Disable trace events prefixed with a '-'.  Useful
to enable a group of tracepoints with exceptions,
like this:

  usb_xhci_port_*
  -usb_xhci_port_read

which will enable all xhci port tracepoints except reads.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

It is convenient for debug to be able to switch on/off some events easily.
The only possibility now is to remove event name from the file completely
and type it again when we want it back.

The patch adds '#' symbol handling as a comment specifier.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>

The "-trace events" argument can be used to provide a file with a list of trace
event names that will be enabled prior to starting execution, thus providing
early tracing.

This saves the user from manually toggling event states through the monitor
interface or whichever backend-specific interface.
Signed-off-by: NLluís Vilanova <vilanova@ac.upc.edu>