UKI: document the case of multiple Device Trees #71
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specs/unified_kernel_image.md
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| @@ -48,7 +48,7 @@ UKIs consist of the following resources: | |||
| * Optionally, information describing the OS this kernel is intended for, in the `.osrel` section. The contents of this section are derived from `/etc/os-release` of the target OS. They can be useful for presentation of the UKI in the boot loader menu, and ordering it against other entries using the included version information. | |||
| * Optionally, information describing kernel release information (i.e. `uname -r` output) in the `.uname` section. This is also useful for presentation of the UKI in the boot loader menu, and ordering it against other entries. | |||
| * Optionally, a splash image to bring to screen before transitioning into the Linux kernel, in the `.splash` section. | |||
| * Optionally, a compiled Devicetree database file, for systems which need it, in the `.dtb` section. | |||
| * Optionally, one or more compiled Device Trees, for systems which need it, each in its separate `.dtb` section. | |||
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Can you add a sentence after this itemized list that says something like this:
"Note that all of the sections defined above are singletons: they may appear once at most – except for the .dtb section which may be appear more than once."
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Also, this should say what it means if multiple .dtb sections exist. i.e. that one is picked according to some rule of picking the most appropriate one. I wouldn't define what the algorithm to pick it is, but it certainly deserves mention that only one is picked, and not all.
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Where would the selection algorithm live? In the stub which is part of the UKI? Which would be available to make the selection? From the DT perspective, there's there top-level compatible, which declares which "boards" are compatible with this DTB, for example By searching through this list, compatible string changes can also be accomodated. |
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As of now the selection algorithm is in the stub, and it just tries to match the first compatible in both the UKI FDTs and the firmware provided one. However I do agree that it would be useful to search through the lists and match that way. If others feel the same way then I can implement it in the stub |
specs/unified_kernel_image.md
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| @@ -48,11 +48,13 @@ UKIs consist of the following resources: | |||
| * Optionally, information describing the OS this kernel is intended for, in the `.osrel` section. The contents of this section are derived from `/etc/os-release` of the target OS. They can be useful for presentation of the UKI in the boot loader menu, and ordering it against other entries using the included version information. | |||
| * Optionally, information describing kernel release information (i.e. `uname -r` output) in the `.uname` section. This is also useful for presentation of the UKI in the boot loader menu, and ordering it against other entries. | |||
| * Optionally, a splash image to bring to screen before transitioning into the Linux kernel, in the `.splash` section. | |||
| * Optionally, a compiled Devicetree database file, for systems which need it, in the `.dtb` section. | |||
| * Optionally, one or more compiled Device Trees, for systems which need it, each in its separate `.dtb` section. If multiple .dtb sections exist then one of them is selected according to an implementation specific algorithm. | |||
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"implementation-specific" (with dash).
specs/unified_kernel_image.md
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| * Optionally, the public part of a public-private key pair in PEM format used to sign the image, in the `.pcrpkey` section. | ||
| * Optionally, a signature made using the abovementioned key pair, in the `.pcrsig` section. | ||
| * Optionally, a JSON file encoding expected PCR 11 hash values seen from userspace once the UKI has booted up, along with signatures of these expected PCR 11 hash values, in the `.pcrsig` section. The signatures must also match the abovementioned key pair. | ||
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| Note that all of the sections defined above are singletons: they may appear once at most – except for the .dtb section which may be appear more than once. |
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Thank you for the review comments, I have addressed these points in the updated push
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Specify how the case of multiple Device Trees is to be handled.
In connection with the discussion in 1 this pull request specifies how the case of multiple Device Trees is to be handled by choosing to append all additional Device Trees in the same .dtb section.