Re: Netboot support for kernels > 6mb

[ppc-dev@storix.com]

On Thursday 28 July 2005 08:25 pm, Ethan Benson wrote:
> On Thu, Jul 28, 2005 at 12:17:06PM -0700, ppc-dev@storix.com wrote:
> > The current version of yaboot support network boot for kernel and initrd
> > images that are < 6mb. There is a hard coded limit in fs_of.c
> >
> > #define LOAD_BUFFER_POS     0x600000
> > /* this cannot be safely increased any further */
> > #define LOAD_BUFFER_SIZE    0x600000
> >
> >
> > I would like to request to the community or anyone who is willing to work
> > on this issue to see if we can increase this to 10mb (8mb at least).
> > Stock RH kernel images are stripped and fall well below this limit,
> > however a stock SuSE kernel is already over the 6mb limit. This means
> > that to netboot a SuSE system you must create a zImage.initrd and boot
> > directly from OF. I would be willing to test/help out as much as I can,
> > however, this is over my head.
> >
> > Even if I can get some insight (specifically) as to why "this cannot be
> > safely increased any further". There was a patch made by Redhat to
> > increase it to 8mb, but that patch caused yaboot to fail to load the
> > etc/yaboot.conf file.
>
> hence the comment saying were at the limits of how far this can go,
> with this codebase anyway.

I would like to get a better understanding of why this limitation exists. This 
information would be helpful to get a jump start at the problem. I suspect 
that the available area of memory is only 12mb and this has been split at 6 x 
2. Since the size of the initrd can be changed easier than the kernel, it 
might be helpful to incorporate some logic into the max size and calculate 
the max size for the initrd based on the amount of memory left over after 
bringing across the kernel. (8 + 4 or 7 + 5 etc.) Again, I am grasping at 
straws and would like to get some information. 

>
> > Essentially the netboot features of yaboot are useless for some distros
> > and I feel will become useless for others as the size of the kernel
> > images increase.
>
> the distros need to trim thier kernels, its still possible to do that.
>
> alternativly someone could provide some hard-core active work on
> rewriting yaboot and completing prom-libc.