dev: Add basic checkpoint support to VirtIO9PProxy device

This patch adds very basic checkpoint support for the VirtIO9PProxy
device. Previously, attempts to checkpoint gem5 with a present 9P
device caused gem5 to fatal as none of the state is tracked. We still
do not track any state, but we replace the fatal with a warning which
is triggered if the device has been used by the guest system. In the
event that it has not been used, we assume that no state is lost
during checkpointing. The warning is triggered on both a serialize and
an unserialize to ensure maximum visibility for the user.

2 files changed, 32 insertions, 6 deletions

diff --git a/src/dev/virtio/fs9p.cc b/src/dev/virtio/fs9p.cc
index 336757bb9..2006006db 100644
--- a/src/dev/virtio/fs9p.cc
+++ b/src/dev/virtio/fs9p.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014 ARM Limited
+ * Copyright (c) 2014-2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -204,7 +204,7 @@ VirtIO9PBase::dumpMsg(const P9MsgHeader &header, const uint8_t *data, size_t siz
 
 
 VirtIO9PProxy::VirtIO9PProxy(Params *params)
-    : VirtIO9PBase(params)
+  : VirtIO9PBase(params), deviceUsed(false)
 {
 }
 
@@ -214,15 +214,29 @@ VirtIO9PProxy::~VirtIO9PProxy()
 
 
 void
-VirtIO9PProxy::VirtIO9PProxy::serialize(CheckpointOut &cp) const
+VirtIO9PProxy::serialize(CheckpointOut &cp) const
 {
-    fatal("Can't checkpoint a system with a VirtIO 9p proxy!\n");
+    if (deviceUsed) {
+        warn("Serializing VirtIO9Base device after device has been used. It is "
+             "likely that state will be lost, and that the device will cease "
+             "to work!");
+    }
+    SERIALIZE_SCALAR(deviceUsed);
+
+    VirtIO9PBase::serialize(cp);
 }
 
 void
 VirtIO9PProxy::unserialize(CheckpointIn &cp)
 {
-    fatal("Can't checkpoint a system with a VirtIO 9p proxy!\n");
+    UNSERIALIZE_SCALAR(deviceUsed);
+
+    if (deviceUsed) {
+        warn("Unserializing VirtIO9Base device after device has been used. It is "
+             "likely that state has been lost, and that the device will cease "
+             "to work!");
+    }
+    VirtIO9PBase::unserialize(cp);
 }
 
 
@@ -230,6 +244,7 @@ void
 VirtIO9PProxy::recvTMsg(const P9MsgHeader &header,
                         const uint8_t *data, size_t size)
 {
+    deviceUsed = true;
     assert(header.len == sizeof(header) + size);
     // While technically not needed, we send the packet as one
     // contiguous segment to make some packet dissectors happy.
diff --git a/src/dev/virtio/fs9p.hh b/src/dev/virtio/fs9p.hh
index ebff9fef7..786f58464 100644
--- a/src/dev/virtio/fs9p.hh
+++ b/src/dev/virtio/fs9p.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014 ARM Limited
+ * Copyright (c) 2014-2015 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -269,6 +269,17 @@ class VirtIO9PProxy : public VirtIO9PBase
      * @param len Number of bytes to write.
      */
     void writeAll(const uint8_t *data, size_t len);
+
+    /**
+     * Bool to track if the device has been used or not.
+     *
+     * We need to keep track of if the device has been used as we are
+     * unable to checkpoint the device in the event that the device
+     * has been mounted in the guest system. This is due to the fact
+     * that we do not, and cannot, track the complete state across
+     * host and guest.
+     */
+     bool deviceUsed;
 };
 
 struct VirtIO9PDiodParams;