pci: msi: Implement Snapshot for MsiConfig

Adding support for snapshot and restore to the MsiConfig structure, as
it will be needed part of VFIO migration.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

pci/src/msi.rs

@@ -3,11 +3,17 @@
 // SPDX-License-Identifier: Apache-2.0 OR BSD-3-Clause
 //
 
+use anyhow::anyhow;
 use byteorder::{ByteOrder, LittleEndian};
+use std::io;
 use std::sync::Arc;
+use thiserror::Error;
+use versionize::{VersionMap, Versionize, VersionizeResult};
+use versionize_derive::Versionize;
 use vm_device::interrupt::{
     InterruptIndex, InterruptSourceConfig, InterruptSourceGroup, MsiIrqSourceConfig,
 };
+use vm_migration::{MigratableError, Pausable, Snapshot, Snapshottable, VersionMapped};
 
 // MSI control masks
 const MSI_CTL_ENABLE: u16 = 0x1;
@@ -32,7 +38,15 @@ pub fn msi_num_enabled_vectors(msg_ctl: u16) -> usize {
     1 << field
 }
 
-#[derive(Clone, Copy, Default)]
+#[derive(Error, Debug)]
+enum Error {
+    #[error("Failed enabling the interrupt route: {0}")]
+    EnableInterruptRoute(io::Error),
+    #[error("Failed updating the interrupt route: {0}")]
+    UpdateInterruptRoute(io::Error),
+}
+
+#[derive(Clone, Copy, Default, Versionize)]
 pub struct MsiCap {
     // Message Control Register
     //   0:     MSI enable.
@@ -157,6 +171,13 @@ impl MsiCap {
     }
 }
 
+#[derive(Versionize)]
+struct MsiConfigState {
+    cap: MsiCap,
+}
+
+impl VersionMapped for MsiConfigState {}
+
 pub struct MsiConfig {
     cap: MsiCap,
     interrupt_source_group: Arc<dyn InterruptSourceGroup>,
@@ -175,6 +196,39 @@ impl MsiConfig {
         }
     }
 
+    fn state(&self) -> MsiConfigState {
+        MsiConfigState { cap: self.cap }
+    }
+
+    fn set_state(&mut self, state: &MsiConfigState) -> Result<(), Error> {
+        self.cap = state.cap;
+
+        if self.enabled() {
+            for idx in 0..self.num_enabled_vectors() {
+                let config = MsiIrqSourceConfig {
+                    high_addr: self.cap.msg_addr_hi,
+                    low_addr: self.cap.msg_addr_lo,
+                    data: self.cap.msg_data as u32,
+                    devid: 0,
+                };
+
+                self.interrupt_source_group
+                    .update(
+                        idx as InterruptIndex,
+                        InterruptSourceConfig::MsiIrq(config),
+                        self.cap.vector_masked(idx),
+                    )
+                    .map_err(Error::UpdateInterruptRoute)?;
+            }
+
+            self.interrupt_source_group
+                .enable()
+                .map_err(Error::EnableInterruptRoute)?;
+        }
+
+        Ok(())
+    }
+
     pub fn enabled(&self) -> bool {
         self.cap.enabled()
     }
@@ -222,3 +276,26 @@ impl MsiConfig {
         }
     }
 }
+
+impl Pausable for MsiConfig {}
+
+impl Snapshottable for MsiConfig {
+    fn id(&self) -> String {
+        String::from("msi_config")
+    }
+
+    fn snapshot(&mut self) -> std::result::Result<Snapshot, MigratableError> {
+        Snapshot::new_from_versioned_state(&self.id(), &self.state())
+    }
+
+    fn restore(&mut self, snapshot: Snapshot) -> std::result::Result<(), MigratableError> {
+        self.set_state(&snapshot.to_versioned_state(&self.id())?)
+            .map_err(|e| {
+                MigratableError::Restore(anyhow!(
+                    "Could not restore state for {}: {:?}",
+                    self.id(),
+                    e
+                ))
+            })
+    }
+}