Re: [PATCH v1 1/2] eventfd: luo: luo support for preserving eventfd

[Pratyush Yadav]

On Thu, Jun 25 2026, Chenghao Duan wrote:

> This patch adds support for preserving eventfd file descriptors across
> kexec live updates using the Live Update Orchestrator (LUO) framework.
> Userspace applications using eventfd for event notification can now
> maintain their state across kernel updates.
>
> Preserved State:
> The following properties of the eventfd are preserved across kexec:
> - Counter Value: The current 64-bit counter value, including any pending
>   events that have been signaled but not yet consumed by readers.
> - File Flags: The creation flags (EFD_SEMAPHORE, EFD_CLOEXEC, EFD_NONBLOCK)
>   are preserved.
>
> Non-Preserved State:
> - File Descriptor Number: The eventfd will be assigned a new fd number
>   in the target process after restore.
> - Wait Queue State: Any processes blocked on read() operations will be
>   woken up and need to re-establish their blocking state.
> - All other internal state is reset to default.
>
> Changes:
> - fs/eventfd.c: Add eventfd_luo_get_state() to safely read eventfd state
>   (count and flags), and eventfd_create() helper function.
> - fs/eventfd_luo.c: New file implementing LUO file operations:
>   preserve, freeze, unpreserve, retrieve, and finish callbacks.
> - include/linux/eventfd.h: Export new functions.
> - include/linux/kho/abi/eventfd.h: Define the ABI contract with
>   eventfd_luo_ser structure for serialization.

Why do you need to preserve this? Why don't you create a fresh one after
kexec? You just preserve the counter, which looks pretty much useless.
You can just as well open a new eventfd after kexec and set the counter
value if you care about it.

[...]

-- 
Regards,
Pratyush Yadav