Re: [Qemu-devel] [PATCH 0/3] Migration cancel with dead network

[Daniel P. Berrange]

On Thu, Jan 08, 2015 at 11:11:29AM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
> 
> If the remote host, or networking dies during a migration, the socket can be
> waiting for a long timeout, and migration_cancel can't complete the cancel
> for a long time (and you can't start a new one to somewhere else).
> (Where 'long' is the TCP timeout, that's ~15 mins)
> 
> This patch set uses the shutdown(2) syscall to unblock any write/sends that
> are in progress to let the migrate_cancel happen quickly.
> 
>   1/3: socket shutdown  - An updated patch from my postcopy world to
>                           add a shut_down method on QEMUFile - only
>                           for 'socket' (where the syscall is supported).
> 
>   2/3: Handle bi-directional communication for fd migration
>                         - A patch from Cristian Klein to use the socket
>                           QEMUFile for FDs that are passed in, if the FDs
>                           are sockets; this is needed so that libvirt
>                           migrations can take advantage of the other patches.
>                           Again this patch (and its naming) come from the
>                           postcopy world.
> 
>   3/3: migration_cancel: shutdown migration socket
>                         - A new patch that uses the shutdown in 
> migrate_fd_cancel
> 
> 
> Note this does not fix the timeout if you try to migrate to an already dead 
> host;
> the connect timeout is typically a much shorter 2 minutes anyway.

In any libvirt managed setup, you'd need to address the connect timeout
issue in libvirt instead, since libvirt always uses fd based migration.
ie libvirt estabishes the connection & then passes the TCP Socket to
QEMU.

It should be possible for libvirt to use a non-blocking connect()
call and catch use of its virDomainMigrateCancel APi to stop the
connection attempt.

Regards,
Daniel
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