bootloader API and dual boot

[Thomas Danckaert]

Hi Guix,

I had to update my system configuration, which contains a boot menu entry for another 
distribution, to use the new bootloader API, but the manual section on dual boot 
configuration (https://www.gnu.org/software/guix/manual/guix.html#index-dual-boot) was 
not updated for this new API.  I would send a patch myself, but I'm afraid I don't really 
understand the “boot-parameters” record well enough (e.g. things like “root-device” vs 
“store-device” confuse me, and I don't know what "boot-name" means).  Can you 
help me?

Currently, the manual states that extra menu entries can be added as a list of 
<menu-entry> records like the following:

(menu-entry
 (label "The Other Distro")
 (linux "/boot/old/vmlinux-2.6.32")
 (linux-arguments '("root=/dev/sda2"))
 (initrd "/boot/old/initrd"))

but menu-entry is specific to grub (and no longer exported from the grub module).  I 
got it to work using a list of <boot-parameters> instead, like the following:

(boot-parameters
 (label "The Other Distro")
 (kernel "/boot/old/vmlinux-2.6.32")
 (kernel-arguments '("root=/dev/sda2"))
 (initrd "/boot/old/initrd")
 (store-device (uuid "xyz"))
 (store-mount-point "/")
 (boot-name #f) ; unnecessary?
 (root-device (uuid "xyz")) ; unnecessary?
)

So I suppose the manual should be changed to reflect this.

I have the impression that “boot-name”, “store-mount-point” and “root-device” are not 
used for a dual boot config record, but I had to add them to get guix system to 
accept my configuration (because there are no default entries for these fields?).  
Also, the names “store-device” and “store-mount-point” are a bit confusing for a 
non-GuixSD distribution (which doesn't necessarily have a store) (or I completely 
misunderstand them :-) ).  Am I right that some of those fields are redundant for 
dual boot configurations?  Can we add default values for some of 
<boot-parameters>'s fields?

Thanks!

Thomas