[syslinux] sys/extlinux booting of kernel on different partition (two linux installs)

[james harvey]

I have LVM volumes:
/dev/disk1/main
/dev/disk1/mainboot
/dev/disk1/other
/dev/disk1/otherboot

I can boot main by using syslinux with syslinux.cfg including:
LABEL main
   MENU LABEL Main
   LINUX ../vmlinuz-linux
   APPEND root=UUID={UUID} {kernel parameters}
   INITRD ../initramfs-linux.img

(1) I see a lot of places saying syslinux can't boot a kernel on
another partition, and that you have to use extlinux for this.  But,
then http://www.syslinux.org/wiki/index.php/Install says "[4.00+]
EXTLINUX has been merged into SYSLINUX, and both use 'ldlinux.sys' as
bootloader file."  Does this mean syslinux can now boot a kernel on
another partition?  Or, am I misunderstanding the scope of the merge,
and do I still need to use extlinux?

(2) What is the label I need to give in the .cfg to boot
/dev/disk1/otherboot/vmlinuz-linux?

(3) Can I just have one installation of syslinux, or do I need to
chain load a second?  If so, how do I do this, using LVM volumes?  The
syntax I see documented is "com32 chain.c32 \ append hd0 0" which
doesn't apply to LVM.  My preference is one installation of syslinux,
but I can chain load if necessary.


In case it's material, I want to have an arch installation on main and
another on other.  Not worth going into reasons.  I need their
respective boot partitions separate, because I'm using compressed
btrfs on main and other, which syslinux can't boot off, so their boot
partitions have to be uncompressed.