Booting Xen from a FIT - Additional discussion about a refactor

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 at 1 {
    description = "Xen 4.6.0-unstable configuration";
    kernel = "xen_kernel at 1";
    fdt = "fdt at 1";
    gen_bin0 = "linux_kernel at 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.

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)

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

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.

+Tom

Hi Karl,

Quoted 24 lines · Karl Apsite

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 at 1 {
    description = "Xen 4.6.0-unstable configuration";
    kernel = "xen_kernel at 1";
    fdt = "fdt at 1";
    gen_bin0 = "linux_kernel at 1";
};

I investigated what effort would be needed to load the additional binary.

Quoted 8 lines

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.

Quoted 11 lines

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.

Quoted 19 lines

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.

Quoted 3 lines

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.

Quoted 22 lines

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

Quoted 3 lines

Summary
1.) RFC: What is the opinion on implementing a FIT configuration option to permit a FIT to boot Xen

Seems OK to me.

Quoted 3 lines

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

Quoted 38 lines · Simon Glass

+Tom

Hi Karl,

Quoted 24 lines · Karl Apsite

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 at 1 {
    description = "Xen 4.6.0-unstable configuration";
    kernel = "xen_kernel at 1";
    fdt = "fdt at 1";
    gen_bin0 = "linux_kernel at 1";
};

I investigated what effort would be needed to load the additional binary.

Quoted 8 lines

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.

Quoted 2 lines

I wonder whether you should add a new type for the target kernel? General binary seems a bit vague. Just a thought.

I do agree, I don't really like the term "generic binary" either.

When preparing to boot Xen, u-boot needs to take a binary, and simply put it in place. Unlike the other images/objects (kernel, fdt, ramdisk, etc) u-boot's role is very simple in this regard: "Take these bits, and make sure they go over here."

In this scenario, the action taken by u-boot should be agnostic to what the image actually is. U-boot should simply move a binary, without any additional behavior. This led me to choose a name just as generic.

Maybe changing the name to "Loadable(s)" would sound a bit better, but going so far as to name it "kernel" could be misleading.

Quoted 11 lines

Quoted 11 lines

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.

This plan was part of the reason we were trying to keep the name more generic. Keeping it generic allows for people other than xen users to take advantage of the new feature in various ways.

Quoted 62 lines

Quoted 19 lines

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.

Quoted 3 lines

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.

Quoted 22 lines

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

Quoted 3 lines

Summary
1.) RFC: What is the opinion on implementing a FIT configuration option to permit a FIT to boot Xen

Seems OK to me.

Quoted 3 lines

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 :-)

Quoted 5 lines

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.

Absolutely, I'll be sure to include some tests in the patch(es).

Hi Karl,

Quoted 50 lines · Karl Apsite

Quoted 38 lines · Simon Glass

+Tom

Hi Karl,

Quoted 24 lines · Karl Apsite

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 at 1 {
    description = "Xen 4.6.0-unstable configuration";
    kernel = "xen_kernel at 1";
    fdt = "fdt at 1";
    gen_bin0 = "linux_kernel at 1";
};

I investigated what effort would be needed to load the additional binary.

Quoted 8 lines

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.

Quoted 2 lines

I wonder whether you should add a new type for the target kernel? General binary seems a bit vague. Just a thought.

I do agree, I don't really like the term "generic binary" either.

When preparing to boot Xen, u-boot needs to take a binary, and simply put it in place. Unlike the other images/objects (kernel, fdt, ramdisk, etc) u-boot's role is very simple in this regard: "Take these bits, and make sure they go over here."

Quoted 3 lines

In this scenario, the action taken by u-boot should be agnostic to what the image actually is. U-boot should simply move a binary, without any additional behavior. This led me to choose a name just as generic.

What is this additional behaviour you are referring to?

Quoted 83 lines

Maybe changing the name to "Loadable(s)" would sound a bit better, but going so far as to name it "kernel" could be misleading.

Quoted 11 lines

Quoted 11 lines

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.

This plan was part of the reason we were trying to keep the name more generic. Keeping it generic allows for people other than xen users to take advantage of the new feature in various ways.

Quoted 62 lines

Quoted 19 lines

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.

Quoted 3 lines

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.

Quoted 22 lines

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

Quoted 3 lines

Summary
1.) RFC: What is the opinion on implementing a FIT configuration option to permit a FIT to boot Xen

Seems OK to me.

Quoted 3 lines

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 :-)

Quoted 7 lines

Quoted 5 lines

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.

Absolutely, I'll be sure to include some tests in the patch(es).

Great. This area of U-Boot has had a lot of undocumented or untested behaviour. It has got a bit better but your boot function sounds like another step in the right direction.

Regards,
Simon

Quoted 57 lines · Simon Glass

Hi Karl,

Quoted 53 lines · Karl Apsite

Quoted 38 lines · Simon Glass

+Tom

Hi Karl,

Quoted 24 lines · Karl Apsite

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 at 1 {
    description = "Xen 4.6.0-unstable configuration";
    kernel = "xen_kernel at 1";
    fdt = "fdt at 1";
    gen_bin0 = "linux_kernel at 1";
};

I investigated what effort would be needed to load the additional binary.

Quoted 8 lines

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.

Quoted 2 lines

I wonder whether you should add a new type for the target kernel? General binary seems a bit vague. Just a thought.

I do agree, I don't really like the term "generic binary" either.

When preparing to boot Xen, u-boot needs to take a binary, and simply put it in place. Unlike the other images/objects (kernel, fdt, ramdisk, etc) u-boot's role is very simple in this regard: "Take these bits, and make sure they go over here."

In this scenario, the action taken by u-boot should be agnostic to what the image actually is. U-boot should simply move a binary, without any additional behavior. This led me to choose a name just as generic.

Quoted 1 line

What is this additional behaviour you are referring to?

In each of the existing boot_get_<thing> functions, I saw that U-boot stores various addresses in the images parameter: bootm_headers_t *images. I am making an assumption that these addresses are used later for any possible "additional behaviors." That could very well be a misunderstanding, but I thought those addresses are used by u-boot later in the boot process.