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「OpenZFS 不変バックアップ」の仕組み

#![forbid(unsafe_code)]

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ZfsSnapshotMeta {
    pub dataset: &'static str,
    pub snapshot_name: &'static str,
    pub txg_id: u64,
    pub creation_unix_sec: u64,
    pub hold_tag_active: bool,
    pub fletcher4_verified: bool,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RollbackPlan {
    ReadyForInstantRollback { target_txg: u64, rpo_seconds: u64 },
    RejectedMissingHoldLock,
    RejectedChecksumMismatch,
    NoValidSnapshotFound,
}

pub fn select_clean_rollback_target(
    snapshots: &[ZfsSnapshotMeta],
    attack_detected_unix_sec: u64,
) -> RollbackPlan {
    let mut best_candidate: Option<&ZfsSnapshotMeta> = None;

    for snap in snapshots {
        if snap.creation_unix_sec >= attack_detected_unix_sec {
            continue;
        }
        if !snap.fletcher4_verified {
            return RollbackPlan::RejectedChecksumMismatch;
        }
        if !snap.hold_tag_active {
            return RollbackPlan::RejectedMissingHoldLock;
        }
        match best_candidate {
            None => best_candidate = Some(snap),
            Some(prev) if snap.creation_unix_sec > prev.creation_unix_sec => {
                best_candidate = Some(snap);
            }
            _ => {}
        }
    }

    match best_candidate {
        Some(target) => RollbackPlan::ReadyForInstantRollback {
            target_txg: target.txg_id,
            rpo_seconds: attack_detected_unix_sec.saturating_sub(target.creation_unix_sec),
        },
        None => RollbackPlan::NoValidSnapshotFound,
    }
}