Hi Pratyush,
On 10.12.25 20:26, Pratyush Yadav wrote:
As live update evolves, there will be a need to update the serialization
formats for the different file types. This could be for adding new
features, for supporting a change in behaviour, or to fix bugs.
If the current kernel does not understand the same set of versions as
the next kernel, live update will inevitably fail. The next kernel will
be unable to understand the handed over data and will be unable to
restore memory, devices, IOMMU page tables, etc.
List the set of versions the kernel understands in a section in vmlinux.
This can then be used by userspace tooling to make sure the set of file
descriptors it uses have the same version between both kernels. If there
is a mismatch, the tooling can catch this early and abort live update
before it is too late.
The versions are listed in a section called ".liveupdate_versions". The
section has a header that contains a magic number and the version of the
data format. The list of version strings directly follow this header.
Only the version strings are listed, and it is up to userspace to map
them to file descriptor types.
The format of the section has the same ABI rules as the rest of LUO ABI.
Introduce a LIVEUPDATE_FILE_HANDLER macro that makes it easy to define a
file handler while also adding its version string to the right section.
Signed-off-by: Pratyush Yadav <[email protected]>
To support multi-version preservation and resume, how about you add a
"profile" hint to the handlers? Then you can tag the handlers with
"current" and a "previous". You then expose one section table with
supported versions per profile. And that means you can from user space
select the local profile to serialize and match that against the target
profile of the target system.
It also allows you to support more "profiles", such as elaborate
downstream version combinations, that upstream will not have to care about.
Alex
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