• Liang Li's avatar
    block/mirror: change the semantic of 'force' of block-job-cancel · b76e4458
    Liang Li authored
    When doing drive mirror to a low speed shared storage, if there was heavy
    BLK IO write workload in VM after the 'ready' event, drive mirror block job
    can't be canceled immediately, it would keep running until the heavy BLK IO
    workload stopped in the VM.
    
    Libvirt depends on the current block-job-cancel semantics, which is that
    when used without a flag after the 'ready' event, the command blocks
    until data is in sync.  However, these semantics are awkward in other
    situations, for example, people may use drive mirror for realtime
    backups while still wanting to use block live migration.  Libvirt cannot
    start a block live migration while another drive mirror is in progress,
    but the user would rather abandon the backup attempt as broken and
    proceed with the live migration than be stuck waiting for the current
    drive mirror backup to finish.
    
    The drive-mirror command already includes a 'force' flag, which libvirt
    does not use, although it documented the flag as only being useful to
    quit a job which is paused.  However, since quitting a paused job has
    the same effect as abandoning a backup in a non-paused job (namely, the
    destination file is not in sync, and the command completes immediately),
    we can just improve the documentation to make the force flag obviously
    useful.
    
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Jeff Cody <jcody@redhat.com>
    Cc: Kevin Wolf <kwolf@redhat.com>
    Cc: Max Reitz <mreitz@redhat.com>
    Cc: Eric Blake <eblake@redhat.com>
    Cc: John Snow <jsnow@redhat.com>
    Reported-by: 's avatarHuaitong Han <huanhuaitong@didichuxing.com>
    Signed-off-by: 's avatarHuaitong Han <huanhuaitong@didichuxing.com>
    Signed-off-by: 's avatarLiang Li <liliangleo@didichuxing.com>
    Signed-off-by: 's avatarJeff Cody <jcody@redhat.com>
    Signed-off-by: 's avatarKevin Wolf <kwolf@redhat.com>
    b76e4458