vm-virtio, vmm, vfio: Store GuestMemoryMmap in an Arc<ArcSwap<T>>

This allows us to change the memory map that is being used by the
devices via an atomic swap (by replacing the map with another one). The
ArcSwap provides the mechanism for atomically swapping from to another
whilst still giving good read performace. It is inside an Arc so that we
can use a single ArcSwap for all users.

Not covered by this change is replacing the GuestMemoryMmap itself.

This change also removes some vertical whitespace from use blocks in the
files that this commit also changed. Vertical whitespace was being used
inconsistently and broke rustfmt's behaviour of ordering the imports as
it would only do it within the block.

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

vm-virtio/src/vhost_user/blk.rs

@@ -1,35 +1,32 @@
 // Copyright 2019 Intel Corporation. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use libc;
-use libc::EFD_NONBLOCK;
-use std::cmp;
-use std::io::Write;
-use std::ptr::null;
-use std::result;
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, RwLock};
-use std::thread;
-use std::vec::Vec;
-
-use crate::VirtioInterrupt;
-
-use super::Error as DeviceError;
-
-use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
-use vm_memory::GuestMemoryMmap;
-use vmm_sys_util::eventfd::EventFd;
-
 use super::super::{ActivateError, ActivateResult, Queue, VirtioDevice, VirtioDeviceType};
 use super::handler::*;
 use super::vu_common_ctrl::*;
+use super::Error as DeviceError;
 use super::{Error, Result};
+use crate::VirtioInterrupt;
+use arc_swap::ArcSwap;
+use libc;
+use libc::EFD_NONBLOCK;
+use std::cmp;
+use std::io::Write;
 use std::mem;
+use std::ptr::null;
+use std::result;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use std::thread;
+use std::vec::Vec;
 use vhost_rs::vhost_user::message::VhostUserConfigFlags;
 use vhost_rs::vhost_user::message::{VhostUserProtocolFeatures, VhostUserVirtioFeatures};
 use vhost_rs::vhost_user::{Master, VhostUserMaster, VhostUserMasterReqHandler};
 use vhost_rs::VhostBackend;
 use virtio_bindings::bindings::virtio_blk::*;
+use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
+use vm_memory::GuestMemoryMmap;
+use vmm_sys_util::eventfd::EventFd;
 
 macro_rules! offset_of {
     ($ty:ty, $field:ident) => {
@@ -222,7 +219,7 @@ impl VirtioDevice for Blk {
 
     fn activate(
         &mut self,
-        mem: Arc<RwLock<GuestMemoryMmap>>,
+        mem: Arc<ArcSwap<GuestMemoryMmap>>,
         interrupt_cb: Arc<VirtioInterrupt>,
         queues: Vec<Queue>,
         queue_evts: Vec<EventFd>,
@@ -260,7 +257,7 @@ impl VirtioDevice for Blk {
 
         let vu_interrupt_list = setup_vhost_user(
             &mut self.vhost_user_blk,
-            &mem.read().unwrap(),
+            mem.load().as_ref(),
             queues,
             queue_evts,
             self.acked_features,

vm-virtio/src/vhost_user/fs.rs

@@ -9,6 +9,7 @@ use crate::{
     ActivateError, ActivateResult, Queue, VirtioDevice, VirtioDeviceType, VirtioInterrupt,
     VirtioSharedMemoryList, VIRTIO_F_VERSION_1,
 };
+use arc_swap::ArcSwap;
 use libc::{self, EFD_NONBLOCK};
 use std::cmp;
 use std::io;
@@ -16,7 +17,7 @@ use std::io::Write;
 use std::os::unix::io::RawFd;
 use std::result;
 use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Mutex, RwLock};
+use std::sync::{Arc, Mutex};
 use std::thread;
 use vhost_rs::vhost_user::message::{
     VhostUserFSSlaveMsg, VhostUserProtocolFeatures, VhostUserVirtioFeatures,
@@ -295,7 +296,7 @@ impl VirtioDevice for Fs {
 
     fn activate(
         &mut self,
-        mem: Arc<RwLock<GuestMemoryMmap>>,
+        mem: Arc<ArcSwap<GuestMemoryMmap>>,
         interrupt_cb: Arc<VirtioInterrupt>,
         queues: Vec<Queue>,
         queue_evts: Vec<EventFd>,
@@ -342,7 +343,7 @@ impl VirtioDevice for Fs {
 
         let vu_call_evt_queue_list = setup_vhost_user(
             &mut self.vu,
-            &mem.read().unwrap(),
+            mem.load().as_ref(),
             queues,
             queue_evts,
             self.acked_features,

vm-virtio/src/vhost_user/net.rs

@@ -1,33 +1,31 @@
 // Copyright 2019 Intel Corporation. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-use libc;
-use libc::EFD_NONBLOCK;
-use std::cmp;
-use std::io::Write;
-use std::result;
-use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, RwLock};
-use std::thread;
-use std::vec::Vec;
-
-use super::Error as DeviceError;
-use crate::VirtioInterrupt;
-use net_util::{MacAddr, MAC_ADDR_LEN};
-
-use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
-use vm_memory::GuestMemoryMmap;
-use vmm_sys_util::eventfd::EventFd;
-
 use super::super::{ActivateError, ActivateResult, Queue, VirtioDevice, VirtioDeviceType};
 use super::handler::*;
 use super::vu_common_ctrl::*;
+use super::Error as DeviceError;
 use super::{Error, Result};
+use crate::VirtioInterrupt;
+use arc_swap::ArcSwap;
+use libc;
+use libc::EFD_NONBLOCK;
+use net_util::{MacAddr, MAC_ADDR_LEN};
+use std::cmp;
+use std::io::Write;
+use std::result;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+use std::thread;
+use std::vec::Vec;
 use vhost_rs::vhost_user::message::{VhostUserProtocolFeatures, VhostUserVirtioFeatures};
 use vhost_rs::vhost_user::{Master, VhostUserMaster, VhostUserMasterReqHandler};
 use vhost_rs::VhostBackend;
 use virtio_bindings::bindings::virtio_net;
 use virtio_bindings::bindings::virtio_ring;
+use vm_device::{Migratable, MigratableError, Pausable, Snapshotable};
+use vm_memory::GuestMemoryMmap;
+use vmm_sys_util::eventfd::EventFd;
 
 struct SlaveReqHandler {}
 impl VhostUserMasterReqHandler for SlaveReqHandler {}
@@ -206,7 +204,7 @@ impl VirtioDevice for Net {
 
     fn activate(
         &mut self,
-        mem: Arc<RwLock<GuestMemoryMmap>>,
+        mem: Arc<ArcSwap<GuestMemoryMmap>>,
         interrupt_cb: Arc<VirtioInterrupt>,
         queues: Vec<Queue>,
         queue_evts: Vec<EventFd>,
@@ -244,7 +242,7 @@ impl VirtioDevice for Net {
 
         let vu_interrupt_list = setup_vhost_user(
             &mut self.vhost_user_net,
-            &mem.read().unwrap(),
+            mem.load().as_ref(),
             queues,
             queue_evts,
             self.acked_features & self.backend_features,