[RFC] passing standard input to host bootloaders

["Fabian Freyer" <fabian.freyer@xxxxxxxxxxxxxxxxxxx>]

Hello list,

Some host boot loaders, e.g. grub-bhyve when using the bhyve
driver, take commands on stdin. While there is the
<bootloader_args> tag to set arbitrary command line tags,
there is no <bootloader_stdin> or similar to provide standard
input to the boot loader.

Typical input could be something along the lines of e.g. the
following grub commands:

    kernel (cd)/path/to/vmlinuz some-cmdline
    initrd (root)/path/to/host/initrd
    boot

Using e.g. the (root) device is especially useful on the bhyve
driver when creating diskless VMs.

Before I start implementing this, I’d appreciate some feedback
on the following two points:

 1) should this be an attr on the <bootloader> tag, e.g.

    <bootloader_stdin=“/path/to/file”>/path/to/bootloader</bootloader>

    or rather, as there already exists a <bootloader_args> tag
    a separate <bootloader_stdin> tag?

 2) should the input be passed verbatim in the domain def,
    e.g. using a CDATA block or from a file? Should this be
    user-specified, e.g. in an attr?

    <bootloader_stdin from=“/path/to/file”/>

    <bootloader_stdin>
    <![CDATA[
      kernel (host)/path/to/kernel with cmdline
      initrd (host)/path/to/ramdisk
      boot
    ]]>
    </bootloader_stdin>

Regards,
Fabian

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