The URN for the local file fetcher is file. The filename can be either absolute or relative. If the filename is relative, FILESPATH and failing that FILESDIR will be used to find the appropriate relative file. The metadata usually extend these variables to include variations of the values in OVERRIDES. Single files and complete directories can be specified.

SRC_URI= "file://relativefile.patch"
SRC_URI= "file://relativefile.patch;this=ignored"
SRC_URI= "file:///Users/ich/very_important_software"