vmm: support removing devices before VM is booted

If the VM has been configured but not yet booted, all we need to do to
support removing a device is to remove it from the config, so it will
never be created.

Signed-off-by: Alyssa Ross <hi@alyssa.is>

vmm/src/config.rs

@@ -2101,6 +2101,69 @@ impl VmConfig {
         Ok(config)
     }
 
+    pub fn remove_device(&mut self, id: &str) -> bool {
+        let mut removed = false;
+
+        // Remove if VFIO device
+        if let Some(devices) = self.devices.as_mut() {
+            let len = devices.len();
+            devices.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= devices.len() != len;
+        }
+
+        // Remove if VFIO user device
+        if let Some(user_devices) = self.user_devices.as_mut() {
+            let len = user_devices.len();
+            user_devices.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= user_devices.len() != len;
+        }
+
+        // Remove if disk device
+        if let Some(disks) = self.disks.as_mut() {
+            let len = disks.len();
+            disks.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= disks.len() != len;
+        }
+
+        // Remove if fs device
+        if let Some(fs) = self.fs.as_mut() {
+            let len = fs.len();
+            fs.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= fs.len() != len;
+        }
+
+        // Remove if net device
+        if let Some(net) = self.net.as_mut() {
+            let len = net.len();
+            net.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= net.len() != len;
+        }
+
+        // Remove if pmem device
+        if let Some(pmem) = self.pmem.as_mut() {
+            let len = pmem.len();
+            pmem.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= pmem.len() != len;
+        }
+
+        // Remove if vDPA device
+        if let Some(vdpa) = self.vdpa.as_mut() {
+            let len = vdpa.len();
+            vdpa.retain(|dev| dev.id.as_ref().map(|id| id.as_ref()) != Some(id));
+            removed |= vdpa.len() != len;
+        }
+
+        // Remove if vsock device
+        if let Some(vsock) = self.vsock.as_ref() {
+            if vsock.id.as_ref().map(|id| id.as_ref()) == Some(id) {
+                self.vsock = None;
+                removed = true;
+            }
+        }
+
+        removed
+    }
+
     /// # Safety
     /// To use this safely, the caller must guarantee that the input
     /// fds are all valid.