This is a very small read-only file system mainly intended for initial ram disks of installation disks, but it could be used for other read-only media as well. Read <file:Documentation/filesystems/romfs.txt> for details. To compile this file system support as a module, choose M here: the module will be called romfs. Note that the file system of your root partition (the one containing the directory /) cannot be a module. If you don't know whether you need it, then you don't need it: answer N.
Select the backing stores to be supported.
This permits ROMFS to use block devices buffered through the page cache as the medium from which to retrieve data. It does not allow direct mapping of the medium. If unsure, answer Y.
This permits ROMFS to use MTD based devices directly, without the intercession of the block layer (which may have been disabled). It also allows direct mapping of MTD devices through romfs files under NOMMU conditions if the underlying device is directly addressable by the CPU. If unsure, answer Y.