contrib/dracut: 90: generator: only log to kmsg if debug set on cmdline

"debug" is also used by systemd itself, and there's really no reason for
the generator to write this much garbage by default

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#11898

contrib/dracut/90zfs/zfs-generator.sh.in

@@ -1,6 +1,7 @@
 #!/bin/sh
 
-echo "zfs-generator: starting" >> /dev/kmsg
+grep -wq debug /proc/cmdline && debug=1
+[ -n "$debug" ] && echo "zfs-generator: starting" >> /dev/kmsg
 
 GENERATOR_DIR="$1"
 [ -n "$GENERATOR_DIR" ] || {
@@ -12,7 +13,7 @@ GENERATOR_DIR="$1"
 [ -f /usr/lib/dracut/modules.d/99base/dracut-lib.sh ] && dracutlib=/usr/lib/dracut/modules.d/99base/dracut-lib.sh
 
 command -v getarg >/dev/null 2>&1 || {
-    echo "zfs-generator: loading Dracut library from $dracutlib" >> /dev/kmsg
+    [ -n "$debug" ] && echo "zfs-generator: loading Dracut library from $dracutlib" >> /dev/kmsg
     . "$dracutlib"
 }
 
@@ -34,7 +35,7 @@ case ",${rootflags}," in
 	*)	rootflags="zfsutil,${rootflags}" ;;
 esac
 
-echo "zfs-generator: writing extension for sysroot.mount to $GENERATOR_DIR"/sysroot.mount.d/zfs-enhancement.conf >> /dev/kmsg
+[ -n "$debug" ] && echo "zfs-generator: writing extension for sysroot.mount to $GENERATOR_DIR/sysroot.mount.d/zfs-enhancement.conf" >> /dev/kmsg
 
 [ -d "$GENERATOR_DIR" ] || mkdir "$GENERATOR_DIR"
 [ -d "$GENERATOR_DIR"/sysroot.mount.d ] || mkdir "$GENERATOR_DIR"/sysroot.mount.d
@@ -67,4 +68,6 @@ ln -s ../sysroot.mount "$GENERATOR_DIR"/initrd-root-fs.target.requires/sysroot.m
     echo "After=zfs-import.target"
 } > "$GENERATOR_DIR"/dracut-pre-mount.service.d/zfs-enhancement.conf
 
-echo "zfs-generator: finished" >> /dev/kmsg
+[ -n "$debug" ] && echo "zfs-generator: finished" >> /dev/kmsg
+
+exit 0