Cleanup libsquashfs invalid argument error codes

 - Add an explicit "you're holding it wrong" error code.
 - Consistently return error codes and not have some special places
   where -1 is returned.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/sqfs/xattr.h b/include/sqfs/xattr.h
index 0f74c94..f2a87d3 100644
--- a/include/sqfs/xattr.h
+++ b/include/sqfs/xattr.h
@@ -173,7 +173,8 @@ SQFS_API const char *sqfs_get_xattr_prefix(E_SQFS_XATTR_TYPE id);
  * This function takes a key and finds the enumerator value that represents
  * its prefix. An error value is returned if the given prefix isn't supported.
  *
- * @return On success an @ref E_SQFS_XATTR_TYPE, -1 if it isn't supported.
+ * @return On success an @ref E_SQFS_XATTR_TYPE. If not supported, the
+ *         @ref SQFS_ERROR_UNSUPPORTED error code.
  */
 SQFS_API int sqfs_get_xattr_prefix_id(const char *key);