5 files changed, 25 insertions, 8 deletions

diff --git a/sys/fs/specfs/spec_vnops.c b/sys/fs/specfs/spec_vnops.c
index 7b2d712fc76b..46b4eb5851f9 100644
--- a/sys/fs/specfs/spec_vnops.c
+++ b/sys/fs/specfs/spec_vnops.c
@@ -168,7 +168,6 @@ spec_open(ap)
 		return (ENXIO);
 
 	switch (vp->v_type) {
-
 	case VCHR:
 		dsw = devsw(dev);
 		if ( (dsw == NULL) || (dsw->d_open == NULL))
@@ -237,6 +236,7 @@ spec_open(ap)
 		if (!dev->si_bsize_max)
 			dev->si_bsize_max = MAXBSIZE;
 	}
+
 	return (error);
 }
 
@@ -263,6 +263,7 @@ spec_read(ap)
 	int n, on;
 	d_ioctl_t *ioctl;
 	int error = 0;
+	int seqcount = ap->a_ioflag >> 16;
 	dev_t dev;
 
 #ifdef DIAGNOSTIC
@@ -284,6 +285,8 @@ spec_read(ap)
 		return (error);
 
 	case VBLK:
+		if (enable_userblk_io == 0)
+			return (EINVAL);
 		if (uio->uio_offset < 0)
 			return (EINVAL);
 		dev = vp->v_rdev;
@@ -309,13 +312,13 @@ spec_read(ap)
 			bn = btodb(uio->uio_offset) & ~(bscale - 1);
 			on = uio->uio_offset % bsize;
 			n = min((unsigned)(bsize - on), uio->uio_resid);
-			if (vp->v_lastr + bscale == bn) {
+			if (seqcount > 1) {
 				nextbn = bn + bscale;
 				error = breadn(vp, bn, (int)bsize, &nextbn,
 					(int *)&bsize, 1, NOCRED, &bp);
-			} else
+			} else {
 				error = bread(vp, bn, (int)bsize, NOCRED, &bp);
-			vp->v_lastr = bn;
+			}
 			n = min(n, bsize - bp->b_resid);
 			if (error) {
 				brelse(bp);
@@ -372,6 +375,8 @@ spec_write(ap)
 		return (error);
 
 	case VBLK:
+		if (enable_userblk_io == 0)
+			return (EINVAL);
 		if (uio->uio_resid == 0)
 			return (0);
 		if (uio->uio_offset < 0)
diff --git a/sys/kern/vfs_export.c b/sys/kern/vfs_export.c
index b452cc1abcef..757e4aa5255c 100644
--- a/sys/kern/vfs_export.c
+++ b/sys/kern/vfs_export.c
@@ -113,6 +113,9 @@ SYSCTL_INT(_vfs, OID_AUTO, reassignbufsortbad, CTLFLAG_RW, &reassignbufsortbad,
 static int reassignbufmethod = 1;
 SYSCTL_INT(_vfs, OID_AUTO, reassignbufmethod, CTLFLAG_RW, &reassignbufmethod, 0, "");
 
+int enable_userblk_io = 1;
+SYSCTL_INT(_vfs, OID_AUTO, enable_userblk_io, CTLFLAG_RW, &enable_userblk_io, 0, "");
+
 #ifdef ENABLE_VFS_IOOPT
 int vfs_ioopt = 0;
 SYSCTL_INT(_vfs, OID_AUTO, ioopt, CTLFLAG_RW, &vfs_ioopt, 0, "");
diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index b452cc1abcef..757e4aa5255c 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -113,6 +113,9 @@ SYSCTL_INT(_vfs, OID_AUTO, reassignbufsortbad, CTLFLAG_RW, &reassignbufsortbad,
 static int reassignbufmethod = 1;
 SYSCTL_INT(_vfs, OID_AUTO, reassignbufmethod, CTLFLAG_RW, &reassignbufmethod, 0, "");
 
+int enable_userblk_io = 1;
+SYSCTL_INT(_vfs, OID_AUTO, enable_userblk_io, CTLFLAG_RW, &enable_userblk_io, 0, "");
+
 #ifdef ENABLE_VFS_IOOPT
 int vfs_ioopt = 0;
 SYSCTL_INT(_vfs, OID_AUTO, ioopt, CTLFLAG_RW, &vfs_ioopt, 0, "");
diff --git a/sys/miscfs/specfs/spec_vnops.c b/sys/miscfs/specfs/spec_vnops.c
index 7b2d712fc76b..46b4eb5851f9 100644
--- a/sys/miscfs/specfs/spec_vnops.c
+++ b/sys/miscfs/specfs/spec_vnops.c
@@ -168,7 +168,6 @@ spec_open(ap)
 		return (ENXIO);
 
 	switch (vp->v_type) {
-
 	case VCHR:
 		dsw = devsw(dev);
 		if ( (dsw == NULL) || (dsw->d_open == NULL))
@@ -237,6 +236,7 @@ spec_open(ap)
 		if (!dev->si_bsize_max)
 			dev->si_bsize_max = MAXBSIZE;
 	}
+
 	return (error);
 }
 
@@ -263,6 +263,7 @@ spec_read(ap)
 	int n, on;
 	d_ioctl_t *ioctl;
 	int error = 0;
+	int seqcount = ap->a_ioflag >> 16;
 	dev_t dev;
 
 #ifdef DIAGNOSTIC
@@ -284,6 +285,8 @@ spec_read(ap)
 		return (error);
 
 	case VBLK:
+		if (enable_userblk_io == 0)
+			return (EINVAL);
 		if (uio->uio_offset < 0)
 			return (EINVAL);
 		dev = vp->v_rdev;
@@ -309,13 +312,13 @@ spec_read(ap)
 			bn = btodb(uio->uio_offset) & ~(bscale - 1);
 			on = uio->uio_offset % bsize;
 			n = min((unsigned)(bsize - on), uio->uio_resid);
-			if (vp->v_lastr + bscale == bn) {
+			if (seqcount > 1) {
 				nextbn = bn + bscale;
 				error = breadn(vp, bn, (int)bsize, &nextbn,
 					(int *)&bsize, 1, NOCRED, &bp);
-			} else
+			} else {
 				error = bread(vp, bn, (int)bsize, NOCRED, &bp);
-			vp->v_lastr = bn;
+			}
 			n = min(n, bsize - bp->b_resid);
 			if (error) {
 				brelse(bp);
@@ -372,6 +375,8 @@ spec_write(ap)
 		return (error);
 
 	case VBLK:
+		if (enable_userblk_io == 0)
+			return (EINVAL);
 		if (uio->uio_resid == 0)
 			return (0);
 		if (uio->uio_offset < 0)
diff --git a/sys/sys/vnode.h b/sys/sys/vnode.h
index e78db4317881..75a824aaa101 100644
--- a/sys/sys/vnode.h
+++ b/sys/sys/vnode.h
@@ -280,6 +280,7 @@ extern	struct vm_zone *namei_zone;
 extern	int prtactive;			/* nonzero to call vprint() */
 extern	struct vattr va_null;		/* predefined null vattr structure */
 extern	int vfs_ioopt;
+extern  int enable_userblk_io;
 
 /*
  * Macro/function to check for client cache inconsistency w.r.t. leasing.