Index: sbin/disklabel/main.c
===================================================================
RCS file: /cvsroot/src/sbin/disklabel/main.c,v
retrieving revision 1.22
diff -u -p -r1.22 main.c
--- sbin/disklabel/main.c	5 Jan 2010 15:45:26 -0000	1.22
+++ sbin/disklabel/main.c	3 Jan 2011 07:09:49 -0000
@@ -150,6 +150,7 @@ static	int	Aflag;		/* Action all labels 
 static	int	Fflag;		/* Read/write from file */
 static	int	rflag;		/* Read/write direct from disk */
 static	int	tflag;		/* Format output as disktab */
+static	int	uflag;		/* Update in-core label only on write */
 	int	Cflag;		/* CHS format output */
 static	int	Dflag;		/* Delete old labels (use with write) */
 static	int	Iflag;		/* Read/write direct, but default if absent */
@@ -281,7 +282,7 @@ main(int argc, char *argv[])
 #endif
 
 	error = 0;
-	while ((ch = getopt(argc, argv, "ACDFINRWb:ef:ilmrs:tvw")) != -1) {
+	while ((ch = getopt(argc, argv, "ACDFINRWb:ef:ilmrs:tuvw")) != -1) {
 		old_op = op;
 		switch (ch) {
 		case 'A':	/* Action all labels */
@@ -334,6 +335,9 @@ main(int argc, char *argv[])
 		case 't':	/* Format output as a disktab entry */
 			tflag = 1;
 			break;
+		case 'u':	/* Update in-core label only on write */
+			uflag = 1;
+			break;
 		case 'v':	/* verbose/diag output */
 			verbose++;
 			break;
@@ -362,6 +366,11 @@ main(int argc, char *argv[])
 	if (Iflag && op != EDIT && op != INTERACT)
 		usage();
 
+	if (rflag && uflag) {
+		(void)fprintf(stderr, "-r and -u are exclusive.\n");
+		usage();
+	}
+
 	dkname = argv[0];
 	f = opendisk(dkname, op == READ ? O_RDONLY : O_RDWR,
 		    specname, sizeof specname, 0);
@@ -530,9 +539,17 @@ write_label(int f)
 		}
 	} else {
 		/* Get the kernel to write the label */
-		if (dk_ioctl(f, DIOCWDINFO, &lab) < 0) {
-			l_perror("ioctl DIOCWDINFO");
-			return (1);
+		if (uflag) {
+			/* update in-core label only */
+			if (dk_ioctl(f, DIOCSDINFO, &lab) < 0) {
+				l_perror("ioctl DIOCSDINFO");
+				return (1);
+			}
+		} else {
+			if (dk_ioctl(f, DIOCWDINFO, &lab) < 0) {
+				l_perror("ioctl DIOCWDINFO");
+				return (1);
+			}
 		}
 	}
 
@@ -1801,9 +1818,9 @@ usage(void)
 		const char *expn;
 	} usages[] = {
 	{ "[-ACFrtv] disk", "(to read label)" },
-	{ "-w [-DFrv] [-f disktab] disk disktype [packid]", "(to write label)" },
-	{ "-e [-CDFIrv] disk", "(to edit label)" },
-	{ "-i [-DFIrv] disk", "(to create a label interactively)" },
+	{ "-w [-DFv] [-r|-u] [-f disktab] disk disktype [packid]", "(to write label)" },
+	{ "-e [-CDFIv] [-r|-u] disk", "(to edit label)" },
+	{ "-i [-DFIv] [-r|-u] disk", "(to create a label interactively)" },
 	{ "-D [-v] disk", "(to delete existing label(s))" },
 	{ "-R [-DFrv] disk protofile", "(to restore label)" },
 	{ "[-NW] disk", "(to write disable/enable label)" },
Index: sbin/disklabel/disklabel.8
===================================================================
RCS file: /cvsroot/src/sbin/disklabel/disklabel.8,v
retrieving revision 1.62
diff -u -p -r1.62 disklabel.8
--- sbin/disklabel/disklabel.8	28 Nov 2009 10:28:22 -0000	1.62
+++ sbin/disklabel/disklabel.8	3 Jan 2011 07:09:49 -0000
@@ -41,27 +41,32 @@
 .Sh SYNOPSIS
 .\" disklabel: read label
 .Nm
-.Op Fl ACDFrtv
+.Op Fl ACDFtv
+.Op Fl r | u
 .Ar disk
 .\" disklabel -e: read/modify/write using $EDITOR
 .Nm
 .Fl e
-.Op Fl CDFIrv
+.Op Fl CDFIv
+.Op Fl r | u
 .Ar disk
 .\" disklabel -i: read/modify/write using builtin commands
 .Nm
 .Fl i
-.Op Fl DFIrv
+.Op Fl DFIv
+.Op Fl r | u
 .Ar disk
 .\" disklabel -R: write from edited output
 .Nm
 .Fl R
-.Op Fl DFrv
+.Op Fl DFv
+.Op Fl r | u
 .Ar disk Ar protofile
 .\" disklabel -w: write from disctab entry
 .Nm
 .Fl w
-.Op Fl DFrv
+.Op Fl DFv
+.Op Fl r | u
 .Op Fl f Ar disktab
 .Ar disk Ar disktype
 .Oo Ar packid Oc
@@ -182,6 +187,14 @@ This is the historic behaviour and can b
 Format the output as a
 .Xr disktab 5
 entry.
+.It Fl u
+Update only in-core label on writing a label via
+.Xr ioctl 2 .
+Cannot be used with
+.Fl r
+and
+other options that imply
+.Fl r .
 .It Fl v
 Be verbose about the operations being done, in particular the disk sectors
 being read and written.