This next patch realizes a long-anticipated advantage of tracepoints, 
namely that it should be possible to disconnect GDB from the target but 
leave the trace experiment running, then reconnect later to see if 
anything interesting turned up.  While conceptually simple, there are a 
couple wrinkles; we need to tell the target what to do if GDB goes away 
without warning, and we also have to decide what should happen when we 
reconnect and find that the target's list of tracepoints is different 
from GDB's list.

The first is easily handled with a new boolean setshow, 
disconnected-tracing.  The second is much more complicated, and 
basically requires uploading tracepoints from the target, and keeping 
track of tracepoint numbers that differ between host and target. I need 
to beg a little indulgence for this right now, because the code in this 
patch is very lame, and a later patch does it right; but that version 
depends heavily on the upcoming target vector changes.  (In fact, the 
big target vector change will be my very next patch!)

Stan

2010-01-05  Stan Shebs  <stan@codesourcery.com>

    Support disconnected tracing.
    * infcmd.c (detach_command): Ask whether to stop tracing.
    * cli/cli-cmds.c (quit_command): Ditto.
    * breakpoint.h (struct breakpoint): New field number_on_target.
    * breakpoint.c (create_tracepoint_from_upload): New function.
    (get_tracepoint_by_number_on_target): New function.
    * remote.c (struct remote): New field disconnected_tracing.
    (remote_disconnected_tracing_feature): New function.
    (remote_protocol_features): Add DisconnectedTracing.
    (struct uploaded_tp): New struct.
    (uploaded_tps): New global.
    (get_uploaded_tp): New function.
    (find_matching_tracepoint): New function.
    (remote_get_tracing_state): New function.
    (remote_start_remote): Call it.
    * tracepoint.c (disconnected_tracing): New global.
    (trace_start_command): Initialize number_on_target.
    (stop_tracing): New function, split out from...
    (trace_stop_command): Call stop_tracing.
    (get_trace_status): New function, split out from...
    (trace_status_command): Call get_trace_status, add info on
    disconnection behavior.
    (disconnect_or_stop_tracing): New function.
    (finish_tfind_command): Translate from number on target.
    (trace_find_tracepoint_command): Translate to number on target.
    (send_disconnected_tracing_value): New function.
    (set_disconnected_tracing): New function.
    (_initialize_tracepoint): Add disconnected-tracing variable.
    * NEWS: Mention disconnected tracing.

    * gdb.texinfo (Starting and Stopping Trace Experiments): Document
    disconnected tracing.
    (Tracepoint Packets): Document new protocol.