Some observations about Xen migration and error handling.
The Xen migration protocol isn't stable between releases. It changed
between 3.0.3 and 3.1.0. There doesn't seem to be any versioning, and
incompatible versions of Xen seem happy to attempt migrations between
them, even though these will certainly fail.
The source host's xend forks an xc_save process. It appears to me that
xc_save will happily write to _anything_ listening on port 8002, even if
that thing closes the socket prematurely. (Try running 'xm migrate' on
one host and at the same time 'nc -l 8002 > /dev/null' on the target
host. The 'xm migrate' will happily complete without error. Meanwhile
the domain you "migrated" just gets deleted.)
Partly because of the lack of error reporting, and partly because the
xend -> xc_save fork will make error reporting difficult to add, libvirt
has a hard time displaying errors in this situation. It is quite
possible to call virDomainMigrate and get a domain back which shortly
afterwards "disappears", all without any indication of error.
Rich.
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