_DIRTY         0x02000         /* dirty page to be pushed out async */
#define B_PGIN          0x04000         /* pagein op, so swap() can count it */
#define B_CACHE         0x08000         /* did bread find us in the cache ? */
#define B_INVAL         0x10000         /* does not contain valid info  */
#define B_LOCKED        0x20000         /* locked in core (not reusable) */
#define B_HEAD          0x40000         /* a buffer header, not a buffer */