Index: head/stand/i386/loader/chain.c
===================================================================
--- head/stand/i386/loader/chain.c	(revision 338187)
+++ head/stand/i386/loader/chain.c	(revision 338188)
@@ -1,134 +1,136 @@
 /*-
  * Copyright 2015 Toomas Soome <tsoome@me.com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 /*
  * Chain loader to load BIOS boot block either from MBR or PBR.
  *
  * Note the boot block location 0000:7c000 conflicts with loader, so we need to
  * read in to temporary space and relocate on exec, when btx is stopped.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <stand.h>
 #include <sys/param.h>
 #include <sys/linker.h>
 #include <sys/diskmbr.h>
 
 #include "bootstrap.h"
 #include "libi386/libi386.h"
 #include "btxv86.h"
 
 /*
  * The MBR/VBR is located in first sector of disk/partition.
  * Read 512B to temporary location and set up relocation. Then
  * exec relocator.
  */
 #define	SECTOR_SIZE	(512)
 
 COMMAND_SET(chain, "chain", "chain load boot block from device", command_chain);
 
 static int
 command_chain(int argc, char *argv[])
 {
 	int fd, len, size = SECTOR_SIZE;
 	struct stat st;
 	vm_offset_t mem = 0x100000;
 	struct i386_devdesc *rootdev;
 
 	if (argc == 1) {
 		command_errmsg = "no device or file name specified";
 		return (CMD_ERROR);
 	}
 	if (argc != 2) {
 		command_errmsg = "invalid trailing arguments";
 		return (CMD_ERROR);
 	}
 
 	fd = open(argv[1], O_RDONLY);
 	if (fd == -1) {
 		command_errmsg = "open failed";
 		return (CMD_ERROR);
 	}
 
 	len = strlen(argv[1]);
 	if (argv[1][len-1] != ':') {
 		if (fstat(fd, &st) == -1) {
 			command_errmsg = "stat failed";
 			close(fd);
 			return (CMD_ERROR);
 		}
 		size = st.st_size;
 	} else if (strncmp(argv[1], "disk", 4) != 0) {
 		command_errmsg = "can only use disk device";
 		close(fd);
 		return (CMD_ERROR);
 	}
 
 	i386_getdev((void **)(&rootdev), argv[1], NULL);
 	if (rootdev == NULL) {
 		command_errmsg = "can't determine root device";
+		close(fd);
 		return (CMD_ERROR);
 	}
 
-	if (archsw.arch_readin(fd, mem, SECTOR_SIZE) != SECTOR_SIZE) {
+	if (archsw.arch_readin(fd, mem, size) != size) {
 		command_errmsg = "failed to read disk";
 		close(fd);
 		return (CMD_ERROR);
 	}
 	close(fd);
 
-	if (*((uint16_t *)PTOV(mem + DOSMAGICOFFSET)) != DOSMAGIC) {
+	if (argv[1][len-1] == ':' &&
+	    *((uint16_t *)PTOV(mem + DOSMAGICOFFSET)) != DOSMAGIC) {
 		command_errmsg = "wrong magic";
 		return (CMD_ERROR);
 	}
 
 	relocater_data[0].src = mem;
 	relocater_data[0].dest = 0x7C00;
-	relocater_data[0].size = SECTOR_SIZE;
+	relocater_data[0].size = size;
 
 	relocator_edx = bd_unit2bios(rootdev->dd.d_unit);
 	relocator_esi = relocater_size;
 	relocator_ds = 0;
 	relocator_es = 0;
 	relocator_fs = 0;
 	relocator_gs = 0;
 	relocator_ss = 0;
 	relocator_cs = 0;
 	relocator_sp = 0x7C00;
 	relocator_ip = 0x7C00;
 	relocator_a20_enabled = 0;
 
 	i386_copyin(relocater, 0x600, relocater_size);
 
 	dev_cleanup();
 
 	__exec((void *)0x600);
 
 	panic("exec returned");
 	return (CMD_ERROR);		/* not reached */
 }