- Fail with an understandable error message if we cannot detect the

sector size, instead of later failing with an error about /boot/mbr
  not being a multiple of the sector size (since we end up with an
  assumed sector size of MAX_SEC_SIZE * 2).
- We query the sector size via an IOCTL anyway, so if that succeeds
  use that instead of probing for it via read(2) calls.  This fixes
  the problem with fdisk failing to operate on at least graid3 and
  md(4) devices on kernels with src/sys/geom/geom_dev.c before
  rev. 1.90, due to fdisk failing to detect the sector size.
- When detecting the root device allow "/" characters in it, which
  happens with e.g. gmirror devices.

Reviewed by:	cperciva
MFC after:	1 week

sbin/fdisk/fdisk.c

@@ -317,7 +317,8 @@ main(int argc, char *argv[])
 	/* (abu)use mboot.bootinst to probe for the sector size */
 	if ((mboot.bootinst = malloc(MAX_SEC_SIZE)) == NULL)
 		err(1, "cannot allocate buffer to determine disk sector size");
-	read_disk(0, mboot.bootinst);
+	if (read_disk(0, mboot.bootinst) == -1)
+		errx(1, "could not detect sector size");
 	free(mboot.bootinst);
 	mboot.bootinst = NULL;
 
@@ -811,6 +812,8 @@ get_params()
 	error = ioctl(fd, DIOCGSECTORSIZE, &u);
 	if (error != 0 || u == 0)
 		u = 512;
+	else
+		secsize = u;
 
 	error = ioctl(fd, DIOCGMEDIASIZE, &o);
 	if (error == 0) {
@@ -1395,7 +1398,7 @@ get_rootdisk(void)
 	if (statfs("/", &rootfs) == -1)
 		err(1, "statfs(\"/\")");
 
-	if ((rv = regcomp(&re, "^(/dev/[a-z]+[0-9]+)([sp][0-9]+)?[a-h]?$",
+	if ((rv = regcomp(&re, "^(/dev/[a-z/]+[0-9]+)([sp][0-9]+)?[a-h]?$",
 		    REG_EXTENDED)) != 0)
 		errx(1, "regcomp() failed (%d)", rv);
 	if ((rv = regexec(&re, rootfs.f_mntfromname, NMATCHES, rm, 0)) != 0)