rc.d/hostid: Skip warning on systems w/o smbios

The first time a FreeBSD system boots, it obtains a hostuuid and hostid
from the smbios.system.uuid kernel environment variable.  If this value
is found to be invalid, a warning is printed and the boot pauses for
two seconds to give the user a chance to read it.

If the FreeBSD kernel is launched directly in a virtual machine rather
than via the FreeBSD boot loader, the smbios.system.uuid environment
variable might not be set; in this case, there's no need to alert the
user and delay the boot process since the lack of a "hardware" uuid is
entirely expected.

Distinguish between the cases of "invalid UUID" and "no UUID", warning
and delaying the boot only in the former case.  In both cases we still
generate a random UUID in software.

Reviewed by:	delphij
Sponsored by:	https://www.patreon.com/cperciva
Differential Revision:	https://reviews.freebsd.org/D36185

libexec/rc/rc.d/hostid

@@ -106,6 +106,8 @@ hostid_hardware()
 
 	if valid_hostid $uuid; then
 		echo "${uuid}"
+	elif [ "$uuid" ]; then
+		echo "INVALID"
 	fi
 }
 
@@ -113,9 +115,16 @@ hostid_generate()
 {
 	# First look for UUID in hardware.
 	uuid=`hostid_hardware`
-	if [ -z "${uuid}" ]; then
+
+	# Warn about invalid UUIDs
+	if [ "${uuid}" = "INVALID" ]; then
 		warn "hostid: unable to figure out a UUID from DMI data, generating a new one"
 		sleep 2
+		uuid=""
+	fi
+
+	# Generate a random UUID if invalid or not found
+	if [ -z "${uuid}" ]; then
 		# If not found, fall back to software-generated UUID.
 		uuid=`uuidgen`
 	fi