Re: Grub-install documentation or override?

[mgreger]

---- Andrei Borzenkov <address@hidden> wrote: 
> В Fri, 26 Jun 2015 12:35:09 +0000
> <address@hidden> пишет:
> 
> > 
> > ---- Andrei Borzenkov <address@hidden> wrote: 
> > > В Thu, 25 Jun 2015 17:20:23 +0000
> > > <address@hidden> пишет:
> > > 
> > > > I have a 15GB image file partitioned using fdisk with a single MBR 
> > > > partition and containing an ext4 file system which contains my LFS 
> > > > system. I used kpartx on this to create /dev/loop0 and 
> > > > /dev/mapper/loop0p1. The file system in /dev/loop0p1 is mounted on 
> > > > /mnt. I am chrooted into /mnt
> > > 
> > > How exactly? chroot must have at least /dev, /sys and /proc available
> > > for device detection to work. 
> > > 
> > 
> > Thanks for the help.
> > 
> > Following the LFS instructions, I create mountpoints before entering the 
> > chroot environment:
> > 
> > mount -v --bind /dev /mnt/dev
> > mount -vt devpts devpts /mnt/dev/pts -o gid=5,mode=620
> > mount -vt proc proc /mnt/proc
> > mount -vt sysfs sysfs /mnt/sys
> > mount -vt tmpfs tmpfs /mnt/run
> > 
> > 
> > >  where my LFS system resides. Grub in the LFS system was built with the
> > >  following (from LFS documentation):
> > > > 
> > > > ./configure --prefix=/usr          \
> > > >             --sbindir=/sbin        \
> > > >             --sysconfdir=/etc      \
> > > >             --disable-grub-emu-usb \
> > > >             --disable-efiemu       \
> > > >             --disable-werror
> > > > 
> > > > Command used:
> > > >  grub-install --target=i386-pc /dev/loop0
> > > >
> > > 
> > > I do not have environment to test chroot, but the following works
> > > using current upstream master (sans two clean up patches):
> > > 
> > > address@hidden:~> sudo losetup --find --show /tmp/floppy
> > > /dev/loop0
> > > address@hidden:~> sudo kpartx -a /dev/loop0
> > > address@hidden:~> sudo mount /dev/mapper/loop0p2 /mnt
> > > address@hidden:~/build/grub> ./configure ; make
> > > address@hidden:~/build/grub> sudo pkgdatadir=$PWD ./grub-install -d 
> > > grub-core --boot-directory=/mnt /dev/loop0
> > > Installing for i386-pc platform.
> > > Installation finished. No error reported.
> > > address@hidden:~/build/grub> 
> > > 
> > > As Jordan suggested, you may be missing libdevmapper dependency.
> > >  
> > 
> > 
> > 
> > It does not appear libdevmapper is a part of LFS.
> 
> Then no kpartx would be possible at all. Where do you think /dev/mapper
> devices come from?
>


I think you misunderstood.
kpartx is run from the host Debian system. It has the mapper but does not have 
grub. The LFS system has grub, but does not have libdevmapper.



>  I could be wrong, but I don't see it anywhere.
> > 
> > I don't understand why grub-install needs to find the partition 
> > /dev/mapper/loop0p1 at all. Surely all it needs to do is install to the MBR 
> > of /dev/loop0 and the embedded space before the first partition. Why would 
> > it need anything other than the device name /dev/loop0 ?
> > 
> 
> Because it needs to know which drivers are requires to access $prefix;
> whether $prefix is on the same drive as primary boot sector; which
> partition $prefix is in; etc etc etc
> 

I'm not sure exactly what you are referring to with $prefix.
Is there no way to manually tell grub that information, rather than have it try 
(unsuccessfully) to auto-detect it?
There should always be a way to manually override any kind of auto-detection 
logic, IMHO.


> > Assuming libdevmapper is not an option, how could I bypass grub-install, 
> > also assuming my /boot/grub directory is empty at start?
> 
> Try partitioned loop - losetup -P ...


I've never heard of that option. I will see if it works.


> 
> > I know a bunch of files in /usr/lib/grub/i386-pc need to be copied to 
> > /boot/grub/i386-pc and LFS provides a simple grub.cfg. Beyond that I'm lost 
> > as to what arguments to grub-mkimage and grub-setup would allow me to build 
> > a core.img and apply it directly to /dev/loop0, to work around the problem.
> > 
> > Thanks for the help.
> > 
> > 
> > > > When that failed, I also tried a number of variations on this command, 
> > > > all of which also failed. I tried following examples on the net 
> > > > regarding creating a device.map and populating it with (hd0) /dev/loop0
> > > > Grub seems to read the file OK, but the install still fails.
> > > > 
> > > > The host machine is a 64-bit install of Debian 8, although that 
> > > > shouldn't matter.
> > > > 
> > > > If I do this on a real drive instead of a mounted image it works, but 
> > > > that doesn't help me. Shouldn't it be possible to install grub to a 
> > > > loopback device?
> > > > 
> > > > Thanks in advance for any help.
> > > > 
> > > > 
> > > > 
> > > > 
> > > > ---- Andrei Borzenkov <address@hidden> wrote: 
> > > > > Please, describe your configuration, and provide exact command you 
> > > > > used. Otherwise it is impossible to say anything.
> > > > > 
> > > > > Отправлено с iPhone
> > > > > 
> > > > > > 25 июня 2015 г., в 14:43, <address@hidden> <address@hidden> 
> > > > > > написал(а):
> > > > > > 
> > > > > > I absolutely cannot get grub-install to do what I need it to do: 
> > > > > > Install to the MBR on a disk image that is loop mounted with 
> > > > > > kpartx, while chrooted into an ext4 filesystem on the first 
> > > > > > partition of that image. The image will be used on a BIOS machine 
> > > > > > but the physical host is EFI.
> > > > > > 
> > > > > > This is for a linux from scratch 7.7 build and so uses the grub 
> > > > > > version found here: 
> > > > > > http://alpha.gnu.org/gnu/grub/grub-2.02~beta2.tar.xz
> > > > > > 
> > > > > > I discovered the "target" argument to override the architecture by 
> > > > > > searching the web (it doesn't seem to be mentioned in any detail in 
> > > > > > the Grub manual), but I can't get it to install regardless. I get 
> > > > > > some nonsensical message about being unable to find 'lvm/loop0p1' 
> > > > > > although I am not using lvm in the image. The image only has a 
> > > > > > single MBR partition.
> > > > > > 
> > > > > > This seems like it should be a simple thing to do and if it is I 
> > > > > > apologize, but I really hate it when software tries to be clever in 
> > > > > > an effort to 'help' and makes assumptions that turn a simple matter 
> > > > > > into a nightmare.
> > > > > > 
> > > > > > _______________________________________________
> > > > > > Help-grub mailing list
> > > > > > address@hidden
> > > > > > https://lists.gnu.org/mailman/listinfo/help-grub
> > > > 
> > > 
> > 
>