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Tunnelled migration can hang if the destination qemu exits despite all the ABI checks. This happens whenever the destination qemu exits before the complete transfer is noticed by source qemu. The savevm state checks at runtime can fail at destination and cause qemu to error out. The source qemu cant notice it as the EPIPE is not propogated to it. The qemuMigrationIOFunc() notices the stream being broken from virStreamSend() and it cleans up the stream alone. The qemuMigrationWaitForCompletion() would never get to 100% transfer completion. The qemuMigrationWaitForCompletion() never breaks out as well since the ssh connection to destination is healthy, and the source qemu also thinks the migration is ongoing as the Fd to which it transfers, is never closed or broken. So, the migration will hang forever. Even Ctrl-C on the virsh migrate wouldn't be honoured. Close the source side FD when there is an error in the stream. That way, the source qemu updates itself and qemuMigrationWaitForCompletion() notices the failure. Close the FD for all kinds of errors to be sure. The error message is not copied for EPIPE so that the destination error is copied instead later. Note: Reproducible with repeated migrations between Power hosts running in different subcores-per-core modes. Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>