lualoader: Add nextboot support

config.parse now takes an extra callback that is invoked on the full text of
the config file. This callback dictates where we should actually try to
parse this file or not.

For nextboot, we use this to halt parsing if we see 'nextboot_enable="NO"'.
If we don't, parse it and write 'nextboot_enable="NO" ' to it. The same
caveat as with forth still applies- writing is only supported by UFS.

stand/lua/config.lua

@@ -124,6 +124,27 @@ pattern_table = {
 	}
 }
 
+local function check_nextboot()
+	local nextboot_file = loader.getenv("nextboot_file")
+	if nextboot_file == nil then
+		return
+	end
+
+	local function check_nextboot_disabled(text)
+		return not text:match("^nextboot_enable=\"NO\"")
+	end
+
+	if not config.parse(nextboot_file, true, check_nextboot_disabled) then
+		-- This only fails if it actually hit a parse error
+		print("Failed to parse nextboot configuration: '" ..
+		    nextboot_file .. "'")
+	end
+
+	local nfile = io.open(nextboot_file, 'w')
+	io.write(nfile, "nextboot_enable=\"NO\" ")
+	io.close(nfile)
+end
+
 -- Module exports
 -- Which variables we changed
 config.env_changed = {}
@@ -273,7 +294,9 @@ function config.loadmod(mod, silent)
 end
 
 -- silent runs will not return false if we fail to open the file
-function config.parse(name, silent)
+-- check_and_halt, if it's set, will be executed on the full text of the config
+-- file. If it returns false, we are to halt immediately.
+function config.parse(name, silent, check_and_halt)
 	if silent == nil then
 		silent = false
 	end
@@ -294,6 +317,13 @@ function config.parse(name, silent)
 		return silent
 	end
 
+
+	if check_and_halt ~= nil then
+		if not check_and_halt(text) then
+			-- We'll just pretend that everything is fine...
+			return true
+		end
+	end
 	local n = 1
 	local status = true
 
@@ -439,6 +469,8 @@ function config.load(file)
 		end
 	end
 
+	check_nextboot()
+
 	-- Cache the provided module_path at load time for later use
 	config.module_path = loader.getenv("module_path")
 end