+Tom
Hi Karl,
On 22 April 2015 at 13:05, Karl Apsite Karl.Apsite@dornerworks.com wrote:
Hi!
I work at DornerWorks with the Xen Hypervisor. We work with a variety of embedded systems, and we wanted to facilitate Xen's boot procedure through U-boot's Flattened Image Tree (FIT) format. I've already prototyped some of the functionality we were hoping to see, so we thought it'd be prudent to begin a discussion with denx to get your opinion on the matter,
First Objective: (Summary of what was prototyped) A Flattened Image Tree is capable of holding all of the necessary binaries already, so we only need to make a quick change to allow u-boot to load an extra binary (in this case, a linux kernel) so that Xen can boot and load the kernel when it's ready. I started by simply adding a line in the configuration of my tree-source (.its) to look like:
config@1 { description = "Xen 4.6.0-unstable configuration"; kernel = "xen_kernel@1"; fdt = "fdt@1"; gen_bin0 = "linux_kernel@1"; };
I investigated what effort would be needed to load the additional binary.
Booting Xen is easy (only a kernel and fdt are required), but Xen will look at a hard-coded memory address to try a load a linux kernel. This has to be placed in memory by u-boot. The only major addition I needed, was to make u-boot care about a config option named "generic-binary" and load it, no questions asked. I chose the name "generic binary" as I simply needed u-boot to load a [thing] without any additional behavior. I'm using it to specifically load a linux kernel at a specific memory address in preparation for xen, but there could be potential future uses, hence the ambiguous name.
I wonder whether you should add a new type for the target kernel? General binary seems a bit vague. Just a thought.
The hack is pretty simple, as most everything was in place to boot xen, and it took a little extra legwork to make u-boot care about my gen_bin. I added the necessary structure to load another object using ramdisk functions as examples. By loading a separate binary, Xen was able to boot, and successively boot Linux as expected. If you have any thoughts on this process overall, we'd like to take your concerns into consideration.
For a little more fun, I extended out the configuration to be able to load N number of generics.
Affected Files: common/bootm.c common/image-fit.c common/image.c doc/uImage.FIT/source_file_format.txt include/configs/xilinx_zynqmp.h include/image.h
Second Objective: While I was there, I noticed that u-boot's binary loading logic isn't as modular as I first expected. Most objects eventually boil down to a boot_get_<thing>(). Example: boot_get_ramdisk() or boot_get_kernel(). These functions are all very similar as they handle the various u-boot image types and load their specific binary. The functions appear to have grown similar in structure and operation overtime. I don't think it is too much to reduce the duplicated structure of the functions into a common boot_get_object() function, while replacing some of the extra function wrappings.
Some quick diagrams to explain what I mean Initial: http://i.imgur.com/H44dXmN.png (29KB) Refactor: http://i.imgur.com/apEpyWz.png (24KB)
SGTM.
The refactor will likely effect the following files, several of which contain trivial name changes, or small changes in a variable type. arch/arm/lib/bootm.c arch/avr32/lib/bootm.c arch/microblaze/lib/bootm.c arch/mips/lib/bootm.c arch/nds32/lib/bootm.c arch/nios2/lib/bootm.c arch/openrisc/lib/bootm.c arch/powerpc/lib/bootm.c arch/sh/lib/bootm.c arch/sparc/lib/bootm.c arch/x86/lib/bootm.c common/bootm.c common/bootm_os.c common/cmd_bootm.c common/image-fdt.c common/image.c include/bootm.h include/image.h
Summary 1.) RFC: What is the opinion on implementing a FIT configuration option to permit a FIT to boot Xen
Seems OK to me.
2.) RFC: What is the opinion on a potential refactor concerning the image-loading functions (boot_get_ramdisk, boot_get_kernel, etc) in order to unify them into one common boot_get_object() function.
That would be good. I spent a bit of time refactoring the code to reduce duplication - fit_image_load() was one of the results of that. If you think the code is duplicated now you should have seen it before :-)
Probably 'boot_get_image()' is better than 'boot_get_object()' given the current naming.
Please do add tests for the new functionality - see test/image for some existing tests. Python is preferred if the test is non-trivial.
Regards, Simon