virtio-devices: mem: Allow for an initial size

This commit gives the possibility to create a virtio-mem device with
some memory already plugged into it. This is preliminary work to be
able to reboot a VM with the virtio-mem region being already resized.

Signed-off-by: Hui Zhu <teawater@antfin.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

virtio-devices/src/mem.rs

@@ -185,6 +185,36 @@ struct VirtioMemConfig {
 // Safe because it only has data and has no implicit padding.
 unsafe impl ByteValued for VirtioMemConfig {}
 
+fn virtio_mem_config_resize(config: &mut VirtioMemConfig, size: u64) -> result::Result<(), Error> {
+    if config.requested_size == size {
+        return Err(Error::ResizeInval(format!(
+            "Virtio-mem resize {} is same with current config.requested_size",
+            size
+        )));
+    } else if size > config.region_size {
+        let region_size = config.region_size;
+        return Err(Error::ResizeInval(format!(
+            "Virtio-mem resize {} is bigger than config.region_size {}",
+            size, region_size
+        )));
+    } else if size % (config.block_size as u64) != 0 {
+        let block_size = config.block_size;
+        return Err(Error::ResizeInval(format!(
+            "Virtio-mem resize {} is not aligned with config.block_size {}",
+            size, block_size
+        )));
+    }
+
+    config.requested_size = size;
+    let tmp_size = cmp::min(
+        config.region_size,
+        config.requested_size + VIRTIO_MEM_USABLE_EXTENT,
+    );
+    config.usable_region_size = cmp::max(config.usable_region_size, tmp_size);
+
+    Ok(())
+}
+
 struct Request {
     req: VirtioMemReq,
     status_addr: GuestAddress,
@@ -622,37 +652,16 @@ impl EpollHelperHandler for MemEpollHandler {
                     let size = self.resize.get_size();
                     let mut config = self.config.lock().unwrap();
                     let mut signal_error = false;
-                    let r = if config.requested_size == size {
+                    let mut r = virtio_mem_config_resize(&mut config, size);
-                        Err(Error::ResizeInval(format!(
+                    r = match r {
-                            "Virtio-mem resize {} is same with current config.requested_size",
+                        Err(e) => Err(e),
-                            size
+                        _ => match self.signal(&VirtioInterruptType::Config) {
-                        )))
+                            Err(e) => {
-                    } else if size > config.region_size {
+                                signal_error = true;
-                        let region_size = config.region_size;
+                                Err(Error::ResizeTriggerFail(e))
-                        Err(Error::ResizeInval(format!(
+                            }
-                            "Virtio-mem resize {} is bigger than config.region_size {}",
+                            _ => Ok(()),
-                            size, region_size
+                        },
-                        )))
-                    } else if size % (config.block_size as u64) != 0 {
-                        let block_size = config.block_size;
-                        Err(Error::ResizeInval(format!(
-                            "Virtio-mem resize {} is not aligned with config.block_size {}",
-                            size, block_size
-                        )))
-                    } else {
-                        config.requested_size = size;
-                        let tmp_size = cmp::min(
-                            config.region_size,
-                            config.requested_size + VIRTIO_MEM_USABLE_EXTENT,
-                        );
-                        config.usable_region_size = cmp::max(config.usable_region_size, tmp_size);
-                        if let Err(e) = self.signal(&VirtioInterruptType::Config) {
-                            signal_error = true;
-                            error!("Error signalling config: {:?}", e);
-                            Err(Error::ResizeTriggerFail(e))
-                        } else {
-                            Ok(())
-                        }
                     };
                     if let Err(e) = self.resize.send(r) {
                         error!("Sending \"resize\" reponse: {:?}", e);
@@ -702,6 +711,7 @@ impl Mem {
         resize: Resize,
         seccomp_action: SeccompAction,
         numa_node_id: Option<u16>,
+        initial_size: u64,
     ) -> io::Result<Mem> {
         let region_len = region.len();
 
@@ -726,6 +736,15 @@ impl Mem {
             config.requested_size + VIRTIO_MEM_USABLE_EXTENT,
         );
 
+        if initial_size != 0 {
+            virtio_mem_config_resize(&mut config, initial_size).map_err(|e| {
+                io::Error::new(
+                    io::ErrorKind::Other,
+                    format!("Virtio-mem resize {} got {:?}", initial_size, e),
+                )
+            })?;
+        }
+
         if let Some(node_id) = numa_node_id {
             avail_features |= 1u64 << VIRTIO_MEM_F_ACPI_PXM;
             config.node_id = node_id;

vmm/src/device_manager.rs

@@ -2451,6 +2451,7 @@ impl DeviceManager {
                             .map_err(DeviceManagerError::TryCloneVirtioMemResize)?,
                         self.seccomp_action.clone(),
                         node_id,
+                        0,
                     )
                     .map_err(DeviceManagerError::CreateVirtioMem)?,
                 ));