string: Introduce strtobool

We have at least two places which convert a string to a boolean type,
so create a common function for this. strtobool treats

- any positive (nonzero) number as true
- "0" as false
- "true" (case insensitive) as true
- "false" (case insensitive) as false

Every other value results in an error and the input *val is not
modified. The caller is expected to initialize *val with the correct
default before calling strtobool.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 43 insertions, 0 deletions

diff --git a/lib/string.c b/lib/string.c
index 6a39eb5ced..a3e9fd819b 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -739,3 +739,46 @@ void *memdup(const void *orig, size_t size)
 	return buf;
 }
 EXPORT_SYMBOL(memdup);
+
+/**
+ * strtobool - convert a string to a boolean value
+ * @str - The string
+ * @val - The boolean value returned.
+ *
+ * This function treats
+ * - any positive (nonzero) number as true
+ * - "0" as false
+ * - "true" (case insensitive) as true
+ * - "false" (case insensitive) as false
+ *
+ * Every other value results in an error and the @val is not
+ * modified. The caller is expected to initialize @val with the
+ * correct default before calling strtobool.
+ *
+ * Returns 0 for success or negative error code if the variable does
+ * not exist or contains something this function does not recognize
+ * as true or false.
+ */
+int strtobool(const char *str, int *val)
+{
+	if (!str || !*str)
+		return -EINVAL;
+
+	if (simple_strtoul(str, NULL, 0) > 0) {
+		*val = true;
+		return 0;
+	}
+
+	if (!strcmp(str, "0") || !strcasecmp(str, "false")) {
+		*val = false;
+		return 0;
+	}
+
+	if (!strcasecmp(str, "true")) {
+		*val = true;
+		return 0;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL(strtobool);