Force systems with kernel option "quiet" to display prompt for password

On systems that utilize TTY for password entry, if the kernel
option "quiet" is set, the system would appear to freeze on a
blank screen, when in fact it is waiting for password entry
from the user.

Since TTY is the fallback method, this has no effect on systemd
or plymouth password prompting.

By temporarily setting "printk" to "7", running the command,
then resuming with the original "printk" state, the user can
see the password prompt.

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Garrett Fields <ghfields@gmail.com>
Closes #9731

contrib/initramfs/scripts/zfs.in

@@ -436,7 +436,11 @@ decrypt_fs()
 
 			# Prompt with ZFS tty, otherwise
 			else
+				# Setting "printk" temporarily to "7" will allow prompt even if kernel option "quiet"
+				storeprintk="$(awk '{print $1}' /proc/sys/kernel/printk)"
+				echo 7 > /proc/sys/kernel/printk
 				$ZFS load-key "${ENCRYPTIONROOT}"
+				echo "$storeprintk" > /proc/sys/kernel/printk
 			fi
 		fi
 	fi