Change how mirror writes are handled, according to the discussion on the

mailing list.

When initiating a write, ccdbuffer() returns two "struct ccdbuf *"s
linked together by the cb_mirror field.  "cb_pflags &
CCDPF_MIRROR_DONE" is set to 0 on both of them.

When a component returns to ccdiodone(), it checks if "cb_pflags &
CCDPF_MIRROR_DONE" is set or not.  If not, it sets the partner's
flag and returns.  If it is, it means its partner has already
returned, so it will go to the regular cleanup (which is in the
fallthrough code).

There should be no performance or functionality changes unless the
higher-level scsi driver does something with the resid value.  The change
is purely aesthetical and prepares us for the parity implementation.

1 files changed, 39 insertions, 9 deletions

diff --git a/sys/dev/ccd/ccd.c b/sys/dev/ccd/ccd.c
index dab208c..1601e89 100644
--- a/sys/dev/ccd/ccd.c
+++ b/sys/dev/ccd/ccd.c
@@ -1,4 +1,4 @@
-/* $Id: ccd.c,v 1.7 1996/01/31 11:25:46 asami Exp $ */
+/* $Id: ccd.c,v 1.8 1996/03/21 04:13:25 asami Exp $ */
 
 /*	$NetBSD: ccd.c,v 1.22 1995/12/08 19:13:26 thorpej Exp $	*/
 
@@ -136,13 +136,32 @@ int ccddebug = CCDB_FOLLOW | CCDB_INIT | CCDB_IO | CCDB_LABEL | CCDB_VNODE;
 #define	ccdunit(x)	dkunit(x)
 #define ccdpart(x)	dkpart(x)
 
+/*
+   This is how mirroring works (only writes are special):
+
+   When initiating a write, ccdbuffer() returns two "struct ccdbuf *"s
+   linked together by the cb_mirror field.  "cb_pflags &
+   CCDPF_MIRROR_DONE" is set to 0 on both of them.
+
+   When a component returns to ccdiodone(), it checks if "cb_pflags &
+   CCDPF_MIRROR_DONE" is set or not.  If not, it sets the partner's
+   flag and returns.  If it is, it means its partner has already
+   returned, so it will go to the regular cleanup.
+
+ */
+
 struct ccdbuf {
 	struct buf	cb_buf;		/* new I/O buf */
 	struct buf	*cb_obp;	/* ptr. to original I/O buf */
 	int		cb_unit;	/* target unit */
 	int		cb_comp;	/* target component */
+	int		cb_pflags;	/* mirror/parity status flag */
+	struct ccdbuf	*cb_mirror;	/* mirror counterpart */
 };
 
+/* bits in cb_pflags */
+#define CCDPF_MIRROR_DONE 1	/* if set, mirror counterpart is done */
+
 #define	getccdbuf()		\
 	((struct ccdbuf *)malloc(sizeof(struct ccdbuf), M_DEVBUF, M_WAITOK))
 #define putccdbuf(cbp)		\
@@ -703,10 +722,7 @@ ccdstrategy(bp)
 		if (bounds_check_with_label(bp, lp, wlabel) <= 0)
 			goto done;
 
-	if (cs->sc_cflags & CCDF_MIRROR && (bp->b_flags & B_READ) == 0)
-		bp->b_resid = bp->b_bcount*2;
-	else
-		bp->b_resid = bp->b_bcount;
+	bp->b_resid = bp->b_bcount;
 
 	/*
 	 * "Start" the unit.
@@ -896,6 +912,11 @@ ccdbuffer(cb, cs, bp, bn, addr, bcount)
 		cbp->cb_buf.b_vp = ci2->ci_vp;
 		cbp->cb_comp = ci2 - cs->sc_cinfo;
 		cb[1] = cbp;
+		/* link together the ccdbuf's and clear "mirror done" flag */
+		cb[0]->cb_mirror = cb[1];
+		cb[1]->cb_mirror = cb[0];
+		cb[0]->cb_pflags &= ~CCDPF_MIRROR_DONE;
+		cb[1]->cb_pflags &= ~CCDPF_MIRROR_DONE;
 	}
 }
 
@@ -923,10 +944,7 @@ ccdintr(cs, bp)
 		dk_busy &= ~(1 << cs->sc_dk);
 #endif
 	if (bp->b_flags & B_ERROR)
-		if (cs->sc_cflags & CCDF_MIRROR && (bp->b_flags & B_READ) == 0)
-			bp->b_resid = bp->b_bcount*2;
-		else
-			bp->b_resid = bp->b_bcount;
+		bp->b_resid = bp->b_bcount;
 	biodone(bp);
 }
 
@@ -965,6 +983,18 @@ ccdiodone(cbp)
 		       unit, bp->b_error, cbp->cb_comp);
 #endif
 	}
+
+	if (ccd_softc[unit].sc_cflags & CCDF_MIRROR &&
+	    (cbp->cb_buf.b_flags & B_READ) == 0)
+		if ((cbp->cb_pflags & CCDPF_MIRROR_DONE) == 0) {
+			/* I'm done before my counterpart, so just set
+			   partner's flag and return */
+			cbp->cb_mirror->cb_pflags |= CCDPF_MIRROR_DONE;
+			putccdbuf(cbp);
+			splx(s);
+			return;
+		}
+		
 	count = cbp->cb_buf.b_bcount;
 	putccdbuf(cbp);