reformatting; bufhd, queues to 3 ...

SCCS-vsn: sys/sys/buf.h 4.7

diff --git a/usr/src/sys/sys/buf.h b/usr/src/sys/sys/buf.h
index be8d040..0fd1261 100644 (file)
--- a/usr/src/sys/sys/buf.h
+++ b/usr/src/sys/sys/buf.h
@@ -1,40 +1,47 @@
-/*     buf.h   4.6     %G%     */
+/*     buf.h   4.7     %G%     */

 
 /*
 
 /*

+ * 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:
  * Each buffer in the pool is usually doubly linked into 2 lists:

- * the device with which it is currently associated (always)
- * and also on a list of blocks available for allocation
- * for other use (usually).
- * The latter list is kept in last-used order, and the two
- * lists are doubly linked to make it easy to remove
- * a buffer from one list when it was found by
- * looking through the other.
- * A buffer is on the available list, and is liable
- * to be reassigned to another disk block, if and only
- * if it is not marked BUSY.  When a buffer is busy, the
- * available-list pointers can be used for other purposes.
- * Most drivers use the forward ptr as a link in their I/O
- * active queue.
- * A buffer header contains all the information required
- * to perform I/O.
- * Most of the routines which manipulate these things
- * are in bio.c.
+ * 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 bufhd
 {
        long    b_flags;                /* see defines below */

-       struct  buf *b_forw;            /* headed by d_tab of conf.c */
-       struct  buf *b_back;            /*  "  */
+       struct  buf *b_forw, *b_back;   /* fwd/bkwd pointer in chain */

 };
 struct buf
 {
 };
 struct buf
 {

-       long    b_flags;                /* see defines below */
-       struct  buf *b_forw;            /* headed by d_tab of conf.c */
-       struct  buf *b_back;            /*  "  */
-       struct  buf *av_forw;           /* position on free list, */
-       struct  buf *av_back;           /*     if not BUSY*/
+       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 */
        dev_t   b_dev;                  /* major+minor device name */

-       unsigned b_bcount;              /* transfer count */

        union {
            caddr_t b_addr;             /* low order core address */
            int *b_words;               /* words for clearing */
        union {
            caddr_t b_addr;             /* low order core address */
            int *b_words;               /* words for clearing */


@@ -43,11 +50,10 @@ struct buf
            daddr_t *b_daddr;           /* indirect block */
        } b_un;
        daddr_t b_blkno;                /* block # on device */
            daddr_t *b_daddr;           /* indirect block */
        } b_un;
        daddr_t b_blkno;                /* block # on device */

-       char    b_xmem;                 /* high order core address */
-       char    b_error;                /* returned after I/O */
-       short   b_hlink;                /* hash links for buffer cache */
-       unsigned int b_resid;           /* words not transferred after error */
-       struct  proc  *b_proc;          /* process doing physical or swap I/O */
+       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        BQUEUES         3               /* number of free buffer queues */


@@ -56,7 +62,7 @@ struct buf
 #define        BQ_AGE          2               /* rubbish */
 
 #ifdef KERNEL
 #define        BQ_AGE          2               /* rubbish */
 
 #ifdef KERNEL

-extern struct buf buf[];               /* The buffer pool itself */
+extern struct buf buf[];               /* the buffer pool itself */

 extern struct buf swbuf[];             /* swap I/O headers */
 extern struct buf bfreelist[BQUEUES];  /* heads of available lists */
 extern struct buf bswlist;             /* head of free swap header list */
 extern struct buf swbuf[];             /* swap I/O headers */
 extern struct buf bfreelist[BQUEUES];  /* heads of available lists */
 extern struct buf bswlist;             /* head of free swap header list */


@@ -77,34 +83,23 @@ unsigned minphys();
 /*
  * These flags are kept in b_flags.
  */
 /*
  * 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_MAP           0x00020 /* UNIBUS map allocated */
-#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 (if not BUSY) */
-#define        B_LOCKED        0x20000 /* this buffer locked in core (not reusable) */
-#define        B_HEAD          0x40000 /* this is a buffer header, not a buffer */
-
-/*
- * special redeclarations for
- * the head of the queue per
- * device driver.
- */
-#define        b_actf          av_forw
-#define        b_actl          av_back
-#define        b_active        b_bcount
-#define        b_errcnt        b_resid
-#define        b_pfcent        b_resid
+#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 */