[Qemu-devel] RAMBlock's named ""

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

We seem to have a couple of weird cases where we end up with
RAMBlocks with no name;  I think they'll badly confuse
the migration code, but I don't quite understand how they're
happening.

1) device_del e1000e
2) -object memory-backend-file  without wiring it up

I added some debug into migration/ram.c ram_save_setup to
dump the names it was seeing in it's FOREACH.

1)
  (from https://bugzilla.redhat.com/show_bug.cgi?id=1425273)
  The simplest reproducer of this is:

./qemu-system-x86_64 -nographic  -device e1000e,id=foo -m 1G -M pc,accel=kvm my.img

  with a Linux image and after it's booted do a device_del foo

  migration at that point sees an empty RAMBlock that was the ROM
  associated with the device.  This doesn't happen on an e1000 device,
  so I've not figured out what the difference is.

  This gives a : Unknown ramblock "", cannot accept migration
  on the destination (correctly).

  (This happens on 2.7.0 as well, so it's nothing new)

2)
  ./qemu-system-x86_64 -nographic -object memory-backend-file,id=mem,size=512M,mem-path=/tmp

  Note I've not wired that memory to a NUMA node or a DIMM or anything, so
  it's just hanging around.
  Again that RAMBlock does exist and shows up in the migration code,
  I think it'll try and migrate it.

The real fun is that there doesn't seem to be anything that stops
two blocks having the same name!

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK