[Qemu-devel] Re: [PATCH] rtl8139: IO memory is not part of vmstate

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Dec 09, 2010 at 03:14:17PM -0700, Alex Williamson wrote:
> On Thu, 2010-12-09 at 22:49 +0100, Juan Quintela wrote:
> > Alex Williamson <alex.williamson@redhat.com> wrote:
> > > The cpu_register_io_memory() value is unique to the VM instance and
> > > should not be restored after migration/save.  Doing so means we
> > > could be pointing at arbitrary device's io regions after migration/restore.
> > >
> > > In this case, if we start a VM with a single rtl8139, hot add a 2nd,
> > > migrate the VM, then hot remove the added NIC, the 1st NIC stops
> > > working and the VM segfaults on reboot.
> > >
> > > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > > ---
> > >
> > >  hw/rtl8139.c |    4 ++--
> > >  1 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/rtl8139.c b/hw/rtl8139.c
> > > index d92981d..9c5fc84 100644
> > > --- a/hw/rtl8139.c
> > > +++ b/hw/rtl8139.c
> > > @@ -3186,7 +3186,7 @@ static void rtl8139_pre_save(void *opaque)
> > >  
> > >  static const VMStateDescription vmstate_rtl8139 = {
> > >      .name = "rtl8139",
> > > -    .version_id = 4,
> > > +    .version_id = 5,
> > 
> > No need to change version, format is still the same.
> > 
> > >      .minimum_version_id = 3,
> > >      .minimum_version_id_old = 3,
> > >      .post_load = rtl8139_post_load,
> > > @@ -3234,7 +3234,7 @@ static const VMStateDescription vmstate_rtl8139 = {
> > >  
> > >          VMSTATE_UNUSED(4),
> > >          VMSTATE_MACADDR(conf.macaddr, RTL8139State),
> > > -        VMSTATE_INT32(rtl8139_mmio_io_addr, RTL8139State),
> > > +        VMSTATE_UNUSED(4),
> > 
> > If we migrate from an old guest: we just ignore the value.
> > If we migrate to one old guest, we send garbage, but as you told that we
> > were already sending garbage, it looks ok, no?
> 
> NAK, if we don't bump the version, we don't know if we're migration
> to/from a version 4 that includes the io address or not.  We have no
> good way to debug different binaries on different systems.  It seems to
> work today if we don't involve hotplug, so I think we have to maintain
> version 4 as including the io address, and let version 5 drop it.  I
> tested old to new migrations, and as you expect, it does work.
> 
> Alex

How about we keep migrating the index for the benefit of
old versions, but ignore the value on load?
Something like the following:


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index d92981d..e999dd9 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -494,6 +494,13 @@ typedef struct RTL8139State {
     QEMUTimer *timer;
     int64_t TimerExpire;
 
+    /* Hack for migration compatibility: older
+     * versions of rtl8139 put mmio index in save image,
+     * and override the index that we have with that one.
+     * This does not make any sense but happens to
+     * work sometimes, if we are lucky and index matches.
+     * On load, we can simply ignore this value. */
+    int compat_rtl8139_mmio_io_addr;
 } RTL8139State;
 
 static void rtl8139_set_next_tctr_time(RTL8139State *s, int64_t current_time);
@@ -3182,6 +3189,7 @@ static void rtl8139_pre_save(void *opaque)
     rtl8139_set_next_tctr_time(s, current_time);
     s->TCTR = muldiv64(current_time - s->TCTR_base, PCI_FREQUENCY,
                        get_ticks_per_sec());
+    s->compat_rtl8139_mmio_io_addr = s->rtl8139_mmio_io_addr;
 }
 
 static const VMStateDescription vmstate_rtl8139 = {
@@ -3234,7 +3242,7 @@ static const VMStateDescription vmstate_rtl8139 = {
 
         VMSTATE_UNUSED(4),
         VMSTATE_MACADDR(conf.macaddr, RTL8139State),
-        VMSTATE_INT32(rtl8139_mmio_io_addr, RTL8139State),
+        VMSTATE_INT32(compat_rtl8139_mmio_io_addr, RTL8139State),
 
         VMSTATE_UINT32(currTxDesc, RTL8139State),
         VMSTATE_UINT32(currCPlusRxDesc, RTL8139State),