The values for blocks and offset in -b should be treated as 512-byte block

counts.

Tweak man page accordingly.

Requested by deraadt@ and kettenis@.

2 files changed, 25 insertions, 8 deletions

diff --git a/sbin/fdisk/fdisk.8 b/sbin/fdisk/fdisk.8
index 94afcd3e923..fe711970480 100644
--- a/sbin/fdisk/fdisk.8
+++ b/sbin/fdisk/fdisk.8
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: fdisk.8,v 1.101 2021/06/21 02:05:30 krw Exp $
+.\"	$OpenBSD: fdisk.8,v 1.102 2021/06/22 14:01:58 krw Exp $
 .\"
 .\"
 .\" Copyright (c) 1997 Tobias Weingartner
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: June 21 2021 $
+.Dd $Mdocdate: June 22 2021 $
 .Dt FDISK 8
 .Os
 .Sh NAME
@@ -69,10 +69,18 @@ all existing partitions except the boot partitions
 and
 .Sq HiFive BBL .
 .It Fl b Ar blocks Ns Op @ Ns Ar offset Ns Op : Ns Ar type
-A special boot partition of the specified size, offset and type will be written to disk.
+Configures a special boot partition of the specified number of blocks, offset
+and type.
+.Ar offset
+defaults to the first available block, and
+.Ar type
+defaults to
+.Sq EF .
+.Pp
 The
 .Ox
-partition will follow the boot partition and use the remaining space on the disk.
+partition will follow the boot partition and use the remaining
+available space.
 .Pp
 Can only be used when initializing a disk with
 .Fl i Op Fl g
@@ -81,8 +89,7 @@ or
 If a GPT is being initialized
 only the
 .Ar blocks
-value will be used, with the boot partition being placed at the first available LBA and
-given the type EFI SYS.
+value is used.
 .It Xo
 .Fl c Ar cylinders
 .Fl h Ar heads
diff --git a/sbin/fdisk/fdisk.c b/sbin/fdisk/fdisk.c
index 12c042f18a5..d6fee5a5976 100644
--- a/sbin/fdisk/fdisk.c
+++ b/sbin/fdisk/fdisk.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fdisk.c,v 1.110 2021/06/21 02:05:30 krw Exp $	*/
+/*	$OpenBSD: fdisk.c,v 1.111 2021/06/22 14:01:58 krw Exp $	*/
 
 /*
  * Copyright (c) 1997 Tobias Weingartner
@@ -16,7 +16,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#include <sys/types.h>
+#include <sys/param.h>	/* DEV_BSIZE */
 #include <sys/disklabel.h>
 
 #include <err.h>
@@ -62,6 +62,7 @@ main(int argc, char *argv[])
 {
 	ssize_t len;
 	int ch, fd, efi, error;
+	unsigned int bps;
 	int e_flag = 0, g_flag = 0, i_flag = 0, u_flag = 0;
 	int verbosity = TERSE;
 	int c_arg = 0, h_arg = 0, s_arg = 0;
@@ -155,6 +156,15 @@ main(int argc, char *argv[])
 
 	disk.name = argv[0];
 	DISK_open(A_flag || i_flag || u_flag || e_flag);
+	bps = DL_BLKSPERSEC(&dl);
+	if (b_sectors > 0) {
+		if (b_sectors % bps != 0)
+			b_sectors += bps - b_sectors % bps;
+		if (b_offset % bps != 0)
+			b_offset += bps - b_offset % bps;
+		b_sectors = DL_BLKTOSEC(&dl, b_sectors);
+		b_offset = DL_BLKTOSEC(&dl, b_offset);
+	}
 
 	/* "proc exec" for man page display */
 	if (pledge("stdio rpath wpath disklabel proc exec", NULL) == -1)