init: code cleanup

init

@@ -1,8 +1,8 @@
 #!/bin/sh
 #
-# tiny init
+# Tiny init
 #
-# false positive
+# https://www.shellcheck.net/wiki/SC2154
 # shellcheck disable=2154
 
 print()
@@ -13,8 +13,10 @@ print()
 panic()
 {
     print "${1:-unexpected error occurred}" \
-          "\033[1;31m!!\033[m"      >&2; sh
-}
+          "\033[1;31m!!\033[m"
+
+    sh
+} >&2
 
 resolve_device()
 {
@@ -28,12 +30,16 @@ resolve_device()
         *)        return 0 ;;
     esac
 
-    # prevent race condition
-    while [ ! -b "$device" ]; do sleep 1
-        [ "$((count += 1))" = "${rootdelay:=30}" ] && {
+    # Race condition may occur if device manager is not yet initialized device.
+    # To fix this, we simply waiting until device is available. If device
+    # didn't appear in specified time, we panic.
+    while [ ! -b "$device" ]; do
+        if [ "$((count += 1))" = "${rootdelay:=30}" ]; then
             panic "failed to lookup partition"
             break
-        }
+        else
+            sleep 1
+        fi
     done || :
 }
 
@@ -41,8 +47,9 @@ run_hook()
 {
     type="$1"
 
-    # run hooks if any
-    # false positive
+    # Run hooks if any exist.
+    #
+    # https://www.shellcheck.net/wiki/SC1090
     # shellcheck disable=1090
     for hook in $hooks; do
         [ -f "/usr/share/tinyramfs/hooks/${hook}/${hook}.${type}" ] || continue
@@ -52,7 +59,7 @@ run_hook()
 
 prepare_environment()
 {
-    # false positive
+    # https://www.shellcheck.net/wiki/SC1091
     # shellcheck disable=1091
     . /etc/tinyramfs/config
 
@@ -92,13 +99,11 @@ mount_root()
 
     resolve_device "$root"
 
-    set -- \
-        "${rorw:--o ro}${root_opts:+,$root_opts}" \
-        "${root_type:+-t $root_type}" "$device" "/mnt/root"
-
-    # word splitting is safe by design
-    # shellcheck disable=2068
-    mount $@ || panic "failed to mount root"
+    # https://www.shellcheck.net/wiki/SC2086
+    # shellcheck disable=2086
+    mount \
+        ${rorw:--o ro}${root_opts:+,$root_opts} ${root_type:+-t $root_type} \
+        -- "$device" /mnt/root || panic "failed to mount root"
 }
 
 boot_system()
@@ -109,19 +114,26 @@ boot_system()
         mount -o move "$dir" "/mnt/root/${dir}"
     done
 
-    set -- "/mnt/root" "${init:-/sbin/init}" "$init_args"
-
-    # POSIX exec has no -c flag to execute command with empty environment
-    # use 'env -i' to prevent leaking exported variables
-    # word splitting is safe by design
-    # shellcheck disable=2068
-    exec env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
-        switch_root $@ || panic "failed to boot system"
+    # POSIX 'exec' has no '-c' flag to execute command with empty environment.
+    # Using 'env -i' instead to prevent leaking exported variables.
+    #
+    # Some implementations of 'switch_root' doesn't conform to POSIX utility
+    # guidelines and doesn't support '--'. This means that we can't guarantee
+    # safety of init_args.
+    # shellcheck disable=2086
+    exec \
+        env -i TERM=linux PATH=/bin:/sbin:/usr/bin:/usr/sbin \
+        switch_root /mnt/root "${init-/sbin/init}" $init_args ||
+        panic "failed to boot system"
 }
 
-# enable exit on error and disable globbing
-# trap EXIT signal
-set -ef; trap panic EXIT
+# Exit if command fails and disable globbing.
+set -ef
+
+# Run emergency shell if init unexpectedly exiting due to error.
+trap panic EXIT
+
+# TODO display fancy colored status info
 
 prepare_environment
 parse_cmdline