Re: [RFC PATCH 0/2] Add support for multiple versions to KHO

0/2 is a typo, should be 0/4 :-)

On Fri, Jul 31, 2026 at 2:53 PM Logan Odell <[email protected]> wrote:

> The format of the preserved-data blob that LUO saves to KHO is expected
> to change as new features are added, bugs are fixed, etc. Currently,
> LUO handles this by embedding a compatibility string into struct luo_ser
> which can be used to compare two kernels. This works if the changes
> between kernels are fundamentally incompatible. In a case where a new
> feature is added, we may want to support both versions in the new
> kernel to retain compatibility.
>
> This series adds a KHO interface to embed multiple versions under a
> single node in a subtree.
>
> We go from something like:
>
>        / (Root Node)
>        └── LUO (Legacy Parent Node)
>            ├── preserved-data = <0xphys_luo>
>            └── blob-size = <0xsize_luo>
>
> To something like this:
>
>        / (Root Node)
>        └── LUO (Versioned Parent Node)
>            ├── 1 (Version 1 Node)
>            │   ├── preserved-data = <0xphys_luo_v1>
>            │   └── blob-size = <0xsize_luo_v1>
>            └── 2 (Version 2 Node)
>                ├── preserved-data = <0xphys_luo_v2>
>                └── blob-size = <0xsize_luo_v2>
>
> We can also support mixed mode, allowing backwards compatibility in case
> of a roll-back to a pre-multi version kernel:
>
>        / (Root Node)
>        └── LUO (Versioned Parent Node)
>            ├── preserved-data = <0xphys_luo>
>            ├── blob-size = <0xphys_luo>
>            ├── 1 (Version 1 Node)
>            │   ├── preserved-data = <0xphys_luo_v1>
>            │   └── blob-size = <0xsize_luo_v1>
>            └── 2 (Version 2 Node)
>                ├── preserved-data = <0xphys_luo_v2>
>                └── blob-size = <0xsize_luo_v2>
>
> The first patch moves some common functionality for preserving a node
> into a separate function. The second patch adds our new APIs. The third
> patch adds support for multiple versions to the debugfs entries. The
> forth patch adds new test cases to test_kho.
>
> Logan Odell (4):
>   kho: Move subtree blob logic to separate function
>   kho: Add support for multiple versions in subtrees
>   kho: Add support for multiple versions to debugfs
>   kho: Add test cases for versioned subtrees
>
>  include/linux/kexec_handover.h             |  14 ++
>  include/linux/kho/abi/kexec_handover.h     |  16 ++
>  kernel/liveupdate/kexec_handover.c         | 234 +++++++++++++++++-
>  kernel/liveupdate/kexec_handover_debugfs.c |  57 ++++-
>  lib/test_kho.c                             | 266 +++++++++++++++++++--
>  5 files changed, 540 insertions(+), 47 deletions(-)
>
> --
> 2.55.0.508.g3f0d502094-goog
>
>