Extlinux Bootmeth

Extlinux (sometimes called syslinux) allows U-Boot to provide a menu of available operating systems from which the user can choose.

U-Boot includes a parser for the extlinux.conf file. It consists primarily of a list of named operating systems along with the kernel, initial ramdisk and other settings. The file is stored in the extlinux/ subdirectory, possibly under the boot/ subdirectory. This list of prefixes ({"/", "/boot"} by default) can be selected with the filename-prefixes property in the bootstd device.

Note that the PXE Bootmeth uses the same file format, but in a network context.

When invoked on a bootdev, this bootmeth searches for the file and creates a bootflow for each label defined in the configuration. Since an extlinux config can contain several labels (each pointing to a different kernel), the bootmeth sets the BOOTMETHF_MULTI flag so that the iterator produces one bootflow per label. The bflow->entry field selects which label to use. Include directives are processed during scanning so labels from included files are also discovered.

When the bootflow is booted, pxe_boot_entry() parses the config, walks to the selected label and boots it directly.

The compatible string “u-boot,extlinux” is used for the driver. It is present if CONFIG_BOOTMETH_EXTLINUX is enabled.