bootconfig: init: Allow admin to use bootconfig for init command line

Since the current kernel command line is too short to describe
long and many options for init (e.g. systemd command line options),
this allows admin to use boot config for init command line.

All init command line under "init." keywords will be passed to
init.

For example,

init.systemd {
	unified_cgroup_hierarchy = 1
	debug_shell
	default_timeout_start_sec = 60
}

Link: http://lkml.kernel.org/r/157867229521.17873.654222294326542349.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

init/main.c

@@ -139,6 +139,8 @@ char *saved_command_line;
 static char *static_command_line;
 /* Untouched extra command line */
 static char *extra_command_line;
+/* Extra init arguments */
+static char *extra_init_args;
 
 static char *execute_command;
 static char *ramdisk_execute_command;
@@ -372,6 +374,8 @@ static void __init setup_boot_config(void)
 		pr_info("Load boot config: %d bytes\n", size);
 		/* keys starting with "kernel." are passed via cmdline */
 		extra_command_line = xbc_make_cmdline("kernel");
+		/* Also, "init." keys are init arguments */
+		extra_init_args = xbc_make_cmdline("init");
 	}
 }
 #else
@@ -507,16 +511,18 @@ static inline void smp_prepare_cpus(unsigned int maxcpus) { }
  */
 static void __init setup_command_line(char *command_line)
 {
-	size_t len, xlen = 0;
+	size_t len, xlen = 0, ilen = 0;
 
 	if (extra_command_line)
 		xlen = strlen(extra_command_line);
+	if (extra_init_args)
+		ilen = strlen(extra_init_args) + 4; /* for " -- " */
 
 	len = xlen + strlen(boot_command_line) + 1;
 
-	saved_command_line = memblock_alloc(len, SMP_CACHE_BYTES);
+	saved_command_line = memblock_alloc(len + ilen, SMP_CACHE_BYTES);
 	if (!saved_command_line)
-		panic("%s: Failed to allocate %zu bytes\n", __func__, len);
+		panic("%s: Failed to allocate %zu bytes\n", __func__, len + ilen);
 
 	static_command_line = memblock_alloc(len, SMP_CACHE_BYTES);
 	if (!static_command_line)
@@ -533,6 +539,22 @@ static void __init setup_command_line(char *command_line)
 	}
 	strcpy(saved_command_line + xlen, boot_command_line);
 	strcpy(static_command_line + xlen, command_line);
+
+	if (ilen) {
+		/*
+		 * Append supplemental init boot args to saved_command_line
+		 * so that user can check what command line options passed
+		 * to init.
+		 */
+		len = strlen(saved_command_line);
+		if (!strstr(boot_command_line, " -- ")) {
+			strcpy(saved_command_line + len, " -- ");
+			len += 4;
+		} else
+			saved_command_line[len++] = ' ';
+
+		strcpy(saved_command_line + len, extra_init_args);
+	}
 }
 
 /*
@@ -759,6 +781,9 @@ asmlinkage __visible void __init start_kernel(void)
 	if (!IS_ERR_OR_NULL(after_dashes))
 		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
 			   NULL, set_init_arg);
+	if (extra_init_args)
+		parse_args("Setting extra init args", extra_init_args,
+			   NULL, 0, -1, -1, NULL, set_init_arg);
 
 	/*
 	 * These use large bootmem allocations and must precede