chore(deps): Bump rust-toolchain from 1.95.0 to 1.96.0

rust-toolchain.toml

@@ -11,7 +11,7 @@
 # allowlisted using a toolchain that requires it, causing the A/B-test to
 # always fail.
 [toolchain]
-channel = "1.95.0"
+channel = "1.96.0"
 targets = ["x86_64-unknown-linux-musl", "aarch64-unknown-linux-musl"]
 profile = "minimal"
 

src/firecracker/src/api_server/mod.rs

@@ -159,6 +159,8 @@ impl ApiServer {
                     &METRICS.latencies_us.diff_create_snapshot,
                     "create diff snapshot",
                 )),
+                // ADR 0045 off-pause flush — no dedicated latency metric.
+                SnapshotType::Msync | SnapshotType::MsyncAndState => None,
             },
             VmmAction::LoadSnapshot(_) => {
                 Some((&METRICS.latencies_us.load_snapshot, "load snapshot"))
@@ -277,6 +279,7 @@ mod tests {
                 snapshot_type: SnapshotType::Diff,
                 snapshot_path: PathBuf::new(),
                 mem_file_path: PathBuf::new(),
+                vmstate_only: false,
             })),
             start_time_us,
         );
@@ -290,6 +293,7 @@ mod tests {
                 snapshot_type: SnapshotType::Diff,
                 snapshot_path: PathBuf::new(),
                 mem_file_path: PathBuf::new(),
+                vmstate_only: false,
             })),
             start_time_us,
         );

src/firecracker/src/api_server/request/snapshot.rs

@@ -112,6 +112,8 @@ fn parse_put_snapshot_load(body: &Body) -> Result<ParsedRequest, RequestError> {
         network_overrides: snapshot_config.network_overrides,
         vsock_override: snapshot_config.vsock_override,
         clock_realtime: snapshot_config.clock_realtime,
+        shared: snapshot_config.shared,
+        uffd_base_file: snapshot_config.uffd_base_file,
     };
 
     // Construct the `ParsedRequest` object.
@@ -147,6 +149,7 @@ mod tests {
             snapshot_type: SnapshotType::Diff,
             snapshot_path: PathBuf::from("foo"),
             mem_file_path: PathBuf::from("bar"),
+            vmstate_only: false,
         };
         assert_eq!(
             vmm_action_from_request(parse_put_snapshot(&Body::new(body), Some("create")).unwrap()),
@@ -161,6 +164,23 @@ mod tests {
             snapshot_type: SnapshotType::Full,
             snapshot_path: PathBuf::from("foo"),
             mem_file_path: PathBuf::from("bar"),
+            vmstate_only: false,
+        };
+        assert_eq!(
+            vmm_action_from_request(parse_put_snapshot(&Body::new(body), Some("create")).unwrap()),
+            VmmAction::CreateSnapshot(expected_config)
+        );
+
+        let body = r#"{
+            "snapshot_path": "foo",
+            "mem_file_path": "bar",
+            "vmstate_only": true
+        }"#;
+        let expected_config = CreateSnapshotParams {
+            snapshot_type: SnapshotType::Full,
+            snapshot_path: PathBuf::from("foo"),
+            mem_file_path: PathBuf::from("bar"),
+            vmstate_only: true,
         };
         assert_eq!(
             vmm_action_from_request(parse_put_snapshot(&Body::new(body), Some("create")).unwrap()),
@@ -191,6 +211,8 @@ mod tests {
             network_overrides: vec![],
             vsock_override: None,
             clock_realtime: false,
+            shared: false,
+            uffd_base_file: None,
         };
         let mut parsed_request = parse_put_snapshot(&Body::new(body), Some("load")).unwrap();
         assert!(
@@ -223,6 +245,8 @@ mod tests {
             network_overrides: vec![],
             vsock_override: None,
             clock_realtime: false,
+            shared: false,
+            uffd_base_file: None,
         };
         let mut parsed_request = parse_put_snapshot(&Body::new(body), Some("load")).unwrap();
         assert!(
@@ -255,6 +279,8 @@ mod tests {
             network_overrides: vec![],
             vsock_override: None,
             clock_realtime: false,
+            shared: false,
+            uffd_base_file: None,
         };
         let mut parsed_request = parse_put_snapshot(&Body::new(body), Some("load")).unwrap();
         assert!(
@@ -296,6 +322,8 @@ mod tests {
             }],
             vsock_override: None,
             clock_realtime: false,
+            shared: false,
+            uffd_base_file: None,
         };
         let mut parsed_request = parse_put_snapshot(&Body::new(body), Some("load")).unwrap();
         assert!(
@@ -325,6 +353,8 @@ mod tests {
             network_overrides: vec![],
             vsock_override: None,
             clock_realtime: false,
+            shared: false,
+            uffd_base_file: None,
         };
         let parsed_request = parse_put_snapshot(&Body::new(body), Some("load")).unwrap();
         assert_eq!(

src/firecracker/swagger/firecracker.yaml

@@ -1621,9 +1621,19 @@ definitions:
         enum:
           - Full
           - Diff
+          - Msync
+          - MsyncAndState
         description:
           Type of snapshot to create. It is optional and by default, a full
-          snapshot is created.
+          snapshot is created. `Msync` flushes a MAP_SHARED file-backed guest
+          memory to its backing memfile via msync(MS_SYNC) without writing the
+          machine state; `MsyncAndState` also writes the state file.
+      vmstate_only:
+        type: boolean
+        description:
+          Write only the microVM state file and skip the guest-memory leg
+          entirely (mem_file_path is ignored). Incompatible with the
+          Msync/MsyncAndState snapshot types. Optional and defaults to false.
 
   NetworkOverride:
     type: object
@@ -1710,6 +1720,23 @@ definitions:
           elapsed since the snapshot was taken. When false (default), kvmclock resumes
           from where it was at snapshot time. This option may be extended to other clock
           sources and CPU architectures in the future."
+      shared:
+        type: boolean
+        description:
+          When set to true and the memory is restored from a file, map the guest
+          memory MAP_SHARED so guest writes flush back to the backing memfile (the
+          page-readable source for post-copy live migration). No effect for the UFFD
+          backend. Optional; defaults to false (MAP_PRIVATE).
+      uffd_base_file:
+        type: string
+        description:
+          Unified-memory-substrate base backing (engrams ADR 0045 v2b). When set
+          with the Uffd memory backend, guest memory is created as MAP_PRIVATE of
+          this shmem file instead of anonymous, and the UFFD registration uses
+          MISSING|MINOR. The external handler resolves base-identical pages with
+          UFFDIO_CONTINUE (page-cache sharing across same-template microVMs) and
+          divergent pages with UFFDIO_COPY; guest writes COW natively. Invalid
+          with the File backend. Optional.
 
 
   TokenBucket:

src/vmm/Cargo.toml

@@ -46,7 +46,8 @@ serde = { version = "1.0.228", features = ["derive", "rc"] }
 serde_json = "1.0.149"
 slab = "0.4.12"
 thiserror = "2.0.18"
-userfaultfd = "0.9.0"
+# linux5_13: RegisterMode::MINOR for the ADR 0045 substrate (v2b) registration.
+userfaultfd = { version = "0.9.0", features = ["linux5_13"] }
 utils = { path = "../utils" }
 uuid = "1.23.1"
 vhost = { version = "0.15.0", features = ["vhost-user-frontend"] }