lib/string_helpers: string_get_size() now returns characters wrote

printbuf now needs to know the number of characters that would have been
written if the buffer was too small, like snprintf(); this changes
string_get_size() to return the the return value of snprintf().
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

include/linux/string_helpers.h

@@ -24,7 +24,7 @@ enum string_size_units {
 	STRING_UNITS_2,		/* use binary powers of 2^10 */
 };
 
-void string_get_size(u64 size, u64 blk_size, enum string_size_units units,
+int string_get_size(u64 size, u64 blk_size, enum string_size_units units,
 		    char *buf, int len);
 
 int parse_int_array_user(const char __user *from, size_t count, int **array);

lib/string_helpers.c

@@ -31,8 +31,10 @@
  * giving the size in the required units.  @buf should have room for
  * at least 9 bytes and will always be zero terminated.
  *
+ * Return value: number of characters of output that would have been written
+ * (which may be greater than len, if output was truncated).
  */
-void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
+int string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
 		    char *buf, int len)
 {
 	static const char *const units_10[] = {
@@ -126,7 +128,7 @@ void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
 	else
 		unit = units_str[units][i];
 
-	snprintf(buf, len, "%u%s %s", (u32)size,
+	return snprintf(buf, len, "%u%s %s", (u32)size,
 			tmp, unit);
 }
 EXPORT_SYMBOL(string_get_size);