[Qemu-devel] Should migration with slirp networking (-netdev user) be backward compatible?

[Guenther Hutzl]

Hello!

I have a problem with migration from qemu-v2.6.0 to qemu-v2.5.0. It looks like
the slirp networking (-netdev user) is not backward compatible. This is the
output I am seeing on the receiving side:

qemu-system-x86_64: savevm: unsupported version 4 for 'slirp' v3
qemu-system-x86_64: load of migration failed: Invalid argument

This is the little test machine I am trying to migrate (using tiny core linux 
iso):

qemu-system-x86_64-2.6.0 -machine pc-i440fx-2.5 \
-m 512 \
-cdrom core-current.iso \
-boot d \
-nographic \
-curses \
-netdev user,id=mynet0 \
-device virtio-net,netdev=mynet0,id=net0

The target machine looks like this:

qemu-system-x86_64-2.5.0 -machine pc-i440fx-2.5 \
-m 512 \
-cdrom core-current.iso \
-boot d \
-nographic \
-curses \
-netdev user,id=mynet0 \
-device virtio-net,netdev=mynet0,id=net0 \
-incoming tcp:0:4444

I am selecting a v2.5-compatible machine so migration to qemu-2.5 should be
possible. The question is: Is the migration of slirp networking backward
compatible or is this unsupported for some reason?

I tested migration from v2.6 to v2.6 with this configuration and it worked.

Thank you,

Guenther Hutzl.

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