[RFC PATCH v2 2/4] liveupdate: Select file handler by name in the preserve ioctl

[sashiko-bot at kernel.org]

> Currently luo_preserve_file() iterates over luo_file_handler_list and
> picks the first registered handler whose .can_preserve() callback
> returns true. When a subsystem introduces a new, backwards-incompatible
> file handler alongside an existing one for the same file type, userspace
> has no way to choose which handler preserves a file descriptor, nor can
> the kernel keep the existing rollback-safe handler as the default while
> allowing callers to opt into the new handler.
> 
> Append char handler[LIVEUPDATE_HNDL_NAME_LENGTH] to struct
> liveupdate_session_preserve_fd immediately after token, keeping
> IOCTL_OP min_size at offsetofend(..., token) so callers passing the
> original 16-byte structure continue to work:
> - When handler is empty (all-zero, or zero-filled when userspace
>   passes the 16-byte structure), luo_preserve_file() selects the first
>   registered handler whose .can_preserve() callback accepts the fd.
> - When handler is non-empty, it must be null-terminated within
>   LIVEUPDATE_HNDL_NAME_LENGTH bytes (returning -EINVAL otherwise);
>   luo_preserve_file() looks up the registered handler with that exact
>   name (returning -ENOENT if unknown) and verifies that its
>   .can_preserve() callback accepts the fd (returning -EINVAL if not).
> 
> The retrieve ioctl is unchanged because the handler is identified by the
> name stored in the serialized payload from the source kernel.
> 
> Signed-off-by: Tarun Sahu <tarunsahu at google.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261021152527.375070-1-tarunsahu@google.com?part=2