On Sat, Sep 20, 2025 at 04:29:57PM +0200, Paolo Bonzini wrote:
> Date: Sat, 20 Sep 2025 16:29:57 +0200
> From: Paolo Bonzini <[email protected]>
> Subject: [PATCH 6/7] rust: migration: implement ToMigrationState for Timer
> X-Mailer: git-send-email 2.51.0
>
> Timer is a complex struct, allow adding it to a struct that
> uses #[derive(ToMigrationState)]; similar to vmstate_timer, only
> the expiration time has to be preserved.
>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> rust/migration/src/migratable.rs | 31 +++++++++++++++++++++++++++++++
> 1 file changed, 31 insertions(+)
>
> diff --git a/rust/migration/src/migratable.rs
> b/rust/migration/src/migratable.rs
> index fa25317eea8..c4ad4f73d5c 100644
> --- a/rust/migration/src/migratable.rs
> +++ b/rust/migration/src/migratable.rs
> @@ -202,6 +202,37 @@ fn restore_migrated_state(
> ) -> Result<(), InvalidError>;
> }
>
> +impl ToMigrationState for util::timer::Timer {
> + type Migrated = i64;
This converts a Timer to i64, then we don't need vmstate_info_timer
anymore. Good idea.
> + fn snapshot_migration_state(&self, target: &mut i64) -> Result<(),
> InvalidError> {
> + // SAFETY: as_ptr() is unsafe to ensure that the caller reasons about
> + // the pinning of the data inside the Opaque<>. Here all we do is
> + // access a field.
> + *target = unsafe { &*self.as_ptr() }.expire_time;
C side checks timer_pending(), which ensures when the timer is
inactive, it always saves u64::MAX.
But now we save the expire_time directly in Rust. I think this would be
possible to break the migration from Rust timer to C timer, because at
C side, timer_get() checks whether expire_time is -1 and we can't ensure
expire_time won't store -2 (or other unusual negative values).
So maybe it's better to follow C side behavior to return u64::MAX for
non-pending case?
> + Ok(())
> + }
> +
> + fn restore_migrated_state_mut(
> + &mut self,
> + source: Self::Migrated,
> + version_id: u8,
> + ) -> Result<(), InvalidError> {
> + self.restore_migrated_state(source, version_id)
> + }
> +}
> +
> +impl ToMigrationStateShared for util::timer::Timer {
> + fn restore_migrated_state(&self, source: i64, _version_id: u8) ->
> Result<(), InvalidError> {
> + if source >= 0 {
This can work for the migration cases of C->Rust and Rust->Rust.
Thanks,
Zhao
> + self.modify(source as u64);
> + } else {
> + self.delete();
> + }
> + Ok(())
> + }
> +}
> +
> impl<T: ToMigrationStateShared, const N: usize> ToMigrationStateShared for
> [T; N]
> where
> [T::Migrated; N]: Default,
> --
> 2.51.0
>
