On 18 January 2016 at 10:43, adrian15 <adrian15...@gmail.com> wrote: > El 18/01/16 a las 07:31, Michal Suchanek escribió: >> >> Hello, >> >> thanks for working on this. >>
> >> As to the primary and secondary bootloader - how is the efi bootloader >> secondary? It boots the same as the legacy bootloader. You probably >> want a concept of compatible bootloaders - that is pairs of >> bootloaders that can be installed alongside on the same medium. > > * What is it a secondary bootloader? > > It's what happens when you request mkisofs that your bootloader to be boot > in second place or as a second partition. I don't know how it actually > works. > > So in grub-efi we just add to the xorriso options: > > -eltorito-alt-boot \ > -e boot/grub/efi.img \ > -no-emul-boot \ > -isohybrid-gpt-basdat \ > -isohybrid-apm-hfsplus > > And in syslinux-efi (currently) we add: > > -eltorito-alt-boot \ > --efi-boot boot/efi.img \ > -append_partition 2 0x01 \ > binary/boot/efi.img -eltorito-alt-boot is not documented option of xorriso. For genisoimage -eltorito-alt-boot denotes start of new bootloader parameters. So any bootloader is made primary by leaving out -eltorito-alt-boot. > > . > > So, I guess the -eltorito-alt-boot does the magic but I'm not sure. Maybe > someone else can explain it better than me. > > > * About current compatible bootloaders. > The technology is there. I mean. This is what it's currently available: > > binary_grub-efi : Secondary bootloader > binary_grub-legacy : Primary bootloader > binary_grub-pc : Primary bootloader > binary_syslinux : Primary bootloader > binary_syslinux-efi : Secondary bootloader > > so that means, in theory you can request one of these 9 combinations: > > grub-legacy > grub-pc > syslinux > > grub-legacy,grub-efi > grub-pc,grub-efi > syslinux,grub-efi > > grub-legacy,syslinux-efi > grub-pc,syslinux-efi > syslinux,syslinux-efi You can probably use only one legacy bootloader but syslinux-efi and grub-efi use different files so it should be possible to install both. I am not sure how selecting one or the other would work, though. > >> Unless >> the user requests two bootloaders that are incompatible the medium can >> be created. >> >> Ignoring bootloaders is not a good idea. If the user requested >> something that is not possible the build should report an error and >> stop. > > Yeah, that it's hard to implement from the perspective of a single > bootloader script. So I decided not to implement it. > > You could add an additional script or function named: > check_compatible_bootable_pairs (as you propose) but then you need to > maintain that fictional database each time a new bootloader gets in. > > That's why I decide to avoid it using it. > > What it's straight-forward to implement is one of the only-secondary > bootloaders finding themselves as a primary bootloader and outputting a > warning message. But, I'm not sure what to put there as a warning. Any > suggestion? Unsupported bootloader combination or whatever. It should not be a warning however. The script should avoid making unbootable medium. Thanks Michal
