From e27e6546b6b4db784cc995f88f0dbc78983b9e34 Mon Sep 17 00:00:00 2001
From: sos <sos@FreeBSD.org>
Date: Fri, 7 Jan 2000 12:01:01 +0000
Subject: Guard against transfers of zero length given to *strategy.

---
 sys/dev/ata/ata-disk.c | 7 +++++++
 sys/dev/ata/atapi-cd.c | 2 +-
 sys/dev/ata/atapi-fd.c | 9 ++++++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/sys/dev/ata/ata-disk.c b/sys/dev/ata/ata-disk.c
index 598d6df..619f1fe 100644
--- a/sys/dev/ata/ata-disk.c
+++ b/sys/dev/ata/ata-disk.c
@@ -301,6 +301,13 @@ adstrategy(struct buf *bp)
     struct ad_softc *adp = bp->b_dev->si_drv1;
     int32_t s;
 
+    /* if it's a null transfer, return immediatly. */
+    if (bp->b_bcount == 0) {
+	bp->b_resid = 0;
+	biodone(bp);
+	return;
+    }
+
     s = splbio();
     bufqdisksort(&adp->queue, bp);
     ad_start(adp);
diff --git a/sys/dev/ata/atapi-cd.c b/sys/dev/ata/atapi-cd.c
index 40eb4b6..50632f7 100644
--- a/sys/dev/ata/atapi-cd.c
+++ b/sys/dev/ata/atapi-cd.c
@@ -1030,7 +1030,7 @@ acdstrategy(struct buf *bp)
 	return;
     }
 #endif
-
+    /* if it's a null transfer, return immediatly. */
     if (bp->b_bcount == 0) {
 	bp->b_resid = 0;
 	biodone(bp);
diff --git a/sys/dev/ata/atapi-fd.c b/sys/dev/ata/atapi-fd.c
index 6c45f6f..f8e3291 100644
--- a/sys/dev/ata/atapi-fd.c
+++ b/sys/dev/ata/atapi-fd.c
@@ -254,6 +254,13 @@ afdstrategy(struct buf *bp)
     struct afd_softc *fdp = bp->b_dev->si_drv1;
     int32_t s;
 
+    /* if it's a null transfer, return immediatly. */
+    if (bp->b_bcount == 0) {
+	bp->b_resid = 0;
+	biodone(bp);
+	return;
+    }
+
     s = splbio();
     bufq_insert_tail(&fdp->buf_queue, bp);
     afd_start(fdp);
@@ -267,7 +274,7 @@ afd_start(struct afd_softc *fdp)
     u_int32_t lba, count;
     int8_t ccb[16];
     int8_t *data_ptr;
-    
+
     if (!bp)
 	return;
 
-- 
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