lib: Add a generic cmdline parse function parse_option_str

There should be a generic function to parse params like a=b,c
Adding parse_option_str in lib/cmdline.c which will return true
if there's specified option set in the params.

Also updated efi=old_map parsing code to use the new function
Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

arch/x86/platform/efi/efi.c

@@ -932,26 +932,8 @@ u64 efi_mem_attributes(unsigned long phys_addr)
 
 static int __init parse_efi_cmdline(char *str)
 {
-	if (*str == '=')
-		str++;
-
-	while (*str) {
-		if (!strncmp(str, "old_map", 7)) {
-			set_bit(EFI_OLD_MEMMAP, &efi.flags);
-			str += strlen("old_map");
-		}
-
-		/*
-		 * Skip any options we don't understand. Presumably
-		 * they apply to the EFI boot stub.
-		 */
-		while (*str && *str != ',')
-			str++;
-
-		/* If we hit a delimiter, skip it */
-		if (*str == ',')
-			str++;
-	}
+	if (parse_option_str(str, "old_map"))
+		set_bit(EFI_OLD_MEMMAP, &efi.flags);
 
 	return 0;
 }

include/linux/kernel.h

@@ -407,6 +407,7 @@ int vsscanf(const char *, const char *, va_list);
 extern int get_option(char **str, int *pint);
 extern char *get_options(const char *str, int nints, int *ints);
 extern unsigned long long memparse(const char *ptr, char **retptr);
+extern bool parse_option_str(const char *str, const char *option);
 
 extern int core_kernel_text(unsigned long addr);
 extern int core_kernel_data(unsigned long addr);

lib/cmdline.c

@@ -160,3 +160,32 @@ unsigned long long memparse(const char *ptr, char **retptr)
 	return ret;
 }
 EXPORT_SYMBOL(memparse);
+
+/**
+ *	parse_option_str - Parse a string and check an option is set or not
+ *	@str: String to be parsed
+ *	@option: option name
+ *
+ *	This function parses a string containing a comma-separated list of
+ *	strings like a=b,c.
+ *
+ *	Return true if there's such option in the string, or return false.
+ */
+bool parse_option_str(const char *str, const char *option)
+{
+	while (*str) {
+		if (!strncmp(str, option, strlen(option))) {
+			str += strlen(option);
+			if (!*str || *str == ',')
+				return true;
+		}
+
+		while (*str && *str != ',')
+			str++;
+
+		if (*str == ',')
+			str++;
+	}
+
+	return false;
+}