• Stefan Hajnoczi's avatar
    trace: fix simple trace "disable" keyword · 736ec167
    Stefan Hajnoczi authored
    The trace-events "disable" keyword turns an event into a nop at
    compile-time.  This is important for high-frequency events that can
    impact performance.
    
    The "disable" keyword is currently broken in the simple trace backend.
    This patch fixes the problem as follows:
    
    Trace events are identified by their TraceEventID number.  When events
    are disabled there are two options for assigning TraceEventID numbers:
    1. Skip disabled events and don't assign them a number.
    2. Assign numbers for all events regardless of the disabled keyword.
    
    The simple trace backend and its binary file format uses approach #1.
    
    The tracetool infrastructure has been using approach #2 for a while.
    
    The result is that the numbers used in simple trace files do not
    correspond with TraceEventIDs.  In trace/simple.c we assumed that they
    are identical and therefore emitted bogus numbers.
    
    This patch fixes the bug by using TraceEventID for trace_event_id()
    while sticking to approach #1 for simple trace file numbers.  This
    preserves simple trace file format compatibility.
    Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
    736ec167
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