nixos/stage-1: Added boot.initrd.logCommands

nixos/modules/system/boot/stage-1-init.sh

···
 mkdir -p /run
 mount -t tmpfs -o "mode=0755,size=@runSize@" tmpfs /run
 
+# Optionally log the script output to /dev/kmsg or /run/log/stage-1-init.log 
+if test -n "@logCommands@"; then
+    mkdir -p /tmp
+    mkfifo /tmp/stage-1-init.log.fifo
+    logOutFd=8 && logErrFd=9
+    eval "exec $logOutFd>&1 $logErrFd>&2"
+    if test -w /dev/kmsg; then
+        tee -i < /tmp/stage-1-init.log.fifo /proc/self/fd/"$logOutFd" | while read line; do
+            if test -n "$line"; then
+                echo "stage-1-init: $line" > /dev/kmsg
+            fi
+        done &
+    else
+        mkdir -p /run/log
+        tee -i < /tmp/stage-1-init.log.fifo /run/log/stage-1-init.log &
+    fi
+    exec > /tmp/stage-1-init.log.fifo 2>&1
+fi
 
 # Process the kernel command line.
 export stage2Init=/init
···
 
 # Stop udevd.
 udevadm control --exit
+
+# Reset the logging file descriptors.
+# Do this just before pkill, which will kill the tee process.
+if test -n "@logCommands@"
+then
+    exec 1>&$logOutFd 2>&$logErrFd
+    eval "exec $logOutFd>&- $logErrFd>&-"
+fi
 
 # Kill any remaining processes, just to be sure we're not taking any
 # with us into stage 2. But keep storage daemons like unionfs-fuse.

nixos/modules/system/boot/stage-1.nix

···
 
     inherit (config.boot) resumeDevice devSize runSize;
 
-    inherit (config.boot.initrd) checkJournalingFS
-      preLVMCommands preDeviceCommands postDeviceCommands postMountCommands kernelModules;
+    inherit (config.boot.initrd) checkJournalingFS 
+      logCommands preLVMCommands preDeviceCommands postDeviceCommands postMountCommands kernelModules;
 
     resumeDevices = map (sd: if sd ? device then sd.device else "/dev/disk/by-label/${sd.label}")
                     (filter (sd: (sd ? label || hasPrefix "/dev/" sd.device) && !sd.randomEncryption) config.swapDevices);
···
         Specify here the device where the file resides.
         You should also use <varname>boot.kernelParams</varname> to specify
         <literal><replaceable>resume_offset</replaceable></literal>.
+      '';
+    };
+
+    boot.initrd.logCommands = mkOption {
+      default = false;
+      type = types.bool;
+      description = ''
+        Whether to replicate command output of stage-1 booting to <filename>/dev/kmsg</filename> or <filename>/run/log/stage-1-init.log</filename> if <filename>/dev/kmsg</filename> is not writable.
       '';
     };