On 09/11/2014 03:10 AM, Adam Williamson wrote:

On Wed, 2014-09-10 at 15:16 -0400, Gene Czarcinski wrote:

Question:  Why isn't this an alpha blocker. RHBZ#1108296 has a patch 
which fixes the problem.

Well, because we don't have a criterion. Which is kinda what the thread
is about. ;) But in general, multiboot isn't an Alpha issue; remember
Alpha requirements are fairly minimal, Alpha is very much a *test*
release, intended for deployment into controlled testing environments,
hence probably not onto production systems with other OSes. We have to
keep the Alpha requirements realistic.

Well, not an alpha blocker but this should be fixed sooner rather than later.

As I said, I have stopped using os-prober and switched to using /etc/grub.d/40_custom to support multiboot (even when the other system is Windows). However, the problem identified in rhbz #1108296 and #1108344 is in response to changes included with grub2-2.02. The change to grub2 was in response to rhbz #880840. Unfortunately, rhbz#880840 is not viewable by me so I have no idea of the reasoning behind the change except from the simple comment in the patch:

The kernel group really would prefer that we use the 16 bit entry point
on x86 bios machines.

As of now, this change appears to be unique to Fedora 21, RHEL 7, and CentOS 7. The problem is that this breaks /etc/grub.d/30_os-prober. The proposed patches to os-prober and grub2 has os-prober returning more information to 30_os-prober so that linux, linux16, or linuxefi (and initrd, initrd16, or initrdefi) is used. You will be able to boot older systems (which do not use the new linux16/initrd16) via the 30_os-prober created entries but you will not able to boot the new system (using linux16/initrd16) from the old system. Previously installed releases of Fedora will be unable to boot the new system although the new system will be able to boot the older releases.

Has the patch forcing the use of 16 bit modules been sent (and accepted) upstream? If not, then Fedora/Red Hat are the responsible parties.

My preferred option is to have the current implementation of /etc/grub.d/30_os-prober and the os-prober package go away and be replaced by something which creates something like:

menuentry "Fedora 20 on sda3 and root on btrfs=root3" { configfile (hd0,3)/grub2/grub.cfg }
Just trying to get this fixed so that anaconda and Fedora 21 does not get blaimed for being able to multiboot.

Gene