fix: use temporary buffer for loading vmstate file

In commit e7504ae ("refactor: cleanup vmm::snapshot module"),
firecracker started reading the snapshot vmstate file in a single pass
instead of first loading it into a Vec and then deserializing. This
seems to have caused some performance regression due to the deserializer
doing many successive reads, resulting in many read(2) syscalls.
Fix this by going back to first reading the snapshot file into a buffer,
and then deserializing from slice instead.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/arch/aarch64/regs.rs

@@ -547,7 +547,9 @@ mod tests {
         let mut buf = vec![0; 10000];
 
         Snapshot::new(&v).save(&mut buf.as_mut_slice()).unwrap();
-        let restored: Aarch64RegisterVec = Snapshot::load(&mut buf.as_slice()).unwrap().data;
+        let restored: Aarch64RegisterVec = Snapshot::load_without_crc_check(buf.as_slice())
+            .unwrap()
+            .data;
 
         for (old, new) in v.iter().zip(restored.iter()) {
             assert_eq!(old, new);
@@ -576,7 +578,7 @@ mod tests {
 
         // Total size of registers according IDs are 16 + 16 = 32,
         // but actual data size is 8 + 16 = 24.
-        Snapshot::<Aarch64RegisterVec>::load(&mut buf.as_slice()).unwrap_err();
+        Snapshot::<Aarch64RegisterVec>::load_without_crc_check(buf.as_slice()).unwrap_err();
     }
 
     #[test]
@@ -598,7 +600,7 @@ mod tests {
         Snapshot::new(v).save(&mut buf.as_mut_slice()).unwrap();
 
         // 4096 bit wide registers are not supported.
-        Snapshot::<Aarch64RegisterVec>::load(&mut buf.as_slice()).unwrap_err();
+        Snapshot::<Aarch64RegisterVec>::load_without_crc_check(buf.as_slice()).unwrap_err();
     }
 
     #[test]

src/vmm/src/arch/x86_64/vm.rs

@@ -321,7 +321,9 @@ mod tests {
         Snapshot::new(state)
             .save(&mut snapshot_data.as_mut_slice())
             .unwrap();
-        let restored_state: VmState = Snapshot::load(&mut snapshot_data.as_slice()).unwrap().data;
+        let restored_state: VmState = Snapshot::load_without_crc_check(snapshot_data.as_slice())
+            .unwrap()
+            .data;
 
         vm.restore_state(&restored_state).unwrap();
     }

src/vmm/src/device_manager/pci_mngr.rs

@@ -659,7 +659,9 @@ mod tests {
         // object and calling default_vmm() is the easiest way to create one.
         let vmm = default_vmm();
         let device_manager_state: device_manager::DevicesState =
-            Snapshot::load(&mut buf.as_slice()).unwrap().data;
+            Snapshot::load_without_crc_check(buf.as_slice())
+                .unwrap()
+                .data;
         let vm_resources = &mut VmResources::default();
         let restore_args = PciDevicesConstructorArgs {
             vm: vmm.vm.clone(),

src/vmm/src/device_manager/persist.rs

@@ -681,7 +681,9 @@ mod tests {
         let mut event_manager = EventManager::new().expect("Unable to create EventManager");
         let vmm = default_vmm();
         let device_manager_state: device_manager::DevicesState =
-            Snapshot::load(&mut buf.as_slice()).unwrap().data;
+            Snapshot::load_without_crc_check(buf.as_slice())
+                .unwrap()
+                .data;
         let vm_resources = &mut VmResources::default();
         let restore_args = MMIODevManagerConstructorArgs {
             mem: vmm.vm.guest_memory(),

src/vmm/src/devices/virtio/balloon/device.rs

@@ -80,7 +80,7 @@ pub struct BalloonConfig {
 }
 
 /// BalloonStats holds statistics returned from the stats_queue.
-#[derive(Clone, Default, Debug, PartialEq, Eq, Serialize)]
+#[derive(Clone, Copy, Default, Debug, PartialEq, Eq, Serialize)]
 #[serde(deny_unknown_fields)]
 pub struct BalloonStats {
     /// The target size of the balloon, in 4K pages.

src/vmm/src/devices/virtio/balloon/persist.rs

@@ -197,7 +197,9 @@ mod tests {
                 mem: guest_mem,
                 restored_from_file: true,
             },
-            &Snapshot::load(&mut mem.as_slice()).unwrap().data,
+            &Snapshot::load_without_crc_check(mem.as_slice())
+                .unwrap()
+                .data,
         )
         .unwrap();
 

src/vmm/src/devices/virtio/block/virtio/persist.rs

@@ -223,7 +223,9 @@ mod tests {
         // Restore the block device.
         let restored_block = VirtioBlock::restore(
             BlockConstructorArgs { mem: guest_mem },
-            &Snapshot::load(&mut mem.as_slice()).unwrap().data,
+            &Snapshot::load_without_crc_check(mem.as_slice())
+                .unwrap()
+                .data,
         )
         .unwrap();
 

src/vmm/src/devices/virtio/net/persist.rs

@@ -175,7 +175,9 @@ mod tests {
                     mem: guest_mem,
                     mmds: mmds_ds,
                 },
-                &Snapshot::load(&mut mem.as_slice()).unwrap().data,
+                &Snapshot::load_without_crc_check(mem.as_slice())
+                    .unwrap()
+                    .data,
             ) {
                 Ok(restored_net) => {
                     // Test that virtio specific fields are the same.

src/vmm/src/devices/virtio/persist.rs

@@ -366,8 +366,13 @@ mod tests {
             mem,
             is_activated: true,
         };
-        let restored_queue =
-            Queue::restore(ca, &Snapshot::load(&mut bytes.as_slice()).unwrap().data).unwrap();
+        let restored_queue = Queue::restore(
+            ca,
+            &Snapshot::load_without_crc_check(bytes.as_slice())
+                .unwrap()
+                .data,
+        )
+        .unwrap();
 
         assert_eq!(restored_queue, queue);
     }
@@ -380,7 +385,9 @@ mod tests {
         let state = VirtioDeviceState::from_device(&dummy);
         Snapshot::new(&state).save(&mut mem.as_mut_slice()).unwrap();
 
-        let restored_state: VirtioDeviceState = Snapshot::load(&mut mem.as_slice()).unwrap().data;
+        let restored_state: VirtioDeviceState = Snapshot::load_without_crc_check(mem.as_slice())
+            .unwrap()
+            .data;
         assert_eq!(restored_state, state);
     }
 
@@ -419,7 +426,9 @@ mod tests {
         };
         let restored_mmio_transport = MmioTransport::restore(
             restore_args,
-            &Snapshot::load(&mut buf.as_slice()).unwrap().data,
+            &Snapshot::load_without_crc_check(buf.as_slice())
+                .unwrap()
+                .data,
         )
         .unwrap();
 

src/vmm/src/devices/virtio/rng/persist.rs

@@ -92,7 +92,9 @@ mod tests {
         let guest_mem = create_virtio_mem();
         let restored = Entropy::restore(
             EntropyConstructorArgs { mem: guest_mem },
-            &Snapshot::load(&mut mem.as_slice()).unwrap().data,
+            &Snapshot::load_without_crc_check(mem.as_slice())
+                .unwrap()
+                .data,
         )
         .unwrap();