Research V6 development

Work on file usr/sys/buf.h

Co-Authored-By: Dennis Ritchie <dmr@research.uucp>
Synthesized-from: v6

diff --git a/usr/sys/buf.h b/usr/sys/buf.h
new file mode 100644 (file)
index 0000000..e526205
--- /dev/null
+++ b/usr/sys/buf.h
@@ -0,0 +1,77 @@
+/*
+ * 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.
+ */
+struct buf
+{
+       int     b_flags;                /* see defines below */
+       struct  buf *b_forw;            /* headed by devtab of b_dev */
+       struct  buf *b_back;            /*  "  */
+       struct  buf *av_forw;           /* position on free list, */
+       struct  buf *av_back;           /*     if not BUSY*/
+       int     b_dev;                  /* major+minor device name */
+       int     b_wcount;               /* transfer count (usu. words) */
+       char    *b_addr;                /* low order core address */
+       char    *b_xmem;                /* high order core address */
+       char    *b_blkno;               /* block # on device */
+       char    b_error;                /* returned after I/O */
+       char    *b_resid;               /* words not transferred after error */
+} buf[NBUF];
+
+/*
+ * Each block device has a devtab, which contains private state stuff
+ * and 2 list heads: the b_forw/b_back list, which is doubly linked
+ * and has all the buffers currently associated with that major
+ * device; and the d_actf/d_actl list, which is private to the
+ * device but in fact is always used for the head and tail
+ * of the I/O queue for the device.
+ * Various routines in bio.c look at b_forw/b_back
+ * (notice they are the same as in the buf structure)
+ * but the rest is private to each device driver.
+ */
+struct devtab
+{
+       char    d_active;               /* busy flag */
+       char    d_errcnt;               /* error count (for recovery) */
+       struct  buf *b_forw;            /* first buffer for this dev */
+       struct  buf *b_back;            /* last buffer for this dev */
+       struct  buf *d_actf;            /* head of I/O queue */
+       struct  buf *d_actl;            /* tail of I/O queue */
+};
+
+/*
+ * This is the head of the queue of available
+ * buffers-- all unused except for the 2 list heads.
+ */
+struct buf bfreelist;
+
+/*
+ * These flags are kept in b_flags.
+ */
+#define        B_WRITE 0       /* non-read pseudo-flag */
+#define        B_READ  01      /* read when I/O occurs */
+#define        B_DONE  02      /* transaction finished */
+#define        B_ERROR 04      /* transaction aborted */
+#define        B_BUSY  010     /* not on av_forw/back list */
+#define        B_PHYS  020     /* Physical IO potentially using UNIBUS map */
+#define        B_MAP   040     /* This block has the UNIBUS map allocated */
+#define        B_WANTED 0100   /* issue wakeup when BUSY goes off */
+#define        B_RELOC 0200    /* no longer used */
+#define        B_ASYNC 0400    /* don't wait for I/O completion */
+#define        B_DELWRI 01000  /* don't write till block leaves available list */