+format, and is documented in the file "buffer-format.txt". There are
+two ways to add an early userspace image: specify an existing cpio
+archive to be used as the image or have the kernel build process build
+the image from specifications.
+
+CPIO ARCHIVE method
+
+You can create a cpio archive that contains the early userspace image.
+Youre cpio archive should be specified in CONFIG_INITRAMFS_SOURCE and it
+will be used directly. Only a single cpio file may be specified in
+CONFIG_INITRAMFS_SOURCE and directory and file names are not allowed in
+combination with a cpio archive.
+
+IMAGE BUILDING method
+
+The kernel build process can also build an early userspace image from
+source parts rather than supplying a cpio archive. This method provides
+a way to create images with root-owned files even though the image was
+built by an unprivileged user.
+
+The image is specified as one or more sources in
+CONFIG_INITRAMFS_SOURCE. Sources can be either directories or files -
+cpio archives are *not* allowed when building from sources.
+
+A source directory will have it and all of it's contents packaged. The
+specified directory name will be mapped to '/'. When packaging a
+directory, limited user and group ID translation can be performed.
+INITRAMFS_ROOT_UID can be set to a user ID that needs to be mapped to
+user root (0). INITRAMFS_ROOT_GID can be set to a group ID that needs
+to be mapped to group root (0).
+
+A source file must be directives in the format required by the
+usr/gen_init_cpio utility (run 'usr/gen_init_cpio --help' to get the
+file format). The directives in the file will be passed directly to
+usr/gen_init_cpio.
+
+When a combination of directories and files are specified then the
+initramfs image will be an aggregate of all of them. In this way a user
+can create a 'root-image' directory and install all files into it.
+Because device-special files cannot be created by a unprivileged user,
+special files can be listed in a 'root-files' file. Both 'root-image'
+and 'root-files' can be listed in CONFIG_INITRAMFS_SOURCE and a complete
+early userspace image can be built by an unprivileged user.
+
+As a technical note, when directories and files are specified, the
+entire CONFIG_INITRAMFS_SOURCE is passed to
+scripts/gen_initramfs_list.sh. This means that CONFIG_INITRAMFS_SOURCE
+can really be interpreted as any legal argument to
+gen_initramfs_list.sh. If a directory is specified as an argument then
+the contents are scanned, uid/gid translation is performed, and
+usr/gen_init_cpio file directives are output. If a directory is
+specified as an arugemnt to scripts/gen_initramfs_list.sh then the
+contents of the file are simply copied to the output. All of the output
+directives from directory scanning and file contents copying are
+processed by usr/gen_init_cpio.
+
+See also 'scripts/gen_initramfs_list.sh -h'.