On Fri, 13 Sep 2013 12:22:13 +0100, Ian Campbell Ian.Campbell@citrix.com wrote:
On Fri, 2013-09-13 at 11:13 +0100, Grant Likely wrote:
On Wed, Sep 4, 2013 at 5:41 PM, Rob Herring robherring2@gmail.com wrote:
For u-boot Andre has proposed some syntactic sugar over the "fdt" command to make boot.scr more trivial to use. We would of course need to implement support for using it in the relevant distro tools (but they tend to be very distro/machine specific already, e.g. Debian's flash-kernel)
And being machine specific is a PITA. flash-kernel is certainly not something we want to expand on. There is not much love for boot.scr either. There is work to address what are not really machine differences, but largely vendor u-boot differences:
http://www.mail-archive.com/u-boot@lists.denx.de/msg119025.html
One option for u-boot which already supports syslinux style menu files is to adopt the syslinux multiboot parsing support:
Even building it into U-Boot is problematic because it leaves older machines out in the cold. Leif's port of Grub to U-Boot is far more interesting since the distro can now be in control of the code that loads the images and jumps into the kernel/hypervisor.
AIUI this is not being developed any further?
Last I checked the patches have been posted for merging, but it is stalled on the Grub maintainer. I believe he wanted to fix a bug on the raspberry pi before merging. Leif would know more. LEG isn't actively working on it anymore since UEFI is the priority, but I wouldn't call it abandoned.
We need to back-up and consider what this looks like in the end for all the pieces and get input from folks on grub, UEFI, and armv8. The UEFI answer may be this is a grub problem. For armv8, this proposal does match up well as the kernel boot interface for v8 is DT. Despite some claims, ACPI will not completely replace DT because of this.
Yes, for UEFI it is absolutely an OS loader problem. UEFI provides an API and runtime environment. Grub is in general moving towards a boot menu system and a tool for loading images. Actual booting however should be done by a separate OS loader application. For Linux, this will be an in-kernel UEFI Stub.
I'm not sure I follow your distinction between loading the images and "actual booting". If grub loads the images and Linux stub does the actual booting how does this stub locate the images which grub loaded?
(Note: this isn't implemented yet, but is in progress) The DTB will need to be passed via the UEFI system table. Initrd is passed by modifying the dtb with linux,initrd-* properties in the device tree.
In the Xen case, I think the original proposal is conceptually sound. I'll quibble about a couple of the details, but I'll address those with a reply to the original proposal. It makes perfect sense to use the same mechanism as the initrd properties to tell the kernel about additional blobs.
Or are you saying the stub should load the initramfs itself? How does it know where to find it? Having the kernel in one config file (grub's) and the initramfs in another (the Linux UEFI stub's) seems likely to result in things getting out of sync. Having Linux's stub parse the grub CFG is even less likely to work well IMHO.
The stub has the ability to load both the dtb and initrd itself by adding "dtb=" and "initrd=" arguments, but it is currently limited to loading images from the same filesystem that the kernel was loaded from. GRUB (or gummiboot/refind/etc) is potentially more flexible.
For Xen I would recommend taking the Linux EFI stub code and doing the same thing. There really isn't a need for a multiboot spec when you can rely on a runtime execution environment for setting things up exactly as you want them.
If this works for Linux on EFI then I see no reason it could work for Xen on EFI (assuming my questions above are just a result of my misunderstanding something)
But... Xen also wants to support non-server and therefore non-EFI systems i.e. u-boot. We also want to support v7 where EFI is not a given even for servers AIUI.
I was only responding to the UEFI question, but that aside, I don't see a problem with adding properties to the DT for telling Xen where they are.
Given that I think it is a given that Xen will have some sort of protocol along these lines, for use in these environments even if it does the EFI stub thing on EFI systems. The question is shall we make it more general and useful to others or just go our own way? I'd prefer to do the former.
Yes, make it general. GRUB and the EFI stub will use it.
g.
boot-architecture@lists.linaro.org
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Grant Likely