• Steven Rostedt (VMware)'s avatar
    tracing/ftrace: Add a better way to pass data via the probe functions · 6e444319
    Steven Rostedt (VMware) authored
    With the redesign of the registration and execution of the function probes
    (triggers), data can now be passed from the setup of the probe to the probe
    callers that are specific to the trace_array it is on. Although, all probes
    still only affect the toplevel trace array, this change will allow for
    instances to have their own probes separated from other instances and the
    top array.
    
    That is, something like the stacktrace probe can be set to trace only in an
    instance and not the toplevel trace array. This isn't implement yet, but
    this change sets the ground work for the change.
    
    When a probe callback is triggered (someone writes the probe format into
    set_ftrace_filter), it calls register_ftrace_function_probe() passing in
    init_data that will be used to initialize the probe. Then for every matching
    function, register_ftrace_function_probe() will call the probe_ops->init()
    function with the init data that was passed to it, as well as an address to
    a place holder that is associated with the probe and the instance. The first
    occurrence will have a NULL in the pointer. The init() function will then
    initialize it. If other probes are added, or more functions are part of the
    probe, the place holder will be passed to the init() function with the place
    holder data that it was initialized to the last time.
    
    Then this place_holder is passed to each of the other probe_ops functions,
    where it can be used in the function callback. When the probe_ops free()
    function is called, it can be called either with the rip of the function
    that is being removed from the probe, or zero, indicating that there are no
    more functions attached to the probe, and the place holder is about to be
    freed. This gives the probe_ops a way to free the data it assigned to the
    place holder if it was allocade during the first init call.
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    6e444319
trace.h 55.1 KB